Materials Degradation Caused by Acid Rain 9780841209886, 9780841211551, 0-8412-0988-X

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Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.fw001

Materials Degradation Caused by Acid Rain

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.fw001

ACS SYMPOSIUM SERIES 318

Materials Degradation Caused by Acid Rain Robert Baboian, E D I T O R

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.fw001

Texas Instruments, Inc.

Developed from a symposium sponsored by the Division of Industrial and Engineering Chemistry, Inc. at the 20th State-of-the-Art Symposium of the American Chemical Society, Arlington, Virginia, June 17-19, 1985

American Chemical Society, Washington, DC 1986

Library of Congress Cataloging-in-Publication Data Materials degradation caused by acid rain. ( A C S symposium series, I S S N 0097 6156; 318)

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.fw001

"Developed from a symposium sponsored by the Division of Industrial and Engineering Chemistry, Inc., at the 20th State-of-the-Art Symposium of the American Chemical Society, Arlington, Virginia, June 17-19, 1985." Bibliography: p. Includes index. 1. Materials—Deterioration—Congresses. 2. Acid rain—Congresses. 3. Weathering—Congresses. 4. A c i d Rain Deposition—Congresses. I. Baboian, Robert. II. American Chemical Society. Division of Industrial and Engineering Chemistry. III. Series. TA418.74.M38 1986 I S B N 0-8412-0988-X

620.1'1223

86-20560

Copyright © 1986 American Chemical Society A l l Rights Reserved. The appearance of the code at the bottom of the first page of each chapter in this volume indicates the copyright owner's consent that reprographic copies of the chapter may be made for personal or internal use or for the personal or internal use of specific clients. This consent is given on the condition, however, that the copier pay the stated per copy fee through the Copyright Clearance Center, Inc., 27 Congress Street, Salem, M A 01970, for copying beyond that permitted by Sections 107 or 108 of the U . S . Copyright Law. This consent does not extend to copying or transmission by any means—graphic or electronic—for any other purpose, such as for general distribution, for advertising or promotional purposes, for creating a new collective work, for resale, or for information storage and retrieval systems. The copying fee for each chapter is indicated in the code at the bottom of the first page of the chapter. The citation of trade names and/or names of manufacturers in this publication is not to be construed as an endorsement or as approval by A C S of the commercial products or services referenced herein; nor should the mere reference herein to any drawing, specification, chemical process, or other data be regarded as a license or as a conveyance of any right or permission, to the holder, reader, or any other person or corporation, to manufacture, reproduce, use, or sell any patented invention or copyrighted work that may in any way be related thereto. Registered names, trademarks, etc., used in this publication, even without specific indication thereof, are not to be considered unprotected by law. PRINTED IN THE UNITED STATES OF AMERICA

ACS Symposium Series M . Joan Comstock, Series Editor

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.fw001

Advisory Board Harvey W. Blanch

Donald E. Moreland

University of California—Berkeley

USDA, Agricultural Research Service

Alan Elzerman

W.H.Norton

Clemson University

J. T. Baker Chemical Company

John W. Finley

James C. Randall

Nabisco Brands, Inc.

Exxon Chemical Company

Marye Anne Fox

W. D. Shults

The University of Texas—Austin

Oak Ridge National Laboratory

Martin L. Gorbaty

Geoffrey K. Smith

Exxon Research and Engineering Co.

Rohm & Haas Co.

Roland F. Hirsch

Charles S.Tuesday

U.S. Department of Energy

General Motors Research Laboratory

Rudolph J. Marcus

Douglas B. Walters

Consultant, Computers & Chemistry Research

National Institute of Environmental Health

Vincent D. McGinniss

C. Grant Willson

Battelle Columbus Laboratories

IBM Research Department

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.fw001

FOREWORD The A C S S Y M P O S I U M S E R I E S was founded in 1974 to provide a

medium for publishing symposia quickly in book form. The format of the Series parallels that of the continuing A D V A N C E S IN C H E M I S T R Y S E R I E S except that, in order to save time, the papers are not typeset but are reproduced as they are submitted by the authors in camera-ready form. Papers are reviewed under the supervision of the Editors with the assistance of the Series Advisory Board and are selected to maintain the integrity of the symposia; however, verbatim reproductions of previously published papers are not accepted. Both reviews and reports of research are acceptable, because symposia may embrace both types of presentation.

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.pr001

Left side-right side comparison of the Statue of Liberty torch shows darkening of the left side facing Manhattan and the northeast. Darkening of the left side is due to erosion of the green patina by acid deposition and the severe weather from the northeast. (Photo by Robert Baboian.)

ix

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.pr001

Corrosion of bronze, commonly termed "bronze plague," in the Torrey monument in Mount Auburn Cemetery, Cambridge, MA, due to the effects of acid deposition. (Photo by Robert Baboian.)

Corrosion of reinforcing steel in concrete (elevated highway, Providence, RI), where road de-icing salts combine with acid precipitation to produce a severe environment. (Photo by Robert Baboian.)

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Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.pr001

PREFACE A C I D R A I N IS A N I M P O R T A N T A N D G R O W I N G T O P I C . This book addresses the important materials problems resulting from acid deposition. It is divided into five sections: Measurement and Monitoring of Atmospheric Deposition, Metallic Corrosion, Masonry Deterioration, Degradation of Organics, and Economic Effects. The section on measurement and monitoring concentrates on the scope of the acid deposition problem. This includes wet deposition chemistry, dry deposition, fog and cloud water, and the composition of dew. The section on metallic corrosion clearly indicates that the conventional method of classification of environments into marine, industrial, and rural no longer is adequate. More specific information is needed about the actual chemical components in the atmosphere as well as humidity and other factors. Specific environments also are addressed in the metallic corrosion section. For example, the automotive environment in the northeastern United States is particularly severe because of the combination of acid deposition and the use of road de-icing salts. These factors exert a synergistic effect on the corrosion behavior of auto-body steel and on exterior anodized aluminum automobile trim. The section on masonry deterioration focuses on limestone, coquina, sandstone, marble, concrete, brick, and mortar as related to acid deposition effects on structures such as buildings and on cultural resources such as monuments.

Auto body corrosion adjacent to stainless steel trim occurs in environments where de-icing salts are used. The effects of acid deposition combined with road salts produces a synergystic effect on the degradation of automobiles. (Photo by Robert Baboian.) XI

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.pr001

The section on degradation of organics deals with paints, plastics, nylon, wood, and architectural organics. The effects of acid deposition on wood and other cellulosic materials are described. Strength losses in wood may be caused by hydrolytic degradation of the hemicelluloses and a sulfonation reaction of the lignin. Thus, the fibrils and matrix structure is affected. Cotton materials can be affected similarly, and soiling will result. The effect of acid deposition of nylon is indicative of a potentially shorter serviceable lifetime for outdoor fabrics. The section on economic effects presents the methodology used in assessing costs of degradation of materials due to acid deposition. The difficulty in accurately assessing the cost of materials degradation by acid deposition is described in this section. Thus, the various techniques used have a high degree of uncertainty. In summary, this book serves to provide information on the wide range of materials affected by acid deposition. Although a large amount of information is presented on this subject, it is evident that much remains to be done. A better understanding of the nature and mechanisms of materials damage by acid deposition could lead to a reduction or avoidance of this kind of damage. Thus, expenditures for work in this field could lead to huge annual dollar savings. ROBERT BABOIAN

Electrochemical and Corrosion Laboratory Texas Instruments Inc. Attleboro, MA 02703 Organizing Committee for the Symposium Robert Baboian, Chairman Texas Instruments Inc.

Richard A. Livingston Environmental Protection Agency

Edward Escalante, Session Chairman National Bureau of Standards

Hugh C. Miller National Park Service

David R. Flinn U.S. Bureau of Mines

Robert S. Shane, Session Chairman Shane Associates

James H. Gibson, Session Chairman Colorado State University

Susan Sherwood, Session Chairman National Park Service

Ray Hermann National Park Service

Thaddeus Whyte The PQ Corporation

Frederick W. Lipfert, Session Chairman Brookhaven National Laboratory

William E. Wilson Environmental Protection Agency

xii

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.pr001

Degradation of paint occurs by reaction at the surface and at the paint interface. Acid deposition can cause paint peeling on wood. (Photo by R. S. Williams.)

Bricks and mortar (New Haven, CT) are susceptible to deterioration through the action of acid deposition. (Photo by Robert Baboian.)

xiii

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.pr001

St. Thomas Church in New York City. Areas on the facade accumulate a layer of gypsum (calcium sulfate) produced by acid deposition attack on the limestone and then darken by dirt, soot, and other combustion products. (Photo by Elena Charola.)

Spoiling of marble column on Department of Justice building, Washington, DC. (Photo by Bruce Doe.) xiv

1 Acidification of Precipitation Β. Ottar

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch001

Norwegian Institute for Air Research, P.O. Box 130, N-2001 Lillestrøm, Norway

The acid rain studies which started with the OECD project 1972-77 have since become a major issue in both North America and Europe. The main cause is sulphuric and nitric acid from the use of fossil fuels. The resulting fish kills in acidified rivers and lakes depend on the soil composition and the release of toxic aluminium ions. This may also be a contributing factor to the forest damage in central Europe., but photochemical oxidants are now believed to be more important. Generally the acidification and the increasing oxidation potential of the atmosphere is slowly changing our chemical environment, and it is not known to what extent the resulting ecological changes will be reversed if the emissions are reduced. In the summer o f 1969, OECD c a l l e d a meeting t o d i s c u s s e v i d e n c e on the a c i d i f i c a t i o n o f the p r e c i p i t a t i o n i n Europe. The year before, the Swedish s c i e n t i s t . S. Odén (1) by a n a l y s i n g p r e c i p i t a t i o n d a t a from a European network o f a t m o s p h e r i c c h e m i s t r y s t a t i o n s , which had been e s t a b l i s h e d i n 1954- 55, had found t h a t a c e n t r a l area w i t h h i g h l y a c i d p r e c i p i t a t i o n had expanded t o i n c l u d e the s o u t h e r n p a r t s of S c a n d i n a v i a . The main a c i d i f y i n g agent was s u l p h u r i c a c i d , and the s o u r c e was assumed t o be the i n c r e a s i n g use o f f o s s i l f u e l s w i t h a h i g h content o f s u l p h u r . H i s f i n d i n g s were r e l a t e d to I he a c i d i f i c a t i o n o f r i v e r s and l a k e s i n S c a n d i n a v i a and the d i s a p p e a r a n c e o f f i s h ' i i these w a t e r s . At. t h i s meeting, the OECD c o u n t r i e s agreed that t h i s d e v e l o p ment d e s e r v e d f u r t h e r a t t e n t i o n , and the N o r d i c countries should produce a c o o r d i n a t e d p l a n t o examine the s i t u a t i o n . A p l a n n i n g committee and a p r e l i m i n a r y r e s e a r c h programme were e s t a b l i s h e d through NORDFORSK (The. N o r d i c Council f o r Pure and A p p l i e d R e s e a r c h ) , and a f t e r c o n s i d e r a b l e p r e p a r a t i o n s and n e g o t i a t i o n s t h e OECD p r o j e c t "Long Range. T r a n s p o r t o f A i r P o l l u t i o n " was s t a r t e d i n J u l y 1972. A f t e r a f i r s t i n t r o d u c t o r y phase, the OECD c o u n t r i e s i n 1973 agreed t h a t t h i s was a s e r i o u s s i t u a t i o n and i n c r e a s e d the. research e f f o r t . f

0097-6156/86/0318-0002506.00/ 0 © 1986 American Chemical Society

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch001

1.

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Acidification of Precipitation

3

The OECD p r o j e c t was completed i n 1977. The f i n a l r e p o r t (2) showed t h a t the a i r over the c e n t r a l p a r t s of Europe was substantially p o l l u t e d . The c o u n t r i e s on t h e c o n t i n e n t r e c e i v e d as much s u l p h u r p o l l u t a n t s from n e i g h b o u r i n g c o u n t r i e s as from t h e i r own sources, and most of the i n c r e a s e d a c i d i t y of the p r e c i p i t a t i o n i n the s u r r o u n d i n g c o u n t r i e s was due t o the e m i s s i o n s of sulphur d i o x i d e and nitrogen oxides i n the c e n t r a l p a r t s of t h e a r e a (3,4,5). In order t o b r i n g t h i s development under some c o n t r o l , c l o s e c o - o p e r a t i o n would be needed between t h e c o u n t r i e s o f both Eastern and Western Europe. The problem was t a k e n up by the U.N. Economic Commission f o r Europe (ECE) i n Geneva, and f u r t h e r p r o g r e s s was made a t the first C o n f e r e n c e on S e c u r i t y and C o - o p e r a t i o n i n Europa i n H e l s i n k i i n 1975, which recommended the development o f an extended programme f o r m o n i t o r i n g and e v a l u a t i o n o f the l o n g range t r a n s p o r t of a i r p o l l u t i o n i n Europe. I n 1978 the f i r s t 3-year phase o f the " C o - o p e r a t i v e Programme f o r M o n i t o r i n g and E v a l u a t i o n of the Long Range T r a n s m i s s i o n o f A i r P o l l u t a n t s i n Europe" (EMEP) was s t a r t e d . The programme was f i n a n c e d by the U.N. E n v i r o n m e n t a l Program (UNEP), and close co-operation was e s t a b l i s h e d w i t h t h e World M e t e o r o l o g i c a l O r g a n i z a t i o n (WMO). EMEP i s now p a r t o f the ECE c o n v e n t i o n on l o n g range t r a n s b o u n d a r y air pollution ( 6 ) . Today 26 countries, with their national a i r sampling networks, p a r t i c i p a t e i n the programme, i n c l u d i n g Canada and USA as o b s e r v e r s . The s c i e n t i f i c work i s c o - o r d i n a t e d t h r o u g h a Chemical C o o r d i n a t i n g C e n t e r (CCC) a t the Norwegian I n s t i t u t e for A i r R e s e a r c h (NILU) and two m e t e o r o l o g i c a l s y n t h e s i z i n g c e n t e r s , one a t the Norwegian M e t e o r o l o g i c a l I n s t i t u t e i n O s l o (MSC-W) and one a t the H y d r o - M e t e o r o l o g i c a l I n s t i t u t e i n Moscow (MSC-E). So f a r EMEP has c o n c e n t r a t e d on measuring s u l p h u r p o l l u t a n t s ( 7 ) . The exchange o f s u l p h u r p o l l u t a n t s between the European c o u n t ries i s now c a l c u l a t e d on a r o u t i n e b a s i s . An example i s shown i n T a b l e 1. From a s c i e n t i f i c p o i n t of view, t h e r e has l o n g been a need t o i n c l u d e measurements o f n i t r o g e n o x i d e s and o t h e r n i t r o g e n compounds, i n o r d e r t o o b t a i n a more complete d a t a base f o r e v a l u a t i o n o f the a c i d i f i c a t i o n of p r e c i p i t a t i o n . A t p r e s e n t t h i s i s o n l y done on a v o l u n t a r y b a s i s i n some of the c o u n t r i e s . For v a r i o u s reasons, i t has so f a r not been p o s s i b l e t o i n c l u d e t h e s e measurements i n the r e g u l a r programme. More r e c e n t l y , t h e rapidly increasing forest damage i n Europe has a l s o p o i n t e d t o the importance o f measurements of ozone and o t h e r p h o t o c h e m i c a l o x i d a n t s . There i s a l s o an i n t e r e s t i n heavy m e t a l s . A c c o r d i n g t o p l a n s , measurements o f 2 4 - h o u r l y mean v a l u e s of NOx w i l l b e g i n i n 1986, and h o u r l y measurements of ozone a r e c o n s i d e r e d f o r the 4 t h phase o f EMEP, which s t a r t s i n 1987. C o n s i d e r i n g the r a p i d expansion of the r e g i o n a l a i r p o l l u t i o n problems i n Europe d u r i n g the l a t e r y e a r s , as e x a m p l i f i e d by the f o r e s t damage, the appearance of "red t i d e " i n the N o r t h Sea, and t h e i n c r e a s i n g mercury c o n t e n t o f the f r e s h w a t e r f i s h , the development o f EMEP has been slow. I t i s i n t e r e s t i n g t o n o t e t h a t when t h e OECD p r o j e c t s t a r t e d i n 1972, Canada p a r t i c i p a t e d as an observer, w h i l e the US EPA d i d not b e l i e v e t h a t a c i d p r e c i p i t a t i o n would become a problem i n N o r t h America as w e l l . S i m i l a r l y , the European c o u n t r i e s d i d not t h i n k t h a t p h o t o c h e m i c a l o x i d a n t s would become a problem i n Europe. There was not enough s u n s h i n e , they reasoned.

4

MATERIALS DEGRADATION CAUSED BY ACID RAIN

Today we have t h e same problems on b o t h s i d e s o f t h e A t l a n t i c , and i t has g r a d u a l l y become e v i d e n t t h a t t h e two phenomena a r e closely i n t e r r e l a t e d w i t h r e s p e c t t o s o u r c e s and e f f e c t s . The o x i d a t i o n o f s u l p h u r d i o x i d e t o s u l p h u r i c a c i d i s l a r g e l y governed by the p h o t o c h e m i c a l a c t i v i t y i n t h e atmosphere, w h i c h a l s o produces the n i t r i c a c i d found i n t h e p r e c i p i t a t i o n . The damage t o v e g e t a t i o n and m a t e r i a l s i n many cases i s t h e r e s u l t o f a c i d i f i c a t i o n , combined w i t h a h i g h e r o x i d a t i o n p o t e n t i a l . I n s o u t h e r n Sweden, t h e e l e v a t e d copper c o n t e n t o f d r i n k i n g w a t e r , due t o i n c r e a s e d c o r r o s i o n o f p i p e l i n e s , can no l o n g e r be t o l e r a t e d by s m a l l c h i l d r e n . As a r e s u l t o f t h e s e developments, t h e term a c i d p r e c i p i t a t i o n has a c q u i r e d a w i d e r p o p u l a r meaning, i n c l u d i n g b o t h a c i d p r e c i p i t a t i o n and o t h e r r e g i o n a l e f f e c t s o f a i r p o l l u t i o n .

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch001

Sources Of A c i d

Precipitation

The OECD p r o j e c t showed t h a t t h e a c i d i f i c a t i o n o f p r e c i p i t a t i o n was due t o an i n c r e a s e d c o n t e n t o f s u l p h u r i c and n i t r i c a c i d . The main cause was i d e n t i f i e d as t h e i n c r e a s e d use o f f o s s i l f u e l s , i n c l u d i n g motor v e h i c l e t r a f f i c . I n t h e atmosphere, s u l p h u r d i o x i d e and n i t r o gen o x i d e s from combustion p r o c e s s e s a r e o x i d i z e d t o s u l p h u r i c a c i d and n i t r i c a c i d , w h i c h a r e t a k e n up and d e p o s i t e d by t h e p r e c i p i t a tion. The growing use o f f o s s i l f u e l s i n Europe d u r i n g t h i s c e n t u r y i s i l l u s t r a t e d i n F i g u r e 1 ( 5 ) . The e a r l y s u l p h u r d i o x i d e emissions i n Europe were m a i n l y due t o t h e combustion o f s u l p h u r c o n t a i n i n g c o a l s and i n some a r e a s t h e p r o c e s s i n g o f s u l p h i d i c o r e s . The i n c r e a s e d demand f o r energy a f t e r 1950 was met by a w i d e - s p r e a d i n t r o d u c t i o n o f p e t r o l e u m p r o d u c t s , and as a r e s u l t t h e s u l p h u r dioxide emissions i n Europe were d o u b l e d i n t h e p e r i o d 1950-75. L a t e l y t h e y have remained l a r g e l y unchanged. Many c o u n t r i e s have reduced their sulphur d i o x i d e emissions considerably, by energy s a v i n g and by c h a n g i n g t o o t h e r f u e l s . I n F r a n c e 60% o f t h e e l e c t r i c i t y demand i s now met by n u c l e a r power p r o d u c t i o n , while i n other countries i n c r e a s e d e l e c t r i c i t y p r o d u c t i o n based on t r a d i t i o n a l f u e l s has l e d to higher sulphur emissions. In North America t h e sulphur d i o x i d e emissions mainly o r i g i n a t e from t h e use o f c o a l s w i t h a r e l a t i v e l y h i g h s u l p h u r c o n t e n t , and from v a r i o u s s p e c i a l i n d u s t r i a l p r o c e s s e s . The r e l a t i v e c o n t r i b u t i o n of s u l p h u r from o i l combustion i s much s m a l l e r t h a n i n Europe. Figure 2 shows t h e summer and w i n t e r c o a l consumption i n USA s i n c e 1940 ( 1 ) . I t shows a peak i n 1943, and s i n c e 1960 t h e summer consumption has grown a t a r a t e o f 5.8% p.a. as compared t o 2.8% p.a. f o r w i n t e r t i m e . I n a d d i t i o n t o t h i s , t h e consumption o f heavy fuel o i l has i n c r e a s e d by 50% s i n c e 1959. On a g l o b a l s c a l e , i n d u s t r i a l p r o c e s s e s ( m a i n l y r o a s t i n g o f s u l p h i d i c copper, n i c k e l , l e a d and z i n c o r e s , m a n u f a c t u r i n g o f s u l phur a c i d , and t h e paper and p u l p i n d u s t r y ) a c c o u n t f o r about 10% o f the t o t a l s u l p h u r p o l l u t i o n ( 1 ) . The e m i s s i o n s o f n i t r o g e n o x i d e s a r e m a i n l y due t o o x i d a t i o n o f n i t r o g e n from t h e a i r d u r i n g combustion p r o c e s s e s . The main sources are motorized traffic, power s t a t i o n s , and space h e a t i n g ( 1 0 ) . I n t h i s l a r g e s c a l e p i c t u r e , process emissions are of l e s s e r s i g n i f i cance. H i g h combustion t e m p e r a t u r e and an e x c e s s o f a i r f a v o u r t h e f o r m a t i o n o f n i t r o g e n o x i d e s . Thus, modern d i e s e l e n g i n e s have about

1.

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5

Acidification of Precipitation

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Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch001

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1

A cidification of Precipitation

t h e h i g h e s t n i t r o g e n o x i d e e m i s s i o n s per u n i t of f u e l consumed. Some t y p i c a l e m i s s i o n f a c t o r s a r e g i v e n i n T a b l e 2. In the atmosphere the n i t r o g e n o x i d e s g i v e r i s e t o a number of d i f f e r e n t c h e m i c a l r e a c t i o n s . N i t r i c o x i d e (NO), i n i t i a l l y formed i n the combustion p r o c e s s , i s o x i d i z e d t o n i t r o g e n d i o x i d e (NO ). The e m i s s i o n i s t h e r e f o r e u s u a l l y g i v e n as t h e e q u i v a l e n t c o n c e n t r a t i o n of N0 , and d e s i g n a t e d as NOx. When exposed t o s u n l i g h t i n t h e atmo­ sphere, N0 i s decomposed t o NO and a t o m i c oxygen, t h e l a t t e r r e a c t ­ i n g w i t h m o l e c u l a r oxygen t o form ozone (0 ). The NO i s r e - o x i d i z e d t o NO by 0 . (There i s always a n a t u r a l background o f 20-30 ppb 0 in trie atmosphere, which i s due t o i n t r u s i o n s from the s t r a t o ­ sphere.) I n t h i s way a p h o t o s t a t i o n a r y e q u i l i b r i u m i s e s t a b l i s h e d . When o r g a n i c components a r e added, a n e t p r o d u c t i o n o f 0 results ( U ) . The m i x t u r e of oxygen atoms and f r e e r a d i c a l s leads a l s o to the formation o f v a r i o u s h i g h l y r e a c t i v e o r g a n i c p e r o x i d e s and n i t r a t e s , as w e l l as a l d e h y d e s and nitric acid. Photochemical r e a c t i o n s a l s o p l a y an i m p o r t a n t p a r t i n t h e homogeneous gas phase o x i d a t i o n of s u l p h u r d i o x i d e . I n p o l l u t e d a r e a s , o x i d a n t p r o d u c t i o n r e a c h e s a maximum i n t h e a f t e r n o o n , and t h e h i g h e s t v a l u e s a r e o f t e n o b s e r v e d some d i s t a n c e away from t h e main p r e c u r s o r e m i s s i o n s . D u r i n g n i g h t t h e r e i s no p r o d u c t i o n of o x i d a n t s , and i n t h e p o l l u t e d urban a i r the oxidants will be r a p i d l y consumed i n v a r i o u s o x i d a t i o n r e a c t i o n s . The f i n a l products are n i t r i c a c i d , various organic nitrates, aldehydes and organic a c i d s . Oxidants, moved out of one p o l l u t e d a r e a , may t h e f o l l o w i n g day enhance t h e problems i n downwind a r e a s more than 500 km away (12,13). I n Europe o x i d a n t s were f i r s t o b s e r v e d i n t h e N e t h e r l a n d s i n the l a t e 1960*s ( 1 4 ) . B e f o r e then many b e l i e v e d t h a t photochemical smog c o u l d o n l y be found a t lower l a t i t u d e s w i t h more i n t e n s e s o l a r r a d i a t i o n . L a t e r e x p e r i e n c e has shown t h a t i f t h e e m i s s i o n s of nitrogen oxides and o r g a n i c components a r e l a r g e enough, photo­ c h e m i c a l o x i d a n t s can be produced anywhere d u r i n g t h e summer season. A simultaneous i n c r e a s e i n t h e ozone c o n c e n t r a t i o n s has on s e v e r a l o c c a s i o n s been o b s e r v e d a l l over w e s t e r n Europe (|5). The e m i s s i o n s o f n i t r o g e n o x i d e s i n Europe have been i n c r e a s i n g a t a f a s t e r r a t e than s u l p h u r d i o x i d e , and a r e s t i l l i n c r e a s i n g . One particular reason f o r t h i s i s t h e i n c r e a s e d motor v e h i c l e t r a f f i c . There has a l s o been some change-over from g a s o l i n e t o d i e s e l engi­ nes. For the photochemical activity and ozone p r o d u c t i o n the e m i s s i o n s of gaseous o r g a n i c components a r e most i m p o r t a n t , but t h e s e e m i s s i o n s a r e not w e l l q u a n t i f i e d i n Europe. A l t h o u g h the use of f o s s i l f u e l s i n Europe i s h i g h e r i n w i n t e r than i n summer, t h e c o n c e n t r a t i o n of n i t r a t e i n t h e p r e c i p i t a t i o n i s higher i n summer, because of t h e h i g h e r p h o t o c h e m i c a l a c t i v i t y . The e f f e c t i s l e s s pronounced f o r s u l p h a t e s , because s u l p h u r dioxide a l s o can be o x i d i z e d , a f t e r a b s o r p t i o n i n l i q u i d d r o p l e t s , c a t a l y t i c a l l y by i r o n o r mangenese i o n s , o r by d i s s o l v e d ozone and hydrogen p e r o x i d e . The l i m i t i n g f a c t o r i s t h a t the a b s o r p t i o n s t o p s , when the a c i d i t y o f t h e d r o p l e t approaches pH 3. 2

2

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Geographical

Distribution

The modelling of l o n g range t r a n s p o r t of s u l p h u r p o l l u t a n t s i n Europe i s based on an e m i s s i o n s u r v e y i n a g r i d o f 150 km χ 150 km.

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8

T a b l e I I . F u e l consumption and e s t i m a t e d Ν ο e m i s s i o n w i t h i n OECD Europe i n 1975. "Reprinted w i t h p e r m i s s i o n from Ref. 18. χ

Emissionfactor kg NO /tonne fuel

Fuel

consumption Tg

NOx-emission Tg NO 2 o

2

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Hard c o a l Power p l a n t s Industry Other

9 6 2

133 22 24

1.2 0.1 0.05

4

137

0.5

12 8 8 •6

69 19 95 27

0.8 0.15 0.75 0.16

8 4 36

24 121 46

0.2 0.5 1.7

25

90

2.2

336 642 554

0.3 0.2 0.1 9.0

Brown c o a l Power p l a n t s Residual fuel o i l Power p l a n t s Refineries Industry Other Gas/diesel o i l Industry Other Transport Motor gas Transport N a t u r a l gas Power p l a n t s Industry Other

1 0.3 0.2

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For s u l p h u r d i o x i d e , t h e s u r v e y has been worked out i n c o - o p e r a t i o n w i t h t h e p a r t i c i p a t i n g c o u n t r i e s . For c o u n t r i e s which have o n l y been a b l e t o p r o v i d e i n f o r m a t i o n on t h e t o t a l e m i s s i o n s f o r d i f f e r e n t i n d u s t r i a l s e c t o r s , the s u r v e y was based on n a t i o n a l f u e l consumption s t a t i s t i c s from OECD and ECE s o u r c e s , e m i s s i o n f a c t o r s , and p o p u l a t i o n d e n s i t i e s . For some c o u n t r i e s the a c c u r a c y i s within ±10-15%; i n o t h e r cases t h e d a t a a r e l e s s a c c u r a t e . The major emiss i o n a r e a s a r e , however, s u f f i c i e n t l y w e l l d e f i n e d f o r model calcul a t i o n s (10). The g e o g r a p h i c a l d i s t r i b u t i o n of sulphur d i o x i d e emissions i n Europe i s shown i n F i g u r e 3 (.16,17.). For l a r g e r a r e a s the sulphur d i o x i d e emissions are approximately p r o p o r t i o n a l t o the p o p u l a t i o n d e n s i t y , are higher i n a r e a s w i t h a p a r t i c u l a r l y h i g h degree o f industrialization. The e m i s s i o n s of n i t r o g e n o x i d e s l a r g e l y f o l l o w the same p a t t e r n ( 1 8 ) . About h a l f of the e m i s s i o n s originate from motor v e h i c l e t r a f f i c , but because t r a f f i c d e n s i t y depends on o t h e r a c t i v i t i e s and t h e p o p u l a t i o n d e n s i t y , an a p p r o x i m a t e p r o p o r t i o n a lity i s obtained f o r s u l p h u r d i o x i d e and t h e n i t r o g e n o x i d e emiss i o n s i n the l a r g e r a r e a s . On a s i m i l a r b a s i s a p p r o x i m a t e emission surveys have a l s o been worked out f o r heavy m e t a l s (J_9) and hydrocarbons (20). The g e o g r a p h i c a l d i s t r i b u t i o n o f s u l p h u r d i o x i d e e m i s s i o n s i n N o r t h America i n F i g u r e 4 (21) shows the e a s t e r n p a r t o f the North American c o n t i n e n t as t h e main e m i s s i o n a r e a . E m i s s i o n s u r v e y s f o r n i t r o g e n o x i d e s and hydrocarbons show s i m i l a r d i s t r i b u t i o n s ( 2 J ) . In c e n t r a l Europe t h e annual mean c o n c e n t r a t i o n o f s u l p h u r d i o x i d e i s about 20 pg/m (see F i g u r e 5). The annual concentration p a t t e r n o f s u l p h a t e p a r t i c l e s i s s i m i l a r , but because o f t h e time r e q u i r e d f o r s u l p h u r d i o x i d e t o be t r a n s f o r m e d i n t o s u l p h a t e p a r t i c l e s the a n n u a l mean c o n c e n t r a t i o n l e v e l i s lower. The maximum v a l u e s of about 10 pg/m (see F i g u r e 5) are s l i g h t l y shifted to the n o r t h - e a s t due t o the predominant w e s t e r l y winds. Dry d e p o s i t i o n of s u l p h u r d i o x i d e i s a s i g n i f i c a n t f a c t o r i n the c e n t r a l p a r t o f the a r e a , and i s r e s p o n s i b l e f o r the removal of about 50% o f t h e t o t a l e m i s s i o n s . Compared t o t h i s , t h e d r y d e p o s i t i o n of s u l p h a t e i s of l e s s e r s i g n i f i c a n c e . About 30% of the total s u l p h u r e m i s s i o n i s removed by p r e c i p i t a t i o n s c a v e n g i n g . Maximum wet d e p o s i t i o n i s found i n o r o g r a p h i c p r e c i p i t a t i o n areas f r e q u e n t l y exposed t o p o l l u t e d a i r masses, such as t h e S c a n d i n a v i a n mountains and t h e A l p s , as seen i n F i g u r e 6 (2J. Measurements d u r i n g r e c e n t y e a r s have shown t h a t much of t h e r e m a i n i n g p o l l u t a n t s move i n t o the A r c t i c . As seen i n F i g u r e 7 (22), t h e main t r a n s p o r t t a k e s p l a c e i n t h e w i n t e r a c r o s s the n o r t h e r n s h o r e l i n e o f t h e USSR. I n summer t h i s pathway i s l a r g e l y b l o c k e d by the p o l a r f r o n t , and t r a n s p o r t from western Europe becomes more important. The day t o day s i t u a t i o n i s v e r y d i f f e r e n t from t h i s average p i c t u r e . W i t h s o u t h e r l y winds, c o n c e n t r a t i o n s of 20-30 ug/m of s u l p h u r d i o x i d e and s u l p h a t e p a r t i c l e s a r e f r e q u e n t l y observed i n s o u t h e r n S c a n d i n a v i a . For t h i s a r e a , more than 90% o f t h e a n n u a l l y d e p o s i t e d s u l p h a t e comes from o t h e r c o u n t r i e s . H a l f o f t h e d e p o s i t i o n may be due t o 10 o r so e p i s o d e s w i t h h i g h l y p o l l u t e d precipit a t i o n . A s i m i l a r s i t u a t i o n i s observed i n o t h e r remote a r e a s . The main a c i d i c component i s s u l p h u r i c a c i d , w i t h an a d d i t i o n of 20-50% of n i t r a t e and ammonium i o n s on an e q u i v a l e n t b a s i s . The 3

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F i g u r e 4. Sulphur d i o x i d e e m i s s i o n s i n N o r t h America, fini t : k i l o t o n n e s S0 /year . ?

1970-75,

(21)

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F i g u r e 5. E s t i m a t e d mean c o n c e n t r a t i o n f i e l d f o r p a r t i c u l a t e s u l p h a t e f o r 1974. Observed mean c o n c e n t r a t i o n s g i v e n by I t a l i c numbers. U n i t : ug SO /m" ( 2 J . 4

F i g u r e 6. E s t i m a t e d s u l p h u r wet d e p o s i t i o n p a t t e r n s f o r 1974. U n i t : g S/m ( 2 J . 2

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1-2

F i g u r e 7b. Average s u m m e r / f a l l c o n c e n t r a t i o n s of SO and 3 0 " i n a i r i n the Norwegian s e c t o r of the A r c t i c . June November 1982. U n i t : pg S/m . 3

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a n n u a l mean c o n c e n t r a t i o n s o f s u l p h a t e i n p r e c i p i t a t i o n i n Europe from World M e t e o r o l o g i c a l O r g a n i z a t i o n d a t a f o r t h e p e r i o d 1972-76 (23) a r e shown i n F i g u r e 8. E p i s o d e s w i t h maximum a c i d i t y a r e o f t e n o b s e r v e d when h i g h l y a c i d i c p a r t i c l e s a r e formed i n a i r , which has remained over t h e s e a f o r s e v e r a l days ( w i t h no ammonia e m i s s i o n ) , and l a t e r a r e scavenged by o r o g r a p h i c p r e c i p i t a t i o n . I n 1978 an e x c e p t i o n a l case o f 10 mm precipitation w i t h a pH o f 2.5 was r e p o r t e d by t h e M e t e o r o l o g i c a l S e r v i c e o f I c e l a n d . Cases o f pH 2.7 have been o b s e r v e d i n S c o t l a n d and on t h e west c o a s t o f Norway. The mean a c i d i t y o f p r e c i p i t a t i o n i n N o r t h America f o r t h e p e r i o d 1976-79 ( 2 4 ) , i s shown i n F i g u r e 9. The maximum v a l u e s ( i . e . , minimum pH) a r e a s s o c i a t e d w i t h t h e e a s t e r n p a r t o f t h e c o n t i n e n t , and a r e c l o s e l y r e l a t e d t o t h e major e m i s s i o n s i n t h e Ohio valley. I n n o r t h e a s t e r n USA and Canada, b o t h d e p o s i t i o n and s u l p h a t e concent r a t i o n s a r e a t a maximum i n summer. In S c a n d i n a v i a the concentrations of sulphate i n p r e c i p i t a t i o n are g e n e r a l l y highest during the s p r i n g , while the emissions of sulphur d i o x i d e i n Europe have a maximum i n J a n u a r y (about 2 times t h e e m i s s i o n s i n summer). T h i s d e l a y can be a t t r i b u t e d t o a p r e c i p i t a t i o n minimum i n w e s t e r n Europe d u r i n g t h e e a r l y s p r i n g , and more rapid conversion of sulphur d i o x i d e t o sulphate with increased s o l a r r a d i a t i o n . The s e a s o n a l v a r i a t i o n o f t h e c o n c e n t r a t i o n o f n i t r a t e i n p r e c i p i t a t i o n i s s i m i l a r , b u t w i t h a l o n g e r maximum p e r i o d ( 2 5 ) . T h i s r e f l e c t s t h e d i f f e r e n t c l i m a t e s and f u e l consumption p a t t e r n s i n Europe and N o r t h A m e r i c a . I n Norway t h e p r e c i p i t a t i o n a t the present c o n t a i n s about e q u i v a l e n t amounts o f n i t r a t e and ammonium i o n s . I n t h e 1950's t h i s r a t i o was a l s o v e r y c o n s t a n t , b u t t h e c o n c e n t r a t i o n o f n i t r a t e i o n s was o n l y 1/2 o f t h e ammonium i o n s . The b a s i c r e a s o n f o r t h i s c o n s t a n t r a t i o seems t o be t h a t i n n o r t h w e s t e r n Europe t h e e m i s s i o n s o f n i t r o g e n o x i d e s from i n d u s t r y and motorized t r a f f i c l a r g e l y take place i n regions o f major agricult u r a l a c t i v i t i e s . The h i g h e r r a t i o today i n d i c a t e s t h a t t h e n i t r o g e n o x i d e e m i s s i o n s have i n c r e a s e d over t h e p a s t y e a r s . I t i s i n t e r e s ting t o note t h a t i n N o r t h America t h e e m i s s i o n s o f ammonia come from t h e mid-western a g r i c u l t u r a l a r e a s , w h i l e most o f t h e n i t r o g e n o x i d e e m i s s i o n s come from a r e a s f u r t h e r e a s t . As a r e s u l t the n i t r a t e t o ammonium i o n s r a t i o i n p r e c i p i t a t i o n i s much more v a r i a b l e . The a c i d i t y o f p r e c i p i t a t i o n i s m a i n l y governed by i t s c o n t e n t of s u l p h a t e , n i t r a t e and ammonium i o n s . I t i s c l o s e l y r e l a t e d t o t h e chmical composition o f t h e a e r o s o l s , and may t o a l a r g e e x t e n t depend on t h e pathway o f t h e p o l l u t e d a i r masses. The e f f e c t s o f t h e acid precipitation are not simply related t o the a c i d i t y of the p r e c i p i t a t i o n , b u t a r e t h e r e s u l t o f complex i n t e r a c t i o n s i n which a l l t h e major i o n s i n p r e c i p i t a t i o n a r e o f s i g n i f i c a n c e . The chemical composition o f a e r o s o l s i s i n f l u e n c e d by o t h e r s u b s t a n c e s p r e s e n t i n t h e a i r . An e q u i l i b r i u m i s r a p i d l y e s t a b l i s h e d between i o n i c components i n t h e p a r t i c l e s o r d r o p l e t s and t h e c o r r e sponding gaseous components, i . e . , NH^ /NH , N0 /HN0 , C l /HC1, 3

3

3

S0 ""/S0 . P a r t i c l e s formed over t h e s e a a r e o f t e n p a r t i c u l a r l y a c i d i c , Decause o f t h e low p a r t i a l p r e s s u r e o f ammonia. I f l a t e r these particles pass over a g r i c u l t u r a l areas, they a r e r a p i d l y n e u t r a l i z e d by ammonia, a t l e a s t a t ground l e v e l . On t h e o t h e r hand, ammonium s u l p h a t e p a r t i c l e s which pass o v e r t h e a c i d i c f o r e s t s o i l s i n S c a n d i n a v i a , have been shown t o g i v e o f f ammonia ( 2 6 ) . 4

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F i g u r e 8.

MATERIALS DEGRADATION CAUSED BY ACID RAIN

Annual mean c o n c e n t r a t i o n of s u l p h a t e i n p r e c i p i t a t i o n mg SO;/I

F i g u r e 9.

1972-76

(23) .

Weighted mean pH o f p r e c i p i t a t i o n f o r N o r t h America f o r the p e r i o d 1976-1979. Dashed l i n e s i n d i c a t e where d a t a a r e s p a r s e and thus o n l y t h e g e n e r a l p a t t e r n i s i n d i c a t e d (24) .

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Acidification of Precipitation

15

S m a l l e r a c i d i c s u l p h a t e p a r t i c l e s may l o s e c h l o r i d e and n i t r a t e i o n s i n the form o f gaseous h y d r o c h l o r i c and n i t r i c a c i d . Thus, the c h l o r i d e i n a i r b o r n e sea s a l t may be d r i v e n o f f as h y d r o c h l o r i c a c i d , which may be s u b s e q u e n t l y absorbed by l a r g e r , l e s s a c i d i c p a r t i c l e s . S i m i l a r c h e m i c a l r e a c t i o n s can a l s o t a k e p l a c e i n samples of p a r t i c l e s c o l l e c t e d on f i l t e r s , p a r t i c u l a r l y i f the c o a r s e and f i n e p a r t i c l e s a r e not s e p a r a t e d . The p r e s s u r e drop a c r o s s the f i l t e r may a l s o cause e v a p o r a t i o n of the more v o l a t i l e components. The chemical a n a l y s i s of the c o l l e c t e d p a r t i c l e s may then g i v e a d i s t o r t e d p i c t u r e of the t r u e a i r b o r n e c o m p o s i t i o n of the a e r o s o l . A e r o s o l p a r t i c l e s s e r v e as c o n d e n s a t i o n n u c l e i f o r c l o u d dropl e t s and p r e c i p i t a t i o n s . As a r u l e o f thumb, about 1 ml H O is precipitated from each m of a i r i n a c l o u d . With a 100% scavenging by p r e c i p i t a t i o n , 1 pg/m of a s u b s t a n c e s h o u l d g i v e 1 mg/1 i n the p r e c i p i t a t i o n . Some t y p i c a l a n a l y s e s of p o l l u t e d a i r masses, which have been t r a n s p o r t e d t o Norway a c r o s s the N o r t h Sea, a r e shown i n Figure 10 (2). The h i g h c o n c e n t r a t i o n s of n i t r a t e and ammonium i n the p r e c i p i t a t i o n , r e l a t i v e t o those i n the a e r o s o l s , i n d i c a t e t h a t a b s o r p t i o n of s u l p h u r d i o x i d e and gaseous n i t r i c a c i d has taken place. Effects

Acidification

of r i v e r s and l a k e s . Loss of f i s h p o p u l a t i o n s due t o a c i d i f i c a t i o n o f r i v e r s and l a k e s was the f i r s t r e c o g n i z e d s i g n of e c o l o g i c a l damage due t o a c i d p r e c i p i t a t i o n . A l t h o u g h problems w i t h a c i d water and salmon and t r o u t s t o c k s i n Southern Norway were noted in the 1920's ( 2 7 ) , the f i s h d e c l i n e has e s c a l a t e d s i n c e 1950 and today i t a f f e c t s many thousand l a k e s i n Norway and Sweden ( F i g u r e 11). Surveys have shown a g e n e r a l c o r r e l a t i o n between the pH and f i s h s t a t u s i n l a k e s , and the p h y s i o l o g i c a l response of f i s h to a c i d i c water i s now w e l l known ( 2 8 ) . A c i d water a f f e c t s t h e uptake of sodium and c h l o r i d e i o n s through the c e l l membranes i n the g i l l s , and leads to a disturbance of t h e e l e c t r o l y t e b a l a n c e ( 2 9 ) . The c o n c e n t r a t i o n of r e a c t i v e (uncomplexed) aluminium i o n s i n a c i d i f i e d waters i s p a r t i c u l a r l y d e t r i m e n t a l ( 3 0 ) , a p p a r e n t l y because t h i s i n t e r f e r e s w i t h the m e t a b o l i c uptake o f e l e c t r o l y t e s from the water, w h i l e c a l c i u m i o n s have an a m e l i o r a t i n g e f f e c t ( 3 1 ) . G e n e r a l l y , the problems w i t h a c i d water occur m o s t l y i n a r e a s w i t h g r a n i t i c or s i m i l a r l y r e s i s t i v e bedrock, and w i t h s p a r s e soil cover d e r i v e d from the same p a r e n t m a t e r i a l . C a l c i u m c o n c e n t r a t i o n l e v e l s i n s u r f a c e waters a r e g e n e r a l l y low, t y p i c a l l y l e s s than 2 mg/1. T h i s e x p l a i n s why the problem so f a r has m a i n l y s u r f a c e d i n S c a n d i n a v i a , and i n a r e a s of s i m i l a r g e o l o g i c a l f o r m a t i o n s on the Canadian s h i e l d and i n the A d i r o n d a c k Mountains. Some a c i d i f i c a t i o n of l a k e s and water courses has a l s o o c c u r r e d i n England and S c o t l a n d (32,33), and i n the E r z g e b i r g e between the German D e m o c r a t i c R e p u b l i c and C z e c h o s l o v a k i a (34,35). The i n t e r a c t i o n s between s o l u b l e i o n s i n p r e c i p i t a t i o n , s o i l , and v e g e t a t i o n , and the e f f e c t of these i n t e r a c t i o n s on r u n o f f water q u a l i t y a r e complex. The s o i l cover which was formed i n S c a n d i n a v i a when g l a c i a t i o n r e t r e a t e d some 9000 y e a r s ago, l a r g e l y c o n s i s t s of g r a n i t i c sand, covered w i t h a t o p l a y e r r i c h i n humus ( p o d s o l ) .

16

MATERIALS DEGRADATION CAUSED BY ACID RAIN

H ÏÏTTÏÏ1

NH

su • i

Ca

ZD

S0

4

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3

ne/m 50

April

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch001

7

Aerosol

Precipitation

, 3 ne/m 150i

Me/I 150·

May

May 100

100·

50

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ne/m 100

100-f

June

June

50·

50-

g mi η Precipitation

Aerosol

F i g u r e 10. C o n c e n t r a t i o n s o f water s o l u b l e compounds i n p r e c i p i t a ­ t i o n and a e r o s o l s a t B i r k e n e s , A p r i l - June 1975 ( 2 ) .

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch001

1.

OTTAR

Acidification of Precipitation

17

The s p a r c e amount on n u t r i e n t elements p r i m a r i l y o r i g i n a t e from the v i t r i f i c a t i o n of the f e l t s p a r m i n e r a l s . The hydrogen i o n s , r e q u i r e d by the v i t r i f i c a t i o n p r o c e s s , a r e a v a i l a b l e from the c a r b o n i c a c i d d i s s o l v e d i n t h e water o r from o r g a n i c a c i d s produced by the r o o t s o f the p l a n t s . In the top s o i l , r o o t s and dead p l a n t m a t e r i a l , i n t h e form o f humus, f u n c t i o n as a c a t i o n exchanger where d i s s o l v e d m e t a l i o n s as c a l c i u m , magnesium and p o t a s s i u m from the v i t r i f i c a t i o n of m i n e r a l s , p r e c i p i t a t i o n and o r g a n i c l i t t e r a r e h e l d back i n exchange f o r hydrogen i o n s . In passing this l a y e r , t h e p r e c i p i t a t i o n water becomes more a c i d , and i r o n and aluminium a r e d i s s o l v e d i n the upper p a r t o f the sand l a y e r . F u r t h e r down, the a c i d i t y i s reduced by t h e d i s s o l u t i o n o f c a l c i u m , magnesium and p o t a s s i u m from the m i n e r a l s , and i r o n and aluminium a r e r e d e p o s i t e d as h y d r o x i d e s (see F i g u r e 12). T h i s i s a n a t u r a l p r o c e s s which d u r i n g some thousand y e a r s has l e d t o format i o n o f the c h a r a c t e r i s t i c p o d s o l p r o f i l e : on t h e t o p a l a y e r of b l a c k humus, t h e n a n e a r l y w h i t e l a y e r of leached silicates, and underneath a d e p o s i t i o n l a y e r , which t a k e s on f i r s t a y e l l o w and then a r e d c o l o u r as the i r o n i s p r e c i p i t a t e d o u t . In t h i s system, t h e a c i d i t y o f t h e s o i l l i q u i d i s l i m i t e d by the amount of m o b i l e a n i o n s . The more i m p o r t a n t are the sulphate, n i t r a t e and c h l o r i d e i o n s , a l l o f which o r i g i n a t e from t h e p r e c i p i t a t i o n . The c h l o r i d e i o n s a r e u s u a l l y accompanied by an equivalent amount o f sodium i o n s , w h i c h a r e n o t t a k e n up by t h e p l a n t s and r e t a i n e d by the humus t o any s i g n i f i c a n t degree. Most o f the nitrates a r e consumed by t h e v e g e t a t i o n . The acidity of the s o i l may c o n v e n i e n t l y be c h a r a c t e r i z e d by t h e c o n t e n t o f m e t a l i o n s , r e l a t i v e t o the total c a t i o n exchange c a p a c i t y of the soil. I n the a c i d t y p e s of s o i l c o n s i d e r e d here, t h i s base s a t u r a t i o n degree i s u s u a l l y below 10%. The degree o f base saturation w i l l be reduced when (1) the r o o t s t a k e up exchangeable c a t i o n s from t h e s o i l , and (2) when a c c u m u l a t i o n o f dead plant material i n c r e a s e s the amount o f humus, and t h e r e b y the c a t i o n exchange c a p a c i t y . To a c e r t a i n degree, b o t h o f t h e s e p r o c e s s e s are reversible, but i f p l a n t p r o d u c t s a r e removed from the a r e a w i t h o u t a p p l i c a t i o n o f f e r t i l i z e r s , manure o r l i m e , t h i s represents an a c i d i f i c a t i o n by r e d u c i n g the a v a i l a b l e s u p p l y o f c a t i o n s . The a c i d i f y i n g e f f e c t o f t h e v e g e t a t i o n i s t h e r e f o r e l i m i t e d t o a r e g u l a t i o n of the wash-out o f the b a s i c components formed by v i trification o f t h e m i n e r a l s . I n a d d i t i o n t o t h i s , humus components ( f u l v i c a c i d ) , and m i n e r a l i z a t i o n of reduced s u l p h u r and nitrogen compounds may t o some e x t e n t c o n t r i b u t e t o the a c i d i t y and t h e a n i o n c o n c e n t r a t i o n i n the d r a i n a g e water. But t h i s seems t o be o f l i m i t e d s i g n i f i c a n c e f o r t h e " r e g i o n a l a c i d i f i c a t i o n problem". The a c i d i f i c a t i o n o f the d r a i n a g e water i s p a r t i c u l a r l y r e l a t e d t o sulphate i o n s . Along t h e i r route i n the s o i l , the sulphate ions must b r i n g w i t h them an e q u i v a l e n t amount o f hydrogen i o n s or o t h e r c a t i o n s . The humus i o n exchanger does not w i l l i n g l y g i v e away cations; on the c o n t r a r y , i t removes m e t a l i o n s from the p r e c i p i t a t i o n . Some c a t i o n s , however, a r e r e l e a s e d a l l the t i m e by vitrification. Aluminium h y d r o x i d e w h i c h i s accumulated i n the d e p o s i t i o n l a y e r , a c t s as a weak b a s i c a n i o n exchanger, and may hold back s i g n i f i c a n t amounts of t h e s u l p h a t e i o n s i n t h e w a t e r . I n s o u t h e r n Norway the t o t a l amount o f s u l p h a t e r e t a i n e d may correspond to

MATERIALS DEGRADATION CAUSED BY ACID RAIN

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch001

18

F i g u r e 11.

The r i g h t s i d e shows a r e a s i n Sweden w i t h l a k e water pH 5.0 ( b l a c k ) a l l year round i n a t l e a s t one t h i r d of t h e l a k e s and a r e a s w i t h pH 5.5 (gray) some time d u r i n g t h e y e a r i n a t l e a s t h a l f of t h e l a k e s (SNV, 1981). The l e f t s i d e shows a r e a s i n Norway when t h e f i s h i s v i r t u a l l y e x t i n c t ( b l a c k ) and a r e a s where t h e f i s h p o p u l a t i o n i s s t r o n g l y a f f e c t e d (gray) (Munitz and L e i v e s t a d , 1980).

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Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch003

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F i g u r e 1 2 . C o n c e n t r a t i o n o f hy dr ox y me thane sulfonate measured S ( I V ) and v s . measured (HCHO).

(HMSA) v s .

4.

HOFFMANN

75

Fog and Cloud Water Deposition

p r o d u c t i o n under pH c o n d i t i o n s c h a r a c t e r i s t i c o f f o g and c l o u d water has been s t u d i e d i n o u r l a b o r a t o r y . Boyce and Hoffmann ( 4 6 ) found t h a t t h e f o r m a t i o n o f HMSA over t h e pH range 0 . 0 t o 3 . 5 o c c u r s by p a r a l l e l r e a c t i o n pathways i n v o l v i n g n u c l e o p h i l i c a d d i t i o n o f HSO3 and SO3 " t o t h e c a r b o n y l C-atom o f formaldehyde as f o l l o w s :

CH (0H) 2

2

CH 0 + H 0

2

S 0 - H 0 2

HS0 " Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch004

3

HSO3-

+ CH 0 2

S 0

3 " 2

H

2

+

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+

+

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)

2

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a 2

)

S0 " 3

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(k ), (k^), ( Κ ) x

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2

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χ

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loVV

1

where ^ = 7 . 9 0 χ l o V s " and k = 2 . 4 8 χ at 2 5 ° C . The f o r m a t i o n c o n s t a n t , Κ ι , has been determined ..recently by D e i s t e r et a l . ( 4 ^ ) and Kok e t a l . ( 4 8 ) t o be 1 0 ' M . T h i s number i s i n agreement w i t h t h o s e r e p o r t e d p r e v i o u s l y by Kerp ( 4 9 ) and D o n a l l y (50). Under more weakly a c i d i c c o n d i t i o n s (pH > 4 ) , t h e d e h y d r a t i o n o f methylene g l y c o l ( e q u a t i o n K.) may become r a t e - d e t e r m i n i n g ( 5 1 ) . A p p l i c a t i o n o f t h e r a t e c o n s t a n t s and a c t i v a t i o n energy parameters o b t a i n e d i n t h e l a b o r a t o r y t o t h e a n a l y s i s o f t h e f i e l d measurements d i s c u s s e d above i n d i c a t e s t h a t HMSA f o r m a t i o n may account f o r t h e o c c u r r e n c e o f S ( I V ) a t e l e v a t e d c o n c e n t r a t i o n s ( 4 4 ) · K i n e t i c data o b t a i n e d f o r o t h e r a l d e h y d e / s u l f u r ( I V ) r e a c t i o n systems s u g g e s t s t h a t t h e mechanism o u t l i n e d above can be g e n e r a l i z e d t o d e s c r i b e t h e f o r m a t i o n o f a wide v a r i e t y o f α - h y d r o x y a l k a n e s u l f o n a t e s ( 5 2 ) . In o r d e r t o develop a comprehensive p h y s i o c h e m i c a l d e s c r i p t i o n o f t h e complex S 0 r e a c t i o n network i n a t m o s p h e r i c d r o p l e t s , r a t e l a w s , mechanisms ana a c t i v a t i o n e n e r g i e s a r e b e i n g determined f o r t h e various pathways of sulfur dioxide transformation i n aqueous solution. However a t t h i s t i m e c o m p l e t e i n f o r m a t i o n h a s been assembled i n o n l y a very few c a s e s . The mechanism o f S ( I V ) o x i d a t i o n by hydrogen p e r o x i d e i s f a i r l y w e l l understood ( 3 3 * 5 3 - 5 7 ) · The r e a c t i o n proceeds by n u c l e o p h i l i c d i s p l a c e m e n t o f water by H 0.£ on bisulfite i o n t o form p e r o x y m o n o s u l f i t e anion (H00S0 2 ~), wnich r e a r r a n g e s t o s u l f a t e under t h e i n f l u e n c e o f s p e c i f i c and g e n e r a l acid catalysis (57-58). The s i g n i f i c a n c e o f t h i s l a t t e r f e a t u r e f o r open a t m o s p h e r i c systems has been d i s c u s s e d by Schwartz ( 5 J , M a r t i n ( 3 5 0 , Jacob and Hoffmann ( 2 3 ) , Hoffmann and Jacob ( 3 7 J , and McArdle and Hoffmann ( 5 7 ) , and Hoffmann and C a l v e r t ( 3 9 ) . Hoffmann ( 5 9 ) has p r o p o s e d a m e c h a n i s m f o r t h e o x i d a t i o n o f S ( I V ) by o z o n e t h a t proceeds v i a t h e s i m u l t a n e o u s n u c l e o p h i l i c a t t a c k on ozone by SO3 ", HSO3", and S 0 ^ * H 0 . Hoffmann ( 5 9 ) has a n a l y z e d t h e k i n e t i c d a t a o f a 1

1

2

2

2

2

MATERIALS DEGRADATION CAUSED BY ACID RAIN

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch004

76

number o f d i f f e r e n t i n v e s t i g a t o r s ( 3 5 , 6 0 - 6 3 ) i n terms of a s i n g l e s e l f - c o n s i s t e n t rate expression. For the metal-catalyzed autoxidation of S(IV), there is c o n s i d e r a b l e a m b i g u i t y about the mechanism(s) o f r e a c t i o n . First-row t r a n s i t i o n - m e t a l s p e c i e s can c a t a l y z e t h e r e a c t i o n of aquated s u l f u r dioxide and 0? t h r o u g h four distinctly different pathways as d e s c r i b e d by Hotfmann and Boyce (36) and Hoffmann and Jacob ( 3 7 ) . These mechanisms i n c l u d e : a t h e r m a l l y - i n i t i a t e d free r a d i c a l chain processes involving a sequence of o n e - e l e c t r o n transfer steps, heterolytic pathways in which formation of an inner-sphere m e t a l - s u l f i t e - d i o x y g e n complex o c c u r s as a p r e l u d e t o t w o - e l e c t r o n t r a n s f e r , iieterogeneous c a t a l y s i s through complexation of HSOg and/or SOg " at the s u r f a c e o f metal o x i d e s and o x y h y d r o x i d e s i n s u s p e n s i o n , and p h o t o c h e m i c a l o x i d a t i o n i n i t i a t e d by t h e a b s o r p t i o n o f l i g h t by S ( I V ) , metal c a t i o n s , m e t a l - o x i d e s e m i c o n d u c t o r s , and/or s p e c i f i c m e t a l - s u l f i t e complexes. Hoffmann and Jacob (37) have compared t h e t h e o r e t i c a l k i n e t i c expressions for each t y p e of mechanism w i t h the e m p i r i c a l r a t e data o b t a i n e d i n experimental s t u d i e s of the c a t a l y t i c a u t o x i d a t i o n of SO^. Q u a n t i t a t i v e a n a l y s i s of d i f f e r e n t r e a c t i o n pathways for the transformation o f aquated s u l f u r d i o x i d e i n atmospheric droplet systems has been a major o b j e c t i v e of the r e s e a r c h conducted i n t h e principal investigator's laboratory for the last four years. A v a i l a b l e thermodynamic and k i n e t i c d a t a f o r the aqueous-phase r e a c t i o n s of SOp have been i n c o r p o r a t e d i n t o a dynamic model of the c h e m i s t r y o f urban f o g t h a t has been developed by Jacob and Hoffmann (23) and Hoffmann and C a l v e r t ( 3 9 ) · The f o g and c l o u d water models developed by them are h y b r i d k i n e t i c and e q u i l i b r i u m models t h a t c o n s i d e r the major chemical r e a c t i o n s l i k e l y to take p l a c e i n a t m o s p h e r i c water droplets. Model r e s u l t s have v e r i f i e d that e x t r e m e l y high a c i d i t y may be imparted t o f o g water d r o p l e t s by c o n d e n s a t i o n and g r o w t h on a c i d i c n u c l e i o r by i n s i t u S(IV) oxidation. Based on both k i n e t i c and e q u i l i b r i u m c o n s i d e r a t i o n s the i m p o r t a n t o x i d a n t s i n t h e aqueous p h a s e were f o u n d t o be 0 c a t a l y z e d by F e ( I I I ) and M n ( I I ) , H 0 , and 0 (See F i g u r e s 13 and 14). The r e s u l t s o f t h e model c a l c u l a t i o n s snow t h a t m e t a l - s u l f i t e complexation (both with and without electron transfer) and hydroxyalkanesulfonate f o r m a t i o n enhance water d r o p l e t c a p a c i t y f o r S0 , but d i d not slow down the net S ( I V ) o x i d a t i o n r a t e l e a d i n g t o fog a c i d i f i c a t i o n . N i t r a t e p r o d u c t i o n i n t h e aqueous phase was found t o be dominated by HNOg gas phase s c a v e n g i n g . Highly a c i d i c fog water appears t o form p r e d o m i n a n t l y from c o n d e n s a t i o n on h i g h l y a c i d i c haze a e r o s o l ( i . e . f o g c o n d e n s a t i o n n u c l e i ) ; i n t h e s e cases ( i . e . pH 1.7 f o g a t Corona del M a r ) , i n s i t u S ( I V ) o x i d a t i o n l e a d s t o l i t t l e f u r t h e r a c i d i f i c a t i o n of the f o g w a t e r . In f i e l d s i t u a t i o n s , t h e u l t i m a t e a c i d i t y l e v e l i n f o g d e p e n d s upon t h e d e g r e e o f n e u t r a l i z a t i o n of f r e e a c i d i t y by ammonia or by scavenged a l k a l i n e aerosol. In Los Angeles more ammonia i s a v a i l a b l e f u r t h e r inland from the c o a s t . T h i s may e x p l a i n i n p a r t why h i g h e r f o g w a t e r a c i d i t i e s are found a l o n g the coast than at i n l a n d s i t e s . Similar o b s e r v a t i o n s have been made i n the Southern San J o a q u i n V a l l e y . 2

2

2

a

s

3

2

Waldman et a l . ( 2 5 j have s t u d i e d t h e c h e m i s t r y and m i c r o p h y s i c s o f i n t e r c e p t e d c l o u d w a t e r on Los Angeles area mountain s l o p e s . From 1982 t o 1985, the observed pH v a l u e s of t h e c l o u d w a t e r ranged from 2.06 t o 3 . 8 7 w i t h t h e median v a l u e below pH 3 (See F i g u r e 1 5 ) . The

4.

HOFFMANN

Fog and Cloud Water Deposition

ι

ι

1

11

1

1

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch004

(a)

2 I 0

I

I 4000

I

I 8000

I

I 12000

TIME ( s e c )

F i g u r e 1 3 . (a) P r o f i l e o f c o n c e n t r a t i o n v e r s u s time o f t o t a l S(VI) i n fogwater and o f the i n d i v i d u a l c o n t r i b u t i o n s to the t o t a l S(VI) due to d i f f e r e n t pathways. Model c a l c u l a t i o n s a r e shown f o r d i f f e r e n t aqueous*phase o x i d a n t s , (b) P r o f i l e o f pH v s . time f o r LWC = 0.1 g ni a t Τ = 10 C.

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch004

MATERIALS DEGRADATION CAUSED BY ACID RAIN

0

4000

TIME

(sec.)

8000

12000

F i g u r e 1 4 . P r o f i l e s o f c o n c e n t r a t i o n v s . time f o r pH, S ( V I ) , N ( - I I I ) , and N(V) as p r e d i c t e d by model c a l c u l a t i o n s .

4.

HOFFMANN

79

Fog and Cloud Water Deposition

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch004

40

30

% SAMPLING TIME

-Henninger Flats Stratus Rainfall (Spring 1983-15.8 mm) Pasadena Rainfall ( 1 9 7 8 / 7 9 - 6 1 0 m m ) *

20

Henninger Flats Storm Rainfall I ( 1 9 8 2 / 8 3 - 1 4 8 1 mm) Mt.Wilson R a i n f a l l * * j (1978/79-1270mm)

10

2.0 10

3.0 10

4

4.0 3

I0

2

5.0

pH

10

/i.eqH r

1

+

Volume-weight average H concentration *Liljestrand and Morgan (1981) +

F i g u r e 1 5 . H i s t o g r a p h o f pH f r e q u e n c y o f c l o u d w a t e r samples c o l l e c t e d a t Henninger F l a t s near A l t a d e n a , CA. Volume-weighted averages a r e i n d i c a t e d w i t h a r r o w s .

80

MATERIALS DEGRADATION CAUSED BY ACID RAIN

e q u i v a l e n t r a t i o o f n i t r a t e t o s u l f a t e i n c l o u d w a t e r at Henninger F l a t s (MSL = 2,520 f t . ) was c l o s e t o two, w h i l e at the same s i t e t h e [N03~]/[S0£ ] ratio in rainwater was * 1. However, the n i t r a t e / s u T f a t e r a t i o observed i n dry a e r o s o l was s i g n i f i c a n t l y lower than t h a t observed i n c l o u d w a t e r ; t h e a d d i t i o n a l n i t r a t e found i n c l o u d w a t e r appears t o be d e r i v e d from the scavenging o f gaseous n i t r i c a c i d (See F i g u r e 1 6 ) . In a d d i t i o n , a h i g h e r f r a c t i o n o f n i t r a t e a e r o s o l appears t o be scavenged by c l o u d d r o p l e t s . This o b s e r v a t i o n i s c o n s i s t e n t w i t h c u r r e n t t h e o r i e s of homogeneous versus heterogeneous g a s - t o - p a r t i c l e pathways open t o s u l f u r d i o x i d e versus nitrogen oxides. C l o u d d r o p l e t c a p t u r e i n the form of i n t e r c e p t e d f o g appears t o be a s e a s o n a b l y i m p o r t a n t s i n k f o r p o l l u t a n t e m i s s i o n s i n the LA Basin. At Henninger F l a t s up t o 50% of t h e t o t a l wet d e p o s i t i o n of H , NOo", and S0^~ may be due t o c l o u d i n t e r c e p t i o n ; low i n t e n s i t y s p r i n g t i m e d r i z z l e accounted f o r 20% of the d e p o s i t i o n measured i n precipitation. The i n t e r c e p t e d c l o u d w a t e r t h a t d e p o s i t e d on p i n e n e e d l e s was c o l l e c t e d and a n a l y z e d . The a c i d i t y o f t h e w a t e r d r i p p i n g f r o m t r e e s was v e r y s i m i l a r t o t h a t o f t h e s u s p e n d e d cloudwater. The c o n c e n t r a t i o n s of major chemical components were found t o be s i g n i f i c a n t l y g r e a t e r than i n t h e o v e r l y i n g c l o u d w a t e r . The a d d i t i o n a l s o l u t e i n t h e d r i p p i n g s i s thought t o be d e r i v e d from previously deposited material and the evaporated residue of intercepted cloudwater. Even a f t e r s u f f i c i e n t r a i n f a l l had removed most o f the accumulated r e s i d u e , the c o n c e n t r a t i o n s o f major c a t i o n s

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch004

+

such as C a , M g , and K showed r e l a t i v e i n c r e a s e s compared t o suspended c l o u d w a t e r samplers. Theje i n c r e a s e s m a y ^ e a t t r i b u t e d i n p a r t t o ion-exchange o f H f o r Κ , Mg , and Ca from t h e p i n e needles (64). The p o t e n t i a l f o r harm t o s e n s i t i v e p l a n t t i s s u e appears to be high given prolonged exposure to the severe m i c r o e n v i r o n m e n t s observed on t h e s l o p e s o f the San G a b r i e l Mountains and i n the Angeles N a t i o n a l F o r e s t . 2 +

2 +

+

The C a l t e c h r o t a t i n g arm c o l l e c t o r (RAC) was c a l i b r a t e d p r e c i s e l y u s i n g a s c a l e model r o t a t i n g arm d e v i c e and a c h e m i c a l l y tagged monodisperse a e r o s o l . Jacob e t a l . (65) have c h a r a c t e r i z e d t h e performance o f t h e r o t a t i n g arm c o l l e c t o r i n great d e t a i l . The r o t a t i n g arm c o l l e c t o r was d e s i g n e d t o meet the f o l l o w i n g c r i t e r i a : 1. The a e r o d y n a m i c h e a t i n g a s s o c i a t e d w i t h t h e f l o w o f a i r towards t h e i m p a c t o r s u r f a c e must be s m a l l enough not t o cause droplet evaporation. 2 . The c o l l e c t e d d r o p l e t s must be r a p i d l y s h e l t e r e d from t h e changing air masses to prevent evaporation and chemical contamination. 3 . The l o w e r s i z e cut must be sharp and i n t h e range o f 1-10 urn, and no s a m p l i n g b i a s e s must be i n t r o d u c e d f o r the d r o p l e t s up t o at l e a s t 50 pm. 4 . The s a m p l i n g r a t e must be h i g h enough t o c o l l e c t s u f f i c i e n t amounts of sample for chemical analysis while allowing a reasonable time r e s o l u t i o n . These c r i t e r i a were met w i t h the e x c e p t i o n of c r i t e r i a 3 . Jacob et a l . (65) found t h a t the s c a l e model v e r s i o n o f the RAC had a p a r t i c l e s i z e cut o f 20 um r a t h e r than the d e s i r e d 1-10 ym c u t . ( S e e F i g u r e 17) The RAC performs w e l l i n p r e s e r v i n g the chemical i n t e g r i t y o f t h e c o l l e c t e d d r o p l e t s and p r o v i d e s a h i g h s a m p l i n g r a t e ; however, i t has t h e d r a w b a c k t h a t i t does not c o l l e c t e f f i c i e n t l y t h e s m a l l e r

HOFFMANN

Fog and Cloud Water Deposition

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch004

1.34

JUNE I I , 1983

F i g u r e 16. C o n c e n t r a t i o n f o r sequential cloudwater

JUNE 12, 1983

( a ) , LWC ( b ) , samples.

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10

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15

20

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I

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F i g u r e 17. C o l l e c t i o n e f f i c i e n c y o f model c o l l e c t o r ( i . e . , a scaled-down v e r s i o n o f the Cal tech r o t a t i n g arm c o l l e c t o r ) v s . g e n e r a l i z e d Stokes number. Predicted ( ) ; Experimental (|—

J

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Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch004

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Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch004

4. HOFFMANN

Fog and Cloud Water Deposition

83

d r o p l e t s i n t h e f o g . T h i s has not proved t o be a s i g n i f i c a n t problem i n t h a t p r e l i m i n a r y d a t a suggest t h a t t h e r e i s very l i t t l e v a r i a t i o n o f c h e m i c a l c o m p o s i t i o n of f o g water d r o p l e t s w i t h s i z e . Changes i n t h e c o l l e c t o r geometry, such as s t r e a m l i n e s h a p i n g t o reduce d r a g , would produce a s m a l l e r s i z e c u t . Jet impactors and s c r e e n c o l l e c t o r s are b e i n g e v a l u a t e d as an a l t e r n a t i v e t o r o t a t i n g arm collectors. In June o f 1 9 8 3 , f i v e different types of f o g / c l o u d water c o l l e c t o r s were compared under f i e l d c o n d i t i o n s at Henninger F l a t s . C o l l e c t o r s designed by A e r o V i r o n m e n t ( A V ) , C a l t e c h ( C I T ) , t h e Desert Research I n s t i t u t e ( D R I ) , G l o b a l Geochemistry(GGC), and t h e S t a t e U n i v e r s i t y of New York(SUNY)-Albany were t e s t e d a g a i n s t one a n o t h e r . The mass and pH o f t h e samples c o l l e c t e d were measured on s i t e w h i l e t h e d e t a i l e d c h e m i c a l a n a l y s e s were performed by an independent l a b o r a t o r y , Rockwell I n t e r n a t i o n a l . Results of the intercomparison s t u d y , sponsored t h e t h e C o o r d i n a t i n g Research C o u n c i l , showed t h a t t h e Cal t e c h and DRI c o l l e c t o r s performed the best over t h e broadest range o f c o n d i t i o n s ( 6 6 , 6 7 ) . At low l i q u i d water content ( i . e . LWC < 0.03 g / n r ) , t h e SUNY-Albany r o t a t i n g s t r i n g c o l l e c t o r , t h e DRI j e t i m p a c t o r , and t h e C a l t e c h r o t a t i n g arm c o l l e c t o r had r e a s o n a b l e collection rates. The G l o b a l Geochemistry mesh c o l l e c t o r and t h e AeroVironment r o t a t i n g rod c o l l e c t o r were not e f f e c t i v e under low LWC c o n d i t i o n s . With r e s p e c t t o s u l f a t e , n i t r a t e , and pH v a l u e s o b t a i n e d under a wide v a r i e t y o f c o n d i t i o n s o v e r 38 hours o f f o g , t h e C a l t e c h and DRI c o l l e c t o r s showed t h e most c o n s i s t e n c y and c l o s e s t agreement. The Suny-Albany and t h e AerVironment c o l l e c t o r s showed t h e g r e a t e s t d e v i a t i o n s from t h e median v a l u e s . For example the s l o p e o f t h e observed [SO^"] v s . median [S0^"] over t h e range o f c o n c e n t r a t i o n from 100 t o 2000 Μ f o r the SUNY, C a l t e c h , DRI, AeroVi ronment, and Global collectors, respectively, were 0.69(SUNY), 0.95(CIT), 0 . 9 1 ( D R I ) , 1.66(AV), and 1.21(GGC). The h i g h v a l u e s f o r t h e AV and GGC c o l l e c t o r s i n d i c a t e t h a t c o n c e n t r a t i o n e f f e c t s due t o e v a p o r a t i o n a r e s i g n i f i c a n t problems i n t h e s e c o l l e c t o r s . In t h e case o f n i t r a t e c o r r e l a t i o n s , t h e s l o p e s of the observed c o n c e n t r a t i o n s v s . the median v a l u e s f o r t h e same sequence of c o l l e c t o r s were found t o be 0.83(SUNY), 0 . 9 4 ( C I T ) , 0 . 9 3 ( D R I ) , 2 . 4 3 ( A V ) , and 1.17(GGC). When i d e n t i c a l RAC's were p l a c e d at d i f f e r e n t l o c a t i o n s at Henninger F l a t s the results correlated quite w e l l . There appeared t o be no s t a t i s t i c a l d i f f e r e n c e between the s e p a r a t e d c o l l e c t o r s ( 6 6 , 6 7 ) . μ

Summary o f M a j o r O b s e r v a t i o n s 1.

2.

and C o n c l u s i o n s

Fogwater c o l l e c t e d at s i t e s i n the South Coast A i r B a s i n of Los Angeles was consistently acidic, with pH values t y p i c a l l y r a n g i n g from 2 t o 4 . The h i g h e s t a c i d i t i e s were observed d u r i n g smog e p i s o d e s . The main c o n t r i b u t o r s t o the a c i d i t y were n i t r i c and s u l f u r i c a c i d s , w i t h a t y p i c a l e q u i v a l e n t r a t i o of 3 : 1 . Secondary s u l f a t e and n i t r a t e a e r o s o l accounted f o r over 80% o f t h e fogwater l o a d i n g . Fogwater c o l l e c t e d at non-urban c o a s t a l s i t e s was u s u a l l y a c i d i c (pH range 3 t o 7 ) . Impact o f e m i s s i o n c e n t e r s on distant coastal locations was documented. The low a l k a l i n i t y of marine atmospheres make them p a r t i c u l a r l y

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch004

MATERIALS DEGRADATION CAUSED BY ACID RAIN

susceptible to acidification. Oxidation of oceanic d i m e t h y l s u l f i d e c o u l d be a n a t u r a l source of s u l f u r i c a c i d . S t r a t u s c l o u d s c o l l e c t e d at 2500' MSL o v e r the Los Angeles B a s i n were c o n s i s t e n t l y a c i d i c , pH range 2 t o 4 . Cloudwater c o n c e n t r a t i o n s were i n the same range as t h o s e observed i n the basin i t s e l f . F o g w a t e r c o l l e c t e d i n t h e Southern San J o a q u i n V a l l e y was not c o n s i s t e n t l y a c i d i c ; pH v a l u e s ranged from 2 . 5 t o 7 . 5 . Millimolar concentrations of sulfate were typically o b s e r v e d , but h i g h ammonia e m i s s i o n s from l i v e s t o c k and c r o p l a n d n e u t r a l i z e d the a c i d i n p u t . V i s a l i a , which i s some d i s t a n c e f r o m t h e m a j o r e m i s s i o n s o u r c e s , had a l k a l i n e f o g w a t e r (pH 6 - 7 . 5 ) . M c K i t t r i c k , l o c a t e d i n an o i l f i e l d w i t h l i t t l e s u r r o u n d i n g a g r i c u l t u r a l a c t i v i t y , had a c i d i c fogwater (pH 2 . 5 - 4 . 5 ) . L i q u i d water content (LWC) was t h e major f a c t o r a f f e c t i n g i o n i c concentrations in fogs. As the fog formed, d r o p l e t growth d i l u t e d t h e d r o p l e t s ; as t h e f o g d i s s i p a t e d , t h e d r o p l e t s became more c o n c e n t r a t e d . E v i d e n c e was found f o r the major p r o c e s s e s r e s p o n s i b l e f o r t h e a c i d i f i c a t i o n of f o g w a t e r : ( i ) the s c a v e n g i n g o f a c i d i c p r e c u r s o r a e r o s o l , ( i i ) t h e s c a v e n g i n g o f gaseous n i t r i c a c i d , and ( i i i ) o x i d a t i o n o f reduced s u l f u r components t o sulfate. C o n v e r s i o n o f S 0 ( g ) t o s u l f a t e i n fogwater does not appear t o proceed f a s t e r than 10% hour" and t h e r e f o r e cannot account f o r the high a c i d i t i e s observed at the b e g i n n i n g o f fog e v e n t s ; however, s u l f a t e p r o d u c t i o n i n t h e precursor air parcel can lead to sulfuric acid fog condensation n u c l e i . Modeling of fogwater chemistry i n d i c a t e d t h a t the high a c i d i t i e s observed can be e x p l a i n e d by e i t h e r o f t h e t h r e e processes l i s t e d above. The main aqueous-phase S(IV) o x i d a n t s were found t o be hydrogen p e r o x i d e , o z o n e , and oxygen (catalyzed by trace metals). Aqueous-phase p r o d u c t i o n o f n i t r a t e was found t o be u n i m p o r t a n t . The r o t a t i n g arm c o l l e c t o r d e s i g n e d i n our l a b o r a t o r y and used to sample fogwater was fully characterized. E v a p o r a t i o n of d r o p l e t s d u r i n g a l l stages o f c o l l e c t i o n was shown t o be n e g l i g i b l e . Experimental c a l i b r a t i o n i n d i c a t e d a l o w e r s i z e c u t o f 1 5 - 2 0 m i c r o n s . F i e l d d a t a show an o v e r a l l l i q u i d water c o l l e c t i o n r a t e o f about 60%. A f i e l d intercomparison of fogwater collectors used by various investigators confirmed that our sampler collects r e p r e s e n t a t i v e samples. 2

A s c r e e n c o l l e c t o r ( l o w e r s i z e cut 2 m i c r o n s , s a m p l i n g r a t e 20 m min ) was designed (68) and has been used i n the field. S i d e - b y - s i d e comparison i n d i c a t e s t h a t samples c o l l e c t e d w i t h t h i s c o l l e c t o r and w i t h t h e r o t a t i n g arm have similar concentrations. C o n c e n t r a t i o n s o f S ( I V ) i n fogwater were f a r i n e x c e s s o f t h o s e e x p e c t e d t o be i n e q u i l i b r i u m w i t h ambient S 0 ( g ) . E l e v a t e d formaldehyde c o n c e n t r a t i o n s suggest t h e f o r m a t i o n o f a f o r m a l d e h y d e - S ( I V ) complex; k i n e t i c and model s t u d i e s have shown t h a t t h i s complex i s very s t a b l e and t h a t i t s f o r m a t i o n l e a d s t o h i g h aqueous-phase S ( I V ) c o n c e n t r a t i o n s . 2

4.

HOFFMANN

11.

12.

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Fog and Cloud Water Deposition

E x t e n s i v e B a k e r s f i e l d fogwater d a t a i n d i c a t e d an i m p o r t a n t removal t o the ground of p o l l u t a n t s scavenged by the f o g droplets. T h i s was a s c r i b e d t o the slow r e s i d e n c e t i m e o f the supermicron fog d r o p l e t s i n the atmosphere. In a stagnant atmosphere this deposition was suspected to a l l e v i a t e b u i l d - u p o f suspended p a r t i c l e s . On t h e mountain slopes surrounding the Los Angeles Basin, such non-recipitating wet deposition was shown to be a s i g n i f i c a n t s o u r c e of o v e r a l l p o l l u t a n t , d e p o s i t i o n . C o n c e n t r a t i o n s o f NH , N 0 " and S 0 / ~ _ i n urban fogwater samples are r o u t i n e l y on the o r d e r o f l O " M . The r e l a t i v e importance of NO3" and S 0 reflects their e m i s s i o n p a t t e r n i n the v i c i n i t y . N i t r a t e exceeds SO^ " by a facto. The r e l a t i v e importance o f NO3"" and S 0 reflects £heir e m i s s i o n p a t t e r n i n the v i c i n i t y . N i t r a t e exceeds SO^ " by a f a c t o r of 2-3 i n Los Angeles where v e h i c l e e m i s s i o n s o f Ν 0 are s i g n i f i c a n t . S u l f a t e e q u a l s o r exceeds n i t r a t e i n the Southern San J o a q u i n Valley where e m i s s i o n s from o i l - p r o d u c t i o n f a c i l i t i e s are i m p o r t a n t . F o g - and c l o u d - w a t e r i n the Los Angeles B a s i n r o u t i n e l y has a pH < 4 w i t h t h e lowest v a l u e b e i n g below 2 . Ammonia e m i s s i o n s i n t h e Southern San J o a q u i n V a l l e y are s u f f i c i e n t t o n e u t r a l i z e most o f t h e a c i d i t y p r e s e n t . Acid a n i o n c o n c e n t r a t i o n s i n B a k e r s f i e l d are comparable t o t h o s e i n L A , but very few fogwater samples had-pH < 4 ; ammonium was about equal t o t h e sum of NO3" and S 0 . D r o p l e t growth and e v a p o r a t i o n i s a major f a c t o r d e t e r m i n i n g f o g w a t e r c o n c e n t r a t i o n s — t h e h i g h e s t c o n c e n t r a t i o n s are observed as f o g d i s s i p a t e s . D e p o s i t i o n of f o g d r o p l e t s appears t o be s i g n i f i c a n t . The mass o f s o l u t e per volume o f a i r d e c r e a s e s over t h e c o u r s e of a fog event. Repeated fogs may d i m i n i s h the b u i l d u p of pollutants during stagnation episodes. No s t a t i s t i c a l e v i d e n c e f o r aqueous-phase s u l f u r o x i d a t i o n c a n be f o u n d f o r e v e n t s . However o v e r t h e c o u r s e o f s t a g n a t i o n e p i s o d e s i n the Southern San J o a q u i n V a l l e y the s u l f a t e f r a c t i o n i n the aerosol i n c r e a s e s . C o n c e n t r a t i o n s o f - S ( I V ) and CH^O i n f o g and c l o u d w a t e r on t h e o r d e r of 10 _M_ are. r o u t i n e l y found i n urban a r e a s . Peak v a l u e s a r e about 1 0 ~ The p a r t i a l p r e s s u r e o f S 0 d u r i n g f o g i s much t o o low t o + s u p p o r t a l l o f t h e S(IV) as f r e e S(IV) ( S 0 / H 0 + HSO3" SO3 " ) . These o b s e r v a t i o n s of h i g h S ( I v ) can b e s t be e x p l a i n e d by t h e f o r m a t i o n of S ( I V ) - a l d e h y d e a d d u c t s . The s o l u t e l o a d i n g (mass/m a i r ) i n f o g i s comparable t o that i n the a e r o s o l . The N 0 3 ~ / S 0 " r a t i o i n f o g i s h i g h e r t h a n i n t h e d r y a e r o s o l p r o c e e d i n g t h e f o g , which suggests t h a t gaseous HNO3 i s incorporated i n t o the f o g . D e p o s i t i o n from f o g by s e d i m e n t a t i o n o r i m p a c t i o n may be comparable t o r a i n f a l l d e p o s i t i o n at some mountain s i t e s . Trees are very e f f i c i e n t c o l l e c t o r s and a r e o f t e n bathed with impacted f o g . Fogwater i m p a c t i n g on vegetation 4

3

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Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch004

13.

4

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J

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4

MATERIALS DEGRADATION CAUSED BY ACID RAIN

86

24.

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r o u t i n e l y had a pH of 3 , which may be i n j u r i o u s t o s e n s i t i v e species. In a d d i t i o n t o f o r m a l d e h y d e , f o g - and c l o u d w a t e r c o n t a i n a v a r i e t y of higher aldehydes. A c e t a l d e h y d e and proponal (or acrolein) often have concentrations comparable to formaldehyde. Low m o l e c u l a r weight c a r b o x y l i c a c i d s are p r e s e n t i n fog and cloudwater at about 1 0 " _M_. Formic and a c e t i c acid dominate. 4

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch004

Acknowledgments We are g r a t e f u l t o t h e C a l i f o r n i a A i r Resources Board and t h e U.S. Environmental P r o t e c t i o n Agency f o r their support of the r e s e a r c h d e s c r i b e d above. In p a r t i c u l a r we would l i k e t o thank D r s . J. H o l m e s , D. L a w s o n , R. P a p e t t i , and M r . E. F u j i t a f o r t h e i r a s s i s t a n c e i n making t h i s r e s e a r c h p o s s i b l e .

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9. Smith, F. B. and Jeffrey, G. H. "Airborne Transport of Sulphur Dioxide from the U.K.," Atmos. Environ. 1975, 9, 643-659.

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10. Cox, R. A. "Particle Formation from Homogeneous Reactions of Sulfur Dioxide and Nitrogen Dioxide," Tellus 1974, 26, 235-240. 11. Zeldin, M. D., Davidson, Α., Brunelle, M. F., and Dickinson, J. E. "A Meteorological Assessment of Ozone and Sulfate Con­ centrations" in Southern California, Evaluation and Planning and Division Report 76-1 Southern California Air Pollution Control District, El Monte,CA,1979.

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch004

12. Diffenhoefer, A.C. and dePena, R. G. "A Study of Production and Growth of Sulfate Particles in Plumes from a Coal-fired Power Plant," Atmos. Environ. 1978, 12, 297-306. 13. Enger, L. and Hogstrom, U. "Dispersion and Wet Deposition of Sulfur from a Power Plant Plume," Atmos. Environ. 1981, 15, 297-306. 14. Wilson, J. C. and McMurry, P. H. "Studies of Aerosol Forma­ tion in Power Plant Plumes. I. Secondary Aerosol Formation in the Navajo Generating Station Plume," Atmos. Environ. 1981, 15, 2329-2339. 15. McMurry, P. Η., Rader, D. J., and Smith, J. L. "Studies of Aerosol Formation in Power Plant Plumes. I. Parameterization of Conversion Rate for Dry, Moderately Polluted Ambient Condi­ tions," Atmos. Environ. 1981, 15, 2315-2329. 16. Hegg, D. A. and Hobbs, P. V. "Cloudwater Chemistry and the Production of Sulfates in Clouds," Atmos. Environ. 1981, 15, 1597-1604. 17. Hegg, D. A. and Hobbs, P. V. "Measurements of Sulfate Produc­ tion in Natural Clouds," Atmos. Environ. 1982, 16, 2663-2668. 18. Daum, P. H., Schwartz, S. Ε., and Newman, L. "Acidic and Related Constituents in Liquid Water Stratiform Clouds," J. Geophys. Res. 1984, 89D, 1447-1458. 19. Jacob, D. J., Waldman, J. M., Munger, J. W., and Hoffmann, M. R. "A Field Investigation of Physical and Chemical Mechanisms Affecting Pollutant Concentrations in Fog Droplets," Tellus, 1984, 36B, 272-285. 20. Waldman, J. M. "Depositional Aspects of Fogs and Clouds," Ph.D. Thesis, California Institute of Technology, Pasadena, CA, 1985. 21. Waldman, J. Μ., Munger, J. W., Jacob, D. J., Flagan, R. C., Morgan, J. J., and Hoffmann, M. R. "Chemical Composition of Acid Fog," Science 1982, 218, 677-680. 22. Munger, J. W., Jacob, D. J., Waldman, J. M., and Hoffmann, M. R. "Foqwater Chemistry in an Urban Atmosphere," J. Geophys. Res. 1983, 88C, 5109-5121.

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23. Jacob, D. J. and Hoffmann, M. R. "A dynamic model for the pro­ duction ofH ,NO-3,andSO-4-inurban fog," J. Geophys. Res. 1983, 88C, 6611-6621. +

24. Jacob, D. J., Waldman, J. Μ., Munger, J. W., and Hoffmann, M. R. "Chemical Composition of Fogwater Collected Along the California Coast," Environ. Sci. Tech. 1985, 19, 730-735. 25. Waldman, J. M., Munger, J. W., Jacob, D. J., and Hoffmann, M. R. "Chemical Characterization of Stratus Cloudwater and Its Role as a Vector for Pollutant Deposition in a Los Angeles Pine Forest," Tellus, 1985, 37B, 91-108.

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch004

26. Martin, L. R. "Comment on Measurements of Sulfate Production in Natural Clouds," Atmos. Environ., 1983, 17, 1603-1604. 27. Schwartz, S. E. and Newman, L. "Comment on Measurements of Sulfate Production in Natural Clouds," Atmos. Environ., 1983, 17, 2629-2632. 28. Jacob, D. J., Munger, J. W., Waldman, J. Μ., and Hoffmann, M. R. "Aerosol composition in a stagnant air mass impacted by dense fogs: Preliminary results," in Proc. 77th Annual Meeting of the Air Pollution Control Assoc., San Francisco, CA, June 24-29, Paper 24.5, 1984. 29. Calvert, J. J. in Acid Precipitation, SO , NO, andNO Oxidation Mechanisms: Atmospheric Considerations, Butterworth Publishers, Stoneham, MA, 1984. 2

2

30. Hegg, D. A. and Hobbs, P. V. "Oxidation of Sulfur Dioxide in Aqueous Systems with Particular Reference to the Atmosphere," Atmos. Environ. 1978, 12, 241-253. 31. Kaplan, D. J., Himmelblau, D. M., and Kanaoka, C. "Oxidation of Sulfur Dioxide in Aqueous Ammonium Sulfate Aerosols Con­ taining Manganese as a Catalyst," Atmos. Environ. 1981, 15, 763-773. 32. Penkett, S. Α., Jones, R. M. R., and Eggleton, A. E. J. "A Study of SO Oxidation in Stored Rainwater Samples," Atmos. Environ., 1979, 13, 139-147. 2

33. Penkett, S. Α., Jones, B. M. R., Brice, Κ. Α., and Eggleton, A. E. J. "The Importance of Atmospheric Ozone and Hydrogen Peroxide in Oxidizing Sulfur Dioxide in Cloud and Rainwater," Atmos. Environ 1979, 13, 123-137. 34. Beilke, S. and Gravenhorst, G. (1978) "Heterogeneous SO2Oxidation in the Droplet Phase, Atmos. Environ. 1978, 12, 231-239.

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35. Martin, L. R. "Kinetic Studies of Sulfite Oxidation in Aqueous Solution," in Acid Precipitation, edited by J. G. Calvert, Butterworth Publishers, Stoneham, MA, 1984, 63-100. 36. Hoffmann, M. R., and Boyce, S. D. "Catalytic Autooxidation of Aqueous Sulfur Dioxide in Relationship to Atmospheric Systems," in Trace Atmospheric Constituents: Properties, Transformations, and Fates, S. E. Schwartz, ed. Adv. Environ. Sci. Technol. 1983, 12, 147-189.

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch004

37. Hoffmann, M. R. and Jacob, D. J. "Kinetics and Mechanisms of the Catalytic Oxidation of Dissolved Sulfur Dioxide in Aqueous Solution: An Application to Nighttime Fog-water Chemistry," in Acid Precipitation, edited by J. G. Calvert, Butterworth Publishers, Boston, MA., 1984. 38. Jacob, D. J. "The Origins of Inorganic Acidity in Fogs," Ph.D. Thesis, California Institute of Technology, Pasadena, CA, 1985. 39. Hoffmann, M. R. and Calvert, J. G. "Chemical Transformation Modules for Eulerian Acid Deposition Models Vol. II: The Aqueous-Phase Chemistry," EPA/MCAR Report DW 930237, March 1985. 40. Grosjean, D. "Formaldehyde and Other Carbonyls in Los Angeles Ambient Air," Environ. Sci. & Tech., 1982, 16, 254-262. 41. National Research Council, Formaldehyde and Other Aldehydes, National Academy Press, Washington, DC, 3981. 42. Grosjean, D. and Wright, B. "Carbonyls in Urban Fog,IceFog, Cloudwater, and Rainwaater, Atmos. Environ. 1983, 17, 2093-2096. 43. Richards, L. W., Anderson, J. Α., Blumenthal, D. L., McDonald, J. Α., Kok, G. L., and Lazrus, A. L. "Hydrogen Peroxide and Sulfur(IV) in Los Angeles Cloudwater," Atmos. Environ. 1983, 17, 2093-2096. 44. Munger, J. W., Jacob, D. J., and Hoffmann, M. R. "The Occur­ rence of Bisulfite-aldehyde Addition Products in Fog- and Cloud­ -water," J. Atmos. Chem. 1984, 1, 335-350. 45. Munger, J. W., Tiller, C., and Hoffmann, M. R. "Identification of Hydroxymethanesulfonate in Fog Water," in press, Science 1986. 46.

Boyce, S. D. and Hoffmann, M. R. "Kinetics and mechanism of the formation of hydroxymethanesulfonic acid at low pH," J. Phys. Chem., 1984, 88, 4740-4746.

47. Deister, U., Neeb, R., Helas, G., Warneck, P. "The Equilibrium CH )OH)S) =+ HO in Aqueous Solution: Temperature Dependence and Importance in Cloud Chemistry," J. Phys. Chem., 1986, in press. 2

3

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48. Kok, G. L., Gitlin, S. Ν., and Lazrus, A. L. "Kinetics of the Formation and Decomposition of Hydroxymethanesulfonate," J. Geophys Res. 1986, in press. 49. Kerp, W. Arbb Kaisel. Gesundh., 421, 1984, 180; Chem. Zentralblatt 1904, 75/II, 55-59. 50. Donally, L. H. Ind. Eng. Chem. Anal. Ed. 1933, 91-

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch004

51. Olson, T. M. and Hoffmann, M. R. "On the Kinetics of Formaldehyde-S(IV) Adduct Formation in Slightly Acidic Solution," Atmos. Environ. 1986, in review. 52. Olson, T. M., Boyce, S. D., and Hoffmann, M. R. "Kinetics, Thermodynamics, and Mechanism of the Formation of Benzaldehyde-S(IV) Adducts," J. Phys. Chem. 1986, in press. 53. Kunen, S. M., Lazrus, A. L., Kok, G. L., and Heikes, B. G. "Aqueous Oxidation of SO by Hydrogen Peroxide," J. Geophys. Res. 1983, 88, 3671-3674. 2

54. Martin, L. R. and Damschen, D. E. "Aqueous Oxidation of Sulfur Dioxide by Hydrogen Peroxide at Low pH," Atmos. Environ. 1981, 15, 1615-1622. 55. Halperin, J. and Taube, H. "The Transfer of Oxygen Atoms in Oxidation-Reduction Reactions. IV. The Reaction of Hydrogen Peroxide with Sulfite, Thiosulfate and of Oxygen, Manganese Dioxide and Permanganate with Sulfite," J. Am. Chem. 1975, 380-382. 56. Hoffmann, M. R. and Edwards, J. O. "Kinetics and Mechanism of the Oxidation of Sulfur Dioxide by Hydroqen Peroxide in Acidic Solution," J. Phys. Chem. 1975, 79, 2096-2098. 57. McArdle, J. V. and Hoffmann, M. R. "Kinetics and Mechanism of the Oxidation of Aquated Sulfur Dioxide by Hydrogen Peroxide at Low pH," J. Phys. Chem. 1983, 87, 5425-5429. 58. Mader, ?. M. "Kinetics of the Hydrogen Peroxide-sulfite Reac­ tion in Alkaline Solution," J. Am. Chem. Soc. 1958, 80, 26342639. 59. Hoffmann, M. R. "On the Kinetics and Mechanism of Oxidation of Aquated Sulfur Dioxide by Ozone," Atmos. Environ. 1986, in press. 60. Larson, T. V., Horike, N. R., and Halstead, H. "Oxidation of Sulfur Dioxide by Oxygen and Ozone in Aqueous Solution: A Kinetic Study with Significance to Atmospheric Processes," Atmos. Environ. 1978, 12, 1597-1611. 61. Maahs, H. G. "Measurements of the Oxidation Rate of Sulfur(IV) by Ozone in Aqueous Solution and Their Relevance to SO2 Conver­

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sion in Nonurban Tropospheric Clouds," Atmos. Environ. 1983, 17, 341-345. 62. Erickson, R. E., Yates, L. M., Clark, R. L., and McEwen "The Reaction of Sulfur Dioxide with Ozone in Water and Its Possible Atmospheric Significance," Atmos. Environ., 1977, 11, 813-817. 63. Hoigne, J., Bader, H., Haag, W. R., and Staehelin, J. "Rate Constants of Reactions with Ozone with organics and Inorganic Compounds in Water III. Inorganic Compounds and Radicals," Water Res. 1985, 19, 993-1004.

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch004

64. Tukey, Jr., H. B. "The Leaching of Substances from Plants," Ann. Rev. Plant Physiol. 1970, 71, 305-324. 65. Jacob, D. J., Wang, R-R. T., and Flagan, R. C. "Fogwater Col­ lector Design and Characterization, Environ Sci. & Technol. 1985, 18, 827-833. 66.

Hering, S. V. and Blumenthal, D. L. "Sampler Intercomparison Study," Final Report to Coordinating Research Council, Atlanta, GA, 1985.

67. Hering, S. V., Pettus, K., Gertler, Α., Brewer, R. L., Hoffmann, M. R., and Kadlecek, J. A. "Field Intercomparison of Five Types of Fog Water Collectors," Environ. Sci. Technol. 1986, in review. 68. Jacob, D. J., Waldman, J. M., Haghi, Μ., Hoffmann, M. R., and Flagan, R. C. "Instrument to Collect Fogwater for Chemical Analysis," Rev. Sci. Instrum. 1985, 56, 1291-1293. RECEIVED February 3, 1986

5 Urban Dew: Composition and Influence on Dry Deposition Rates Patricia A. Mulawa, Steven H . Cadle, Frank Lipari, Carolina C. Ang, and René T. Vandervennet

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch005

Environmental Science Department, General Motors Research Laboratories, Warren, MI 48090-9055

The composition of dew collected from a Teflon surface was compared to summer rainwater concentrations at a site in Warren, Michigan. This comparison showed that natural dew is similar to rainwater with the exception that dew has much higher concentrations of Ca and Cl and much lower acidity. Dry deposition rates of several species were measured to artificially-generated dew and a dry surface. It was found that deposition rates were 2 to 20 times greater to the artificial dew than to the dry surface indicating that the presence of dew enhances both the retention of dry deposited particles and the absorption of water soluble gases. Measurement of the atmospheric concentrations of the depositing species permitted the calculation of deposition velocities for particulate Cl , NO-3, SO-24, Ca , Mg , Na , andNH+4.Deposition velocities for gaseous HNO , HCl,SO andNH were also determined after correction for particle deposition. These results indicate that acid dew is not a problem at this site. However, the ability of dew to increase the deposition rate of acids and acid precursors to some surfaces suggests that dew may be more acidic at sites with lower deposition rates of basic particles. +2

-

-

+2

+2

+

3

2

3

Recently, interest in acid deposition has broadened to include s p e c i a l a c i d i c events such as dew, f r o s t , and fog. L i t t l e i s known about the frequency with which a c i d i c dew occurs, i t s composition, or i t s effect on dry deposition rates. However researchers have long recognized that surface wetness contributes to the corrosion of metal surfaces O ) and to the deterioration of stonework (2). 0097-6156/86/0318-0092S06.00/ 0 © 1986 American Chemical Society

5.

MULAWA ET A L .

93

Urban Dew

Additionally, acid dew may also be involved in plant e f f e c t s since i t has been reported that acid r a i n can damage protective surfaces on leaves, i n t e r f e r e with guard c e l l s , and poison plant c e l l s (3). A few studies on the composition of dew have been reported. Yaalon and Ganor (4), Brimbleeombe and Todd (5), Anderson and Landsberg (6) and Smith and Friedman (7) c o l l e c t e d dew from a variety of surfaces and report median pH values in the range of 5.7 to 7.7. Wisniewski (8) reviewed the sparse acid dew l i t e r a t u r e and calculated that dew could have a pH as low as 2 based s o l e l y on the oxidation of a l l deposited S0 to ^SOjj and no subsequent n e u t r a l i z a t i o n . Recently Pierson et a l . (9) found the pH of dew samples from Alleghany Mountain in Pennsylvania ranged from 3.5 to 5.3 with a volume weighted average of 4.0.

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch005

2

Cadle and G r o b l i c k i (JO) determined the composition of dew deposited naturally on glass, Teflon, and p l a s t i c surfaces in Warren, MI. Dew composition was compared to wet and dry deposition obtained the previous year at the same s i t e . In this paper, the comparison of dew and r a i n composition i s updated and the r e s u l t s of a new study of the composition of a r t i f i c i a l l y - g e n e r a t e d dew are reported. Deposi­ tion v e l o c i t i e s to the dew of S0 , HNO3, HC1, NH^, C a , Mg"", Na , and K are also presented. + 2

1

2

+

2

+

Experimental S i t e . Samples were collected from a s i t e located on a 330 acre parcel of undeveloped land in Warren, MI, a suburb north of Detroit. Most of the surrounding area i s highly developed. A major surface street 300 m south of the s i t e has a t r a f f i c flow of 20 000 vehicles/day. Another s t r e e t , 800 m east of the s i t e has a t r a f f i c flow of 38 000 vehicles/day. Annual emissions of Ν 0 , S0 , and TSP for the surrounding area have been presented elsewhere (11). χ

2

Dew C o l l e c t i o n . In our previous work, natural dew was c o l l e c t e d from a Teflon surface. The Teflon c o l l e c t o r consisted of a sheet of aluminum backed FEP Teflon bonded to a 1 m copper plate mounted on a plywood base. The c o l l e c t o r was t i l t e d 30° from horizontal with the centerpoint 1 m above the ground. In t h i s work the intent was to perform a more comprehensive analysis of the dew and to compare deposition v e l o c i t i e s to a wet and a dry surface. In order to bring more control to the experiment, dew was generated a r t i f i c i a l l y by attaching cooling c o i l s to the Teflon covered copper plate. The dry plate counterpart consisted of a 1 m glass c o l l e c t o r covered with Teflon and mounted in the same manner as the copper plate. A l l deposition rates are based on the actual area of the plate rather than the projected horizontal area, which was 0.87 m. 2

2

2

The natural dew c o l l e c t i o n procedure used previously consisted of washing the c o l l e c t o r with deionized water l a t e in the afternoon. Dew was collected the following morning at approximately 7:00 a.m.

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch005

94

MATERIALS DEGRADATION CAUSED BY ACID RAIN

The average elapsed time between cleaning and dew c o l l e c t i o n was 17 h. Since dew was not present the e n t i r e time, the dew concentra­ tions reported below include some material which was deposited on the dry c o l l e c t i o n plate and subsequently dissolved i n the dew. The samples were f i l t e r e d through 0.2 ym Gelman Acrodisc f i l t e r s prior to determining pH. The samples were then refrigerated u n t i l the remain­ ing analyses could be performed. Generation of a r t i f i c i a l dew started at approximately 7:30 a.m. and lasted for periods of 1.5 to 4.5 h. The average generation time was 3.1 h. A r t i f i c i a l dew generation was done only during periods with wind speeds less than 2 mph. Higher wind speeds limited our a b i l i t y to generate dew. Also, this procedure minimized turbulent mixing and thus approached more r e a l i s t i c nighttime deposition rates. The c o l l e c t o r was washed with deionized water immediately before use. Samples were processed i n the same manner as the natural dew samples. The dry c o l l e c t i o n plate was likewise cleaned with deionized water immediately prior to the onset of a r t i f i c i a l dew formation. Thus, the two c o l l e c t i o n plates were exposed for essen­ t i a l l y the same time periods. At the end o f an experiment the a r t i f i c i a l l y - g e n e r a t e d dew was collected and the dry plate was misted twice with deionized water. This wash water was c o l l e c t e d i n the same manner as dew samples. Contact time between the water and the plate was approximately 5 minutes. Atmospheric Concentrations. Atmospheric concentrations of the major depositing species were determined during the a r t i f i c i a l dew forma­ tion period. The species measured were NO, N 0 , 0o, HNOo, S 0 , HC1, NH3, and p a r t i c u l a t e NO3, SOij , CI", NH]J, C a , Mg* , Na , and K . NO, N 0 , and 0^ were monitored continuously with a Monitor Labs dual channel chemiluminescence Ν 0 analyzer and an AID portable ozone analyzer. S 0 was determined with the carbonate-glycerol impregnated f i l t e r technique. HNO^ was determined by the dénuder difference method {VZ). HC1 was determined with the Na C0o impregnated f i l t e r technique (J_3). The o x a l i c acid impregnated f i l t e r method was used to determine NHg. Total p a r t i c u l a t e was collected on 1-ym pore s i z e Ghia Tefweb f i l t e r s . Aqueous extracts of the f i l t e r s were analyzed to determine p a r t i c u l a t e NO3, SOjJ , CI", NH]J, C a , Mg , Na , and K concentrations. 2

2

+ 2

2

2

+

2

χ

2

2

2

+

+ 2

+2

+

2

Analysis. S O ^ » SOjj , NO^, and CI" were measured on a Dionex 2110i ion chromatograph. SO^ responses were attributed to the c o l l e c t i v e presence o f S(IV) species, without any attempt to i d e n t i f y the s p e c i f i c form, and hereafter w i l l be referred to as S(IV). Ca , Mg , Na , and K were determined on a Perkin-Elmer atomic absorption spectrometer. H concentrations were calculated from pH measurements obtained using an Orion combination electrode and pH meter. NHjJ was determined using a modified indophenol blue method on either a Technicon Autoanalyzer or a Lachat flow i n j e c t i o n analyzer. 2

+ 2

+2

+

+

+

Urban Dew

5. M U L A W A E T A L .

95

Results and Discussion

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch005

Natural dew samples were c o l l e c t e d between June 14, 1982 and October 14, 1982. Dew and rain event frequencies were recorded for 74 days. Dew occurred on 61? of the days and rain occurred on 15? of the days. A r t i f i c i a l dew samples were generated between June 21, 1984 and August 17, 1984. Dew and rain event frequencies were not recorded. However, t h i s period was t y p i c a l of a normal summer for the area. Dew, Rainwater and Dry Plate Wash Composition. Table I contains the average concentrations of measured ions in natural dew, a r t i f i c i a l l y generated dew and dry plate washes. Also included are the volume weighted average summer rainwater concentrations of these same species for the period June 1981 through July 1983 (J_5). Table I.

Species Ca+ Mg

2

+2

K+

Average Dew,

31 ±

±

CI"

106 ±

252

NO3

166 ±

282

SOiJ

2

242 ±

1.5

19 ±

29

9.5

5.1

37 ±

75

52 ±

39

40

52 ±

38

ND

50 ±

57

96

112 ±

69

6.7

312

±

4.4

±

6.5

18 ± 10 6.9

140 ± 108

31

ND*

S(IV)

62 ± 43

16

3 6

Average Dry Plate Cone. yeq/L

26 ±

6.7

26

Average A r t i f i c i a l Dew Concentration yeq/L

6.9

11

65 ±

NHj

Concentrations

155 ± 121

24

690 ± 935

20 ±

Na

Average Rainwater Concentration yeq/L

Average Natural Dew Concentration yeq/L

4.1 +

Rainwater and Dry Plate

±

6.6

24 ± 17 17 ± 13 8.2

± 5

16 ± 12

* not determined The pH of natural dew samples ranged from 3.62 to 8.20 with a median of 6.5 (0.3 yeq H /L). The average natural dew volume was 82.4 mL. The average pH of the rainwater samples was 4.14 (73 yeq H"7L). Natural dew concentrations of NH]j, Mg , Na , K , NO3, and SOjJ were 2 to 4.6 times higher than t h e i r concentration in r a i n water, while C a and C l ~ were 29 and 16 times more concentrated, respectively, in the dew. Ca concentrations are elevated because Ca i s present in predominately large p a r t i c l e s at t h i s s i t e (16) and large amounts of dry deposited C a are incorporated into the dew. Some large p a r t i c l e chloride i s also present at t h i s s i t e during the summer which may account for the higher dew chloride concentrations. S(IV) and N0 were frequently present in natural dew +

+2

2

+ 2

+ 2

+ 2

2

+

+

96

MATERIALS DEGRADATION CAUSED BY ACID RAIN

samples. S e m i - q u a n t i t a t i v e a n a l y s i s by i o n chromatography i n d i c a t e d t h a t S ( I V ) s p e c i e s can be a major component i n t h e dew a t t h i s s i t e , but t h a t Ν 0 was a minor component. A r t i f i c i a l dew and d r y p l a t e washes were c o l l e c t e d on 2 4 morn­ i n g s . The average dew volume was 8 2 mL and t h e average d r y p l a t e wash volume was 7 6 mL. The pH o f a r t i f i c i a l dew ranged from 4 . 4 2 t o 8 . 1 6 w i t h a median o f 5 . 3 0 ( 5 . 0 yeq H " V L ) . The pH o f d r y p l a t e washes ranged from 5 . 2 8 t o 9 . 0 4 w i t h a median o f 6 . 3 ( 0 . 5 yeq H / L ) . Thus t h e a r t i f i c i a l dew samples were more a c i d i c than e i t h e r t h e n a t u r a l dew o r t h e d r y p l a t e washes. I n s p e c t i o n o f T a b l e I shows t h a t t h e h i g h e r a c i d i t y o f t h e a r t i f i c i a l dew samples can be e x p l a i n e d by t h e r e l a t i v e l y lower C a concentrations i n the a r t i ­ f i c i a l dew. The average r a t i o s o f e q u i v a l e n t s o f C a to the equiv­ a l e n t s o f SOJj i n a r t i f i c i a l dew, n a t u r a l dew, and d r y p l a t e samples were 1 . 5 9 , 3 . 5 5 , and 4 . 6 6 , r e s p e c t i v e l y . 2

+

+ 2

+ 2

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch005

2

Average a r t i f i c i a l dew c o n c e n t r a t i o n s were 2 t o 2 0 t i m e s h i g h e r than average d r y p l a t e c o n c e n t r a t i o n s f o r t h e measured i o n s . The l a r g e s t d i f f e r e n c e s appear f o r NHjJ, SOJJ , and S ( I V ) . There a r e two e x p l a n a t i o n s f o r these d i f f e r e n c e s . The most l i k e l y i s t h a t t h e p r e s e n c e o f m o i s t u r e on t h e s u r f a c e o f t h e c o l l e c t o r i n c r e a s e s t h e r e t e n t i o n o f d r y d e p o s i t e d p a r t i c l e s and enhances t h e c a p t u r e o f gases. T h i s p o s s i b i l i t y w i l l be e x p l o r e d i n g r e a t e r d e t a i l below. The second p o s s i b i l i t y i s t h a t t h e d r y d e p o s i t e d m a t e r i a l on t h e d r y p l a t e was n o t c o m p l e t e l y d i s s o l v e d by t h e wash p r o c e d u r e which c o n s i s t e d o f m i s t i n g t w i c e w i t h a s p r a y o f f i n e d r o p l e t s and p h y s i ­ c a l l y sweeping t h e water around t h e p l a t e d u r i n g c o l l e c t i o n . We do not b e l i e v e t h a t i n c o m p l e t e d i s s o l u t i o n was a problem s i n c e c o l l e c ­ t i o n o f second washes were v e r y c l e a n . 2

D e p o s i t i o n Rates. D e p o s i t i o n r a t e s which were c a l c u l a t e d from t h e sample c o n c e n t r a t i o n s , volumes, and t h e sample times a r e t a b u l a t e d i n T a b l e I I . D e p o s i t i o n r a t e s t o t h e a r t i f i c i a l dew samples were 1 . 4 t o 7 . 2 times g r e a t e r than t h e r a t e s t o t h e n a t u r a l dew samples f o r a l l s p e c i e s e x c e p t K and Wa . The K and N a were d e p o s i t e d a t r a t e s 1 9 and 1 6 t i m e s g r e a t e r t o t h e a r t i f i c i a l dew than t o t h e n a t u r a l dew, r e s p e c t i v e l y . There i s c o n s i d e r a b l e u n c e r t a i n t y i n t h e s e v a l u e s because t h e r e were r e l a t i v e l y few measurements o f t h e s e s p e c i e s made i n t h e n a t u r a l dew samples and because t h e v a l u e s were f r e q u e n t l y c l o s e t o the blank c o n c e n t r a t i o n s . Three f a c t o r s c o n t r i b u t e t o t h e h i g h e r d e p o s i t i o n r a t e s t o t h e a r t i f i c i a l dew samples. F i r s t , t h e a r t i f i c i a l dew samples were wet t h e e n t i r e sampling time whereas t h e n a t u r a l dew samples were wet o n l y p a r t o f t h e average 1 7 hour c o l l e c ­ t i o n p e r i o d . F o r many s p e c i e s a wet s u r f a c e i s e x p e c t e d t o be a b e t t e r c o l l e c t o r than t h e d r y s u r f a c e . F o r example, Dasch ( j _ 7 ) found t h a t a l l t h e s e s p e c i e s had h i g h e r d e p o s i t i o n r a t e s t o water than t o a Teflon f i l t e r . T h e r e f o r e , t h e d e p o s i t i o n r a t e s t o n a t u r a l dew r e p o r t e d i n T a b l e I I s h o u l d be taken a s l o w e r l i m i t s . Second, meteorological conditions i n f l u e n c e the d e p o s i t i o n r a t e s . Greater a t m o s p h e r i c t u r b u l e n c e i n t h e morning compared t o t h e n i g h t would +

+

+

+

Table I I .

Species Ca

+ 2

2

Mg+ K

+

Average Deposition Rates

Nat. Dew Deposition Rate yeq/m /h

Number of Samples

Art. Dew Deposition Rate yeq/m /h

Number of Samples

2

Number of Samples

2

Dry P l a t e Deposition Rate yeq/m /h 2

2.06

± 1.09

24

2.87

± 1.65

24

1.64

9

0.14

± 0.12

24

0.54

± 0.31

24

0.17

± 0.13

± 0.02

24

0.32

± 0.26

24

0.25

± 0.18

0.62

± 0.66

24

0.47

± 0.34

24

0.20

± 0.24

31

± 1.34

9

0.02

9

0.04

± 0.05

24

NHJ

14

0.34

± 0.21

24

2.45

± 1.31

CI"

39

0.23

± 0.23

24

0.86

± 0.44

24

0.69

± 0.62

N 0

39

0.45

± 0.33

24

1.06

± 0.64

24

0.46

± 0.50

ND*

23

0.92

± 0.83

5

0.19

± 0.13

± 0.88

24

2.26

± 1.28

24

0.45

± 0.47

Na

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch005

97

Urban Dew

MULAWAETAL.

5.

+

3

S(IV)

so;j

0

2

* not

39

0.82

determined

increase the deposition rates to the a r t i f i c i a l dew samples. Third, diurnal variations i n atmospheric concentrations have not been taken into account. For example, since the a r t i f i c i a l dew samples were generated during the morning rush hour they were exposed to higher average Ν 0 l e v e l s than the natural dew samples. The greatest differences between the deposition rates to the 2 a r t i f i c i a l dew and to the dry plate were for NHjJ, S(IV), and SOjj . The r a t i o s o f the a r t i f i c i a l dew and the dry plate rates for these species were 12.3, 4.8, and 5.0, respectively. This difference i n rates i s most l i k e l y due to the enhanced retention of water soluble gases. Therefore, these r e s u l t s suggest that dry deposited NH^ and are important contributors to the dew composition. As noted above, soluble oxidant gases such as 0^ and f^C^ may also play an important role in determining the concentration of SOjj . χ

2

Deposition V e l o c i t i e s . Deposition v e l o c i t i e s , v ' s , were calculated from the a r t i f i c i a l dew deposition rates discussed above and the atmospheric concentrations of the depositing species measured during dew generation. The average atmospheric concentrations and t h e i r ranges appear in Table I I I . Average v ' s are shown i n Table IV. The c a l c u l a t i o n of V 's for Ca"*", M g , Na , and K i s straightforward since there i s only one dry deposition source for these speciesatmospheric p a r t i c l e s . The average v ' s to the Teflon plate were 0.69, 0.33, 0.23 and 0.15 cm/s for K , Na , C a , and Mg , respec­ t i v e l y . V 's to the dew were higher with average values of 0.88, 0.42, 0.46 and 0.41 cm/s for K , Na , C a and Mg , respectively. Since p a r t i c l e s i z e d i s t r i b u t i o n s were not measured during t h i s study, i t i s not possible to determine i f the differences i n v ' s are due to the differences i n the p a r t i c l e s i z e s . d

d

2

+2

+

d

d

+

+

+ 2

+2

d

+

+

+ 2

+2

d

The v calculations for HNOg, S0 , HC1 and NH^ become more complex due to the l i k e l i h o o d that more than one species contributed to the observed a r t i f i c i a l dew deposition rates. I f we assume that d

2

98

MATERIALS DEGRADATION CAUSED BY ACID RAIN

Table I I I .

Species

Average Concentration yg/rn^

Wo. of Samples

sof

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch005

Average Ambient Concentrations

24

6 .51

+

6.74

+

3.24

N03

24

2 .97

CI"

24

0 .28 +

0.25

NHjJ

24

4 .09 +

3.54

24

8,.02 +

9.70

24

0,.50 + 0,.82 +

0.29

20 20

1..59 +

1.09

24

0..57 +

0.36

HN0

20

2..55 ±

2.36

NH

23

0.,40 ±

0.47

20

11.. 1 ±

4.08

Ca

+ 2

Mg

+2

K

+

Na

+

HC1 3

3

N0 * 2

NO*

24

13. 4

±

12.1

21

28. 4

±

18.5

so *

23

* concentration

9. 19

±

0 .17

28.5

0 .01 0 .06 1,.13 0,.07 0..16 0..33 0..07 0.,0 0.,02 4.8 1. 2 0.0 0.0 0 .09

1.18

O3* 2

Range

9.12

14.4 0.74 15.5 37.9 1.63

5.97 4.15 1.37

7.08 2.22 22.9 43.7 70 32.5

i n ppb

adsorption of these gases onto Teflon i s minimal then the observed dry plate deposition of N O 3 , SOjj , CI" and NHjJ can be attributed to p a r t i c u l a t e deposition. Using t h i s approach the average v ' s f o r p a r t i c u l a t e N O 3 , SOJJ , CI" and NHjJ were estimated to be 0.33, 0.10, 2.36 and 0.06 cm/s, respectively. Since most of the SOjj and NHjJ has been shown to be i n the submicron s i z e range at t h i s s i t e (16,18), their v^'s appear to be reasonable. S i m i l a r l y , the higher v^'s f o r N O 3 and CI" are consistent with the fact that they are present as larger p a r t i c l e s . These v ' s are then used to correct the observed a r t i f i c i a l dew H N O 3 , S0 , HC1 and NH3 deposition rates f o r the corresponding p a r t i c u l a t e dry deposition contribution. The corrected v ' s for HNO3 and S 0 averaged 0.39 and 0.15 cm/s, respectively, r e f l e c t i n g a 47? and a M% decrease i n the v a f t e r correction f o r p a r t i c u l a t e N O 3 and SOjj input. Likewise, WH3 v and HC1 v decreased 36 and 54? a f t e r correction for p a r t i c u l a t e NHjJ and CI" to 1.90 and 0.73 cm/s, respectively. 2

d

2

2

d

2

d

2

d

2

d

d

Conclusions Concentrations of a l l measured species were higher i n natural dew than i n r a i n . The biggest differences were much higher C a and CI" + 2

5.

Urban Dew

MULAWAETAL.

Table IV.

Estimated Deposition to A r t i f i c i a l Dew

Species

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch005

99 Velocities

V , cm/s

Surface

d

HNO3

dew

0.39 ± 0.31

so

dew

0.15 ± 0.11

HC1

dew

0.73 ± 0.11

NH3 NO3 SO4

dew

1.9

2

± 1.55

Teflon

0.33 ± 0.22

Teflon

0.10 ±

NHjj

Teflon

0.06 ± 0.09

CI"

Teflon

2.36

Ca

2

+ 2

Ca+ Mg

+2

Mg

+2

Na

+

Na

+

K

+

K

+

Teflon

2

±

0.09

1.77

0.23 ± 0.18

dew

0.46 ± 0.36

Teflon

0.15 ± 0.12 0.41 ± 0.20

dew Teflon

0.33 ± 0.34

dew

0.42 ± 0.67

Teflon

0.69 ± 0.72

dew

0.88 ± 0.89

+

concentrations i n the dew than the rain and much lower H concentrations. Thus, i t was concluded that the a c i d i t y of dew at this s i t e i s controlled more by the deposition of large basic p a r t i c l e s than by the deposition of acids and acid precursors. This suggests a potent i a l for higher dew a c i d i t y i n areas where C a deposition i s lower or under conditions which minimize the deposition of large p a r t i c l e s . This effect was demonstrated previously when i t was shown that the a c i d i t y of dew was much higher on downward-facing surfaces than upward-facing surfaces (J_0). I t i s also seen i n this study with the a r t i f i c i a l dew samples which had much lower C a concentrations than the natural dew samples and thus more H . Deposition rates of a l l species except K and Na were 1.4 to 7.2 times greater to the a r t i f i c i a l dew than to the natural dew. Apparently the moisture increased the retention of p a r t i c l e s and permitted the deposition of water soluble gases. This l a t t e r effect was p a r t i c u l a r l y important f o r the deposition o f N0Ô, NHjJ, S(IV) and + 2

+ 2

+

+

+

The deposition v e l o c i t i e s to the a r t i f i c i a l dew and the dry plates appear reasonable under the experimental conditions of this study. The particulate SOJJ v of 0.10 cm/s i s somewhat lower than the weekly summertime average SOjj v of 0.29 cm/s to a dry deposition bucket reported by Dasch and Cadle (J_5) for t h i s s i t e . This 2

d

2

d

100

MATERA ILS DEGRADATO IN CAUSED BY ACID RAIN

difference i s reasonable since their estimate did not account for any SO2 deposition which may have occurred when the bucket was damp. Also, average atmospheric s t a b i l i t y conditions may have been d i f f e r ­ ent. The p a r t i c u l a t e NHjJ v to the Teflon plate, 0.06 cm/s, was in good agreement with the SOjj v . Both these species are present as small p a r t i c l e s at this s i t e . The p a r t i c u l a t e NO3, CI", and K v 's were i n good agreement with those reported by Dasch and Cadle (15), while the Ca and M g v ' s to the dry plate were lower by factors of 9 and 7, respectively. The v ' s of gaseous species to the a r t i f i c i a l dew were calculated a f t e r correcting the t o t a l deposition rates f o r the deposition of p a r t i c l e s . Particulate deposition rates were assumed to be close to those observed to the dry plate. The estimated S 0 v was 0.15 cm/s as compared to the -0.04 cm/s recently reported by Pierson et a l . (9). The difference between these r e s u l t s r e f l e c t s the l e s s turbulent nighttime conditions during their study and the decreased S 0 s o l u b i l i t y due to the low pH of their samples. A higher estimate for S 0 v of 0.69 cm/s to a deionized water sur­ face has been reported by Dasch and Cadle (j_9) f o r spring days at this s i t e . The HNO^ v , 0.39 cm/s, was also higher than the 0.24 cm/s reported by Pierson et a l . (9). The HC1 v , 0.73 cm/s, i s in reasonable agreement with the HNO^ v . However, the NH^ v , 1.9 cm/s, appears to be inconsistent with our other r e s u l t s . Overall, i t i s concluded that acid dew i s not a s i g n i f i c a n t environmental concern at t h i s s i t e . However, the a b i l i t y of dew to increase the deposition rate of water soluble gases to some surfaces, and thus increase the a c i d i t y of the dew, may be important at other locations. The deposition v e l o c i t i e s reported above can be used to estimate dew concentrations at other s i t e s as long as differences i n p a r t i c l e s i z e s and atmospheric conditions are taken into consideration. d

2

d

+

d

+2

d

d

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch005

2

d

2

2

d

d

d

d

d

Acknowledgments The authors wish to acknowledge Kenneth Kennedy of the Environmental Science Department f o r the a n a l y t i c a l assistance he provided and Sudarshan Kumar for his h e l p f u l discussions.

Literature Cited 1. Anderson, E. A. In "Atmospheric Corrosion of Non-ferrous Metals"; ASTM STP 175, American Society for Testing and Materials, Philadelphia, PA, 1955. 2. Fassina, V. Atmos. Environ. 1978, 12, 2205-2211. 3. Bangay, G. E.; Riordan C. United States-Canada Memorandum of Intent on Transboundary Air Pollution, Impact Assessment. 4-39, 1983. 4. Yaalon, D. H.; Ganor, Ε. Nature 1968, 217, 1139-1140. 5. Brimblecombe, P.; Todd, I. J. Atmos. Environ. 1977, 11, 649-650.

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch005

5. MULAWA ET AL.

Urban Dew

6. Anderson, Ε. Α.; Landsberg, Η. Ε. Environ. Sci. Technol. 1979, 13, 992-994. 7. Smith, Β. E.; Friedman, E. J. "The Chemistry of Dew as Influenced by Dry Deposition: Results of Sterling, Virginia and Champaign, Illinois Experiments," Mitre Corporation Working Paper WP82W00141, 1982. 8. Wisniewski, J. Water, Air, Soil Pollution 1982, 17, 361-377. 9. Pierson, W. R.; Brachaczek, W. W.; Gorse, R. Α., Jr.; Japar, S. M.; Norbeck, J. M. "On the Acidity of Dew," Presented at the 78th Annual Meeting of the Air Pollution Control Association, Detroit, MI, 1985, Paper No. 85-7.4. 10. Cadle, S. H.; Groblicki, P. J. In "Transactions of the APCA Specialty Conference, The Meteorology of Acid Deposition"; Samson, P. J., Ed., 1983, pp. 17-29. 11. Dasch, J. M.; Cadle, S. H. Atmos. Environ. 1984, 18, 1009-1015. 12. Shaw, R. W.; Bowermaster, J.; Tesch, J. W.; Tew, E. Atmos. Environ. 1982, 16, 845-853. 13. Okita, T.; Kaneda, K.; Yanaka, T.; Sugai, R. Atmos. Environ. 1974, 8, 927-936. 14. Shendrikar, A. D.; Lodge, J. P., Jr. Atmos. Environ. 1975, 9, 431-435. 15. Dasch, J. M.; Cadle, S. H. Atmos. Environ., in press. 16. Dasch, J. M. "Measurement of Dry Deposition to a Deciduous Canopy," General Motors Research Publication GMR-5019, 1985. 17. Dasch, J. M. In "Precipitation Scavenging, Dry Deposition, and Resuspension; Pruppacher, H. R.; Semonin, R. G.; Slinn, W. G. N., Eds.; Elsevier Publishing: New York, Amsterdam, Oxford, 1983, Vol. 2, 883-902. 18. Cadle, S. H. Atmos. Environ. 1985, 19, 181-188. 19. Dasch, J. M.; Cadle, S. H. "Dry Deposition to Snow in an Urban Area," Presented at the 78th Annual Meeting of the Air Pollution Control Association, Detroit, MI, 1985, Paper No. 85-6B.3. RECEIVED

January 13, 1986

101

6 Influence of Acid Deposition on Atmospheric Corrosion of Metals: A Review Vladimir Kucera Swedish Corrosion Institute, Box 5607, S-114 86 Stockholm, Sweden In outdoor atmospheres dry deposition of S-pollutants and especially of SO is of greatest importance. Dose response functions describing corrosion as function of SO and time of wetness are available for some materials as steel and zinc. NO in combination with SO has a synergistic corrosion effect especially indoors on electrical contact materials, copper and steel. The influence of acid precipitation may differ for different metals and depends also on the pollution level. The atmospheric corrosion of metals due to acid deposition is in most regions mainly a local problem restricted to areas close to the pollution source. A reduction of losses due to corrosion has been achieved in many Swedish cities by reduction of SO emissions and by introduction of district heating systems.

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch006

2

2

x

2

2

The i n c r e a s e d combustion o f f o s s i l f u e l s has c r e a t e d t h e problem o f a c i d i f i c a t i o n o f the e n v i r o n m e n t , which today i s c o n s i d e r e d t o be one o f the most s e r i o u s e n v i r o n m e n t a l p r o b l e m s . In S c a n d i n a v i a , where s c i e n t i s t s f i r s t gave warning o f t h e p r o b l e m , t h e l o n g d i s tance t r a n s p o r t o f p o l l u t a n t s from Europe and u n f a v o u r a b l e geol o g i c a l c o n d i t i o n s i n b i g areas make t h e s i t u a t i o n e s p e c i a l l y s e r i o u s . Among t h e e f f e c t s caused by a c i d i f i c a t i o n t h e c o r r o s i o n o f m a t e r i a l s belongs t o t h e f i r s t observed and b e s t documented. I t has thus been known f o r a l o n g time t h a t S - p o l l u t a n t s o r i g i n a t i n g from b u r n i n g o f f o s s i l f u e l s a c c e l e r a t e s i n t h e f i r s t p l a c e t h e a t m o s p h e r i c c o r r o s i o n o f c e r t a i n m e t a l s . T h e i r i n f l u e n c e was d e s c r i b e d e . g . i n Sweden's case study f o r t h e U.N. c o n f e r e n c e on human environment i n 1972, which was t h e f i r s t e f f o r t t o d e s c r i b e the g e n e r a l p i c t u r e o f t h e a c i d i f i c a t i o n problem Q J . More r e c e n t l y a l s o t h e i n f l u e n c e o f N - p o l l u t a n t s on the a t m o s p h e r i c c o r r o s i o n has a t t r a c t e d a t t e n t i o n . T h i s may be seen i n the l i g h t o f t h e f a c t t h a t d u r i n g t h e 1970s t h e wet d e p o s i t i o n o f s u l p h a t e i n Sweden remained by and l a r g e a t a c o n s t a n t l e v e l . The wet 0097-6156/86/0318-0104$06.00/ 0 © 1986 American Chemical Society

6. K U C E R A

105

Atmospheric Corrosion of Metals

deposition of n i t r a t e c e n t a y e a r (2).

by c o n t r a s t

i n c r e a s e d a t a r a t e o f 3-4 per

The c o r r o s i o n e f f e c t on c o n s t r u c t i o n s i n the atmosphere due t o a c i d i f i c a t i o n i s i n most areas m a i n l y o f l o c a l n a t u r e . It s h o u l d be s t r e s s e d , however, t h a t a c i d i f i c a t i o n o f s o i l and water can l e a d t o i n c r e a s e d c o r r o s i o n o f b u r i e d i n s t a l l a t i o n s and o f i n s t a l l a t i o n s i n water i n c l u d i n g water p i p e s ( 3 , _4). T h i s i s on the o t h e r hand m a i n l y a r e g i o n a l p r o b l e m , where the l o n g - r a n g e t r a n s p o r t o f a i r p o l l u t a n t s p l a y s an i m p o r t a n t r o l e . The f o l l o w i n g s u b d i v i s i o n may thus be u s e d .

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch006

C o r r o s i o n due t o acidification

X

C o r r o s i o n i n s o i l and water - r e g i o n a l p r o b lem - i n d i r e c t e f f e c t

Atmospheric c o r r o s i o n l o c a l problem, d i r e c t effect

In the p r e s e n t l e c t u r e a b r i e f r e v i e w w i l l be g i v e n o f the i n f l u e n c e o f a c i d i f y i n g a i r p o l l u t a n t s on the a t m o s p h e r i c c o r r o s i o n o f m e t a l s based m a i n l y on more r e c e n t r e s u l t s from Europe and e s p e c i a l l y from S c a n d i n a v i a . The d e p o s i t i o n p r o c e s s Both s u l p h u r and n i t r o g e n p o l l u t a n t s a r e e m i t t e d i n t o the a i r i n the form o f o x i d e s , SCL and NO r e s p e c t i v e l y , which may then f u r t h e r be o x i d i z e d d u r i n g the t r a n s p o r t i n the a i r . The p r o c e s s e s of d e p o s i t i o n of a i r p o l l u t a n t s a r e : a b s o r p t i o n o f gas on m a t e r i a l s u r f a c e s 1 - dry d e p o s i t i o n impaction of p a r t i c l e s J removal o f gas and a e r o s o l s by p r e c i p i t a t i o n - wet d e p o s i t i o n The relative s i g n i f i c a n c e of the individual deposition mechanisms f o r c o r r o s i o n o f m a t e r i a l s may v a r y i n d i f f e r e n t areas depending e . g . on the d i s t a n c e from the e m i s s i o n s o u r c e , and a l s o f o r d i f f e r e n t m a t e r i a l s depending on d i f f e r e n c e s i n c o r r o s i o n mechanisms and n a t u r e o f p r o t e c t i v e l a y e r s o f c o r r o s i o n p r o d u c t s . The i n f l u e n c e o f s u l p h u r p o l l u t a n t s The i n f l u e n c e o f m a i n l y S 0 on the c o r r o s i o n r a t e o f s e v e r a l m a t e r i a l s has been shown i n numerous n a t i o n a l exposure programs. D u r i n g the l a s t decades a number o f e m p i r i c a l r e l a t i o n s have been d e r i v e d from measurements o f a t m o s p h e r i c c o r r o s i o n r a t e s o f the most i m p o r t a n t s t r u c t u r a l m e t a l s and from measurements o f e n v i r o n mental f a c t o r s . The r e s u l t s are u s u a l l y p r e s e n t e d i n form o f e q u a t i o n s i n c l u d i n g p o l l u t i o n and m e t e o r o l o g i c a l parameters (j>). ?

106

MATERIALS DEGRADATION CAUSED BY ACID RAIN

Carbon_steel S e v e r a l i n v e s t i g a t i o n s have shown the d o m i n a t i n g e f f e c t o f S(L on the c o r r o s i o n r a t e , r e c e n t r e s u l t s from an i n t e r - N o r d i c and from a S w e d i s h - C z e c h o s l o v a k exposure may s e r v e as examples ( 6 , 2 ) · The f o l l o w i n g d o s e - r e s p o n s e f u n c t i o n s have been o b t a i n e d (FIG. 1 ) : 1 year:

K

R e

=

4.0 S 0 + 5 8

r = 0.98

4 years:

K

p e

=

8.0 S 0 +160

r = 0.94

2

2

w h e r e Κ = w e i g h t l o s s f o r s t e e l (g/m ) , SO2 = d e p o s i t i o n r a t e (mg/m .d) and r = c o r r e l a t i o n c o e f f i c i e n t . These i n v e s t i g a t i o n s show t h a t i n a broad range o f the temperate c l i m a t i c zone and i n S 0 p o l l u t i o n l e v e l s r e p r e s e n t a t i v e f o r Western and C e n t r a l Europe a s ^ w e l l as f o r Southern S c a n d i n a v i a most o f the v a r i a t i o n s i n the c o r r o s i o n r a t e may be e x p l a i n e d s o l e l y by the S 0 d e p o s i t i o n r a t e . In t h i s r e g i o n the average wetness c o n d i t i o n s do not d i f f e r t o a g r e a t e r e x t e n t . T h i s e x p l a i n s t h e f a c t t h a t time o f wetness i s not i n c l u d e d i n the dose response r e l a t i o n s h i p . 2

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch006

o

2

I t s h o u l d be p o i n t e d o u t , however, t h a t d u r i n g s h o r t e r time p e r i o d s , the v a r i a t i o n s o f wetness c o n d i t i o n s a r e v e r y e x t e n s i v e . P r e d i c t i o n s o f one o r t h r e e months s t e e l c o r r o s i o n needs a p a r t from the SO,, p o l l u t i o n d a t a a l s o a t l e a s t v a l u e s o f the time o f wetness as i l l u s t r a t e d by the f o l l o w i n g e q u a t i o n ( 1 0 ) : 1 month: K

p e

= 0 . 5 1 S 0 + 0 . 1 1 TOW - 9

r = 0.82

2

w h e r e Κ = w e i g h t l o s s f o r s t e e l (g/m ) , S0 = deposition rate (mg/m . d ) , TOW = time o f wetness (hours w i t h TW >80% and Τ > ° C ) , r = correlation coefficient. ?

9

The r e s u l t s from l e n g t h y exposure p e r i o d s are o f c o u r s e more r e l e v a n t f o r p r a c t i c a l purposes e . g . f o r c l a s s i f i c a t i o n o f the c o r r o s i v i t y o f atmosphere on a g i v e n l o c a t i o n o r f o r c o s t - b e n e f i t a n a l y s i s . In t h i s case the c o r r o s i o n r a t e may be a s s e s s e d from y e a r l y mean v a l u e s o f the c o n c e n t r a t i o n o f p o l l u t a n t s and from the t i m e - o f - w e t n e s s c l a s s e s t i m a t e d from m e t e o r o l o g i c a l measurements. Zinc Z i n c belongs t o the m a t e r i a l s t h a t e x e r t s a s t r o n g dependence o f the c o r r o s i o n r a t e on the c o n c e n t r a t i o n o f s u l p h u r p o l l u t a n t s . In s e v e r a l i n v e s t i g a t i o n s the c o r r o s i o n r a t e i n urban atmospheres was found t o be 2-6 times h i g h e r than i n r u r a l atmospheres ( 5 , 8 J . A l s o f o r z i n c d o s e - r e s p o n s e f u n c t i o n s o b t a i n e d i n the temperate c l i m a t i c zone show the d o m i n a t i n g i n f l u e n c e o f S 0 on i n l a n d s i t e s . The i n c l u s i o n o f time o f wetness i n the l i n e a r model d i d not f u r t h e r s i g n i f i c a n t l y improve the c o r r e l a t i o n . The f o l l o w i n g dose-response f u n c t i o n s have been o b t a i n e d i n the previously mentioned i n v e s t i g a t i o n ( F I G . 2 ) : 2

1 year:

K

Z p

= 0.13 S 0

2

+

7.21

r = 0.81

KUCERA

Atmospheric Corrosion of Metals

1200r

Steel

1000

800

600

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch006

400

200

100

F i g u r e 1. The weight l o s s o f s t e e l a f t e r 1, 2 , and 4 y e a r s ' e x posure as a f u n c t i o n o f S02 d e p o s i t i o n r a t e a t 7 t e s t s i t e s i n Sweden and C z e c h o s l o v a k i a ( 7 ) .

120

Zinc

1100

•

1 year

•

2 years

80

60

40

20

0

100 S0 deposition rate, mg/rrvd 2

F i g u r e 2 . The w e i a h t l o s s o f z i n c a f t e r 1, 2 , and 4 years* posure as a f u n c t i o n o f S 0 d e p o s i t i o n r a t e a t 7 t e s t s i t e s Sweden and C z e c h o s l o v a k i a "(7). ?

exin

108

M A T E R I A L S DEGRADATION C A U S E D BY ACID RAIN

4 years:K

= 0 . 6 6 S 0 + 14.20

Z n

r = 0.97

2

The c o r r o s i o n r a t e o f z i n c i s s t r o n g l y dependent on t h e wetness c o n d i t i o n s d u r i n g t h e e a r l y days o r weeks o f exposure ( 9 ) . T h e r e f o r e o f t e n no u s e f u l e q u a t i o n s f o r c o r r o s i o n can be found i n terms o f monthly averages o f environmental f a c t o r s ( 1 0 ) . The c o r r o s i o n r a t e o f z i n c may be e l e v a t e d d u r i n g t h e f i r s t y e a r o f exposure e s p e c i a l l y a t r u r a l s i t e s w i t h l a r g e amount o f p r e c i p i ­ t a t i o n . T h i s so c a l l e d memory e f f e c t may e x e r t i t s i n f l u e n c e d u r i n g t h e f i r s t y e a r s o f e x p o s u r e . A f t e r some y e a r s o f exposure the c o r r o s i o n r a t e has d i m i n i s h e d and i n t h e l o n g run i t seems t o reach a v a l u e c o r r e s p o n d i n g t o t h e p o l l u t i o n l e v e l ( 6 J .

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch006

Copper I t i s a w e l l known f a c t t h a t f o r m a t i o n o f t h e green p a t i n a t a k e s a s u b s t a n t i a l l y s h o r t e r time i n urban than i n r u r a l atmosphere, where o f t e n v e r y l o n g time e l a p s e s b e f o r e t h e s u r f a c e i s covered by p a t i n a o r i n very pure atmospheres t h e s u r f a c e remains covered by a b l a c k o x i d e l a y e r . A l s o t h e c o r r o s i o n r a t e i n r u r a l atmos­ phere i s u s u a l l y lower (15

FeOOH (0/Fe~2.2) 0 a/o C l / S

0-1

10-55 ZnO

1-15

0.5-5 a/o C l / S ZnO, w i t h 2-4 a/o excess Zn

>15

0>Zn, c o m p o s i t i o n towards c a r b o n a t e

0-1

3-13 a/o Cr .2-2 a/o A l 16-29 a/o Zn 55-80 a/o 0

>1

ZnO 9-13 a/o Cr 2-7 a/o A l

0-0.3

3-8 a/o C l / S 30-85 a/o Cu 10-62 a/o 0

0.3-2

>2 Data normalized

Descript ion

to t h i s value

CuO 1-3 Cu

~

1)

1

a/o

Cl/S

shifting or h y d r o x i d e

1

a/o

Cl/S

r i c h phase

(Cu/0~1.6)

f o r computational

purposes.

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch007

7.

F L I N N ET A L .

Environmental Effects on Metallic Corrosion Products

133

g i v e the smooth f l a t s u r f a c e c h a r a c t e r i s t i c o f the c o r r o s i o n f i l m formed i n l o n g e x p o s u r e s . F o r such a r e e f - l i k e f e a t u r e t o grow, the " v a l l e y " or d e p r e s s e d a r e a between mounds must be f i l l e d w i t h a c o n c e n t r a t e d s o l u t i o n o f d i s s o l v e d r u s t . T h i s o f c o u r s e c o u l d not have o c c u r r e d d u r i n g a r a i n because the s o l u t i o n would have washed away and the f e a t u r e s seen i n F i g u r e 2 o b l i t e r a t e d . I n s t e a d , i t i s proposed t h a t the t h i n l a y e r o f water which remains a f t e r a r a i n f a l l p r e c i p i t a t i o n event a b s o r b s a c i d i c gases from the a i r b e f o r e the s u r f a c e d r i e s and r e s u l t s i n an a c i d e l e c t r o l y t e t h a t d i s s o l v e s rust. Then, on d r y i n g the d i s s o l v e d m a t e r i a l p r e c i p i t a t e s i n the " v a l l e y s " and at the edge o f the " r e e f - l i k e " s t r u c t u r e s t o g r a d u a l l y f i l l i n the " v a l l e y " areas and l e v e l the c o r r o s i o n f i l m . The numerous s m a l l mounds i n the v a l l e y s appear t o be p r e c i p i t a t e n u c l e a t i o n sites. The s i t e s are fewer and l a r g e r at the r i m of the s o l u t i o n f i l l e d a r e a s , i n d i c a t i n g a lower r a t e of p r e c i p i t a t i o n when t h e s o l u t i o n volume i s l a r g e r . But, as e l e c t r o l y t e e v a p o r a t e s and the s o l u t i o n draws down i n t o the v a l l e y , the r a t e o f p r e c i p i t a t e n u c l e a t i o n i n c r e a s e s and numerous s m a l l mounds c o n s i s t e n t w i t h a c c e l e r a t e d d r y i n g are formed. C r a c k s from an e a r l i e r d r y i n g c y c l e would not s u r v i v e such e x t e n s i v e a l t e r a t i o n o f the s u r f a c e . This e v i d e n t l y accounts f o r the absence of h e a l e d or p a r t i a l l y h e a l e d c r a c k s i n the s u r f a c e . The c r a c k s a p p a r e n t l y form as the l a s t s t e p i n the d r y i n g c y c l e . New c r a c k s , of c o u r s e , can form a l o n g the path of e a r l i e r c r a c k s . The o v e r a l l l e v e l i n g t h a t o c c u r s i n l o n g e r exposures s u g g e s t s t h a t the c r e s t s of the mounds are the most a c t i v e s i t e s f o r d i s s o l u t i o n when wet. The water l a y e r i s t h i n n e s t h e r e , and exchange w i t h a c i d i c gases from the atmosphere t o produce a s o l u t i o n which w i l l d i s s o l v e the r u s t s h o u l d o c c u r most r a p i d l y at such s i t e s . I f the c r e s t s are s i t e s of most a c t i v e d i s s o l u t i o n , then the " v a l l e y s " are the s i t e s o f most a c t i v e p r e c i p i t a t i o n and one f o l l o w s the o t h e r as the volume o f water r e t a i n e d on the s u r f a c e d e c r e a s e s d u r i n g d r y i n g . H o r t o n (25) has o b s e r v e d t h a t dust p a r t i c l e s are found e x c l u s i v e l y i n the o u t e r l a y e r o f the c o r r o s i o n f i l m . This i s consistent with the m a s s i v e r e o r g a n i z a t i o n o f the f i l m proposed h e r e by a c y c l e o f d i s s o l u t i o n and p r e c i p i t a t i o n d u r i n g the l a t t e r stages of d r y i n g . The o u t e r l a y e r then c o r r e s p o n d s t o a s o l u t i o n a l t e r e d s t r u c t u r e m o d i f i e d i n t i m a t e l y by c o n t a c t w i t h the environment, w h i l e the i n n e r l a y e r i s m o d i f i e d b a s i c a l l y by d i f f u s i o n and c o n d u c t i o n processes and i s r e l a t i v e l y i s o l a t e d , except a l o n g c r a c k l i n e s , t o m a s s i v e i n t r u s i o n s o f water. In a few cases p r e c i p i t a t i o n of m a t e r i a l a l o n g c r a c k s was o b s e r v e d , F i g u r e 3. T h i s was more l i k e l y t o be seen on the g r o u n d ward s i d e than the skyward s i d e , more o f t e n f o r exposures at the N o r t h C a r o l i n a s i t e than New J e r s e y , and i n l o n g e r exposures than i n s h o r t e x p o s u r e s . The p r e c i p i t a t e d m a t e r i a l i s seen i n F i g u r e 3B t o be densest a l o n g t h a t p o r t i o n of the c r a c k l y i n g i n the d e p r e s s i o n s above and below the r i m i n the c e n t e r of t h i s f i g u r e . T h i s i s cons i s t e n t w i t h the o b s e r v a t i o n t h a t the h i g h e r areas o f the f i l m are s i t e s of d i s s o l u t i o n and the lower areas are s i t e s f o r p r e c i p t a t i o n . E v i d e n t l y , i n the case shown i n F i g u r e 3, d i s s o l v e d m a t e r i a l from w i t h i n the c r a c k has moved t o the s u r f a c e where i t p r e c i p i t a t e d as the c o r r o s i o n f i l m d r i e d . F u r t h e r d r y i n g then reformed the c r a c k .

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The t h r e e f e a t u r e s d e s c r i b e d h e r e suggest t h a t the o u t e r p a r t of the c o r r o s i o n f i l m s on c a r b o n s t e e l and Cor-Ten A undergo m a s s i v e r e o r g a n i z a t i o n by a mechanism of s o l u t i o n and p r e c i p i t a t i o n d u r i n g the l a t t e r s t a g e s o f d r y i n g . In many ways t h i s p r o c e s s i s s i m i l a r f o r both m a t e r i a l s and o n l y d i f f e r s i n s m a l l but s i g n i f i c a n t d e t a i l s r e l a t e d t o the p r e s e n c e of a l l o y i n g elements i n the w e a t h e r i n g steel. The a b i l i t y t o h e a l and s e l f - r e p a i r the c o r r o s i o n f i l m i s an e s s e n t i a l aspect of f o r m i n g a more p r o t e c t i v e c o r r o s i o n f i l m and would appear l i n k e d not o n l y t o the c h e m i s t r y of the a l l o y but a l s o t o the c h e m i s t r y o f the i n t e r a c t i n g environment. 191 Z i n c . In c o n t r a s t t o the s t e e l s , z i n c does not y i e l d a s i m p l e l i n e a r r e l a t i o n s h i p between the amount o f c o r r o s i o n f i l m r e t a i n e d on the s u r f a c e and the z i n c l o s s due t o c o r r o s i o n , F i g u r e 4. The d a t a fans out c o n s i d e r a b l y w i t h i n c r e a s i n g weight l o s s . A mass b a l a n c e on the 1-and 3-month d a t a which d e f i n e an upper l i m i t t o the amount of c o r r o s i o n f i l m r e t a i n e d on the s u r f a c e , u s i n g E q u a t i o n 6, y i e l d s a l i n e w i t h a s l o p e b = 1.645. The s m a l l c o n f i d e n c e i n t e r v a l f o r b, T a b l e I I I , and the l a r g e number of p o i n t s (N = 280) used i n computi n g b would suggest t h a t r u n o f f and s p a l l i n g of the z i n c c o r r o s i o n f i l m are not a s i g n i f i c a n t f a c t o r i n the s h o r t - t e r m exposures and t h a t b i s a consequence o n l y of E q u a t i o n s 1 and 2. V a l u e s of b computed f o r the i n d i v i d u a l s i t e s agree w e l l w i t h t h a t shown i n F i g u r e 4 except f o r the D i s t r i c t o f Columbia s i t e , where b = 1.41. Comparison of b w i t h the t h e o r e t i c a l v a l u e s f o r v a r i o u s compounds, T a b l e I I I , s u g g e s t s t h a t the c o r r o s i o n f i l m at the N o r t h C a r o l i n a , New J e r s e y , and New York s i t e s i s l a r g e l y a c o m b i n a t i o n o f Z n ( 0 H ) and Z n C 0 . A p p l y i n g E q u a t i o n 7 f o r a f i l m composed of two main c o n s t i t u e n t s , the d i f f e r e n c e between the e x p e r i m e n t a l s l o p e 1.645 and the t h e o r e t i c a l s l o p e s , 1.52 f o r Z n ( 0 H ) and 1.92 f o r Z n C 0 , i n d i c a t e s a f i l m c o n s i s t i n g o f about 30 wt pet Z n C 0 and 70 wt pet Zn(0H) i n short-terra exposures. The lower s l o p e f o r the D i s t r i c t of Columbia s i t e s t r o n g l y i n d i c a t e s the p r e s e n c e of ZnO. Slopes were a l s o computed from E q u a t i o n 8 u s i n g the r e s u l t s from the wet c h e m i c a l a n a l y s e s o f the s t r i p p i n g s o l u t i o n s . The r e s u l t s agree w i t h those from g r a v i m e t r i c d e t e r m i n a t i o n s and l e a d t o the same s e t of major c o n s t i t u e n t s f o r the c o r r o s i o n f i l m , T a b l e I I I . The computed s l o p e s were, however, somewhat h i g h e r , as would be e x p e c t e d i f t h e r e were some r u n o f f l o s s e s , and recoraputation o f the c o r r o s i o n f i l m c o m p o s i t i o n based on t h e s e s l o p e s gave v a l u e s n e a r e r t o 65 wt pet Z n C 0 and 35 wt pet Z n ( 0 H ) f o r s h o r t - t e r m exposures at the N o r t h C a r o l i n a , New J e r s e y , and New York s i t e s . 2

3

2

3

3

2

3

2

C o r r o s i o n f i l m c o n s t i t u e n t s i d e n t i f i e d by TGA i n an i n e r t atmosphere, T a b l e IV, agree w e l l w i t h those determined by the mass b a l a n c e on the c o r r o s i o n f i l m . C o r r o s i o n f i l m s on samples exposed at the D i s t r i c t o f Columbia and N o r t h C a r o l i n a s i t e s f o r 1 t o 12 months gave s i m i l a r r e s u l t s . Pure Z n C 0 was run as a s t a n d a r d . The l a r g e weight l o s s at 2 0 0 - 2 5 0 ° C c o i n c i d e d e x a c t l y w i t h the decompos i t i o n of Z n C 0 and r e s u l t s r e p o r t e d by Anderson (26). Mass b a l a n c e c a l c u l a t i o n s i n d i c a t e t h a t the weight l o s s c o r r e s p o n d s t o between 40 and 100 wt pet Z n C 0 . No weight l o s s of the Z n C 0 s t a n d a r d was o b s e r v e d below 200° C. T h e r e f o r e , a s m a l l l o s s of weight from the c o r r o s i o n f i l m t h a t o c c u r s i n the range 110°-200° C was i n t e r p r e t e d as Z n ( 0 H ) d e c o m p o s i t i o n . X-ray d i f f r a c t i o n s p e c t r a from the 3

e

3

3

2

3

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch007

7.

FLINN ET AL.

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F i g u r e 3. Groundward s i d e of 1010 c a r b o n s t e e l microsample M 6 exposed 3 y e a r s a t NC s i t e showing d i s s o l u t i o n and p r e c i p i t a t i o n features. Magnifications: (a) 80X; (b) 240X.

τ

2

Γ

Slope= 1.645 Ο •

%

ο ο •

Ο Ο • Δ

KEY North Carolina District of Columbia New Jersey New York

60 80 WEIGHT LOSS, mg/dm

2

F i g u r e 4. Mass o f c o r r o s i o n p r o d u c t r e t a i n e d on 191 z i n c weightl o s s p a n e l s i n exposures o f 1, 3, and 12 months a t 4 s i t e s . Exposures were i n i t i a t e d i n p e r i o d May 1982 - May 1983.

136

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RAIN

c o r r o s i o n f i l m on samples exposed f o r 3 y e a r s , T a b l e V, c o n t a i n e d s e v e r a l peaks which c o u l d not be matched w i t h known phases. X~ray d i f f r a c t i o n of the samples f o l l o w i n g TGA showed the c o r r o s i o n f i l m to be ZnO, the normal thermal d e c o m p o s i t i o n product of Z n ( 0 H ) and ZnC0 . 2

3

Ion s c a t t e r i n g s p e c t r o s c o p y o f the c o r r o s i o n f i l m formed i n 1raonth exposures at the New York s i t e gave an O/Zn atomic r a t i o con­ s i s t e n t w i t h ZnO i n the o u t e r 15 nm of the s u r f a c e and which trended towards Z n C 0 or Z n ( O H ) deeper i n t o the f i l m , T a b l e V I I . The v e r y o u t e r 1 nm was r i c h i n the s u r f a c e contaminants CI or S. Some Zn enrichment of the o u t e r 15 nm of the f i l m i s observed which c o u l d be a s s o c i a t e d w i t h the s u r f a c e contaminants or r e l a t e d t o d r y i n g effects.

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch007

3

2

A l t h o u g h many of the d a t a p o i n t s i n F i g u r e 4 l i e on the mass b a l a n c e l i n e d e f i n e d by the s h o r t - t e r m d a t a , a s i g n i f i c a n t number of 3- and 12-month p o i n t s l i e i n the fan-shaped area t o the r i g h t of the l i n e . G i v e n the c h e m i s t r y of long-terra z i n c c o r r o s i o n p r o d u c t s i n the atmosphere (27), t h i s s h i f t cannot be due t o the t r a n s f o r m a ­ t i o n of s h o r t - t e r r a c o r r o s i o n p r o d u c t s by w e a t h e r i n g i n t o some lower m o l e c u l a r weight compound. Instead, i t represents a s u b s t a n t i a l l o s s of z i n c c o r r o s i o n product from the s u r f a c e i n r u n o f f or pos­ s i b l y by s p a l l i n g . SEM e x a m i n a t i o n of the c o r r o s i o n f i l m on z i n c samples exposed up t o 36 months showed no e v i d e n c e o f s p a l l i n g and, hence, i t i s assumed t h a t t h i s m a t e r i a l l o s s i s due e n t i r e l y t o runoff. The v e r t i c a l d i f f e r e n c e between the d a t a p o i n t s i n F i g u r e 4 and the mass b a l a n c e l i n e r o u g h l y approximates the amount of t h i s loss. However, a b e t t e r e s t i m a t e of the z i n c l o s s t o the e n v i r o n ­ ment i n r u n o f f i s g i v e n by the d i f f e r e n c e i n the g r a v i m e t r i c z i n c weight l o s s and the z i n c r e t a i n e d i n the c o r r o s i o n f i l m as d e t e r ­ mined from the wet c h e m i c a l a n a l y s e s , i . e . , (m^-R^-S^). T h i s quan­ t i t y i s p l o t t e d i n F i g u r e 5 f o r 1-raonth exposures and i n F i g u r e 6 f o r 3- and 12-month exposures as a f u n c t i o n of the t o t a l hydrogen i o n load d u r i n g the exposure p e r i o d . The 1-raonth d a t a i n F i g u r e 5 show that l i t t l e , i f any, of the c o r r o s i o n f i l m i s l o s t i n r u n o f f due t o hydrogen i o n l o a d or through d i s s o l u t i o n i n water. The z i n c l o s s e s e x h i b i t a r o u g h l y normal d i s t r i b u t i o n about z e r o , and the wide d i s t r i b u t i o n i n v a l u e s , p a r t i c u l a r l y the n e g a t i v e v a l u e s , are due t o low p r e c i s i o n i n the wet c h e m i c a l a n a l y s i s of the c o r r o s i o n f i l m chemistry. T h i s o b s e r v a t i o n , that e s s e n t i a l l y no r u n o f f l o s s e s occur i n s h o r t - t e r m e x p o s u r e s , i s c o n s i s t e n t w i t h the e a r l i e r i n t e r ­ p r e t a t i o n of the mass b a l a n c e r e s u l t s f o r c o r r o s i o n f i l m s formed i n 1- and, i n some c a s e s , 3-raonth e x p o s u r e s . The z i n c l o s s e s f o r l o n g e r e x p o s u r e s , F i g u r e 6, show a d e c i d ­ edly d i f f e r e n t r e s u l t . Here t h e r e i s an i n c r e a s i n g t r e n d of z i n c l o s s from the c o r r o s i o n f i l m as the hydrogen i o n l o a d i n c r e a s e s . A l e a s t squares f i t of the d a t a y i e l d s the f o l l o w i n g r e l a t i o n s h i p between the z i n c r u n o f f l o s s , R ( i n mg Zn/dm ), and the hydrogen i o n l o a d , χ (mg H / m ) : 2

L

+

2

R

L

= 0.746 χ

(11)

Assume, f o r s i m p l i c i t y , t h a t the c o r r o s i o n f i l m i s Z n C 0 and t h a t hydrogen i o n r e a c t s w i t h the c o r r o s i o n f i l m t o form b i c a r b o n a t e . E q u a t i o n 9 then becomes 3

F U N Ν ET AL.

Environmental

Effects on Metallic Corrosion

Products

137

Ε Ε 20h-

Ο

ο

φ

0 0

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch007

0 < 0

ο

ο ο_

ο ο ο

ο

ο°°ο

0

ο ο

ο

ο ο

2

4

6

ο

ο

ο

8

ο ο

10

12

14

16

2

HYDROGEN ΙΟΝ LOAD, mg/m

F i g u r e 5. I n f l u e n c e of hydrogen i o n l o a d i n g on t h e d i s s o l u t i o n of c o r r o s i o n p r o d u c t d u r i n g one-month exposures of 191 z i n c a t 4 sites.

138

M A T E R I A L S D E G R A D A T I O N C A U S E D BY A C I D

Z11CO3 + H+ U s i n g the annual average pH tr-af liln- nf- a F all l1 Ιvolume ;Λ1 i t m a

and

R

L

rewritten

= 0.0043 [ f S

Z

n

C

_

3

+

P

H

)

estimate

X

ajj—i

y= then be

(12)

the hydrogen i o n l o a d to

( I O

E q u a t i o n 10 can

+ HCO3

2 +

> Zn

0

3

(13)

i n form o f E q u a t i o n 11

10

RAIN

-3+pH Μ(s^)

,

_ +

MJ Z

to

give

Y

^

(14)

The s o l u b i l i t y o f Z n C 0 i n n e u t r a l water i s g i v e n as 10 mg/L (28). (The o f t e n quoted v a l u e g i v e n by Ageno and V a l l a ( 2 9 ) , 206 mg/L"7 i s e v i d e n t l y i n e r r o r by a f a c t o r o f 10 s i n c e they a l s o r e p o r t t h e i r v a l u e as 1.64X10"** mole/L.) S u b s t i t u t i n g i n t o E q u a t i o n 14, u s i n g 4.2 as a r e a s o n a b l e annual average pH f o r the s i t e s ( 6 ) , and assuming t h a t the r u n o f f from the sample i s s a t u r a t e d w i t h ZnCO^, i . e . , f=l g i v e s

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch007

3

R

L

=

0.28DX

(0.356 +

- 0.637X

(15)

T h i s i s i n good agreement w i t h E q u a t i o n 11 and i n d i c a t e s that r u n o f f l o s s e s from z i n c are due t o a c o m b i n a t i o n of d i s s o l u t i o n of c o r r o ­ s i o n product i n water, the p r i n c i p a l e f f e c t , and hydrogen i o n l o a d ­ ing. E q u i l i b r i a i n v o l v i n g C 0 , H C 0 , c a r b o n a t e , and bicarbonate are a l s o i n v o l v e d i n the d i s s o l u t i o n r e a c t i o n and rough c a l c u l a t i o n s have i n d i c a t e d t h a t the r u n o f f w i l l be d e c i d e d l y more b a s i c than the incident rain. However, t h i s does not a l t e r the f a c t t h a t hydrogen i o n l o a d i s a s i g n i f i c a n t f a c t o r i n the d i s s o l u t i o n of the z i n c c o r r o s i o n product. Z i n c c o r r o s i o n r a t e s d e c r e a s e s u b s t a n t i a l l y w i t h exposure time, T a b l e I, i n d i c a t i n g t h a t the c o r r o s i o n f i l m i s becoming i n c r e a s i n g l y more p r o t e c t i v e and r e t a r d i n g f u r t h e r c o r r o s i o n . Moreover, c o r r o ­ s i o n r a t e s at the f o u r s i t e s are c o n v e r g i n g t o s i m i l a r v a l u e s even though t h e r e was a 6 - f o l d d i f f e r e n c e i n t h e i r i n i t i a l r a t e s . Thus, i t would appear that a c e r t a i n mass of c o r r o s i o n product must form on the metal s u r f a c e t o p r o v i d e the degree o f p r o t e c t i o n observed i n longer exposures. I f r u n o f f l o s s e s are s i g n i f i c a n t , as s u g g e s t e d by F i g u r e 6 and E q u a t i o n 11, then z i n c must c o r r o d e at a r a t e s u f f i ­ c i e n t t o r e p l a c e the c o r r o s i o n product l o s t by d i s s o l u t i o n i n long exposure times when r o u g h l y s t e a d y s t a t e c o n d i t i o n s e x i s t . I n t h i s way hydrogen i o n l o a d and a c i d d e p o s i t i o n have a very s p e c i f i c and d e f i n a b l e r o l e i n a c c e l e r a t i n g the c o r r o s i o n o f z i n c . 2

2

3

S c a n n i n g e l e c t r o n m i c r o s c o p i c e x a m i n a t i o n s of z i n c samples exposed 1, 12, and 36 months showed e x t e n s i v e r e o r g a n i z a t i o n of the c o r r o s i o n f i l m through r e p e a t e d c y c l e s of d i s s o l u t i o n and p r e c i p i t a ­ t i o n not u n l i k e that which o c c u r s on c a r b o n s t e e l and Cor-Ten A. The c o r r o s i o n product on z i n c exposed 3 y e a r s at the New Jersey s i t e , where s h o r t - t e r m z i n c c o r r o s i o n r a t e s are low, i s u n i f o r m , somewhat n o d u l a r , and f i n e g r a i n e d on both the skyward and groundward s i t e s , F i g u r e 7. The same was t r u e f o r samples from the D i s t r i c t of Columbia s i t e . On the o t h e r hand, the c o r r o s i o n f i l m on

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Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch007

FLINN E T A L .

F i g u r e 7. M i c r o s a m p l e s of z i n c 191 exposed 3 y e a r s , (a) s k y ward s i d e and (b) groundward s i d e , sample C43, from NJ s i t e ; (c) skyward s i d e and (d) groundward s i d e , sample C31, from NC site. Magnification: 136X.

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z i n c exposed 3 y e a r s at the North C a r o l i n a s i t e , where s h o r t - t e r m c o r r o s i o n r a t e s were h i g h e s t , was v e r y d i f f e r e n t from those f o r New J e r s e y and skyward and groundward s i t e s were d i s s i m i l a r . M a s s i v e d i s s o l u t i o n and p r e c i p i t a t i o n f e a t u r e s are superimposed on the skyward s i d e over a u n i f o r m , n o d u l a r c o r r o s i o n product s i m i l a r t o that o b s e r v e d at New J e r s e y . These f e a t u r e s , the e n l a r g e d and filled o v a l shapes and the c u r v i n g s o l i d b a r r i e r c r o s s i n g dozens of the s m a l l e r n o d u l a r shapes, are e v i d e n c e f o r a p r o c e s s of d i s s o l u t i o n , c o n c e n t r a t i o n , r e d i s t r i b u t i o n , and p r e c i p i t a t i o n t h a t b u i l d s l a r g e r s t r u c t u r e s on the m e t a l s u r f a c e . Were t h i s t o happen d u r i n g r a i n f a l l the d i s s o l v e d m a t e r i a l would wash away. I n s t e a d , as f o r the s t e e l s , i t would appear t o happen when the s u r f a c e i s d r y i n g and i n v o l v e s a b s o r p t i o n of a c i d i c gases from the atmosphere. The groundward s i d e , F i g u r e 7D, shows broad open areas covered by o n l y a t h i n , porous c o r r o s i o n p r o d u c t and bound by l o o p i n g b a r r i e r s o f precipitated material. I t would appear t h a t c o r r o s i o n on the groundward s i d e of z i n c exposed at the North C a r o l i n a s i t e i s subs t a n t i a l l y l e s s than on the skyward s i d e . S i n g l e - s i d e d experiments are now i n p r o g r e s s t o c o n f i r m t h i s p o s s i b i l i t y ( 6 ) . F i g u r e 8 shows i n g r e a t e r d e t a i l the c o r r o s i o n product t h a t forms on the skyward s i d e of z i n c exposed at the N o r t h C a r o l i n a and New J e r s e y s i t e s f o r 1 and 3 y e a r s . The massive f e a t u r e s that d e v e l o p at N o r t h C a r o l i n a i n 3 y e a r s , F i g u r e 8B, are not yet apparent a f t e r 1 y e a r and the c o r r o s i o n p r o d u c t t h a t u n i f o r m l y c o v e r s the s u r f a c e , and on which i s superimposed the n o d u l a r shapes, appears porous, F i g u r e 8A. In c o n t r a s t , the u n i f o r m l a y e r c o v e r i n g the s u r f a c e at New J e r s e y a f t e r 1 y e a r , w h i l e c r a c k e d , i s dense and shows e v i d e n c e of d i s s o l u t i o n and r e d i s t r i b u t i o n o f m a t e r i a l t o g i v e a c o r r o s i o n f i l m of more u n i f o r m t h i c k n e s s , F i g u r e 8C. The c o r r o s i o n p r o d u c t formed i n 3 y e a r s e x h i b i t s s e v e r a l types of s t r u c t u r e s due t o s t i l l u n i d e n t i f i e d phases, F i g u r e 8D. The SEM p h o t o m i c r o g r a p h s i n F i g u r e s 7 and 8 show that r e o r g a n i z a t i o n o f the z i n c c o r r o s i o n product on w e a t h e r i n g i s a complex phenomena i n v o l v i n g competing p r o c e s s e s . F o r the h i g h l y s t r u c t u r e d f e a t u r e s t o d e v e l o p and be p r e s e r v e d over l o n g p e r i o d s , i t i s c l e a r t h a t , w h i l e d i s s o l u t i o n does o c c u r , the c o r r o s i o n p r o d u c t s are not r e a d i l y s o l u b l e and accumulate r a t h e r than wash from the s u r f a c e . G a l v a n i z e d S t e e l . The r e l a t i o n s h i p between c o r r o s i o n f i l m weight and z i n c weight l o s s f o r g a l v a n i z e d s t e e l was s i m i l a r t o t h a t shown i n F i g u r e 4 f o r z i n c . There were, however, fewer p o i n t s d e f i n i n g the l i n e f o r the upper l i m i t t o the amount of c o r r o s i o n p r o d u c t r e t a i n e d on the s u r f a c e . T h e r e was a l s o much more s c a t t e r i n the d a t a below t h i s l i n e i n d i c a t i n g that s u b s t a n t i a l c o r r o s i o n p r o d u c t was l o s t i n r u n o f f . The s l o p e f o r the l i m i t i n g l i n e was 1.178, which would i n d i c a t e t h a t ZnO was a major c o n s t i t u e n t o f the c o r r o sion film. However, the s l o p e was recomputed u s i n g the z i n c p r e s e n t i n the c o r r o s i o n f i l m as determined by wet c h e m i c a l a n a l y s i s o f the f i l m s t r i p p i n g s o l u t i o n , E q u a t i o n 8. T h i s produced a l i n e a r r e l a t i o n s h i p w i t h v e r y l i t t l e s c a t t e r between f i l m weight and z i n c i n the c o r r o s i o n f i l m . S l o p e s computed from t h i s d a t a f o r each o f the s i t e s , i n c l u d i n g the Washington, DC, s i t e , were i n good agreement and ranged from 1.45 t o 1.55. These v a l u e s are c o n s i s t e n t w i t h a c o r r o s i o n f i l m c o n t a i n i n g ZnCOg, ZnO, and Z n ( O H ) , as r e p o r t e d by 2

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Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch007

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F i g u r e 8. Skyward s i d e of 191 z i n c m i c r o s a m p l e s . (a) 1-year exposure and (b) 3-year exposure a t NJ s i t e ; (c) 1-year and (d) 3-year exposure a t NC s i t e . Samples a r e (a) C229; (b) C31 (c) C231; (d) C43. Magnification: 720X.

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B i e s t e k (27) and B a r t o n ( 3 0 ) . Assuming a 2 - c o n s t i t u e n t corrosion f i l m of ZnC0 and ZnO, a sTope of 1.5 c o r r e s p o n d s r o u g h l y t o a c o r r o s i o n f i l m c o n s i s t i n g of 60 wt pet Z n C 0 and 40 wt pet ZnO. The s l o p e s and the c o n s t i t u e n t s a s s o c i a t e d w i t h those s l o p e s are d i f f e r e n t f o r z i n c and g a l v a n i z e d s t e e l . T h i s was unexpected s i n c e , t o the atmosphere, they s h o u l d appear the same. However, t h e r e was one s i g n i f i c a n t d i f f e r e n c e between the two m a t e r i a l s . The s u r f a c e o f the g a l v a n i z e d s t e e l r e c e i v e d a chromate treatment t o improve i t s r e s i s t a n c e to "white r u s t i n g " d u r i n g s t o r a g e (31, 32). X-ray p h o t o e l e c t r o n s p e c t r o s c o p y , and ISS a n a l y s i s of the c o r r o s i o n f i l m on g a l v a n i z e d s t e e l has shown that the s u r f a c e i s r i c h i n chromium from t h i s chromate t r e a t m e n t , T a b l e s VI and V I I . XPS a n a l y s i s shows both C r and C r p r e s e n t i n the c o r r o s i o n f i l m f o l l o w i n g a 1-raonth exposure at the New York s i t e ; C r was as much as 6 times more abundant i n the c o r r o s i o n f i l m than C r . Lead was a minor c o n s t i t u e n t o f the c o r r o s i o n f i l m , p r o b a b l y as PbO or Pb^O^. T h r e e peaks were found f o r oxygen; a r e l a t i v e l y s m a l l one f o r the chromium o x i d e s ; one f o r Z n C 0 ; and a t h i r d i d e n t i f i e d as Z n ( 0 H ) . ISS shows as much as 13 at pet Cr i n the o u t e r 1 nm of the c o r r o s i o n f i l m s and s m a l l amounts of aluminum. Beyond 1 nm i n t o the c o r r o s i o n f i l m , the oxygen c o n c e n t r a t i o n , a f t e r c o r r e c t i n g f o r the amount combined w i t h Cr i n C r 0 and A l i n A 1 0 , was s t o i c h i o r a e t r i c a l l y e q u i v a l e n t t o ZnO. The c o r r o s i o n f i l m on g a l v a n i z e d s t e e l may be s i m i l a r t o t h a t on z i n c where t h e r e appears to be a ZnO l a y e r on the o u t e r s u r f a c e , perhaps as a consequence of d r y i n g , and Z n ( 0 H ) i s a c o n s t i t u e n t deeper i n t o the c o r r o s i o n f i l m . These r e s u l t s c l e a r l y show that Cr i s present i n s u b s t a n t i a l amounts on the s u r f a c e o f the g a l v a n i z e d s t e e l c o r r o s i o n f i l m and e v i d e n t l y s e r v e s t o i n h i b i t the c o r r o s i o n of the z i n c c o a t i n g . SEM e x a m i n a t i o n o f g a l v a n i z e d s t e e l exposed 3 y e a r s at the N o r t h C a r o l i n a s i t e shows v e r y d i f f e r e n t c o r r o s i o n f i l m s on the groundward and skyward s i t e s , F i g u r e 9. The l a r g e s o l u t i o n - a l t e r e d f e a t u r e s on the skyward s i d e look not u n l i k e those f o r z i n c exposed at the same s i t e . However, the s m a l l n o d u l a r s t r u c t u r e observed on z i n c was not p r e s e n t i n the c o r r o s i o n f i l m on g a l v a n i z e d s t e e l and t h e r e were areas (one appears as a smooth white a r e a i n the lower r i g h t c o r n e r o f F i g u r e 9A) which are u n c o r r o d e d . These areas are presumed t o be due t o the c o n t i n u e d p a s s i v a t i o n of the s u r f a c e by the r e s i d u a l chromate c o a t i n g . The groundward s i d e , F i g u r e 9B, i s c h a r a c t e r i z e d by l a r g e areas of u n c o r r o d e d s u r f a c e . S m a l l areas of l o c a l i z e d breakdown are d i s t r i b u t e d over t h i s s u r f a c e i n c l u d i n g a r e a s where c o r r o s i o n has proceeded a l o n g s c r a t c h marks. It is p r o b a b l e t h a t these s c r a t c h e s o c c u r r e d a f t e r the chromate t r e a t m e n t and p e n e t r a t e the p r o t e c t i v e chromate l a y e r . By removing the c h r o mate i n t h e s e areas the s c r a t c h e s have made the z i n c c o a t i n g more s u s c e p t i b l e to c o r r o s i o n . 3

3

3 +

6 +

3 +

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6 +

3

2

3

2

2

3

2

G i v e n the n o n u n i f o r m d i s t r i b u t i o n o f c o r r o s i o n on the s u r f a c e of the g a l v a n i z e d s t e e l i t i s p o s s i b l e t h a t the ISS and XPS r e s u l t s c o n c e r n i n g ZnO and Z n ( 0 H ) are not i n c o n f l i c t ; two d i s t i n c t l y d i f f e r e n t areas may have been examined. Perhaps a l a r g e l y u n c o r r o d e d s u r f a c e , as seen i n F i g u r e 9B, was examined by ISS. T h i s area would then be c h a r a c t e r i z e d as p a s s i v a t e d by Cr and c o n s i s t i n g of a t h i n ZnO l a y e r . On the o t h e r hand, c o r r o s i o n product from a more a c t i v e l y c o r r o d i n g s u r f a c e , as i n F i g u r e 9A, may have been examined by 2

7.

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XPS. T h i s a r e a would be c h a r a c t e r i z e d as c o n t a i n i n g s u b s t a n t i a l water and Z n ( O H ) and Z n C 0 as w e l l as ZnO. T h r e e - y e a r c o r r o s i o n f i l m s on g a l v a n i z e d s t e e l from the New J e r s e y s i t e d i d not p o s s e s s s o l u t i o n - a l t e r e d f e a t u r e s on the skyward side. T h i s was t r u e a l s o f o r the c o r r e s p o n d i n g z i n c samples. There were, however, s u b s t a n t i a l areas of uncorroded s u r f a c e on both the skyward and groundward s i d e s . W h i l e s h o r t - t e r m c o r r o s i o n r a t e s are d i f f e r e n t between z i n c and g a l v a n i z e d s t e e l , i n long-term exposures t h e r e are c l o s e p a r a l l e l s i n the development of the weathered c o r r o s i o n f i l m on both m a t e r i a l s .

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2

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Galvalume. A p l o t of f i l m weight v e r s u s weight l o s s showed a s c a t t e r of p o i n t s w i t h a p o o r l y d e f i n e d upper l i m i t l i k e t h a t f o r g a l vanized s t e e l . C o r r o s i o n f i l m w e i g h t s were o f t e n l e s s than the weight of m a t e r i a l which had d i s s o l v e d t o form the c o r r o s i o n f i l m . T h i s i n d i c a t e s t h a t Galvalume, l i k e the o t h e r z i n c c o n t a i n i n g mater i a l s , l o s e s c o r r o s i o n product t o r u n o f f d u r i n g exposure. SEM photomicrographs of an unexposed Galvalume b l a n k and Galvalume exposed 3 years at the New J e r s e y s i t e are shown i n F i g u r e 10. Galvalume i s a 2-phase A l Z n c o a t i n g which c o n s i s t s of an A l r i c h d e n d r i t i c phase and a Z n - r i c h i n t e r d e n d r i t i c phase ( 3 3 ) . These s t r u c t u r e s are c l e a r l y e v i d e n t i n F i g u r e 10A f o r the b l a n k , w i t h most of the s u r f a c e c o v e r e d by the o x i d e on the A l - r i c h phase, and w i t h i s o l a t e d windows through t h i s d e n d r i t i c phase e x p o s i n g the Znr i c h phase. C o r r o s i o n appears t o be c o n f i n e d l a r g e l y t o those areas where the Z n - r i c h phase i s exposed, F i g u r e 10B. Average c o r r o s i o n r a t e s were l e s s than 1 ym/y i n 1-month exposures at the New Jersey s i t e from May 1982 through May 1984 (j6). A c t u a l c o r r o s i o n r a t e s would be s u b s t a n t i a l l y h i g h e r than t h i s i f based on the a r e a that i s c o r r o d i n g , i . e . , the i n t e r d e n d r i t i c phase. The v o i d s t h a t are p r o duced i n t h i s a r e a leave a s u r f a c e which, on a m i c r o s c o p i c s c a l e , i s q u i t e rough and can r e a d i l y t r a p f i n e dust p a r t i c l e s , a e r o s o l s , and c o r r o s i o n product. 110 Copper. P l o t s of f i l m weight v e r s u s metal l o s s f o r 1- and 3month exposures o f 110 copper g e n e r a l l y show a l i n e a r r e l a t i o n s h i p between f i l m weight and m e t a l l o s s . I f 1-year exposures are i n c l u d e d i n the p l o t they w i l l be s c a t t e r e d and f a l l below the l i n e e s t a b l i s h e d by the 1- and 3-month e x p o s u r e s . T h i s may be an i n d i c a t i o n of r u n o f f l o s s e s i n l o n g e r e x p o s u r e s . The l i n e s based on s h o r t - t e r m d a t a had s l o p e s of 1.12, 1.19, 1.10, and 1.08 f o r the N o r t h C a r o l i n a , New J e r s e y , New York, and D i s t r i c t of Columbia s i t e s , r e s p e c t i v e l y , when based on g r a v i m e t r i c d a t a , E q u a t i o n 6. The D i s t r i c t of Columbia d a t a p o i n t s e x h i b i t e d somewhat g r e a t e r s c a t t e r then the o t h e r s i t e s , which c o u l d r e p r e s e n t i n c r e a s e d r u n o f f l o s s f o r these samples. P l o t s of f i l m weight v e r s u s the copper determined by wet chemi s t r y from the s t r i p p i n g s o l u t i o n s , E q u a t i o n 8, are l i n e a r . The s l o p e s — 1 . 1 2 , 1.15, 1.14, and 1.20 f o r the North C a r o l i n a , New J e r s e y , New York, and D i s t r i c t o f Columbia s i t e s — g e n e r a l l y c o n f i r m the r e s u l t s from the g r a v i m e t r i c d a t a . No s i g n i f i c a n t s i t e - t o - s i t e d i f f e r e n c e s were apparent i n the s l o p e s . The D i s t r i c t of Columbia s i t e had a s l i g h t l y h i g h e r s l o p e u s i n g the wet c h e m i c a l analyses, but i t a l s o had the lowest s l o p e by g r a v i m e t r i c methods. The s l o p e s f e l l between the t h e o r e t i c a l v a l u e s f o r pure CuO and C u 0 , 2

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F i g u r e 9. Skyward (a) and groundward (b) s i d e s of g a l v a n i z e d s t e e l microsample G51 exposed 3 y e a r s a t NC s i t e . Magnification: 80X.

F i g u r e 10. Galvalume b l a n k (a) and skyward s i d e of microsample F38 (b) exposed 3 y e a r s a t NJ s i t e . Magnification: 720X.

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T a b l e I I I , i n d i c a t i n g t h a t the f i l m i s composed p r i m a r i l y o f t h e s e two c o n s t i t u e n t s . These r e s u l t s are c o n s i s t e n t w i t h o b s e r v a t i o n s o f M a t t s o n ( 3 4 ) , who i n d i c a t e d t h a t C u 0 was the p r i m a r y f i l m c o n s t i t u e n t f o r short-term exposures. ISS a n a l y s i s o f copper f i l m s c o n f i r m e d t h a t the f i l m i s composed m o s t l y o f oxygen and c o p p e r . The atomic p e r c e n t a g e o f c h l o r i n e or s u l f u r i s r e l a t i v e l y s m a l l and d i m i n i s h e s r a p i d l y w i t h d i s t a n c e i n t o the f i l m . Thermal a n a l y s i s r e s u l t s f o r 1-month and 1y e a r e x p o s u r e s , T a b l e IV, r u l e out the p o s s i b i l i t y t h a t l a r g e amounts o f s u l f u r , c h l o r i n e , or c a r b o n a t e c o n t a i n i n g compounds a r e p r e s e n t i n the f i l m . A slow, c o n s t a n t r a t e o f weight l o s s was o b s e r v e d at temperatures between 110° and 350° C by TGA which was not t y p i c a l o f the t h e r m a l d e c o m p o s i t i o n r e p o r t e d f o r any i n o r g a n i c copper compounds ( 2 3 ) . I n measurements on pure CuO, no weight change was observed i n t h i s temperature range. I n t e r a c t i o n of carbonaceous m a t e r i a l d e p o s i t e d on the f i l m w i t h CuO t o produce C u 0 and C 0 c o u l d p o s s i b l y e x p l a i n the slow weight l o s s from samples d u r i n g TGA. X - r a y d i f f r a c t i o n r e s u l t s , T a b l e V, show the p r e s e n c e o f C u 0 i n samples both b e f o r e and a f t e r TGA. The SEM photomicrographs i n F i g u r e 11 show t h a t copper c o r r o d e s l o c a l l y and n o n u n i f o r m l y . F i g u r e 1 IB shows a sample, exposed f o r 1 y e a r at the N o r t h C a r o l i n a s i t e , which has had i t s c o r r o s i o n f i l m stripped. F l a t u n c o r r o d e d a r e a s , i d e n t i f i e d by the r o l l i n g marks from t h e o r i g i n a l copper s u r f a c e , are p r e s e n t . F i g u r e 11A shows a s i m i l a r sample w i t h the c o r r o s i o n f i l m i n t a c t . T h i c k mounds formed i n the c o r r o s i o n f i l m appear t o be a s s o c i a t e d w i t h the a r e a s o f l o c a l i z e d m e t a l a t t a c k seen i n F i g u r e 11B. XPS was used t o study f i l m s on copper samples from s e v e r a l s i t e s f o r d i f f e r e n t exposure p e r i o d s . As i n d i c a t e d i n T a b l e V I I I major changes i n the c o m p o s i t i o n o f the c o r r o s i o n f i l m s u r f a c e appear t o be o c c u r r i n g w i t h t i m e . D i f f e r e n t s i t e s gave s i m i l a r r e s u l t s f o r the same exposure p e r i o d , a l t h o u g h t h e r e was some v a r i a t i o n i n the C l S peaks among the s i t e s . This could i n d i c a t e that the n a t u r e o f the c a r b o n compounds b e i n g d e p o s i t e d on the f i l m v a r i e s from s i t e t o s i t e . The C u 2 P peak was i n t e r p r e t e d u s i n g d a t a from Schon (35) t o d i s t i n g u i s h CuO from Cu and C u 0 . I t was not p o s s i b l e t o s e p a r a t e the c o n t r i b u t i o n s o f Cu and C u 0 . The 1-month samples showed l a r g e amounts o f both CuO and Cu or C u 0 . At l o n g e r exposures the amount o f CuO i n c r e a s e d w h i l e the amount o f the l e s s o x i d i z e d s p e c i e s d e c r e a s e d . The groundward s i d e s of the samples tended t o have l e s s CuO and more C u 0 or Cu than the skyward. The r e s u l t s i n d i c a t e t h a t a l a y e r o f CuO i s produced i n the o u t e r 10 nm o f the f i l m s u r f a c e w i t h i n c r e a s i n g exposure time and t h a t t h i s p r o c e s s proceeds f a s t e r on the skyward s i d e than the groundward side.

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch007

2

2

2

2

1 / 2

3 / 2

2

2

2

2

3003-H14 Aluminum. The Al-Mn 3003 a l l o y c o r r o d e s at r a t e s l e s s t h a n 0.1 pm/y i n exposures o f 1, 3, and 12 months. Rates at the New J e r s e y s i t e a r e 2 t o 3 times those at the o t h e r s i t e s . SEM examinat i o n showed p i t t i n g i n exposures o f 12 and 36 months, F i g u r e 12. The p i t s were i n the e a r l y s t a g e s of development w i t h a s m a l l , deeper c e n t r a l a r e a surrounded by s h a l l o w l o c a l i z e d a t t a c k r a d i a t i n g outwards, p a r t i c u l a r l y a l o n g g r a i n b o u n d a r i e s . T h i s type o f a t t a c k i s s i m i l a r t o t h a t d e s c r i b e d by S o w i n s k i ( 3 6 ) . P i t s were more f u l l y d e v e l o p e d at the New J e r s e y s i t e , encompassing a l a r g e r a r e a o f

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146

MATERIALS DEGRADATION C A U S E D BY ACID

RAIN

F i g u r e 11. Skyward s i d e of 110 copper exposed 1 y e a r at NC s i t e , (a) microsample D231 w i t h c o r r o s i o n f i l m i n t a c t ; (b) w i e g h t - l o s s p a n e l D l - 9 1 a f t e r removing c o r r o s i o n f i l m . Magnification: 240X.

F i g u r e 12. Skyward s i d e o f aluminum 3003-H14 w e i g h t - l o s s p a n e l B2-73 exposed 1 y e a r a t NJ s i t e a f t e r removing c o r r o s i o n f i l m . Magnification: 720X.

Environmental Effects on Metallic Corrosion Products

FLINN ETAL.

Table V I I I .

X-ray photoelectron spectroscopic analysis of c o r r o s i o n f i l m on m i c r o a n a l y s i s samples

Metal/Exposure

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch007

HO

C o p p e r / l month

110 Copper/1

year

XPS Peak

Cu2P

Observation*

3 / 2

cis

1 / 2

ois

1 / 2

Cu2P

3 / 2

Cu, C u 0 : major CuO: major L e s s Cu as CuO on groundward s i d e t h a n skyward s i d e . 2

C-H, C-0,

C-C: C=0:

major minor

Oxide [CuO, C u 0 ] : h y d r o x i d e , water: C=0, C - 0 : minor

major minor

2

Cu, C u 0 : major CuO: major CuO > C u , C u 0 2

2

cis

110 Copper/3

year

1 / 2

CulP

3 / 2

C=0, C-H,

C-O: C-C:

major minor

skyward s i d e - C u O : major groundward s i d e - C u O : major Cu, C u 0 : minor 2

cis

1 / 2

ois

1 / 2

C«=0, C - 0 : C-H, C-C:

major minor

C=0, C - O : major o x i d e [CuO, C u 0 ] : 2

Phases

i n brackets

minor

i n d i c a t e probable i d e n t i t i e s of

peaks.

148

MATERIALS

DEGRADATION

CAUSED

BY ACID

RAIN

l o c a l i z e d breakdown and i n v o l v i n g more i n t e n s e d i s s o l u t i o n of g r a i n s and g r a i n b o u n d a r i e s . P i t t i n g was more e v i d e n t on the skyward s i d e t h a n the groundward s i d e of the samples. A l s o p r e s e n t on the s k y ward s i d e was a f i n e l y s t r u c t u r e d n o n u n i f o r m g e n e r a l a t t a c k which t e x t u r e d the s u r f a c e i n exposures o f 3 y e a r s and o b s c u r e d o r i g i n a l s u r f a c e d e t a i l such as r o l l i n g marks and f i n e s c r a t c h e s . This a t t a c k may be a s s o c i a t e d w i t h s m a l l i n t e r m e t a l l i c F e A l g and FeMnAlg p r e c i p i t a t e s d i s p e r s e d i n the 3003 a l l o y . S i m i l a r t e x t u r i n g o f the groundward s i d e had not o c c u r r e d i n 3-year exposures and much o f the s u r f a c e d e t a i l was r e t a i n e d .

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch007

Conclusions F o r purposes of a n a l y s i s , growth of an a t m o s p h e r i c c o r r o s i o n f i l m was viewed s c h e m a t i c a l l y as a t h r e e s t e p p r o c e s s c o n s i s t i n g o f : (1) f o r m a t i o n of a c o r r o s i o n p r o d u c t ; (2) w e a t h e r i n g o f t h a t p r o d u c t w h i l e c o n s e r v i n g mass of the m e t a l ; and (3) c o r r o s i o n product l o s s e s through r u n o f f and s p a l l i n g . One or more o f these s t e p s may be o c c u r r i n g d u r i n g any stage i n f i l m growth depending upon the mater i a l and the environment. C o r r o s i o n f i l m s formed on m e t a l s and m e t a l - c o a t e d s t e e l p r o d u c t s exposed by the Bureau o f Mines at f i e l d s i t e s i n the e a s t e r n U.S. f o r times from 1 t o 36 months had: (1) c h e m i s t r i e s t h a t were independent of environment i n s h o r t - t e r m expos u r e s ; (2) m o r p h o l o g i e s t h a t were, i n some c a s e s , h i g h l y a l t e r e d by s o l u t i o n p r o c e s s e s ; and (3) r u n o f f l o s s e s f o r z i n c that were dependent upon h y d r o g e n i o n l o a d i n g . C o r r o s i o n F i l m C h e m i s t r y . A l i n e a r r e l a t i o n s h i p e x i s t s between the mass of c o r r o s i o n p r o d u c t formed on c a r b o n s t e e l , Cor-Ten A, z i n c , g a l v a n i z e d s t e e l , and copper and the mass o f m e t a l i n the c o r r o s i o n film. T h i s r e l a t i o n s h i p i s independent of s i t e and the wide v a r i a t i o n i n e n v i r o n m e n t a l parameters between the s i t e s i n s h o r t - t e r m exposures of 1 and 3 months. The r a t i o o f the two masses i s r e l a t i v e l y s e n s i t i v e t o the c o m p o s i t i o n of the c o r r o s i o n f i l m . The independence of t h i s r a t i o from s u b s t a n t i a l v a r i a t i o n s i n a i r q u a l i t y , m e t e o r o l o g y , and r a i n c h e m i s t r y i s i n t e r p r e t e d as i n d i c a t i n g , at l e a s t f o r the major c o n s t i t u e n t s , t h a t the c o m p o s i t i o n o f the c o r r o s i o n f i l m i s independent o f the environment i n s h o r t - t e r m exposures. The c o r r o s i o n f i l m on Cor-Ten A c o n t a i n s between 30 and 70 wt pet FeOOH, about 4-12 wt pet l o o s e l y - b o u n d water, about 1-5 wt pet water o f h y d r a t i o n , and the b a l a n c e h y d r a t e d F e 0 . No s i g n i f i c a n t c o n c e n t r a t i o n s o f FeO, F e 0 , F e 0 , FeSO^, and F e ( 0 H ) are p r e s e n t . The c o r r o s i o n f i l m on carbon s t e e l i s s i m i l a r t o t h a t on Cor-Ten A i n short exposures. The c o r r o s i o n f i l m on z i n c c o n t a i n s about 65 wt pet Z n C 0 and 35 wt pet Z n ( 0 H ) . The c o r r o s i o n f i l m from the Washington, DC, site may a l s o c o n t a i n ZnO. The c o r r o s i o n f i l m on g a l v a n i z e d s t e e l c o n s i s t s of Z n C 0 , Zn(OH)^, and ZnO. The p r e s e n c e of the ZnO i s p r o b a b l y due t o the s t a b i l i z a t i o n o f an i n i t i a l p a s s i v e ZnO f i l m by C r ^ which p e r s i s t s over p a r t s o f the s u r f a c e i n exposures up to 3 years. The c o r r o s i o n f i l m on copper c o n t a i n s m o s t l y C u 0 and some CuO. The c o r r o s i o n f i l m s from the Washington, DC, s i t e c o n t a i n a h i g h e r p e r c e n t a g e of CuO, i . e . , 40 wt pet C u 0 and 60 wt pet CuO. The 2

2

3

3

3

1 +

2

3

2

3

+

2

2

7. FLINN ET A L .

Environmental Effects on Metallic Corrosion Products

149

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f i l m s do not c o n t a i n l a r g e amounts o f the copper s u l f i d e s , s u l f a t e s , hydroxides, carbonates, c h l o r i d e s , or combinations o f these compounds. C o r r o s i o n F i l m Weathering. S i g n i f i c a n t s p a l l i n g and r u n o f f l o s s e s o c c u r f o r a l l o f t h e metals i n exposures o f 1 y e a r . Z i n c and g a l v a n i z e d s t e e l e x h i b i t r u n o f f l o s s e s i n 3- and 12-raonth e x p o s u r e s . M a s s i v e r e o r g a n i z a t i o n o f t h e c o r r o s i o n f i l m s on carbon s t e e l , C o r Ten A, z i n c , and g a l v a n i z e d s t e e l o c c u r s which produces new morpholo g i e s i n t h e weathered f i l m . These morphologies a r e dependent on s i t e , exposure t i m e , and o r i e n t a t i o n (skyward and groundward). They d e v e l o p over extended p e r i o d s o f time, i n d i c a t i n g t h a t t h e s o l u t i o n and p r e c i p i t a t i o n p r o c e s s e s p r o d u c i n g them do not o c c u r p r i m a r i l y d u r i n g p r e c i p i t a t i o n e v e n t s , when washing would t o t a l l y remove d i s s o l v e d c o r r o s i o n p r o d u c t s , but d u r i n g the d r y i n g phase o f p r e c i p i t a t i o n events and when m o i s t u r e c o l l e c t s on t h e s u r f a c e w i t h l i t t l e or no r u n o f f , as w i t h dew. The s o l u t i o n p r e s e n t on t h e s u r f a c e d u r i n g the d r y i n g phase i s a p o w e r f u l s o l v e n t , a l t e r i n g f e a t u r e s o f the c o r r o s i o n f i l m which appear u n a f f e c t e d by the c o n t i n u o u s washing o f rain. A b s o r p t i o n o f a c i d i c gases from the atmosphere i s p r o b a b l y important t o the f o r m a t i o n o f t h i s s o l v e n t . With c o n t i n u i n g e v a p o r a t i o n o f the s o l u t i o n , d i s s o l u t i o n o f c o r r o s i o n p r o d u c t d i m i n i s h e s and p r e c i p i t a t i o n b e g i n s . D i f f e r e n c e s e x i s t i n the d e t a i l s o f t h i s p r o c e s s f o r t h e i n d i v i d u a l m e t a l s , e.g., Cor-Ten A and z i n c . Corros i o n r a t e s f o r a l l o f the m e t a l s except Galvalurae and aluminum d e c r e a s e w i t h i n c r e a s i n g time, i n d i c a t i n g t h e f o r m a t i o n o f a more p r o t e c t i v e c o r r o s i o n f i l m i n the l o n g e r e x p o s u r e s . C o n d i t i o n s which a f f e c t t h e w e a t h e r i n g p r o c e s s e s d e s c r i b e d here w i l l have a marked e f f e c t on the c o r r o s i o n o f the metals themselves, as t h e i r a b i l i t y t o a c h i e v e a s t a b l e , low c o r r o s i o n r a t e i n long-term exposures depends e n t i r e l y on the development o f the c o r r o s i o n f i l m . R u n o f f L o s s e s Due t o Hydrogen I o n L o a d i n g . Runoff l o s s e s from z i n c , and presumably g a l v a n i z e d s t e e l , a r e dependent upon hydrogen i o n l o a d i n 3- and 12-month e x p o s u r e . Such an e f f e c t i s not apparent i n 1-month e x p o s u r e s . Hydrogen i o n d i s s o l v e s z i n c c a r b o n a t e , perhaps the major c o n s t i t u e n t o f the c o r r o s i o n f i l m , by the r e a c t i o n ZnC0

3

+ H

+

Zn

2 +

+ HC0 " 3

A d d i t i o n a l c o r r o s i o n f i l m i s l o s t i n the r u n o f f due t o the l i m i t e d s o l u b i l i t y o f t h e c o r r o s i o n product i n r a i n . The r e l a t i v e c o n t r i b u t i o n o f t h e s e e f f e c t s t o the r u n o f f i n 3- and 12-raonth exposures was 55 pet d i s s o l u t i o n and 45 pet hydrogen i o n l o a d i n g . To m a i n t a i n t h e s t a b l e c o r r o s i o n f i l m t h a t d e v e l o p s on z i n c i n l o n g - t e r m e x p o s u r e s , i t i s e v i d e n t t h a t z i n c must c o r r o d e at a r a t e s u f f i c i e n t t o r e p l a c e the c o r r o s i o n product l o s t i n r u n o f f . Acknowledgment T h i s r e s e a r c h has been funded by the Bureau o f Mines and t h e N a t i o n a l A c i d P r e c i p i t a t i o n Assessment Program through a c o s t s h a r i n g I n t e r a g e n c y Agreement between t h e Bureau and t h e E n v i r o n m e n t a l P r o t e c t i o n Agency. Use o f t r a d e names or company names does not imply endorsement by t h e Bureau o f Mines.

150

MATERIALS DEGRADATION CAUSED BY ACID RAIN

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch007

Literature Cited 1. Flinn, D. R.; Cramer, S. D.; Carter, J. P.; Lee, P. K; Sherwood, S. I. "Acidic Deposition and the Corrosion and Deterioration of Materials in the Atmosphere: A Bibliography. 1880-1982"; PB83-126091; National Technical Information Service, July 1983. 2. Haynie, F. H.; Upham, J. B. In "Corrosion in Natural Environments"; STP 558; American Society for Testing and Materials: Philadelphia, 1974; 33-51. 3. Mansfeld, F. B. "Effects of Airborne Sulfur Pollutants on Materials"; PB81-126351; National Information Service, January 1980. 4. Lipfert, F. W.; Benarie, M.; Daura, M. L. Derivation of Metallic Corrosion Damage Functions For Use in Environmental Assessments. Draft Report, available from senior author, Dept. of Energy and Environment, Brookhaven National Laboratory, Upton, NY 11973. 5. Franey, J. P.; Graedel, T. E.; Kammlott, G. W. In "Atmospheric Corrosion"; Ailor, W. H., Ed.; John Wiley and Sons: New York, 1982; 383-392. 6. Flinn, D. R.; Cramer, S. D.; Carter, J. P.; Spence, J. W. Durability of Building Materials, 1985, 3(2), 147-175. 7. Bureau of Mines. Quality Assurance Project Plan. Interagency Agreement AD-14-F-1-452-0 between Bureau of Mines and Environmental Protection Agency, October 1983. (Available from D. R. Flinn, Bureau of Mines, Avondale Research Center, Avondale, MD 20782-3393.) 8. Reddy, M. M.; Sherwood, S. I. Limestone and Marble Dissolution by Acid Rain. In this book. 9. Youngdahl, C. Α.; Doe, B. R.; Sherwood, S. I. Roughening Recession and Chemical Alteration of Marble and Limestone Sample Surfaces After Atmospheric Exposure in the Northeastern United States. In this book. 10. Cohen, M.; Hashimoto, K. J. Electrochem. Soc., 1974, 121(1), 42-45. 11. Inouye, K.; Ichimura, K.; Kaneko, K.; Ishikawa, T. Corrosion Sci., 1976, 16, 507-517. 12. Kameko, K.; Inouye, K. Bull. Chem. Soc. of Japan, 1976, 49(12), 3689-3690. 13. Suzuki, I.; Masuko, N.; Hisamatsu, Y. Corrosion Sci., 1979, 19, 521-535. 14. Cramer, S. D.; Carter, J. P.; Covino, B. S., Jr. "Atmospheric Corrosion Resistance of Steels Prepared from the Magnetic Fraction of Urban Refuse"; U.S. Bureau of Mines, RI 8477, 1980. 15. Suzuki, I.; Hisamatsu, Y.; Masuko, N. J. Electrochem. Soc., 1980, 127(10), 2210-2215. 16. Matijevic, E. Pure and Applied Chemistry, 1980, 52(5), 11791193. 17. Spedding, D. J.; Sprott, A. J. Proc. 8th Intern. Congr. Met. Corr.; Dechema: Frankfurt, 1981; Vol. 1, 329-335. 18. de Meybaum, B. R.; Ayllon, E. S.; Bonard, R. T.; Granesse, S. L.; Ikeha, J. L. Proc. 8th Intern. Congr. Met. Corr.; Dechema: Frankfurt, 1981; Vol. 1, 317-322.

7. FLINN ET AL. 19. 20. 21. 22.

23. 24.

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25. 26. 27. 28. 29. 30. 31. 32. 33.

34. 35. 36.

Environmental Effects on Metallic Corrosion Products

Keiser, J . T . ; Brown, C. W.; Heidersbach, R. H. Corrosion, 1982, 38(7), 357-360. Leidheiser, H . , Jr.; Czako-Nagy, I. Corrosion S c i . , 1984, 24(7) 569-577. Cleary, H. J. Corrosion, 1984, 40(11), 606-608. Albrecht, P.; Naeemi, A. H. "Performance of Weathering Steel in Bridges"; National Cooperative Highway Research Program Report 272, Transportation Research Board, National Research Council: Washington, DC, 1984. Liptay, G. "Atlas of Thermoanalytical Curves"; Heyden and Sons: New York, 1971; Vol. 2, Section 89. Evans, U. R. "The Corrosion and Oxidation of Metals"; Ε. Arnold: London, 1960; p. 25. Horton, J . B. Proc. San Francisco Regional Technical Meeting; American Iron and Steel Institute: Washington, DC, November 18, 1965; 171-195. Anderson, Ε. Α.; Fuller, M. L. Metals and Alloys, 1939; Vol. 10, pp. 292-287. Biestek, T. In "Atmospheric Corrosion"; Ailor, W. H . , Ed.; John Wiley and Sons: New York, 1982; 631-643. Handbook of Chemistry and Physics; 60th Ed.; CRC Press: Boca Raton, FL, 1979; B-142. Ageno, F . ; Valla, E. Hydrolysis. Atti Accad. Lincei, 1911; Vol. 20, Part II, 706-712. Barton, K. "Protection Against Atmospheric Corrosion"; Wiley and Sons: New York, 1973; 49. Williams, L. F. G. Plating, 1971, 59(10), 931-938. Duncan, J . R. Surface Technology, 1982, 16, 163-173. Zoccola, J . C . ; Townsend, H. E.; Borzillo, A. R.; Horton, J . B. In "Atmospheric Factors Affecting the Corrosion of Engineering Materials"; STP 646; Coburn, S. Κ., Ed.; American Society for Testing Materials: Philadelphia, 1978; 165-184. Mattson, E.; Holm, R. In "Atmospheric Corrosion"; Ailor, W. H., Ed.; John Wiley and Sons: New York, 1982; 365-381. Schon, G. Surface S c i . , 1973, 35, 96-108. Sowinski, G.; Sprowls, D. O. In "Atmospheric Corrosion"; Ailor, W. H . , Ed.; John Wiley and Sons: New York, 1982; 297328.

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8 Bronze, Zinc, Aluminum, and Galvanized Steel: Corrosion Rates as a Function of Space and Time over the United States 1,3

1

2

D. E . Patterson , R. B.Husaron ,and E. Escalante 1

Washington University, St. Louis, M O 63130

2

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch008

National Bureau of Standards, Gaithersburg, M D 20899

The corrosion of metals exposed to the atmosphere is known to be caused by a mixture of natural and anthropogenic factors. To apportion the cause of metal corrosion, one may conduct controlled laboratory experiments or well designed field exposure experiments. A complicating factor may arise in the case that the progress of corrosion is not constant in time, but may change significantly after an initial period, e.g. due to erosion or formation of protective surface layers. Such erratic behavior has been documented by Guttman (1) for variability of zinc corrosion with season of first exposure. Therefore it is also desirable to examine the records of long term exposure studies to better reflect the actual fate exposed metals. Unfortunately, the environmental data associated with such exposures are generally insufficient to document the meteorological and chemical causes of the corrosion. The usefulness of existing long term exposure metals corrosion data thus depends upon reconstruction of the meteorological and chemical histories which are relevant to corrosion. To do so i n v o l v e s a n a l y s i s o f d a t a o n m e t e o r o l o g y and p o l l u t a n t e m i s s i o n s i n conjunction with data i n t e r p o l a t i o n t o o l s , i . e . p o l l u t a n t d i s p e r s i o n models. T h i s r e p o r t d i s c u s s e s t h e c u r r e n t s t a t u s o f s u c h an e f f o r t at Washington U n i v e r s i t y , and examines t h e e x i s t i n g exposure d a t a f o r e v i d e n c e o f key f e a t u r e s which may c l a r i f y t h e l i k e l y importance of manmade p o l l u t a n t s i n m e t a l s c o r r o s i o n . Metal

Corrosion

Data

The e x i s t i n g l o n g term e x p o s u r e m e t a l c o r r o s i o n d a t a has been r e p o r t e d i n a number o f papers i n j o u r n a l s and p r o c e e d i n g s o v e r t h e years. The c o n s i d e r a b l e t a s k o f l o c a t i n g , v e r i f y i n g , s t a n d a r d i z i n g and a s s e m b l i n g t h e numerous b i t s o f i n f o r m a t i o n i n t o a coherent whole was undertaken by E. E s c a l a n t e o f t h e N a t i o n a l Bureau o f S t a n d a r d s . Thus, t h e f i n a l d a t a s e t c o n t a i n s o n l y t h o s e e x p e r i m e n t s w h i c h were conducted a c c o r d i n g t o s t a n d a r d ASTM p r o c e d u r e s and had adequate d o c u m e n t a t i o n o f t h e s i t e c h a r a c t e r i s t i c s and p e r i o d o f e x p o s u r e . ^Current address: 3073 Andover, St. Louis, MO 63121 0097-6156/ 86/ 0318-0152$06.00/ 0 © 1986 American Chemical Society

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The c o r r o s i o n d a t a i n c l u d e s p e r i o d s from 1936 t o 1978, w i t h exposure d u r a t i o n s o f 1 t o 20 y e a r s . Most d a t a r e f e r t o t h e p e r i o d o f the 1960s, and r e f l e c t d u r a t i o n s o f 1 t o 7 y e a r s . The s i t e s a r e p r e d o m i n a n t l y i n the e a s t e r n U n i t e d S t a t e o r i n C a l i f o r n i a . S i x m e t a l s a r e i n c l u d e d i n the assembled r e c o r d s : carbon s t e e l , w e a t h e r i n g s t e e l , g a l v a n i z e d s t e e l , z i n c , aluminum and bronze. A t o t a l o f 63 s i t e s a r e found i n the d a t a base, w i t h many s i t e s r e p o r t i n g v a l u e s f o r numerous m e t a l s . S i t e s were c l a s s i f i e d as m a r i n e , i n d u s t r i a l , or u r b a n . The s i t e d i s t r i b u t i o n i s g i v e n below.

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch008

Metal Aluminum Bronze Galvanized Steel Weathering S t e e l Zinc Carbon S t e e l

Rural

Industrial

5 5 9 2 8 10

7 3 5 2 17 22

Marine 6 2 1 10 16

The parameters f o r the c o r r o s i o n d a t a i n c l u d e s i t e l o c a t i o n and c l a s s i f i c a t i o n , d u r a t i o n and time p e r i o d o f e x p o s u r e , s o u r c e r e f e r e n c e , and a s e r i e s of c o r r o s i o n measures: c o r r o s i o n r a t e (mg/dm^/da, o r mdd), p e r c e n t a g e change i n s t r e n g t h and e l o n g a t i o n , p i t depth, y e a r s t o f i r s t r u s t , and o t h e r s which were r a r e l y used. The change i n s t r e n g t h and i n e l o n g a t i o n a r e more d i r e c t l y i m p o r t a n t as measures o f s t r u c t u r a l i n t e g r i t y t h a n i s the more commonly measured weight l o s s measure o f mdd. In the p r o c e s s o f e x a m i n i n g the metal c o r r o s i o n d a t a , c a r e was t a k e n t o a v e r a g e o n l y over narrow time r a n g e s . A g r a p h i c a l presen­ t a t i o n o f the averaged d a t a v a l u e i s c o n t a i n e d i n t h e f i n a l r e p o r t a s s o c i a t e d w i t h the metal c o r r o s i o n s t u d y ( 2 ) . The r e a d e r i s r e f e r r e d t o t h a t r e p o r t f o r the d e t a i l s o f the d a t a s e t . I n t h i s paper we p r e s e n t some key r e s u l t s . Paradigm The r e t r o s p e c t i v e s t u d y has been f o r m u l a t e d w i t h a c l e a r paradigm o f the parameters o f the c o r r o s i o n system. I t i s assumed t h a t the s i g n i f i c a n t c o n t r i b u t o r s t o the c o r r o s i o n o f m e t a l s exposed t o the atmosphere a r e water, s e a s a l t s , s u l f u r o x i d e s , n i t r o g e n o x i d e s , and the a c i d i t y o f p r e c i p i t a t e d w a t e r . I n the absence of w a t e r , i t i s presumed t h a t no s i g n i f i c a n t c o r r o s i o n a c t i v i t y w i l l t a k e p l a c e . S u r f a c e s may be m o i s t due t o p r e c i p i t a t i o n , dew, h y g r o s c o p i c a c t i o n , and o t h e r c a u s e s . Precipi­ t a t i o n i s presumed t o a c t i n t h r e e modes: by c l e a n s i n g the s u r f a c e o f accumulated d r y d e p o s i t e d m a t t e r , by m o i s t e n i n g t h e s u r f a c e , and (at low pH) by d i r e c t c h e m i c a l a t t a c k upon the m e t a l and c o r r o s i o n products. I n the presence o f m o i s t u r e , i t i s assumed t h a t the key c h e m i c a l r e a c t i o n s a r e i n i t i a t e d by S 0 and perhaps by Ν 0 gases. O t h e r mechanisms, s u c h as d r y d e p o s i t i o n o f a c i d i c a e r o s o l or d e p o s i t i o n o f HNO^ t o d r y s u r f a c e s , a r e n o t c o n s i d e r e d . Synergis­ t i c e f f e c t s are s i m i l a r l y disregarded. 2

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With t h i s o u t l o o k , the key f a c t o r s appear t o be the c o i n c i d e n t occurrence of S 0 and m o i s t u r e . The c o n t r o l l e d m e t a l exposures from the ASTM s t u d i e s were o f f l a t p a n e l s i n s t a n d a r d o r i e n t a t i o n . The s i m p l e geometry a v o i d s many c o m p l i c a t i o n s from m o i s t u r e r e t a i n e d i n s u r f a c e t e x t u r e f e a t u r e s . T h e r e f o r e , as a f i r s t approximation, we take the r e l e v a n t time o f wetness t o be s h o r t p e r i o d s f o l l o w i n g p r e c i p i t a t i o n and p e r i o d s o f dew f o r m a t i o n . The f o r m a t i o n o f a f i l m o f water i s most l i k e l y a t h i g h r e l a t i v e h u m i d i t i e s ; h i g h h u m i d i t i e s a r e most p r e v a l e n t d u r i n g t h e n i g h t h o u r s . I n the e a s t e r n U.S., summer predawn h u m i d i t y i s t y p i c a l l y 80-90$ compared t o a f t e r n o o n h u m i d i t i e s of 50-60$; w i n t e r p a t t e r n s a r e l e s s pronounced i n a r e a s n o r t h o f the Ohio r i v e r , but a l s o show a f t e r n o o n minima (3). The impact o f near s u r f a c e and e l e v a t e d e m i s s i o n s o u r c e s o f SOp on s u r f a c e c o n c e n t r a t i o n s has been shown t o d i f f e r v e r y s t r o n g l y E l e v a t e d e m i s s i o n s o u r c e s c o n t r i b u t e l i t t l e t o n i g h t time S 0 c o n c e n t r a t i o n s , w i t h the plume t y p i c a l l y t o u c h i n g down i n midmorning d u r i n g summer c o n d i t i o n s . Near s u r f a c e e m i s s i o n s , however, cause high concentrations of S 0 (and Ν 0 ) o v e r n i g h t . These s u r f a c e source emissions are trapped w i t h i n a shallow nocturnal mixing l a y e r w i t h r e l a t i v e l y l i t t l e d i s p e r s i o n , thus making S 0 a v a i l a b l e a t the same time t h a t m o i s t u r e i s most l i k e l y t o be p r e s e n t . The " c o r r o s i o n p o t e n t i a l " f o r nearby s u r f a c e s o u r c e s i s thus d i s p r o p o r ­ t i o n a t e l y large f o r i t s emissions. 2

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch008

2

2

χ

2

Retrospective

Reconstruction

of Environmental H i s t o r i e s

The r e c o n s t r u c t i o n o f the p o l l u t a n t c o n c e n t r a t i o n s t o which a m a t e r i a l i s l i k e l y t o have been exposed r e q u i r e s b o t h e m i s s i o n i n f o r m a t i o n and d i f f u s i o n models t o r e l a t e e m i s s i o n t r e n d s t o ambient c o n c e n t r a t i o n s downwind. U s i n g h i s t o r i c a l a r c h i v e s o f f u e l use, Husar (5) has d e v e l o p e d and a p p l i e d a methodology f o r e s t i m a t i n g the h i s t o r i c a l S 0 emis­ s i o n s on a s t a t e by s t a t e b a s i s back t o 1900. No s u c h c e r t r a l r e c o r d e x i s t s , u n f o r t u n a t e l y , f o r e m i s s i o n s on the urban s c a l e . The CAPITA Monte C a r l o r e g i o n a l model of p o l l u t a n t t r a n s m i s s i o n t h r o u g h the atmosphere was d e v e l o p e d as a d i a g n o s t i c t o o l t o s i m u l a t e the f o r m a t i o n and t r a n s p o r t o f s u l f a t e a e r o s o l . I t has s u b s e q u e n t l y been m o d i f i e d and a p p l i e d t o s i m u l a t i o n o f s u l f u r wet d e p o s i t i o n as w e l l as s u l f a t e c o n c e n t r a t i o n ( 6 , 7 ) . For the c u r r e n t p u r p o s e s , t h e model was s u b s t a n t i a l l y m o d i f i e d i n o r d e r t o a d e q u a t e l y model the d i u r n a l p a t t e r n s o f S 0 impact from near s u r f a c e and elevated sources. The s i m u l a t i o n i s a p p r o p r i a t e f o r t h e r e g i o n a l s c a l e , w i t h time s t e p o f 3 hours and s p a t i a l r e s o l u t i o n o f about 100 km i n a g r i d o f r o u g h l y 12000 km . T h i s s c a l e , however, i s i n a d e q u a t e f o r s i m u l a t i o n o f p r i m a r y p o l l u t a n t s s u c h as S 0 within t h e f i r s t 100-200 km o f t r a n s p o r t . The a v e r a g e o v e r the g r i d , even i f c o r r e c t , d o e s not r e v e a l the o r d e r s o f magnitude h i g h e r c o n c e n t r a ­ t i o n s e x p e r i e n c e d i n s m a l l a r e a s n e a r e s t the s o u r c e s o f e m i s s i o n s . T h e r e f o r e a l o c a l model was d e v e l o p e d t o b e t t e r s i m u l a t e the n e a r f i e l d c o n c e n t r a t i o n and d e p o s i t i o n impacts of p r i m a r y e m i s s i o n s . T h i s s i m u l a t i o n u t i l i z e s much o f the same f o r m u l a t i o n i n terms o f m e t e o r o l o g y as the r e g i o n a l model ( w i t h improved i n i t i a l v e r t i c a l d i s p e r s i o n s i m u l a t i o n ) , and w i t h the i d e n t i c a l k i n e t i c s f o r t r a n s 2

2

2

2

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f o r m a t i o n o f S 0 t o SO^", d r y d e p o s i t i o n o f s u l f u r , and wet d e p o s i t i o n o f s u l f u r . T h i s model was used t o e s t i m a t e c o r r e c t i o n f a c t o r s t o be a p p l i e d t o t h e r e g i o n a l model r e s u l t s . The f u l l methodology o f r e t r o s p e c t i v e a n a l y s i s was a p p l i e d f o r the c a s e o f marble tombstone d e t e r i o r a t i o n i n an urban and a remote cemetery near New York C i t y (8,90. In t h i s e x e r c i s e i t was f o u n d t h a t our t e c h n i q u e may e s t i m a t e r u r a l S 0 c o n c e n t r a t i o n s acceptably w e l l , but i t does not r e p r o d u c e d e t a i l e d s t r u c t u r e o f urban concent r a t i o n s adequately. The main r e a s o n s a r e u n c e r t a i n t y about t h e e f f e c t i v e r e l e a s e h e i g h t s o f s o u r c e s and a l a c k o f d e t a i l e d l o c a l emission information. F o r t h e purposes o f metal c o r r o s i o n , t h e current s t a t e of the r e t r o s p e c t i v e r e c o n s t r u c t i o n of environmental h i s t o r i e s i s not s u f f i c i e n t l y q u a n t i t a t i v e t o warrant e x t r a c t i o n o f damage f u n c t i o n s . The d a t a s e t o f m e t a l c o r r o s i o n p r o v i d e s a v a l u a b l e i n s i g h t as t o which parameters dominate t h e c o r r o s i o n p r o c e s s . The g e n e r a l m e t e o r o l o g i c a l f e a t u r e s a r e w e l l e s t a b l i s h e d i n N o r t h America ( a l t h o u g h m i c r o m e t e o r o l o g i c a l f a c t o r s may dominate a t any s i n g l e exposure s i t e ) . The p o l l u t a n t r e l a t e d q u e s t i o n s may be s i m p l y s t a t e d : (1) what a r e t h e magnitudes o f marine and i n d u s t r i a l c o r r o s i o n r a t e s compared t o t h e r u r a l v a l u e s ; (2) what a r e t h e r e l a t i v e r a t e s i n t h e r u r a l e a s t e r n U n i t e d S t a t e s compared t o t h e w e s t e r n r u r a l v a l u e s ; (3) what a r e t h e broad t r e n d s i n c o r r o s i o n r a t e over the years? Roughly s p e a k i n g , t h e f i r s t q u e s t i o n a d d r e s s e s t h e importance o f S 0 , w h i l e t h e s e c o n d and t h i r d r e l a t e t o t h e r e g i o n a l s c a l e impacts o f S 0 , S 0 ^ , and a c i d i c d e p o s i t i o n . S 0 i n urban a r e a s i s a m a t t e r f o r l o c a l c o n t r o l e f f o r t s , whereas t h e r e g i o n a l impacts (which a r e due t o l o n g range t r a n s p o r t o f e m i t t e d m a t e r i a l ) r e q u i r e l a r g e r s c a l e c o n t r o l s and f a l l i n t o t h e c a t e g o r y o f " a c i d r a i n " a s s o c i a t e d damage. 2

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch008

2

2

=

2

2

Observations T h i s s e c t i o n d i s c u s s e s a few o f t h e major p a t t e r n s e v i d e n t i n t h e metals c o r r o s i o n database. I n many r e s p e c t s , t h e r e s u l t s a r e r e s t a t e m e n t s o f the f i n d i n g s o f e a r l i e r r e s e a r c h by t h o s e a s s o c i a t e with the o r i g i n a l p r o j e c t s . F o r t h e purposes o f t h e r e t r o s p e c t i v e r e c o n s t r u c t i o n p r o j e c t , i t i s nevertheless u s e f u l t o determine whether t h e i n i t i a l assumptions appear r e a s o n a b l e and t o examine the r e l a t i v e importance o f the m e t e o r o l o g i c a l and c h e m i c a l f a c t o r s as r e v e a l e d i n t h e d a t a . T h i s w i l l t e l l where t o p l a c e a d d i t i o n a l e f f o r t f o r t h e b e s t improvement. More s p e c i f i c a l l y , i f t h e aim o f the study i s t o e x p l a i n t h e observed v a r i a t i o n s i n c o r r o s i o n r a t e , we f i r s t w i s h t o know what v a r i a t i o n s a r e s t r o n g enough t o w a r r a n t f u r t h e r study. F i r s t t h e d a t a were examined f o r v a r i a b i l i t y . The c o n v e n i e n t measure o f n o i s e t o s i g n a l ( s t a n d a r d d e v i a t i o n d i v i d e d by t h e mean) y i e l d e d v a l u e s which were q u i t e l a r g e f o r a l a r g e number o f c a r b o n s t e e l exposure t e s t s . Due t o t h i s v a r i a b i l i t y and t h e t y p i c a l l y s h o r t exposure t i m e s , c a r b o n s t e e l was n o t examined i n g r e a t e r detail. S i n g l e year e x p o s u r e s o f z i n c p l a t e s i n d i c a t e d t h a t t h e r e l a t i v e v a r i a b i l i t y was 30% f o r marine s i t e s , 20? f o r r u r a l s i t e s , and 10% f o r i n d u s t r i a l s i t e s . The m a r i n e s i t e s had t h e h i g h e s t

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c o r r o s i o n r a t e s as w e l l as the h i g h e s t r e l a t i v e v a r i a b i l i t y , w h i l e t h e i n d u s t r i a l s i t e s i n d i c a t e d r a t h e r c o n s i s t e n t b e h a v i o r even o v e r t h i s s h o r t time p e r i o d . At the o t h e r extreme, bronze t r i p l i c a t e p a n e l s y i e l d e d r e l a t i v e v a r i a b i l i t y of below 10$ a f t e r 20 year e x p o s u r e s . The o v e r a l l r e s u l t of such c o n s i d e r a t i o n s was the d e c i s i o n t o average d a t a wherever m u l t i p l e v a l u e s were a v a i l a b l e with n e a r l y i d e n t i c a l exposure times. S i m i l a r l y , i t indicated that s m a l l d i f f e r e n c e s i n c o r r o s i o n r a t e s ( p a r t i c u l a r l y d u r i n g the f i r s t few y e a r s ) s h o u l d not be o v e r i n t e r p r e t e d . The near c o a s t a l e f f e c t of wetness and s e a s a l t i s e v i d e n t i n the d a t a , p a r t i c u l a r l y f o r 1 and 2 y e a r e x p o s u r e s . Zinc corrosion r a t e s a t Cape Kennedy, FL, dropped by a f a c t o r of M as d i s t a n c e from the c o a s t i n c r e a s e d from 60 t o 880 m. At Kure Beach,NC, Zn r a t e s dropped by a f a c t o r of 3 as d i s t a n c e i n c r e a s e d from 25m t o 250m from sea; c o r r e s p o n d i n g A1 c o r r o s i o n r a t e s f e l l by a f a c t o r of 2. C l e a r l y s i t e s w i t h i n a few hundred meters of t h e s e a must be s e g r e g a t e d from o t h e r s i t e s i n any f u r t h e r a n a l y s i s . The g e n e r a l m e t e o r o l o g i c a l environment i n the c o n t i n e n t a l U.S. i s w e l l known, r a n g i n g from the d e s e r t Southwest t o t h e r o u g h l y 1m a n n u a l r a i n f a l l o v e r much o f the c o u n t r y e a s t of the M i s s i s s i p p i river. The number o f days w i t h measurable p r e c i p i t a t i o n i s about 50$ h i g h e r i n t h e n o r t h e a s t e r n quadrant of t h e n a t i o n t h a n i n the G r e a t P l a i n s . The number o f days w i t h heavy f o g i s h i g h e r by a f a c t o r of 2 or more i n t h e mountainous p o r t i o n s o f t h e e a s t e r n U.S. and i n c o a s t a l a r e a s than i n the G r e a t P l a i n s or lower Ohio R i v e r v a l l e y (3). T h e r e f o r e some v a r i a t i o n i n c o r r o s i o n r a t e s w i t h i n t h e e a s t e r n U.S. may be e x p e c t e d j u s t from v a r i a t i o n i n time of w e t n e s s . Four s i t e s w i t h m u l t i p l e a l l o y s exposed over the y e a r s r e c u r i n most of t h e m e t a l c o r r o s i o n d a t a s e t s . These s i t e s i n c l u d e r u r a l marine exposures at P o i n t Reyes, CA and Kure Beach, NC; industrial e x p o s u r e s a t Newark, NJ; and an e a s t e r n U.S r u r a l i n l a n d l o c a t i o n a t S t a t e C o l l e g e , PA. Aluminum a l l o y s i n d i c a t e g e n e r a l l y low c o r r o s i o n r a t e s , except i n the C h i c a g o a r e a ; f o r s e v e r a l a l l o y s , c o r r o s i o n r a t e s t h e r e were n e a r l y an o r d e r o f magnitude h i g h e r t h a n a t o t h e r s i t e s . For AL 6061 ( T 6 ) , t h e i n d u s t r i a l environment caused s u b s t a n t i a l c o r r o s i o n and l o s s of s t r e n g t h . For t h r e e o t h e r a l l o y s (AL 201M ( T 4 ) , AL 202M (T81) and AL 7075 ( T 6 ) ) , the h i g h e r r a t e s were noted a t t h e marine s i t e s , with less i n d u s t r i a l e f f e c t . For a l l t h e s e a l l o y s , the r u r a l P e n n s y l v a n i a c o r r o s i o n r a t e s were lower t h a n the c o r r e s p o n d i n g r a t e s a t i n d u s t r i a l s i t e s , by a f a c t o r o f 2 t o 7 a f t e r 7 y e a r s e x p o s u r e . The r u r a l s i t e e x p o s u r e s i n d u c e d no s i g n i f i c a n t s t r e n g t h l o s s . T h e r e f o r e i t may be t e n t a t i v e l y c o n c l u d e d t h a t the r e g i o n a l s c a l e causes o f aluminum c o r r o s i o n a r e not s u f f i c i e n t l y pronounced t o warrant f u r t h e r r e s e a r c h a t t h i s t i m e . Weathering s t e e l data i n d i c a t e d r a t h e r constant c o r r o s i o n r a t e s a f t e r 8 year e x p o s u r e s (1967-1975) a t m a r i n e , urban and r u r a l s i t e s i n the e a s t e r n U.S. Although t h i s data i s l i m i t e d , i t s u g g e s t s t h a t the c o r r o s i o n h i s t o r y of t h i s w e a t h e r i n g s t e e l a l l o y must be r e l a t i v e l y i n s e n s i t i v e t o b o t h S 0 c o n c e n t r a t i o n and t o the pH o f r a i n f a l l . An a l t e r n a t i v e e x p l a n a t i o n i s t h a t p o l l u t a n t l e v e l s above some t h r e s h o l d v a l u e a r e s u f f i c i e n t t o induce the o b s e r v e d corrosion. Even s o , the d a t a do not o f f e r c l u e s as t o the p o l l u t a n t effect. 2

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch008

8.

P A T T E R S O N ET

AL.

Corrosion Rates as a Function of Space and Time

157

G a l v a n i z e d s t e e l d a t a i s a v a i l a b l e from 20 year exposures (1936-1956) and from 2 year exposures (1971-1973). The twenty year exposures show t h a t c o r r o s i o n r a t e s i n the Great P l a i n s range from 0.2 t o 0.4 mdd, w h i l e r u r a l r a t e s i n the Ohio R i v e r v a l l e y and t h e n o r t h e a s t e r n U.S. range 0.5 t o 0.6 mdd. Such r u r a l d i f f e r e n c e s a r e l i k e l y a t t r i b u t a b l e t o v a r i a t i o n s i n time of wetness. I n d u s t r i a l exposures are a s s o c i a t e d w i t h r a t e s of 1-3 mdd. The more r e c e n t s h o r t term exposures a t the r u r a l S t a t e C o l l e g e s i t e i n d i c a t e lower c o r r o s i o n r a t e s than were r e g i s t e r e d d u r i n g the e a r l i e r 20 year e x p o s u r e s . A l t h o u g h i t i s d i f f i c u l t t o make such comparisons, the s u g g e s t i o n t h a t r u r a l e a s t e r n U.S. c o r r o s i o n r a t e s have i n c r e a s e d over the p a s t s e v e r a l decades i s not s u p p o r t e d by t h e s e measurements. Z i n c p r o v i d e s the most e x t e n s i v e s e t of measurements among the m e t a l s . Data are a v a i l a b l e from 7 year exposures e n d i n g i n 1956 and i n 1965, as w e l l as d u a l s e t s of 20 year exposures ending i n 1951 and 1978. The d a t a show s t r o n g dependence on presumed time of wetness. The two d i s t i n c t 20 year exposure p e r i o d s i n c l u d e use o f the same s i t e a t S t a t e C o l l e g e , PA. At t h i s r u r a l s i t e , t h e l o n g term c o r r o s i o n r a t e s over the 1931-1951 p e r i o d were i d e n t i c a l t o those of the 1958=1978 p e r i o d . Thus t h e i d e a of i n c r e a s i n g r u r a l c o r r o s i o n r a t e s over the p a s t 5 decades i s not s u p p o r t e d . Indust­ r i a l c o r r o s i o n r a t e s are s u b s t a n t i a l l y h i g h e r t h a n r u r a l r a t e s ; d u r i n g the e a r l i e r exposure s t u d y , n e i g h b o r i n g s i t e s i n d i c a t e d i n d u s t r i a l r a t e s 3 t o 6 t i m e s h i g h e r t h a n those r e c o r d e d a t r u r a l s i t e s (Figure 1). These d a t a do not o f f e r enough s p a t i a l coverage t o a s s e s s the d i f f e r e n c e s between e a s t e r n and n o n e a s t e r n r u r a l c o r r o s i o n r a t e s . The I n t e r s t a t e S u r v e i l l a n c e P r o j e c t (10) p r o v i d e d measures of z i n c c o r r o s i o n r a t e s a t a number o f s i t e s i n t h e Great P l a i n s s o u t h t o Texas as w e l l as i n the e a s t e r n U.S. T h i s d a t a r e p r e s e n t s the e f f e c t s a f t e r s i n g l e year e x p o s u r e s , so t h a t l a r g e v a r i a b i l i t y i s e x p e c t e d . A c l e a r o v e r a l l p a t t e r n i s e v i d e n t , however, w h i c h s u g g e s t s t h a t e a s t e r n U.S. r u r a l c o r r o s i o n r a t e s f o r z i n c are h i g h e r than the c o r r e s p o n d i n g r a t e s i n the Great P l a i n s by a f a c t o r of 2 t o 3· T h i s i s more t h a n can be accounted f o r by m e t e o r o l o g i c a l f a c t o r s a l o n e ; i t i s presumed, t h e r e f o r e , t h a t r u r a l z i n c c o r r o s i o n r a t e s i n the e a s t e r n U.S. are a f f e c t e d t o a s i g n i f i c a n t degree by r e g i o n a l p o l l u t i o n . The r e g i o n a l e f f e c t i s not l i k e l y t o be a new phenomena. Bronze d a t a i s s p a r s e . An a l l o y o f 92% Cu exposed from 19311951 showed no c o r r o s i o n i n the d e s e r t environment and very l i t t l e a t the r u r a l s i t e s . C o i n c i d e n t z i n c d a t a i n d i c a t e s t h a t over the 20 year p e r i o d the average c o r r o s i o n r a t e s were h i g h e r f o r bronze a t marine s i t e s but much lower f o r bronze than f o r z i n c a t r u r a l s i t e s (Figure 2). At the r u r a l S t a t e C o l l e g e , PA, s i t e the c o r r o s i o n r a t e f o r two d i f f e r e n t bronze a l l o y s d u r i n g the 1958-1978 p e r i o d was n e a r l y t w i c e t h a t of the e a r l i e r bronze e x p o s u r e , w h i l e the i n d u s t r i a l Newark a r e a c o r r o s i o n r a t e s appeared t o have d e c l i n e d . A bronze w i t h 99% Cu i n a l l o y w i t h 1.25% Sn and Ρ was exposed d u r i n g the 1958-1978 p e r i o d a t the f o u r s t a n d a r d ASTM s i t e s . The c o r r o s i o n r a t e s at the r u r a l s i t e and the w e s t e r n marine s i t e were l e s s than h a l f those a t the e a s t e r n marine and i n d u s t r i a l s i t e s .

158

M A T E R I A L S D E G R A D A T I O N C A U S E D BY A C I D R A I N

Zinc 7-year exposures 1956

Zinc 1-year exposures 1965

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch008

ψ \

68

Zinc 7-year exposures 1956

20-year

Zinc exposures 1951

Zinc

1-year exposures 1965

Zinc 20-year exposures 1978

jïio I 33

/ J

y\ /

\

22 132

Zinc 20-year exposures 1951

Figure

1.

Corrosion rates

20-year

2

Zinc exposures 1978

(mg/dm ,da) f o r z i n c .

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch008

8.

PATTERSON ET AL.

Corrosion

Rates as a Function

Bronze C o r r o s i o n 1.25% Sn, P: 1958-1978 20 y r

Bronze C o r r o s i o n 1.25% Sn, P: 1958-1978 % S t r e n g t h (7)

Figure

2.

Corrosion

rates

of Space and Time

2

(mg/dm ,da) o f bronze

(92% C u ) .

159

M A T E R I A L S D E G R A D A T I O N C A U S E D BY A C I D

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch008

160

RAIN

Chemical a n a l y s e s of the c o r r o s i o n product i n d i c a t e d t h a t no s u l f u r compounds were p r e s e n t a t e i t h e r of t h e marine s i t e s ; a p p a r e n t l y p o l l u t a n t s d i d not cause the marine bronze d e t e r i o r a t i o n . Over 90% of the c o r r o s i o n p r o d u c t was s t i l l a d h e r i n g a t t h e s e m a r i n e s i t e s a f t e r 20 y e a r s . At the r u r a l s i t e , 67% remained, w h i l e o n l y 27% of the c o r r o s i o n p r o d u c t remained at the i n d u s t r i a l s i t e . A bronze a l l o y more r e p r e s e n t a t i v e o f s t a t u a r y bronzes (5% Sn and P) was a l s o exposed a t t h e f o u r s t a n d a r d s i t e s . The r u r a l and Western marine s i t e s a g a i n show c o r r o s i o n r a t e s l e s s than h a l f t h o s e of the e a s t e r n marine and the i n d u s t r i a l s i t e . The c o r r o s i o n r a t e s at the i n d u s t r i a l and the marine s i t e i n c r e a s e w i t h e x p o s u r e time f o r t h i s a l l o y , i n marked c o n t r a s t t o t h e u s u a l p a t t e r n of d e c l i n i n g c o r r o s i o n r a t e with time. I t i s a l s o c u r i o u s t h a t the measured l o s s of s t r e n g t h a t t h e r u r a l PA s i t e i s d i s p r o p o r t i o n a t e l y l a r g e f o r i t s c o r r o s i o n r a t e (1.4% vs 2.0% a t the i n d u s t r i a l s i t e ) . The bronze a l l o y s were exposed at t h e same time and p l a c e as the z i n c d u r i n g t h e p e r i o d 1958-1978, w i t h measurements a t 2, 7 and 20 year e x p o s u r e s . E x a m i n a t i o n of the c o r r o s i o n r a t e s r e v e a l e d two s e p a r a t e p a t t e r n s : a m a r i n e t r e n d o f h i g h i n i t i a l c o r r o s i o n r a t e w i t h s h a r p r e d u c t i o n i n r a t e a f t e r t h e f i r s t few y e a r s , and an i n d u s t r i a l - r u r a l t r e n d c o r r e s p o n d t o d i f f e r e n t c h e m i c a l mechanisms at work, w i t h o n l y t h e i n d u s t r i a l - r u r a l c o r r o s i o n b e i n g r e l a t e d t o s u l f u r compounds. The c o r r o s i o n r a t e s over d i s t i n c t time p e r i o d s a r e g i v e n below. The t h r e e s e t s o f r a t e s c o r r e s p o n d t o t h e i n i t i a l two y e a r s o f e x p o s u r e , the 5 y e a r s c o v e r i n g the p e r i o d from 2 t o 7 y e a r s a f t e r e x p o s u r e , and t h e f i n a l 13 y e a r s f o r the p e r i o d of 7 t o 20 y e a r s a f t e r exposure. Site

Kure Beach, NC P o i n t Reyes, CA Newark, NJ S t a t e C o l l e g e , PA

Zinc

1% Bronze

5%

Bronze

2

5

13

2

5

13

2

5

13

.77 .26 .68 .18

.81 .05 1.11 .24

.30

.51 .26 .42 .20

.40 .04 .38 .14

.18 .09 .33 .15

.92 .55 .34 .1.4

.49

.30

—

.13 .51 .20

.13 .56 .23

.51 .14

A l t h o u g h r a t i o s of the a c c u m u l a t e d w e i g h t l o s s e s do not show a c o n s i s t e n t p a t t e r n , the d i s c r e t e time p e r i o d s do show a sudden agreement a f t e r t h e i n i t i a l 7 year exposure p e r i o d . D u r i n g the l a s t 13 y e a r s , the r a t i o o f bronze t o z i n c c o r r o s i o n r a t e s ( i n mdd) f a l l s i n t o t h e range 0.65 ± .05 f o r b o t h t h e marine and nonmarine s i t e s f o r the 1% a l l o y , w i t h marine v a l u e s of 1.00 and nonmarine v a l u e s o f 0.90 ± .03 f o r the 5% a l l o y . These r a t i o s c o r r e s p o n d t o f a c t o r s of the c o e f f i c i e n t s f o r C1 and S 0 , r e s p e c t i v e l y , i n damage f u n c t i o n s such as proposed by B e n a r i e (J_2). An a d d i t i o n a l bronze a l l o y c o n t a i n i n g 7% A1 was examined, and no s u c h r e l a t i o n s h i p was f o u n d . C l e a r l y the b e h a v i o r o f a bronze i s s t r o n g l y dependent upon the a l l o y ; i t appears t h a t the phosphor bronzes e x h i b i t c o r r o s i o n b e h a v i o r q u a n t i t a t i v e l y s i m i l a r t o t h a t of z i n c a f t e r the f i r s t few years of exposure. 2

8.

PATTERSON ET AL.

Corrosion Rates as a Function of Space and Time

161

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch008

Summary A p r o j e c t was undertaken t o perform r e t r o s p e c t i v e r e c o n s t r u c t i o n of e n v i r o n m e n t a l h i s t o r i e s a t t h e s i t e s o f p r e v i o u s l o n g term a t m o s p h e r i c m e t a l e x p o s u r e s . The e f f o r t r e q u i r e d development o f a p p r o p r i a t e e m i s s i o n i n f o r m a t i o n and d i s p e r s i o n m o d e l i n g c a p a b i l i t i e s on both t h e r e g i o n a l and urban s p a t i a l s c a l e s . The development of u s e f u l urban s c a l e e m i s s i o n i n v e n t o r i e s d a t i n g back s e v e r a l decades proved t o be a l i m i t i n g f a c t o r . A t p r e s e n t , t h e r e f o r e , t h e r e t r o s p e c t i v e r e c o n s t r u c t i o n o f environmental h i s t o r i e s i s not p o s s i b l e f o r t h e l a r g e number o f s i t e s i n t h e m e t a l s c o r r o s i o n d a t a base. T h i s p r e c l u d e s d e r i v a t i o n o f damage f u n c t i o n s a t t h i s t i m e . E x a m i n a t i o n o f t h e m e t a l c o r r o s i o n d a t a base i t s e l f has i n d i c a t e d t h a t t h e r e p o r t e d c o r r o s i o n v a l u e s f o r z i n c and b r o n z e , at l e a s t , may be a s s o c i a t e d w i t h r e g i o n a l p o l l u t i o n as w e l l as l o c a l S 0 sources. I t a l s o was found t h a t z i n c and t h e two t i n phosphor bronzes behave s i m i l a r l y a f t e r an i n i t i a l p e r i o d o f exposure t o t h e atmosphere. 2

Literature Cited 1. Guttman, H. (1968) Effects of atmospheric factors on rolled zinc. Atmospheric Corrosion of Metals, ASTM STP 767, American Society for Testing and Materials, 286-308. 2. Patterson, D.E. and Husar, R.B. (1985) Final Report on Metals Damage. Submitted to National Park Service, Preservation Assistance Division, Washington, DC. 3. Baldwin, J.L.(1973) Climate of the United States. Environmental Data Service, NOAA, U.S. Dept. of Commerce, UDC 551.582(73). 4. Husar, R.B., Patterson, D.E., Husar, J.D., Gillani, N.V. and Wilson, W.E. (1978). Sulfur budget of a power plant plume. Atmos. Environ. 12, 549-568. 5. Husar, R.B. (1985). Manmade SO andNO Emission Patterns and Trends. In National Academy of Sciences Trend Report. 6. Husar, R.B., Patterson, D.E. and Wilson, W.E. (1985a) Monte Carlo simulation of regional air pollution: transport dynamics. Submitted to Journal of Climate and Applied Meteorology, June 1985. 7. Husar, R.B., Patterson, D.E. and Wilson, W.E. (1985b) Monte Carlo simulation of regional air pollution: semiempirical regional scale source-receptor relationship. In internal EPA review. 8. Husar, R.D., Patterson, D.E.(1985c) SO concentration estimates for New York City,1880-1980. Report to EPA Atmospheric Sciences Research Laboratory, Research Triangle Park, NC. 9. Husar, R.B., Patterson, D.E. (1985d). Marble tombstone deterioration in New York City area.Report to EPA Atmospheric Research Laboratory, Research Triangle Park, NC. 10. Cavendar, J., Cox, W., Georgevich, M., Huey, N., Yutze, G. and Zimmer C. (1971). Interstate Surveillance Project. US EPA, GPO 5503-0006, Washington, DC. 11. Costas, L.(1982) Atmospheric corrosion of copper alloys exposed for 15 to 20 years. Atmospheric Corrosion of Metals, ASTM STP 767, American Society for Testing and Materials, 106-115. x

x

2

162

MATERIALS DEGRADATION CAUSED BY ACID RAIN

12. Benarie, M. (1984) Metallic corrosion functions of atmospheric pollutant concentrations and rain pH. Report under contract DE-ACO2-76CH0016 to Department of Energy.

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch008

RECEIVED

March 19, 1986

9 Environmental Factors Affecting Corrosion of Weathering Steel Fred H . Haynie Atmospheric Sciences Research Laboratory, U.S. Environmental Protection Agency,

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch009

Research Triangle Park, NC 27711

Weathering steel samples were exposed for periods of up to 30 months at nine air monitoring sites in the St. Louis, Missouri area. Climatic and air quality data were recorded during the exposure period and subjected to a rigorous evaluation to eliminate recording errors and to estimate missing values. Weight loss was used as the measure of steel corrosion. Corrosion rate was evaluated with respect to, 1) flux of pollutants (sulfur oxides, nitrogen oxides, oxidants, and particles) to the steel during both wet and dry periods, 2) temperature, and 3) exposure history. Different definitions of when the steel was wet were evaluated to determine the most likely "critical relative humidity." Non-linear multiple regression techniques were used to determine the statistical significance of each factor and develop a theoretically consistent environmental damage function. From t h e f a l l of 1974 t o t h e s p r i n g o f 1977, EPA c o n d u c t e d an a i r p o l l u t i o n modeling s t u d y i n S t . L o u i s , M i s s o u r i (1)· N i n e o f 25 c o n t i n u o u s a i r m o n i t o r i n g s i t e s were s e l e c t e d f o r s t u d y i n g t h e e f f e c t s o f p o l l u t a n t s on e i g h t t y p e s o f m a t e r i a l s (2^). W e a t h e r i n g s t e e l was one o f t h e m a t e r i a l s . T h i s paper p r e s e n t s t h e r e s u l t s o f a n a l y z i n g the c o r r o s i o n o f weathering s t e e l w i t h r e s p e c t t o environmental d a t a . Theoretical

Considerations

Many m e t a l s f o r m c o r r o s i o n p r o d u c t f i l m s as t h e y c o r r o d e . These f i l m s tend t o r e s t r i c t t h e r a t e o f c o r r o s i o n . In general, the rate of c o r r o s i o n i s i n v e r s e l y p r o p o r t i o n a l t o t h e t h i c k n e s s o f t h e c o r r o s i o n p r o d u c t f i l m ( r a t e c o n t r o l l e d by d i f f u s i o n t h r o u g h t h e film). When t h e f i l m i s i n s o l u b l e and does n o t change s t r u c t u r e w i t h time, the c o r r o s i o n - t i m e f u n c t i o n i s p a r a b o l i c (c = a / t ) . Many m e t a l c o r r o s i o n p r o d u c t s have s o l u b i l i t i e s t h a t a r e p r o p o r tional to acidity. Thus, i n v e r y a c i d s o l u t i o n s , f i l m s a r e v e r y This chapter not subject to U.S. copyright. Published 1986, American Chemical Society

MATERIALS

164

DEGRADATION

C A U S E D BY ACID RAIN

t h i n and the r e s u l t i n g c o r r o s i o n - t i m e f u n c t i o n i s almost l i n e a r . In a t m o s p h e r i c e x p o s u r e s , t h e r e a r e many s e t s o f e n v i r o n m e n t a l c o n d i t i o n s where t h e s e two mechanisms a r e competing. The r e s u l t s i s the e m p i r i c a l l y o b s e r v e d r e l a t i o n s h i p s , c - A t , where the exponent, n, most o f t e n has a v a l u e between 0.5 and 1.0 (2-4). T h e o r e t i c a l l y , the amount of c o r r o s i o n ( c ) i s the sum o f the m e t a l accumulated i n the c o r r o s i o n p r o d u c t f i l m ( T ) and the amount of m e t a l s o l u b i l i z e d from t h a t f i l m w i t h time ( 3 t ) . n

w

c = Τ + 3t

(1)

w

where t i s time-of-wetness and 3 i s a s o l u b i l i z a t i o n r a t e which i s a f u n c t i o n of a c i d i c p o l l u t a n t f l u x e s . The r a t e o f f i l m t h i c k ­ ness growth i n u n i t s of m e t a l c o r r o d e d i s ;

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch009

w

dT/dt

= α/Τ -

w

3

(2)

where α i s a f u n c t i o n o f d i f f u s i v i t i e s through the f i l m . Pollu­ t a n t s may a l s o a f f e c t t h i s c o e f f i c i e n t . Under c o n s t a n t c o n d i t i o n s , i n t e g r a t i o n of e q u a t i o n (2) y i e l d s ; -3 t

- 3T + a l n ( l - 3T/a)

2

w

s u b s t i t u t i n g e q u a t i o n (1) i n t o e q u a t i o n (3) the t r a n s c e n d e n t a l e q u a t i o n : c - 3t

w

(3) and r e a r r a n g i n g

+ a(l-exp(-3C/a))/3

produces

(4)

which i s e q u i v a l e n t t o : c - 3t

w

(5)

+ a/(dc/dt ) w

A l e a s t squares f i t o f e q u a t i o n ( 4 ) cannot be used t o determine the e f f e c t s o f e n v i o r n m e n t a l f a c t o r s on t h e c o e f f i c i e n t s α and 3 be­ cause as a/ 3 becomes l a r g e the e q u a t i o n approaches b e i n g an identity. When 3c/α i s l a r g e , exp(-3c/a) approaches zero and e q u a t i o n (4) becomes; c = 3t

w

+ a/3

(6)

At e a r l y s t a g e s of c o r r o s i o n , however, from the e m p i r i c a l l y o b s e r v e d r e l a t i o n s h i p , d c / d t ^ n c / t which y i e l d s ; w

c - 3t

w

w

(7)

+ at /nc w

D u r i n g t h e f i r s t few y e a r s o f c o r r o s i o n of w e a t h e r i n g s t e e l , n e a r l y a l l o f t h e c o r r o s i o n i s accumulated i n the f i l m and α/nc i s much g r e a t e r than 3, which would i n d i c a t e t h a t t h e c o r r o s i o n time f u n c t i o n s h o u l d be n e a r l y p a r a b o l i c . The c o r r o s i o n p r o d u c t f i l m on w e a t h e r i n g s t e e l , however, has the p r o p e r t y t h a t , g e n e r a l l y , a g i v e n f i l m t h i c k n e s s becomes more p r o t e c t i v e w i t h t i m e . An e x c e p t i o n i s when the f i l m s t a y s wet. I n t h a t c a s e , the c o r r o s i o n b e h a v i o r of w e a t h e r i n g s t e e l i s not much b e t t e r than carbon s t e e l s . T h i s means t h a t η i n the e m p i r i c a l e q u a t i o n A t can be l e s s than n

9.

HAYNIE

165

Environmental Factors Affecting Corrosion of Steel

0,5 and i s e x p e c t e d t o i n c r e a s e w i t h f r a c t i o n o f t i m e - o f - w e t n e s s (f). Measurement and Data A n a l y s i s E n v i r o n m e n t a l d a t a . Hern, e t a l . , (_5) d e s c r i b e s the d a t a c o l l e c ­ t i o n and e v a l u a t i o n system f o r the e n v i r o n m e n t a l parameters a t the nine s i t e s . S u b s e q u e n t l y , the r e s u l t i n g R e g i o n a l A i r P o l l u t i o n Study (RAPS) d a t a base was r e v i s e d s e v e r a l times u s i n g b e t t e r v a l i d a t i o n t e c h n i q u e s . The p o r t i o n s of t h a t d a t a base used i n t h i s s t u d y a r e h o u r l y averages of t e m p e r a t u r e , dew p o i n t , windspeed, wind d i r e c t i o n , t o t a l o x i d a n t , Ν 0 , S 0 , and 24-hour t o t a l suspended p a r t i c u l a t e m a t t e r (TSP) samples. The v a l i d a t e d d a t a base c o n t a i n s a l o t of m i s s i n g h o u r l y a v e r a g e s and the system was not o p e r a t i n g d u r i n g the f i r s t month o r the l a s t f i f t e e n days i n which w e a t h e r i n g s t e e l samples were exposed. A methodology was d e v e l o p e d (6) to e s t i m a t e t h e s e m i s s i n g v a l u e s u s i n g t o t a l system r e l a t i o n s h i p s and r e l a t i o n s h i p s between the system and c l i m a t o l o g i c a l d a t a from Lambert F i e l d ( a i r p o r t m e t e o r o l o g i c a l s t a t i o n l o c a t e d about 16 k i l o m e t e r s northwest from the S t . L o u i s c e n t r a l b u s i n e s s d i s t r i c t ) . Rainfall was not r e c o r d e d a t the exposure s i t e s . With r a i n f a l l e x p e c t e d t o be an i m p o r t a n t parameter, d a t a from Lambert F i e l d were used i n this study.

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch009

χ

X

Weathering S t e e l C o r r o s i o n . T r i p l i c a t e specimens were exposed f o r p e r i o d s v a r y i n g f r o m t h r e e t o t h i r t y months w i t h exposures s t a r t e d at each of t h e f o u r seasons d u r i n g the f i r s t y e a r . The e x p e r i m e n t a l p r o c e d u r e and exposure s c h e d u l e a r e documented i n an EPA r e p o r t (2). The r e s u l t s a r e 153 s e t s of t r i p l i c a t e weight l o s s d a t a w i t h s i t e , exposure time and i n i t i a l exposure s e a s o n as p r i m a r y v a r i a b l e s . A n a l y s i s of E n v i r o n m e n t a l D a t a . A l t h o u g h the methodology f o r a n a l y z i n g the d a t a has been p r e v i o u s l y r e p o r t e d (6) t h e r e a r e some d i f f e r e n c e s t h a t s h o u l d be n o t e d . F i r s t , a l a t e r v e r s i o n o f the RAPS d a t a base was used as an i n i t i a l s o u r s e . Second, t i m e - o f - w e t n e s s i n t h i s paper i s d e f i n e d d i f f e r e n t l y , t h u s , a r e l a t i o n s h i p t o c a l c u l a t e r e l a t i v e h u m i d i t y from temperature and dew p o i n t i s based on d a t a f o r dew p o i n t s g r e a t e r than 0°C. Third, deposition v e l o c i ­ t i e s a r e c a l c u l a t e d from boundary l a y e r t h e o r y r a t h e r than e m p i r i c a l relationships· T h i s l a t e r v e r s i o n o f RAPS d a t a base e l i m i n a t e d many e r r o r s but produced more m i s s i n g d a t a . Time-of-wetness as p r e v i o u s l y d e f i n e d was the time e x c e e d i n g some c r i t i c a l r e l a t i v e h u m i d i t y (6^). I n t h i s paper t i m e - o f - w e t n e s s i s the time a c r i t i c a l r e l a t i v e h u m i d i t y i s exceeded and t h e dew p o i n t i s g r e a t e r than 0°C, p l u s any time the c r i t i c a l h u m i d i t y i s not exceeded and i t i s r a i n i n g . For t h a t r e a s o n a r e g r e s s i o n r e l a t i n g r e l a t i v e h u m i d i t y t o dew p o i n t s above 0°C and temperature was used t o c a l c u l a t e r e l a t i v e h u m i d i t y f o r each h o u r . This r e l a ­ tionship i s : RH - 100 exp{[-0.0722 + 0.0002 5(T

+ DP)][T-DP]}

(8)

166

MATERA ILS DEGRADATO IN CAUSED BY ACID RAIN

where RH i s r e l a t i v e h u m i d i t y , Τ i s temperature and DP i s dew p o i n t , the l a t e r b o t h i n °C. D e p o s i t i o n v e l o c i t i e s were c a l c u l a t e d f r o m windspeed d a t a . Windspeeds a t tower h e i g h t can be used t o c a l c u l a t e windspeeds a t specimen r a c k h e i g h t u s i n g t h e r e l a t i o n s h i p f o r rough s u r f a c e s (J)* V

+

= 8.5 + 2.5 l n ( Z / e )

(9)

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch009

where v+ i s t h e d i m e n s i o n l e s s v e l o c i t y and ζ and e a r e m e a s u r i n g h e i g h t and roughness h e i g h t r e s p e c t i v e l y . The r a c k h e i g h t was about t h r e e meters from the ground. A t t h r e e o f t h e s i t e s t h e m e t e o r o l o g i c a l towers were 10 meters w h i l e a t t h e o t h e r s they were 30 m e t e r s . The average ground roughness h e i g h t was assumed t o be 0.1 m. Thus, t h e r a c k h e i g h t windspeed i s 0.7 5 times t h e windspeed at 30 meters o r 0.85 times t h e windspeed a t 10 m e t e r s . From a n o l o g y w i t h momentum t r a n s p o r t , gases w i t h a Schmidt number o f a p p r o x i m a t e l y one t h a t r e a d i l y r e a c t a t a s u r f a c e , have a d e p o s i t i o n v e l o c i t y of : 2

u - V* /V

(10)

where u i s t h e d e p o s i t i o n v e l o c i t y , V* i s t h e f r i c t i o n v e l o c i t y and V i s t h e average windspeed. The f r i c t i o n v e l o c i t y i s e q u a l t o V / f / 2 where f i s t h e f r i c t i o n f a c t o r . From boundary l a y e r t h e o r y f o r smooth f l a t p l a t e s ( 7 ) : f

= 0.03/(RE ) L

1 / 7

(11)

where R E = LV/ v, L = l e n g t h o f s u r f a c e over which t h e a i r f l o w s , and ν i s t h e k i n e m a t i c v i s c o s i t y o f a i r ( 0 . 1 5 cm^/sec). L i s assumed t o be t h e g e o m e t r i c mean o f t h e p a n e l dimensions (/10.2 χ 15.2 = 12.45 cm). Thus: L

u = 0.35 V 5 u = 0.31 V 5

8 6

x

8 6

3

(12a) (12b)

ANA

V^Q * V30

w i t h u i n cm/sec and i n m/sec. D e p o s i t i o n v e l o c i t i e s were c a l c u l a t e d on an h o u r l y b a s i s and averaged over exposure p e r i o d s . Because windspeeds a r e n o t n o r m a l l y d i s t r i b u t e d , t h e average d e p o s i t i o n v e l o c i t y i s about 91% of t h e d e p o s i t i o n v e l o c i t y c a l c u l a t e d from average windspeed f o r an expo­ sure p e r i o d . Pollutant Fluxes. H o u r l y d e p o s i t i o n v e l o c i t i e s were m u l t i p l i e d by h o u r l y p o l l u t a n t c o n c e n t r a t i o n s t o get h o u r l y p o l l u t a n t f l u x e s . These were summed over exposure p e r i o d s f o r hours o f wetness w i t h d i f f e r e n t c r i t i c a l r e l a t i v e h u m i d i t y c r i t e r i a ( 7 5 t o 90% i n 5% intervals). Average f l u x e s were then c a l c u l a t e d by d i v i d i n g by t h e time-of-wetness. The r e s u l t s were compared w i t h f l u x e s c a l c u l a t e d by m u l t i p l y i n g average d e p o s i t i o n v e l o c i t i e s f o r a p e r i o d by t h e average p o l l u t a n t c o n c e n t r a t i o n d u r i n g times o f wetness. The v a l u e s by t h e two methods were f a i r l y c o n s i s t e n t .

HAYNIE

9.

167

Environmental Factors Affecting Corrosion of Steel

F l u x e s o f TSP were c a l c u l a t e d by m u l t i p l y i n g average TSP by two-tenths o f t h e average d e p o s i t i o n v e l o c i t y f o r gases ( a c t u a l deposition v e l o c i t i e s vary considerably with the s i z e d i s t r i b u t i o n of p a r t i c l e s ) . R a i n f l u x e s were c a l c u l a t e d by d i v i d i n g t h e amount of r a i n f o r an exposure p e r i o d by time o f w e t n e s s . S t a t i s t i c a l A n a l y s i s o f Data An i n i t i a l l i n e a r r e g r e s s i o n was performed on t h e d a t a t o d e t e r m i n e the r e l a t i v e s i g n i f i c a n c e o f each o f t h e f a c t o r s . The form o f t h e model was: In(C)=OoIn(t)+Σ o ^ l n f +30+Σy P

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch009

±

i

(13)

i

where C i s amount o f s t e e l c o r r o s i o n , t i s t o t a l time o f e x p o s u r e , f i s f r a c t i o n o f time o f wetness f o r d i f f e r e n t c r i t i c a l r e l a t i v e h u m i d i t i e s , Q i s a temperature f a c t o r (1000[l/(273.16+T°C)-1/ (273.16+T°C a v g ] ) ( 6), and the P ^ a r e t h e f l u x e s o f p o l l u t a n t s and rain. B o t h f o r w a r d and backward s t e p w i s e r e g r e s s i o n s were done. The r e s u l t s i n d i c a t e d t h a t f r a c t i o n o f time o f wetness ( f ) f o r a c r i t i c a l r e l a t i v e h u m i d i t y o f 85% was t h e most s i g n i f i c a n t o f the f v a l u e s , t h e temperature f a c t o r was somewhat l e s s s i g n i f i c a n t , and o n l y ozone f l u x was n o t a s i g n i f i c a n t f a c t o r . TSP and S O 2 had p o s i t i v e c o e f f i c i e n t s w h i l e the N O 2 and r a i n c o e f f i c i e n t s were negative. Because t h e amount o f c o r r o s i o n o f s t e e l i s e x p e c t e d t o f o l l o w the e m p i r i c a l form C = A t , where b o t h A and η a r e v a r i a b l e s w i t h changing e n v i r o n m e n t a l f a c t o r s , a l i n e a r r e g r e s s i o n on t h e l n - l n form was performed on t h e f o l l o w i n g model: n

w

l n ( C ) = a + a l n ( t ) + a f l n ( t ) + a 3 l n ( f ) + 3 Q + ly V± 0

1

w

2

w

(14)

±

where t and f a r e time-of-wetness and f r a c t i o n o f t i m e - o f wetness r e s p e c t i v e l y , f o r a c r i t i c a l r e l a t i v e h u m i d i t y o f 85%. The r e s u l t s are g i v e n i n T a b l e I . w

Table I .

Results of the Linear Regression of Equation: ln(C)=a ^a ln(t )+a 0

Variable ln(C) ln(t ) f ln(t ) ln(f) Q TSP F l u x S0 Flux N0 Flux Rain Flux w

w

2

2

1

Units ln(y) ln(years) ln(years)

w

t

( w)

Coefficient

2

3

= = = =

+ c x

3

l n

(

f

E

p

TL i

Standard e r r o r

4.245 0.3116 0.8 583 0.4399 3 = -0.7023 ^1 = 0.8729 Ύ2 - 0.1152 Ύ = -0.0370 -4 -3.18x10 ο 1 α α

α

3

mg/cm^ year mg/cm2 year mg/cm year cm/year

f l n 2

0.0444 0.1561 0.0819 0.1809 0.1004 0.0299 0.0128 -4 1.24x10

P a r t i a l F**

49.19 30.23 28.82 15.07 75.62 14.87 8.33 6.58

168

M A T E R I A L S D E G R A D A T I O N C A U S E D BY A C I D R A I N

* Q = 1000(1/273.16+T)-1/(273.16+Tavg) where Τ i s i n °C and Tavg i s o v e r a l l average o f average temperatures d u r i n g t i m e s - o f wetness ( 1 3 . 5 5 ° C ) . **A measure o f t h e s t a t i s t i c a l s i g n i f i c a n c e o f a d d i n g t h e s p e c i f i c v a r i a b l e t o a l l of the o t h e r s . The p e r c e n t o f v a r i a b i l i t y e x p l a i n e d by r e g r e s s i o n i s ' 95.85%. The f r a c t i o n o f time-of-wetness a f f e c t s t h e v a l u e o f η i n t h e e m p i r i c a l e q u a t i o n C = A t , (n=0.312+0.858f), w h i c h means t h a t t h e f i l m becomes more p r o t e c t i v e w i t h time when f i s low, b u t l e s s p r o ­ t e c t i v e w i t h time when f i s h i g h . A l l o f t h e o t h e r terms i n e q u a t i o n 14 a r e c o n s i d e r e d t o be a p a r t o f t h e A c o e f f i c i e n t . A pseudo S t e e l c o r r o s i o n £ ^ J Ç x a s c a l c u l a t e d by d i v i d i n g s t e e l c o r r o s i o n by f " ^(0-312+0.858f) (- .702Q). T h i s v a l u e was r e g r e s s e d a g a i n s t t h e p o l l u t a n t and r a i n f l u x e s t o determine n o n e x p o n e n t i a l c o e f f i c i e n t s t h a t make up t h e A term. The r e s u l t s a r e given i n Table I I . n

w

w

0

4

4

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch009

e x p

Table I I .

0

R e s u l t s o f R e g r e s s i o n o f Pseudo C o r r o s i o n Rate A g a i n s t Pollutant Fluxes

Variable Pseudo C o r r o s i o n Rate TSP F l u x S0 Flux N0 Flux Rain Flux 2

2

Units

Coefficient

V

r 85.13 A = 10.67

2

2

2

Partial F

65.63

A

mg/cm y e a r mg/cm y e a r mg/cm y e a r cm/year

Standard error

A = -3.51 A = -0.0302 3

4

9.39 2.46 1.04 0.0085

82.26 18.88 11.36 12.51

n

The r e s u l t i n g e m p i r i c a l damage f u n c t i o n , C = A t , has t h e c o efficients: w

A - (65.63+85.13TSP+10.67S0 -3.51N0 -.03Rain)f 2

η

2

u,44

e x p ( - . 7 Q ) (15a)

- 0.3 1 2+0.858f

where t h e p o l l u t a n t f l u x e s have t h e u n i t s i n T a b l e I I . t i o n a c c o u n t s f o r 95.93 p e r c e n t o f t h e v a r i a b i l i t y .

(15b) T h i s equa­

Evaluation of data with respect to theory. The s i g n i f i c a n t f a c t o r s i n t h e e m p i r i c a l e q u a t i o n s 15a and 15b may a f f e c t e i t h e r o r b o t h α and 3 c o e f f i c i e n t s i n e q u a t i o n 7. The r e l a t i v e e f f e c t s of each parameter on α and 3 were d e t e r m i n e d by r e g r e s s i n g s t e e l c o r r o s i o n / t i m e - o f - w e t n e s s (c/tw) a g a i n s t a l l o f t h e f l u x e s , 1/nCp (where C = A t with the c o e f f i c i e n t s c a l c u l a t e d u s i n g equations 15a and 15b), e x p ( - . 7 Q ) / n C , f / n C , and a l l o f t h e p r o d u c t s o f f l u x e s and 1/nCp. Stepwise r e g r e s s i o n was used i n t h e o r d e r o f most s i g n i f i c a n t t o l e a s t s i g n i f i c a n t v a r i a b l e and i n c l u d i n g o n l y those v a r i a b l e s w i t h a 0.95 p r o b a b i l i t y o f s i g n i f i c a n c e . A total of 13 independent v a r i a b l e s were c o n s i d e r e d . Table I I I gives the results· n

w

p

p

9.

Environmental

HAYNIE

Factors Affecting

Corrosion

169

of Steel

T a b l e I I I . R e g r e s s i o n C o e f f i c i e n t s f o r T h e o r e t i c a l Model o f Weathering S t e e l C o r r o s i o n C / t = + ^a ? /nC w

Variable

c/t

Units μ/year

w

TSP/nC f/nC l/nC N0 Flux S0 Flux Rain Flux* EXP(-.7Q)/nC„ p

a =1573 a =1381 3^-8.85 3 =18.32 33=-0.0798 a y 1104 Q

mg/cm^ y e a r mg/cm year cm/year

2

2

p

Partial F

Q

2

p

Standard e r r o r

±

3 =39.12

αχ-2292 p

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch009

Coefficient

±

2

175 262 308 1.85 4.62 0.0227 335

171.10 36.05 20.15 22.88 15.71 12.37 10.85

* R a i n F l u x i s e x p r e s s e d i n c u b i c c e n t i m e t e r s o f r a i n p e r square c e n t i m e t e r o f s u r f a c e p e r y e a r o f wet t i m e . V a r i a b l e s a r e l i s t e d i n t h e o r d e r i n which they were e n t e r e d i n t o the r e g r e s s i o n . The r e s u l t i n g damage f u n c t i o n ( C = ( Z 3 P + E a P / n C ) t ) c a n a c c o u n t f o r 95.65% o f t h e v a r i a b i l i t y . i

i

Discussion

1

i

p

w

of Results

The e m p i r i c a l damage f u n c t i o n w i t h c o e f f i c i e n t s c a l c u l a t e d u s i n g e q u a t i o n s 15a and 15b p r o v i d e s t h e b e s t f i t o f t h e d a t a ( g r a p h i c a l l y presented i n Figure 1). The gaseous p o l l u t a n t f l u x e s a r e based on h o u r l y c o n c e n t r a t i o n s and d e p o s i t i o n v e l o c i t i e s d u r i n g p e r i o d s of wetness. These do n o t d i f f e r d r a m a t i c a l l y from f l u x e s c a l c u l a t e d f r o m exposure p e r i o d a v e r a g e s o f d e p o s i t i o n v e l o c i t i e s and c o n c e n ­ trations. The TSP f l u x e s a r e c a l c u l a t e d from exposure p e r i o d averages o f d e p o s i t i o n v e l o c i t i e s and c o n c e n t r a t i o n s . The r a i n f l u x e s a r e t h e amounts o f r a i n d i v i d e d by times o f w e t n e s s . Frac­ t i o n o f time when wet ( f ) i s f o r a c r i t i c a l r e l a t i v e h u m i d i t y o f 85%. T h i s e q u a t i o n c a n be used t o p r e d i c t w e a t h e r i n g s t e e l c o r r o s i o n as a f u n c t i o n o f e n v i r o n m e n t a l c o n d i t i o n s . The c o e f f i c i e n t s i n T a b l e 3 p r o v i d e a b e t t e r t h e o r e t i c a l u n d e r ­ s t a n d i n g o f how t h e d i f f e r e n t f a c t o r s a f f e c t t h e c o r r o s i o n of weathering s t e e l . The 3 c o e f f i c i e n t s a f f e c t t h e s o l u b i l i t y o f the p r o t e c t i v e o x i d e l a y e r and t h e α c o e f f i c i e n t s a f f e c t t h e d i f f u s i v i t y through the l a y e r . The l a r g e r a t i o o f a/3 c o n f i r m s t h e r e l a t i v e I n s o l u b i l i t y o f t h e r u s t on w e a t h e r i n g s t e e l i n most environments. S u l f u r dioxide increases the s o l u b i l i t y of the f i l m w h i l e N 0 and r a i n d e c r e a s e t h e s o l u b i l i t y . R a i n a p p a r e n t l y washes away a c i d i c components ( d e p o s i t e d d u r i n g dew f o r m a t i o n ) t h a t i n c r e a s e the s o l u b i l i t y . The α c o e f f i c i e n t f o r TSP i s h i g h l y s i g n i f i c a n t . Accumulation of p a r t i c l e s i n t h e o x i d e l a y e r appears t o i n c r e a s e t h e d i f f u s i v i t y of i o n s o r t h e e l e c t r i c a l c o n d u c t i v i t y o f t h e f i l m . TSP does n o t appear t o enhance t h e s o l u b i l i t y o f t h e f i l m . Increasing the f r a c t i o n o f t i m e - o f - w e t n e s s appears t o i n c r a s e the d i f f u s i v i t y t h r o u g h t h e l a y e r . T h i s c o u l d a c t u a l l y be a time f u n c t i o n o f a matter of hours. The d i u r n a l c y c l e s u g g e s t s t h a t w h i l e t h e f i l m i s wet i t becomes l e s s p r o t e c t i v e w i t h time; when i t i s d r y i t becomes 2

M A T E R I A L S D E G R A D A T I O N C A U S E D BY A C I D

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch009

170

PREDICTED CORROSION -

Figure

1.

Micrometers

F i t of weathering s t e e l c o r r o s i o n data to A t ^

where A and η a r e f u n c t i o n s

RAIN

of environmental

parameters

n

model,

9.

HAYNIE

Environmental Factors Affecting Corrosion of Steel

171

more p r o t e c t i v e w i t h t i m e . When f i s l a r g e t h e f i l m a p p a r e n t l y i s not d r y l o n g enough t o r e a c h a d e s i r e d l e v e l o f p r o t e c t i v i t y . The temperature e f f e c t i s as e x p e c t e d ; d i f f u s i o n i n c r e a s e s as temperature increases.

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch009

Conclusions W e a t h e r i n g s t e e l c o r r o s i o n c a n be d e s c r i b e d as competing mechanisms of f o r m a t i o n and d i s s o l u t i o n o f a p r o t e c t i v e o x i d e l a y e r d u r i n g p e r i o d s o f wetness. E m p i r i c a l l y , the best f i t of the c o r r o s i o n data suggests that time-of-wetness o f t h e s t e e l i s b e s t d e f i n e d as t h e time when t h e dew p o i n t exceeds 0°C and t h e r e l a t i v e h u m i d i t y exceeds 85% p l u s the time d u r i n g r a i n when t h e r e l a t i v e h u m i d i t y does n o t exceed 85%. Three v a r i a b l e s i n c r e a s e t h e d i f f u s i v i t y t h r o u g h t h e o x i d e f i l m ; 1) f r a c t i o n o f time when wet, 2) t e m p e r a t u r e , and 3) TSP flux. S o l u b i l i t y o f t h e o x i d e f i l m i s i n c r e a s e d by i n c r e a s i n g t h e f l u x o f s u l f u r o x i d e s d u r i n g p e r i o d s o f wetness. D i s s o l u t i o n o f t h e o x i d e f i l m i s reduced by i n c r e a s i n g t h e f l u x e s o f n i t r o g e n o x i d e s and r a i n . Ozone appears t o have no s i g n i f i c a n t e f f e c t on t h e c o r r o s i o n of w e a t h e r i n g s t e e l .

Literature Cited 1. Schiermeier, F. A. Environmental Sci. Technol. 1978, 12, 644. 2. Mansfeld, F. "Regional Air Pollution Study: Effects of Airborne Sulfur Pollutants on Materials"; EPA-600/4-80-007, 1980. 3. Haynie, F. H.; Upham, J. B. Materials Protection and Performance 1971, 10, 18. 4. Mattsson, E. Materials Performance 1982, 21, 9. 5. Hern, D. H.; Taterka, M. H. "Regional Air Monitoring System Flow and Procedures Manual"; EPA Contract 68-02-2093, Rockwell International, Creve Coeur, Mo. 1977. 6. Haynie, F. H. Durability of Building Materials 1982/1983, 1, 241. 7. Knudson, J. G.; Katz, D. L. "Fluid Dynamics and Heat Transfer"; University of Michigan, Ann Arbor, Michigan, 1954, p. 38 and p. 149. RECEIVED January 2, 1986

10 A Laboratory Study to Evaluate the Impact of NO , SO , and Oxidants on Atmospheric Corrosion of Galvanized Steel x

x

1

1

2

2

Edward O. Edney , David C. Stiles , John W. Spence , Fred H. Haynie , and William E. Wilson 2

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch010

1

Northrop Services, Inc., Research Triangle Park, NC 27709 Atmospheric Sciences Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711

2

A series of laboratory experiments was conducted in which galvanized steel samples were exposed to NO in air and irradiated propylene/nitrogen oxides/air mixtures in the absence and presence of SO . Dew was produced periodically on the test panels, and, at the end and/or during the experiments, panels were sprayed with either deionized water or an ammonium bisulfate solution (pH of 3.5). Gas phase concentrations were monitored, and dew and rain rinse samples were analyzed for nitrite, nitrate, sulfite, sulfate, formaldehyde, and zinc. The average deposition velocities measured during periods of wetness were sulfur dioxide, 0 . 8 cm/s; formaldehyde, 0 . 6 cm/s; nitric acid, 0 . 7 cm/s; and nitrogen dioxide, 0 . 0 3 cm/s. Analysis of dew samples suggests that the dry deposition of sulfur dioxide, nitric acid, formaldehyde, and possibly nitrogen dioxide accelerates the atmospheric corrosion of galvanized steel. Wet deposition of acidic species accelerates corrosion. A general model for the atmospheric corrosion of galvanized steel is presented. 2

2

G a l v a n i z i n g s t e e l i s a well-known t e c h n i q u e f o r p r o t e c t i n g s t e e l a g a i n s t c o r r o s i o n . G a l v a n i z e d s t e e l c o n s i s t s of a z i n c (Zn) c o a t i n g s t r o n g l y bonded t o a s t e e l s u b s t r a t e . Zn i s a n o d i c w i t h r e s p e c t t o i r o n and w i l l r e a c t e l e c t r o c h e m i c a l l y b e f o r e i r o n i n t h e p r e s e n c e of an e l e c t r o l y t i c s o l u t i o n . Because i t i s one of t h e l e a s t e x p e n s i v e methods f o r p r o t e c t i n g s t e e l a g a i n s t a t m o s p h e r i c c o r r o s i o n , a number of f i e l d s t u d i e s have been conducted t o measure t h e a t m o s p h e r i c c o r r o s i o n r a t e of g a l v a n i z e d s t e e l and/or Zn ( 1 - 1 1 ) . Many of t h e s t u d i e s have f o c u s e d on t h e e f f e c t of SO2 and time of wetness on t h e corrosion rate. W h i l e t h e s e parameters c l e a r l y p l a y an i m p o r t a n t r o l e i n c o r r o s i o n , any model based s o l e l y on t h e s e parameters i s 0097-6156/86/0318-0172$06.25 / 0 © 1986 American Chemical Society

EDNEYETAL.

10.

Impact of NO ,

SO ,

K

x

and Oxidants on Galvanized Steel

173

l i k e l y t o be incomplete because the e f f e c t s o f wet d e p o s i t i o n and dry d e p o s i t i o n o f o t h e r a i r p o l l u t a n t s have been n e g l e c t e d . Recent s t u d i e s have shown t h a t the d e p o s i t i o n o f a compound r a t h e r than the c o n c e n t r a t i o n s h o u l d be used t o a s s e s s the impact o f SO2 o r o t h e r compounds on a t m o s p h e r i c c o r r o s i o n ( 9 . 1 1 - 1 2 ) . The d r y deposition D o f a r e a c t i v e s p e c i e s χ i s d e f i n e d by the f o l l o w i n g relationship: x

(1) D

where t Fx(t) Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch010

e

χ

= ο*

F

(t)dt

= exposure time, and - the molar f l u x a t time t, i . e .

F(t)=[x(t))v, χ

a

where [x(t)] = the gas phase c o n c e n t r a t i o n a t time t, vd = the dry d e p o s i t i o n v e l o c i t y .

and

One approach t o d e v e l o p i n g a c o r r o s i o n model f o r g a l v a n i z e d s t e e l based on dry d e p o s i t i o n i s t o assume t h a t the c o r r o s i o n C ( i n moles o f Zn l o s t per u n i t a r e a ) can be r e p r e s e n t e d as a l i n e a r c o m b i n a t i o n o f the c o r r o s i o n induced i n a c l e a n a i r environment and t h a t a s s o c i a t e d w i t h a i r p o l l u t a n t x, i . e . , C=(A+7[xb,)i a

(3) w

where tw = the time o f wetness, A = a c o n s t a n t , and 7 = number o f moles o f Zn c o r r o d e d per mole o f χ

deposited.

I f no antagonisms or synergisms o c c u r , E q u a t i o n 3 can be extended t o i n c l u d e the e f f e c t s o f o t h e r compounds by c o n v e r t i n g the second term t o a sum over a l l p o l l u t a n t s d e p o s i t i n g onto the surface. E q u a t i o n 3 assumes t h a t d e p o s i t i o n t a k e s p l a c e o n l y when the s u r f a c e i s covered by a f i l m o f m o i s t u r e . The i n a b i l i t y t o e s t i m a t e dry d e p o s i t i o n v e l o c i t i e s and the l a c k o f knowledge o f the compounds t h a t a r e l i k e l y t o c o n t r i b u t e t o c o r r o s i o n makes E q u a t i o n 3 d i f f i c u l t to apply in evaluating corrosion data. The r e s u l t s o f the experiments r e p o r t e d here w i l l a d d r e s s b o t h o f these i s s u e s and w i l l be used t o d e v e l o p the framework f o r a model f o r a n a l y s i s o f g a l v a n i z e d s t e e l c o r r o s i o n d a t a o b t a i n e d from f i e l d s t u d i e s . In the presence o f a m o i s t u r e f i l m , but i n the absence o f p o l l u t a n t s o t h e r than CO2, the e f f e c t i v e o p e r a t i v e e l e c t r o c h e m i c a l r e a c t i o n s t a k i n g p l a c e on a wet galvanized s t e e l surface are b e l i e v e d t o be (H) Anode

Zn + 2Η2θ->Ζη(ΟΗ)2 + 2H + + 2e"

Cathode

O2 + 2H2O + 4e~ -

40H".

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch010

174

M A T E R I A L S D E G R A D A T I O N C A U S E D BY A C I D R A I N

The zinc hydroxide (Zn(0H)2) formed w i l l react with dissolved CO2 to produce zinc carbonate (ZnC03), a compound that i s s l i g h t l y soluble in water, i . e . , solubility=80 nmol/ml in water at 15°C ( 14). Buildup of the insoluble corrosion products such as Zn(0H)2 and ZnC03 w i l l create a protective layer that serves to i n h i b i t further corrosion. The corrosion rate w i l l then be small unless there i s some means f o r either preventing the formation of the protective layer or destroying i t once i t has formed. The d e t a i l s of the mechanism for S02-induced corrosion of galvanized s t e e l have not been established; however, i t i s l i k e l y that the corrosion process i s i n i t i a t e d by the reaction of Zn with the sulfurous (H2SO3) and s u l f u r i c (H2SO4) acids generated i n the dew. In p a r t i c u l a r , H2SO4 w i l l react with either the base metal or the protective corrosion products, ZnC03 or Zn(0H)2, producing soluble zinc s u l f a t e (ZnSOlj) that has l i m i t e d protective properties. D i s s o l u t i o n of the p r o t e c t i v e l a y e r w i l l s t i m u l a t e f u r t h e r electrochemical corrosion which w i l l tend to reform the insoluble layer. The extent of formation of the protective l a y e r i s determined by the SO2 deposition to the surface. In clean a i r environments, a t h i c k adhesive protective layer w i l l form, whereas in polluted areas of high SO2 concentrations only a very t h i n layer w i l l be produced (15). The production of soluble ZnS04 suggests that the precursor to the anion, gas phase SO2, accelerates corrosion. Based on this mechanism, it is likely that other air pollutants that readily adsorb on a surface, producing acidic compounds that can react with the corrosion products to form soluble Zn compounds, can accelerate the corrosion rate.

The objective of t h i s study was to determine whether a i r pollutants other than SO2 accelerate the atmospheric corrosion rate of galvanized s t e e l . Short-term laboratory experiments were conducted in which galvanized s t e e l panels were exposed to the f o l l o w i n g mixtures in a i r : (1) NO2, (2) irradiated propylene/nitrogen oxides (C3H6/NOX), and (3) irradiated C3H6/NOX/SO2. The t e s t panels were c h i l l e d below the dew point p e r i o d i c a l l y to produce dew. Dew samples were c o l l e c t e d and analyzed for Zn and t h e i r anion composition. To investigate the impact of a c i d i c wet deposition, during some of the experiments, panels were removed p e r i o d i c a l l y from the chamber and sprayed with either deionized water or d i l u t e solutions of ammonium b i s u l f a t e (NH4HSO4; pH of 3.5). The r e s u l t s of these experiments, as w e l l as the framework for a corrosion model for galvanized s t e e l , are presented i n t h i s paper. Experimental

The exposure system consists of two exposure chambers i n p a r a l l e l , coupled to an 11.3-m3 aluminum and Teflon smog chamber (Figure 1). Light banks are located on two sides of the smog chamber and consist of 56 black lamps and 9 sun lamps. The smog chamber, operated as a continuous s t i r r e d tank reactor (CSTR), serves as a r e s e r v o i r for the exposure chambers. Ambient a i r f i r s t passes through a clean a i r t r a i n , where pollutants and H2O are removed, and then through a glass manifold where i t i s mixed with reactants to the desired concentration before entering the smog chamber. The flow rate through the smog chamber i s 95 Lpm, producing a residence time of 112 min. Steam i s injected into the chamber by the dew point

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch010

10.

EDNEY ET AL.

Impact of NO

Kt

175

SO , and Oxidants on Galvanized Steel x

control system that i s programmed to maintain the a i r dew point at 15°C. The a i r temperature i s not controlled. A cross-sectional drawing of one of the exposure chambers i s shown in Figure 2 . The chambers are constructed of clean Teflon glued to a 13x13xl52-cm welded aluminum frame. Glass piping i s used to connect the exposure chambers to the smog chamber. Both exposure chambers have seven positions for mounting test panels. Each exposure position has a c h i l l e r back plate with supplied coolant so that the panel can be c h i l l e d below the a i r dew point to produce dew on the panels. Individual positions can be disconnected from the coolant manifold to remain dry. The coolant temperature enables dew to form in a s u f f i c i e n t quantity to drop into the c o l l e c t i o n trough below each panel. The collected dew then drains into a Nalgene bottle. The exposure chambers are also equipped with heating lamps. Blowers were mounted on the exposure chambers to maintain turbulent conditions (Reynolds number - 3 0 , 0 0 0 in the chambers), and the blower settings were selected to produce wind speeds of approximately 300 cm/s ( - 7 mi/h) in each chamber. The galvanized steel panels were 8x13-cm Zn-coated (hotdipped), 20-gauge steel plates. The average thickness of the coating was 20 urn, and the exposed surface area per panel was 84.7 cm2. Before each exposure experiment, the panels were f i r s t cleaned by immersion into a 10? by weight solution of ammonium chloride (NH1|C1) at a temperature of 60°-80°C for 2 min. The panels were rinsed in deionized water and then dried in methanol to remove the moisture. During and/or at the completion of some of the exposure experiments, galvanized steel panels were sprayed with e i t h e r deionized water or an NH4HSO4 (pH 3.5) solution. The deionized water quickly equilibrated with CO2 in the laboratory a i r , producing a value of 5.6 for the pH. By removing the panels from the exposure chambers and mounting them into a Teflon rack, each panel could be sprayed with a s p e c i f i c volume of either deionized H2O or an NH4HSO4 solution. The spray runoff was collected for chemical analysis. For a typical spray condition, - 1 0 s was the average residence time of a droplet on the surface, whereas the corresponding time for a dew droplet was - 1 h. The galvanized steel panels were exposed to a i r masses that contained NO2 and irradiated mixtures of C3H6/NOX and C3H6/NOX/SO2. A b r i e f description of the protocol used for each of the three experiments i s presented. The NO2 exposure was a short-term experiment where the panels were exposed to a mixture of 649 ppb NO2 in a i r . The t o t a l exposure time was 25 h. The microprocessor-controlled c h i l l e r system was used to generate two 7-h periods where the panels were covered with dew. The two wet periods were separated by a 5-h dry period. Ν0χ concentrations were monitored continuously. At the end of the experiment, the panels were sprayed with either 50 mL of deionized H2O or NH4HSO4 solution (pH=3.5). The volume of collected dew was determined. The dew was then analyzed for NO2", N03~, SOy, and S 0 4 by ion chromatography and for Zn by atomic absorption spectroscopy. The rain rinse was analyzed in a similar way. The C3H6/NOx+hv experiment was a 14-day exposure which consisted of two 7-h dew periods per day separated by 5-h dry periods. Panels were weighed both prior to the experiment and at =

176

M A T E R I A L S D E G R A D A T I O N C A U S E D BYACID

! Gas Monitor

Dew Point Control System

Humidification System

Smog Chamber Vol=11.3 m3 F=95 Lpm

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch010

I I n l e t I I Clean I . Mani- , , A i r < — fold I ( S y s t e m J

Light Bank Exposure Chamber Vol=26 L V =3 m/s Re«30,000 w

Sample Ports Dew Collection System

Figure

Figure

2.

1.

Temperature Control System

Schematic

o f Exposure

Cross-sectional

System.

View o f E x p o s u r e

Chamber.

RAIN

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch010

10.

EDNEY ET AL.

Impact of NO , SO , and Oxidants on Galvanized Steel x

x

111

the c o m p l e t i o n o f t h e experiment a f t e r t h e c o r r o s i o n p r o d u c t s were removed u s i n g t h e c l e a n i n g procedure d e s c r i b e d above. A correction to t h e Zn weight l o s s was made t o account f o r t h e l o s s o f base m e t a l d u r i n g c l e a n i n g . Panels were exposed t o ( 1 ) dew o n l y , (2) dew p l u s a c i d r a i n , and ( 3 ) dew p l u s c l e a n r a i n c o n d i t i o n s . The p a n e l s exposed under c o n d i t i o n s 2 and 3 were removed from t h e exposure chambers a f t e r f o u r and n i n e days o f exposure and sprayed with e i t h e r 400 mL o f d e i o n i z e d H2O o r NH4HSO4 (pH o f 3.5) s o l u t i o n s . The p a n e l s were a l s o sprayed a t t h e end o f t h e e x p e r i m e n t . Dew samples were c o l l e c t e d d a i l y and a n a l y z e d . The ΝΟχ and O3 c o n c e n t r a t i o n s were m o n i t o r e d c o n t i n u o u s l y and p e r o x y a c e t y l n i t r a t e (PAN), n i t r i c a c i d (HNO3), and aldehyde c o n c e n t r a t i o n s were measured d u r i n g both d r y and wet p e r i o d s . The exposure c o n d i t i o n s f o r t h e C3H6/NOX/SO2 + hv experiment were e s s e n t i a l l y t h e same as those used i n t h e NO2 e x p e r i m e n t . The exposure p e r i o d c o n t a i n e d two 7-h wet p e r i o d s s e p a r a t e d by a 5-h d r y period. A l l s p e c i e s measured i n t h e C3H6/NOX experiment were measured and, i n a d d i t i o n , gas phase SO2 c o n c e n t r a t i o n s were determined as w e l l as SO3" and S0l\~ i n t h e dew. No r a i n d a t a were o b t a i n e d f o r t h i s experiment. To i n v e s t i g a t e t h e d e p o s i t i o n o f r e a c t i o n p r o d u c t s o f an i r r a d i a t e d HC/N0x/S02 m i x t u r e d u r i n g d r y p e r i o d s , one p a n e l was kept d r y d u r i n g t h e e n t i r e e x p o s u r e . ΝΟχ c o n c e n t r a t i o n s were measured u s i n g a Bendix Ν0/Ν02/Ν0χ analyzer. The a n a l y z e r was c a l i b r a t e d w i t h a c e r t i f i e d s t a n d a r d o f NO i n N 2 o b t a i n e d from MG S c i e n t i f i c . Ozone was measured on a Bendix ozone a n a l y z e r c a l i b r a t e d u s i n g a D a s i b i Environmental C o r p o r a t i o n u l t r a v i o l e t (UV) ozone g e n e r a t o r . Formaldehyde (HCHO) and a c e t a l d e h y d e (CH3CHO) were measured by u s i n g t h e DNPH/high performance l i q u i d chromatography t e c h n i q u e (16). C a l i b r a t i o n s were p e r f o r m e d by u s i n g d i l u t e d solutions of twice-recrystalized hydrazone samples f o r each a l d e h y d e . PAN was d e t e r m i n e d w i t h an Analog Technology C o r p o r a t i o n e l e c t r o n capture detector after s e p a r a t i o n on a packed column c o n t a i n i n g 10? Carbowax 400 on 80/100 Supelcoport operated a t room temperature. The i n s t r u m e n t was c a l i b r a t e d a c c o r d i n g t o t h e procedure d e s c r i b e d by Lonneman etal. (12). SO2 c o n c e n t r a t i o n s were determined u s i n g a Thermo E l e c t r o n C o r p o r a t i o n SO2 m o n i t o r . The i n s t r u m e n t was z e r o e d u s i n g c l e a n a i r t h a t had passed through brominated c h a r c o a l , r e d u c i n g t h e SO2 c o n c e n t r a t i o n t o l e s s than 0.5 ppb. An SO2 p e r m e a t i o n tube was used to c a l i b r a t e t h e i n s t r u m e n t . A CTE dew p o i n t hydrometer was used i n the dew p o i n t c o n t r o l system and was c a l i b r a t e d w i t h a s a t u r a t e d s o l u t i o n o f sodium bromide (NaBr) ( r e l a t i v e h u m i d i t y = 58% a t 20°C). Chamber HNO3 c o n c e n t r a t i o n s were measured by drawing -500 L o f a i r through a 25-mm n y l o n f i l t e r (1-um pore s i z e ) , e x t r a c t i o n o f t h e f i l t e r w i t h 10*5 M p e r c h l o r i c a c i d s o l u t i o n , and a n a l y s i s o f n i t r a t e ( N03") by i o n chromatography. The c o l l e c t e d dew and r a i n r i n s e samples were a n a l y z e d f o r HCHO u s i n g t h e c h r o m o t r o p i c a c i d method. I n a d d i t i o n , t h e samples were analyzed f o r n i t r i t e ( N O 2 ) , N O 3 - , s u l f i t e ( S 0 3 ) , and S O 4 " u s i n g i o n chromatography. The a n a l y s i s was performed on a Dionex Auto Ion System 12 i o n chromatograph w i t h a 6-mmX250-mm f a s t r u n a n i o n s e p a r a t o r column. C a l i b r a t i o n s c u r v e s f o r S O 3 " and S 0 l j were o b t a i n e d u s i n g anhydrous sodium s u l f a t e (Na2S04) and sodium s u l f i t e (Na2S03) s a l t s d i l u t e d with deionized H2O. The S O 3 " s t a n d a r d s r e q u i r e d an a d d i t i o n o f 0,7% HCHO t o t h e s t o c k s o l u t i o n t o d e t e r =

=

M A T E R I A L S D E G R A D A T I O N C A U S E D BY A C I D

178

RAIN

o x i d a t i o n o f S03~ t o SOlj". N 0 2 ~ and NO3" c a l i b r a t i o n c u r v e s were o b t a i n e d by d i l u t i n g the c o r r e s p o n d i n g Na s a l t s i n d e i o n i z e d H 2 O . The c o l l e c t e d dew and r a i n r i n s e samples were a n a l y z e d f o r Zn u s i n g an Instrument Labs, I n c . a t o m i c absorbance a n a l y z e r . The instrument was c a l i b r a t e d by measuring the absorbance o f a s e r i e s o f American Chemical S o c i e t y c e r t i f i e d Zn s t a n d a r d s .

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch010

Data Reduction Analysis of Gas Phase and Dew Data. In p r i n c i p l e , the amount o f compound t h a t d e p o s i t s onto the p a n e l s d u r i n g a wet p e r i o d can be c a l c u l a t e d two ways: ( 1 ) by u s i n g the d i f f e r e n c e i n the gas phase c o n c e n t r a t i o n s d u r i n g the d r y and wet p e r i o d s , o r ( 2 ) by employing the c o n c e n t r a t i o n o f the compound i n the dew and the volume o f dew. D e p o s i t i o n t o a dry p a n e l can a l s o o c c u r , b u t , as w i l l be shown, f o r the m a j o r i t y o f the compounds r e p o r t e d h e r e , most o f the d e p o s i t i o n took p l a c e i n the presence o f dew. T h e r e f o r e , emphasis w i l l be p l a c e d on c a l c u l a t i n g the d e p o s i t i o n d u r i n g wet p e r i o d s . During wet p e r i o d s , the gas phase c o n c e n t r a t i o n s d e c r e a s e d due to uptake by the p a n e l s . The time dependence o f the gas phase c o n c e n t r a t i o n o f s p e c i e s χ d u r i n g a p e r i o d o f dew f o r m a t i o n can be approximated by the f o l l o w i n g e q u a t i o n :

where t

= time parameter (t-0 c o r r e s p o n d s t o the o n s e t o f dew formation for the wet period under investigation), [x (t)] = gas phase c o n c e n t r a t i o n , and [x ] = steady c o n c e n t r a t i o n o f χ d u r i n g the preceding dry p e r i o d . d

The r e s i d e n c e time χ i s e q u a l t o V /Q, where Q i s the f l o w r a t e through the smog chamber and V i s the t o t a l volume o f the system (smog chamber p l u s exposure chambers). The e f f e c t i v e f i r s t - o r d e r r a t e c o n s t a n t f o r d e p o s i t i o n t o the p a n e l i s k and i s e q u a l t o s

s

ι/»Α d y

,

(1)

, where υ , d

s

i s the dry d e p o s i t i o n v e l o c i t y and A i s the t o t a l a r e a o f the p a n e l s . The s o l u t i o n t o E q u a t i o n 4 i s as f o l l o w s :

— [xj a

= -

- +

1 + kz

exp[-(l +kx)t/x)

wet

(5.

1 + kz

E q u a t i o n 5 can be f u r t h e r reduced i f t i s chosen such t h a t the second term can be n e g l e c t e d . Under t h e s e c i r c u m s t a n c e s , the p a n e l s remain wet l o n g enough f o r a new s t e a d y s t a t e c o n d i t i o n t o be obtained; i . e . , for t / i > 2 ,

E D N E Y ET A L .

10.

Impact of NO ,

SO , and Oxidants on Galvanized Steel

x

x

1+

d

kz

179

w

Steady state concentrations were reached during the exposure experiments reported here since the time of wetness per cycle was 420 min and the residence time was 112 min. An expression f o r the dry d e p o s i t i o n v e l o c i t y vd i s immediately obtained from Equation 6, i . e . , (1)

AV[XJ

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch010

D

J

Use of Equation 7 i s l i m i t e d by the accuracy of the measurement of the decrease i n the gas phase concentration and i n p r a c t i c e can only be used to c a l c u l a t e dry deposition v e l o c i t i e s of compounds that readily absorb onto the surface. The amount of material deposited during a wet period i s found by integrating the expression f o r the molecular f l u x over time, i.e.,

I Vw«»= ^ ^ [ ^ + -*V

+ kz)tjz))\

where t = the time of wetness per period. w

The deposition can also be calculated from analysis of the dew i f the fate of the dissolved gas i s known. The deposition per wet period i n terms of dew parameters i s calculated by the f o l l o w i n g equation: x)

(2)

D

=

*

V

( dew dew

(9)

A

ρ

where (*) dew = the concentration of χ i n the dew, Vdew - the amount of dew produced during a wet period, and A = the area per t e s t panel. p

I f the compound under i n v e s t i g a t i o n deposits r e a d i l y onto the wet panel and can be associated with a p a r t i c u l a r dew ion, then both Equations 8 and 9 can be used to c a l c u l a t e the deposition. Equality of the two depositions establishes a mass balance f o r the system. Approximate values f o r the dry deposition v e l o c i t i e s can be obtained by equating the two expressions f o r the d e p o s i t i o n (Equations 8 and 9) and solving f o r the deposition v e l o c i t y . The result i s

180

MATERA ILS DEGRADATO IN CAUSED BY ACID RAN I (2)__ ^dew^dew V d

~

(10)

[x ]A t w ρw

where i t has been assumed that the second term i n Equation 8 can be neglected. (Calculations show that t h i s approximation introduces a t most a 10% error.) Equation 10 can be used to c a l c u l a t e the dry deposition v e l o c i t y o f compounds that r e a d i l y adsorb onto a wet surface as w e l l as weakly adsorbing species as long as the f a t e o f the dissolved compound i s known. Analysis o f Rain Rinse Data.

The concentration o f Zn i n the r a i n

rinse can be interpreted as a r a i n f l u x . The concentration nmol/mL i s equal to the Zn r a i n f l u x i n nanomoles/cm2-cmR, number of nanomoles of Zn dissolved into the r a i n per cm per cm of r a i n . The amount of Zn corroded by IR cm of r a i n

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch010

2

R =iZn ]l zn

R

of Zn i n i . e . , the o f panel is (11)

R

where [Zn ]- the concentration of Zn i n the r a i n r i n s e , and R = the Zn corrosion expressed as a deposition. R

zn

Results

NOp Exposure Experiment. The experimental conditions and r e s u l t s for the short-term NO2 exposure experiment are given i n Table I . The average concentration of NO2 during the dry periods was 649 ppb which decreased to 627 ppb i n the presence o f dew, thus y i e l d i n g (according to Equation 7) a value o f 0.05 cm/s f o r the dry deposition v e l o c i t y . Both NO2" and NO3" were detected i n the dew with the NO2" concentration (203 nmol/ml) representing 95? o f the ΝΟχ" concentration. Trace amounts of S04 were found i n the dew. A value o f 149 nmol/ml was found f o r the Zn dew concentration. Equation 10 y i e l d s a value of 0.06 cm/s f o r the NO2 dry deposition v e l o c i t y , i n reasonable agreement with the value found from the decrease i n gas phase concentrations. A separate NO2 exposure experiment was conducted to determine whether the amount o f NO2 deposited on the surface during a dry period could be ignored r e l a t i v e to that adsorbed i n the presence o f dew. I t was found that saturation occurs on a dry galvanized s t e e l surface and that the adsorbed NO2 saturation surface density was approximately 2 nmol/cm2. The saturation density i s l e s s than 5% o f the amount o f NO2 deposited per 7 h o f dew (41 nmol/cm2), and therefore i t s contribution can be ignored. Comparison o f the NO2 dry deposition v e l o c i t y with that found for SO2 under s i m i l a r conditions (vd (SO2) = 0.8 cm/s; Table IV) indicates a s u b s t a n t i a l difference i n the processes of uptake of the two gases on the test panels. The gas phase resistances f o r both compounds are expected to be e s s e n t i a l l y the same. Therefore, the difference between the dry deposition v e l o c i t i e s i s l i k e l y due to a difference i n the aqueous reaction and d i f f u s i v e mechanisms that take place on the metal surface covered by a thin f i l m of moisture. =

10.

EDNEY ET AL.

Impact of NO , SO , and Oxidants on Galvanized Steel x

x

181

The d i s p a r i t y i n v e l o c i t i e s i s c o n s i s t e n t w i t h t h e r e c e n t f i n d i n g s o f Lee and Schwartz ( 1 8 ) , who e v a l u a t e d t h e r a t e o f uptake o f N02 by s u r f a c e water. They found t h a t t h e NO2 d e p o s i t i o n v e l o c i t y was c o n t r o l l e d by aqueous phase mass t r a n s p o r t and/or r e a c t i o n . In a d d i t i o n , Lee and Schwartz found t h a t NO2 r e a c t s w i t h l i q u i d water according to the f o l l o w i n g r e a c t i o n :

2 N0 (g) + H 0 (1) 2H + + N0 - +

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch010

2

2

2

NO3-

T h i s r e a c t i o n cannot e x p l a i n t h e r e s u l t s o f t h e exposure e x p e r i m e n t s i n c e t h e dominant Ν0χ~ compound i s NO2". T h i s r e s u l t may n o t be s u r p r i s i n g s i n c e h e r e t h e r e a c t i o n s took p l a c e on a r e a c t i v e Zn surface. J u d e i k i s et ai r e c e n t l y i n v e s t i g a t e d t h e uptake o f NO2 on a s e r i e s o f surfaces (JJi). They found t h a t t h e i d e n t i t y o f t h e dominant Ν0χ~ s p e c i e s i n t h e r e a c t i o n p r o d u c t s depended on t h e c h e m i c a l c o m p o s i t i o n o f t h e s u r f a c e s . Ten B r i n k etal. found t h a t t h e presence o f Zn p a r t i c u l a t e s g r e a t l y enhanced t h e p r o d u c t i o n r a t e o f n i t r o u s a c i d (HONO) i n a i r c o n t a i n i n g NO2 ( 2 0 ) . The chemical c o m p o s i t i o n o f t h e dew can be c l a r i f i e d by n o t i n g that

0.5 [NO-] + [SO~] + S where S i s t h e s o l u b i l i t y o f ZnC03. I f φ = 1, t h e c h e m i c a l c o m p o s i t i o n i s c o n s i s t e n t w i t h a m i x t u r e o f z i n c n i t r a t e (Zn(N03)2), z i n c n i t r i t e (Zn(N02)2), ZnCC>3, ZnSOlj. proposed minor compounds Zn(N03)2 and ZnSCty a r e water s o l u b l e and can be produced by t h e r e a c t i o n s o f t h e s t r o n g a c i d s HNO3 and H2SO4 w i t h e i t h e r t h e base metal o r t h e r e l a t i v e l y i n s o l u b l e c o r r o s i o n p r o d u c t s ZnC03 and Zn(0H)2. The s o l u b i l i t y o f ZnC03 i s i n c l u d e d t o take i n t o a c c o u n t the p o s s i b i l i t y t h a t some o f t h e Zn may have a r i s e n from t h e d i s s o l u t i o n o f the corrosion products that i s not associated with r e a c t i o n s w i t h a c i d i c components o f t h e dew. T h i s c o n t r i b u t i o n i s expected t o be p r e s e n t even i n t h e absence o f a i r p o l l u t a n t s o t h e r than CO2. The presence o f r a t h e r l a r g e amounts o f NO2" s u g g e s t s t h a t Zn(N02)2 i s produced; however, no i n f o r m a t i o n on t h e proposed compound c o u l d be found i n t h e l i t e r a t u r e . I f produced, t h e f o r m a t i o n mechanism i s l i k e l y a r e a c t i o n o f t h e c o r r o s i o n p r o d u c t s w i t h HONO. The f a c t t h a t HONO i s a weak a c i d c o u l d e x p l a i n why a v a l u e l e s s than 1 i s found f o r φ, s i n c e t h e c a l c u l a t i o n assumes t h a t a l l o f t h e N02~ i s a s s o c i a t e d w i t h Zn. I f the p r o d u c t i o n o f Zn(N02)2 i s i g n o r e d , a v a l u e o f 1.5 i s found f o r φ. Under t h e s e circumstances, t h e r e i s e x c e s s Zn i n t h e dew t h a t cannot be accounted f o r . The e x p e r i m e n t a l r e s u l t s suggest t h a t t h e d e p o s i t i o n o f NO2 i n t o dew a c c e l e r a t e s t h e c o r r o s i o n o f g a l v a n i z e d s t e e l ; however, i t is difficult to establish this definitively because the c o n c e n t r a t i o n o f d i s s o l v e d Ν0χ~ i n t h e dew i s s m a l l , t h u s i t s c o n t r i b u t i o n t o t h e p r o d u c t i o n o f s o l u b l e Zn c o r r o s i o n p r o d u c t s i s s i m i l a r i n magnitude t o t h a t a s s o c i a t e d w i t h t h e d i s s o l u t i o n o f t h e relatively insoluble corrosion products i n non-acidic aqueous solutions. a

n

d

T

n

e

182

MATERIALS DEGRADATION CAUSED BYACID RAIN

The r a i n r i n s e d a t a r e s u l t s a r e shown i n T a b l e I . The Zn c o n c e n t r a t i o n i n t h e r a i n r i n s e w i t h a pH o f 3.5 was 13 t i m e s t h e v a l u e o b t a i n e d from t h e a n a l y s i s o f t h e c l e a n r a i n (pH o f 5.6) rinse. CjHfi/NOg + hv Exposure Experiment. The s t e a d y s t a t e r e a c t a n t and p r o d u c t d i s t r i b u t i o n i n t h i s experiment c o n t a i n e d a complex m i x t u r e o f o x i d a n t s whose c o n c e n t r a t i o n s were, i n g e n e r a l , much l a r g e r than those t h a t o c c u r under ambient c o n d i t i o n s b u t l i k e l y c o n t a i n s many of t h e a i r p o l l u t a n t s that a r e present d u r i n g smog c o n d i t i o n s (Table I I ) . The s t e a d y s t a t e ΝΟχ, PAN, and O3 c o n c e n t r a t i o n s were n o t v e r y s t a b l e , and t h e c i t e d d r y c o n c e n t r a t i o n v a l u e s a r e t h e average values f o r t h e e n t i r e experiment, i . e . , [ x d l ^ t x w l * quantity ΝΟχ-ΡΑΝ was c a l c u l a t e d t o o b t a i n an e s t i m a t e o f t h e NO2 concentrations. I t was assumed t h a t t h e ΝΟχ m o n i t o r responded t o PAN a s ΝΟχ. The HNO3 c o n c e n t r a t i o n s were so s m a l l (7 ppb) t h a t i t was n o t p o s s i b l e t o o b s e r v e a d e c r e a s e i n t h e c o n c e n t r a t i o n d u r i n g p e r i o d s o f wetness. NO2", N03~, S04=, HCHO, and Zn were d e t e c t e d i n the dew. E q u a t i o n 10 i s used t o c a l c u l a t e t h e d r y d e p o s i t i o n v e l o c i t y f o r NO2. I t i s assumed t h a t a l l o f t h e N02~ i n t h e dew came from the d i s s o l u t i o n o f NO2. A v a l u e o f 0.03 cm/s i s found f o r t h e deposition velocity. To c a l c u l a t e t h e d r y d e p o s i t i o n v e l o c i t y f o r HNO3, i t i s assumed t h a t t h e s o u r c e o f dew NO3" was t h e d r y d e p o s i t i o n o f HNO3. The c a l c u l a t e d v a l u e , 2.0 cm/s, appears h i g h r e l a t i v e t o t h e v e l o c i t i e s o f o t h e r s o l u b l e gases such a s HCHO (see T a b l e s I I and IV) and l i k e l y r e f l e c t s t h a t HNO3 can be adsorbed o n t o a dry surface. E v i d e n c e t o s u b s t a n t i a t e t h i s p o i n t appears i n t h e next s e c t i o n . I t i s a l s o p o s s i b l e t h a t some o f the NO3" and/or NO2" a r o s e from t h e d e p o s i t i o n o f s m a l l amounts o f PAN; however, t h e i o n i c f a t e o f d i s s o l v e d PAN i s n o t known and t h e r e f o r e more i n f o r m a t i o n i s r e q u i r e d f o r an assessment o f i t s r o l e i n a t m o s p h e r i c corrosion. The CH3CHO d e p o s i t i o n v e l o c i t y i s found u s i n g E q u a t i o n 7. The v a l u e o b t a i n e d i s 0.35 cm/s. D e p o s i t i o n v e l o c i t i e s f o r HCHO a r e found u s i n g E q u a t i o n s 7 and 10. Equation 7 y i e l d s a value o f 0.93 cm/s whereas t h e d r y d e p o s i t i o n v e l o c i t y based on t h e dew a n a l y s i s i s 0.35 cm/s. The d i s c r e p a n c y i n d i c a t e s e i t h e r t h a t t h e r e i s an e r r o r i n one o f t h e measurements (gaseous HCHO o r aqueous HCHO) o r t h a t t h e d i s s o l v e d HCHO undergoes r e a c t i o n . I t i s not a p p a r e n t t h a t any measurement e r r o r s were made, a n d , a s w i l l be shown, t h e d i s c r e p a n c y does n o t o c c u r when a n a l y z i n g t h e HCHO d a t a f o r t h e C3H6/NOX/SO2 e x p e r i m e n t . The d i f f e r e n c e i n v e l o c i t i e s c a n be e x p l a i n e d i f i t i s assumed t h a t some o f t h e d i s s o l v e d HCHO i s o x i d i z e d t o f o r m i c a c i d (HC00H), a s p e c i e s t h a t i s n o t d e t e c t e d by the c h r o m o t r o p i c a c i d method. An e s t i m a t e o f t h e amount o f HC00H produced can be o b t a i n e d by s u b t r a c t i n g t h e amount o f HCHO d e p o s i t e d , c a l c u l a t e d by t h e dew a n a l y s i s method ( E q u a t i o n 9) from the amount d e p o s i t e d u s i n g E q u a t i o n 8. The r e s u l t s a r e a s f o l l o w s :

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch010

T

D

HCHO

=

3

8

0

2"

(

E

c

l

u

a

t

i

o

n

8

^

a

n

d

n

e

10.

E D N E Y ET AL.

Impact of NO , SO , and Oxidants on Galvanized Steel x

Table I .

x

183

Results of NO2 Exposure Experiment

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch010

Total Exposure Time: 25 h Total Time of Wetness: 14 h (7-h periods) Air Temperature: 26°C Plate Temperature when Wet: 10°C Rain Frequency: Once at the end of the experiment Amount of Rain per Event: 0.59 cm Gas Phase J

NO2

feJW>

txJ(PP6)

649

627

"X

= ) 0.05

Dew

N02"

203

39

NO3-

11

2

ΝΟχ"

214

41

S04

=

Zn

12 149

2 29

Rain

( nmol\ 5.6

2

3.5

26

( nmol\

1.2 15

ff(

= ) 0.06

184

MATERIALS DEGRADATION C A U S E D BY ACID RAIN

T a b l e I I . R e s u l t s o f C3H6/NOx+hv Exposure Experiment T o t a l Exposure Time: 336 h T o t a l Time o f Wetness: 196 h ( 7 - h p e r i o d s ) A i r Temperature: 32°C P l a t e Temperature when Wet: 10°C R a i n Frequency: A f t e r f o u r and n i n e days exposure and a t the end o f t h e e x p e r i m e n t Amount o f R a i n p e r E v e n t : 4.7 cm Gas

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch010

X

0

Phase

4(τ) 2,

Ixjippb)

3

PAN ΝΟχ-ΡΑΝ HN03

134 57 0.03

359

2.0

7

HCHO

621

389

0.93

0.33

CH3CHO

254

207

0.35

Dew X v

cm '

NO2-

95

11

NO3-

118

15

ΝΟχ-

213

26

S04

=

1

6

HCHO

940

133

Zn

590

77

Rain pH

r~

,/

/

nmol\

nmol\

R

Zn{—) v

cm

5.6

4

17

3.5

27

127

7

10.

EDNEYETAL.

Impact of NO , SO , and Oxidants on Galvanized Steel x

D

HCHO

=

1

3

x

2

3

185

e q u a t i o n 9)

cm

The difference i n deposited HCHO converted into an equivalent HCOOH concentration gives a value o f 1746 nmol/ml. The chemical composition o f the dew i s analyzed i n the same way as i n the NO2 experiment. The presence o f ΝΟχ i n the dew suggests, as before, the formation o f Zn(N02)2> ZnC03, and Ζη(Νθ3)2· Assuming that these, plus a small amount of ZnS04, are the only Zn compounds in the dew, produces the following r e s u l t f o r φ : -

[Zn] = 3.0

φ =

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch010

0.5 [ Μ Γ Ί + [SO~] + S

The large value f o r φ indicates the presence of other soluble Zn compounds f o r which a prime candidate i s zinc formate (Zn(CH00)2), a w e l l known water-soluble compound that i s formed when HCOOH reacts with Zn. I f the estimated value f o r the CHOO" concentrations i s included i n the expression f o r φ , the following r e s u l t i s obtained: [Zn] = 0.55

φ =

0.5 [NO~] + 0.5 [CHOO] + [SO~] + S

The introduction o f Zn(CH00)2 narrows the difference between the calculated value for φ and the t h e o r e t i c a l value o f 1 for which the soluble Zn compounds have been t o t a l l y accounted. However the introduction o f CHOO" r e s u l t s i n more anions than can be accounted for by the Zn concentration. A possible explanation i s that HCOOH i s a weak acid and that some o f the acid remained undissociated. The presence o f CHOO" i n the dew i s consistent with the findings o f Knotkovà, who observed that HCHO accelerated the corrosion o f a number o f metals, including galvanized s t e e l , and that the corrosion products contained CHOO" (21). In addition to HCHO oxidation i n s o l u t i o n , the p o s s i b i l i t y e x i s t s that CH3CHO coud be oxidized to acetic acid. However, no measurements were made during the experiments to evaluate t h i s reaction. Table I I I shows the r a i n rinse data f o r the experiment. The Zn dissolved per r a i n event increased by nearly a factor o f 7 as the pH was decreased from 5.6 to 3.5, a r e s u l t i n q u a l i t a t i v e agreement with that found i n the NO2 experiment. The Zn corrosion determined by weight loss measurements ( D ) and the t o t a l amounts o f Zn corrosion induced by dew and r a i n are also shown i n Table I I I . The t o t a l Zn l o s t due to dew ( D ) i s obtained by m u l t i p l y i n g D ( ) by 28, the number o f dew cycles i n the exposure experiment. Total Zn corrosion caused by r a i n ( R n ) i s found by m u l t i p l y i n g the average Zn r a i n rinse concentration by the t o t a l r a i n f a l l (14.2 cm). The Zn corrosion determined by weight loss i s consistent with the r a i n rinse data. The maximum Zn corrosion took place on those panels sprayed with r a i n having a pH of 3.5. For each exposure condition, the sum of the Zn found i n the r a i n and dew i s l e s s than that found by weight l o s s . The difference i s l i k e l y due to the presence o f an W L

z n

T

2

z n

z n

T

Z

186

MATERIALS DEGRADATION CAUSED BYACID RAIN

insoluble protective layer that i s not dissolved i n the dew or r a i n but i s dissolved by the cleaning process. C^Hfi/MOg/SO?

+

hv Exposure

Experiment.

Table IV

contains

the

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch010

experimental conditions and r e s u l t s for the i r r a d i a t e d C3H6/NOX/SO2 mixture. The chemical composition was s i m i l a r to the steady state mixture o f the i r r a d i a t e d C3H6/NOX system except for the presence o f SO2 and i t s oxidation products. No decreases were found i n the ΝΟχ, O3, or PAN concentrations during dew formation. The NO2 and HNO3 deposition v e l o c i t i e s were calculated using the same method as was employed i n the C3H6/NOX experiment. The NO2 dry deposition v e l o c i t y was 0.02 cm/s, and the deposition v e l o c i t y f o r HNO3 was 2.0 cm/s, both i n reasonable agreement with the previous r e s u l t s . Analysis of the dry panel, deionized H2O rinse indicated that as much as 60? o f the HNO3 deposition took place during the dry periods. I f t h i s contribution i s taken into account, Equation 11 y i e l d s a value o f 0.7 cm/s for the HNO3 dry deposition v e l o c i t y . The SO2 dry deposition v e l o c i t y based on the decrease i n gas phase SO2 concentration was 0.77 cm/s. The value obtained from the dew analysis was 0.82 cm/s. The approximate equality o f the deposition v e l o c i t i e s demonstrates a reasonable mass balance for the s u l f u r species. Good agreement i s also found for the HCHO dry deposition v e l o c i t i e s (0.45 cm/s vs. 0.47 cm/s). Analysis o f the dry panels showed no evidence for s u b s t a n t i a l HCHO deposition to dry surfaces. The dominant S0x species i n the dew was SO3". This r e s u l t d i f f e r s from that found i n s i n g l e component SO2 exposure experiments where the dominant species was S04 ( 1 2 ) . I t appears that a reaction took place which t i e d up the S 0 3 or i t s precursor b i s u l f i t e (HSO3-) prevented i t from o x i d i z i n g to S04 . The r e s u l t that the S 0 3 to aqueous HCHO r a t i o i s 1.1 i s consistent with the formation of a HCHOHSO3" adduct, i . e . , =

=

a n d

=

=

HCHO + HSO3-

HCHOHSO3-,

the anion associated with hydroxymethane s u l f o n i c a c i d . This species i s detected as S03 by ion chromatography and as aqueous HCHO by the chromotropic acid method. Munger etal. have recently found t h i s species present i n the Los Angeles fog samples (22). The dew molar r a t i o s suggest that the dew consisted o f a mixture o f Zn(N02)2, Zn(N03)2, ZnC03, ZnS04, and Zn(HCH0HS03)2. The corresponding value f o r φ i s determined as follows: =

[Zn]

φ=

=

-

= 1.0

0.5 [NO~] + [ S O " ] + 0 . 5 [HCHOHSO'] + S

where i t has been assumed that the HCHOHSO3" concentration i s equal to the aqueous HCHO concentration, and the S 0 concentration i s equal to the sum o f the S04 concentration and the difference between the aqueous HCHO concentration and the S 0 3 concentration. This r e s u l t shows that soluble Zn dew compounds can be completely accounted for by the above mentioned mixture. The presence o f the HCH0HS03" ion indicates that the contributions of dissolved HCHO and SO2 to corrosion are not a d d i t i v e . However, i t i s not clear to what =

X

=

=

10.

EDNEY ET A L .

Impact of NO , SO , and Oxidants on Galvanized Steel x

187

x

Table I I I . Comparison o f Zn C o r r o s i o n Based on Weight Loss Determine a t i o n s and That O b t a i n e d by A n a l y s i s o f Dew and R a i n R i n s e Samples / η mol

\

*L

Exposure C o n d i t i o n pH=5.6 R a i n + Dew

2,460

2,160

50

pH=3.5 R a i n + Dew

3,450

2,160

380

Dew Only

2,880

2,160

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch010

T a b l e IV.

0

R e s u l t s o f C3H6/NOx/S02+hv Exposure E x p e r i m e n t

T o t a l Exposure Time: 25 h T o t a l Time o f Wetness: 14 h (7-h p e r i o d s ) A i r Temperature: 32°C P l a t e Temperature when Wet: 10°C R a i n Frequency: No r a i n e v e n t s Gas

Phase

[x,](pp6)

frjfcp»

^ff)

S02

1J90

798

0.77

O3

240

PAN

114

ΝΟχ-ΡΑΝ

159

HNO3 HCHO CH3CHO

2.0

1,550

1,195

0.47

792

715

0.17

Dew

N02-

35

4

N03-

182

19

ΝΟχ-

217

23

S03=

5,650

595

826

91

S0 =

6,476

686

HCHO

5,100

560

Zn

4,174

441

S04 X

0.82

0.02

9

=

= )

0.45

188

MATERIALS DEGRADATION CAUSED BYACID RAIN

e x t e n t t h e adduct would form under ambient c o n d i t i o n s r e a c t i o n pathways may be i m p o r t a n t .

where

other

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch010

Discussion The r e s u l t s o f the exposure e x p e r i m e n t s suggest t h a t compounds o t h e r than SO2 s h o u l d be c o n s i d e r e d when d e s i g n i n g and a n a l y z i n g galvanized s t e e l corrosion f i e l d data. These compounds i n c l u d e HNO3, HCHO, and p o s s i b l y NO2. I t was n o t p o s s i b l e t o d e t e r m i n e whether o t h e r p h o t o c h e m i c a l o x i d a n t s such a s CH3CHO, PAN, H2O2, o r O3 a c c e l e r a t e c o r r o s i o n . SO2, NO2, and HCHO w i l l d e p o s i t on a d r y s u r f a c e until s a t u r a t i o n occurs. I n the case o f SO2, p r e v i o u s work has shown t h a t the s a t u r a t i o n s u r f a c e d e n s i t y i s s i m i l a r t o t h a t o f a monolayer o f adsorbed SO2 ( J 2 ) . D u r i n g wet p e r i o d s , the dry deposition v e l o c i t i e s o f SO2 and HCHO w i l l be c o n t r o l l e d e s s e n t i a l l y by the gas phase r e s i s t a n c e o f t h e atmosphere. However, t h e NO2 d e p o s i t i o n v e l o c i t y i s c o n t r o l l e d by the s u r f a c e r e s i s t a n c e . The d e p o s i t i o n o f HNO3 i s more d i f f i c u l t t o p a r a m e t e r i z e because, a p p a r e n t l y , i t ' i s r e a d i l y adsorbed on a d r y s u r f a c e . Each o f t h e above mentioned compounds can form a c i d s i n dew t h a t r e a c t t o produce s o l u b l e Zn corrosion products. The c o r r o s i o n induced p e r mole o f compound d e p o s i t e d depends on t h e s t o i c h i o m e t r i c c o e f f i c i e n t ( l ) f o r t h e r e a c t i o n . The c o e f f i c i e n t s f o r the compounds d e t e c t e d i n t h i s s t u d y and t h e e x p e r i m e n t a l l y d e t e r m i n e d average d r y d e p o s i t i o n v e l o c i t i e s f o r t h e p r e c u r s o r gas phase s p e c i e s a r e g i v e n i n T a b l e V. I t has been assumed t h a t t h e a c i d s produced i n t h e dew a r e t o t a l l y d i s s o c i a t e d and r e a c t s t o i c h i o m e t r i c a l l y w i t h t h e l a y e r compounds. The presence o f t h e HCHOHSO3" adduct i n t h e dew produced i n t h e i r r a d i a t e d C3H6/NOX/SO2 m i x t u r e i n d i c a t e s t h e p o s s i b i l i t y that a n t a g o n i s t i c and/or s y n e r g i s t i c e f f e c t s w i l l have t o be c o n s i d e r e d when e v a l u a t i n g f i e l d d a t a . I t has been shown t h a t r a i n can induce Zn c o r r o s i o n . Analysis o f t h e r a i n r i n s e samples showed t h a t t h e c o r r o s i o n r a t e i n c r e a s e d as the pH o f the i n c i d e n t s p r a y d e c r e a s e d . However, i t i s d i f f i c u l t t o e x t r a p o l a t e t h e r e s u l t s t o a t m o s p h e r i c c o n d i t i o n s because t h e l a b o r a t o r y s p r a y c o n d i t i o n s were such t h a t t h e r e s i d e n c e time o f a s p r a y d r o p l e t was on the o r d e r o f seconds. I t i s n o t c l e a r whether t h e r e was adequate time f o r the r e a c t i o n t o take p l a c e . The Zn c o r r o s i o n p r o d u c t s i n the dew r e p r e s e n t o n l y t h e s o l u b l e c o r r o s i o n products. I n f o r m a t i o n on t h e i n s o l u b l e c o r r o s i o n p r o d u c t s was o b t a i n e d o n l y i n t h e C3H6/NO experiment i n which w e i g h t l o s s d e t e r m i n a t i o n s were made. I t was found t h a t t h e t o t a l Zn c o r r o s i o n d e t e r m i n e d by t h e weight l o s s method was l a r g e r than t h a t found i n the dew and r i n s e . The d i f f e r e n c e i s e q u a l t o t h e amount o f i n s o l u b l e c o r r o s i o n p r o d u c t formed. The r e s u l t s o f t h e e x p e r i m e n t s suggest t h a t t h e amount o f s o l u b l e Zn c o r r o s i o n p r o d u c t formed can be e s t i m a t e d i f the d e p o s i t i o n o f t h e p r e c u r s o r gas phase s p e c i e s can be d e t e r m i n e d . However, t h e q u e s t i o n o f what c o n t r o l s t h e f o r m a t i o n o f the p r o t e c t i v e l a y e r has n o t been d i s c u s s e d . In t h e next s e c t i o n , a model f o r t h e a t m o s p h e r i c c o r r o s i o n o f galvanized steel i s f o r m u l a t e d i n w h i c h b o t h t h e r o l e o f d e p o s i t i o n and t h e parameters t h a t c o n t r o l b o t h t h e f o r m a t i o n o f s o l u b l e and i n s o l u b l e p r o d u c t s are addressed. F o r t h e r e m a i n i n g d i s c u s s i o n , t h e term ' i n s o l u b l e t

x

EDNEY ET AL.

10.

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch010

T a b l e V. Gas Phase

189

Impact of NO , SO , and Oxidants on Galvanized Steel x

x

Properties of P o t e n t i a l Corrosion Stimulations Anion

•l") 0.8

1.0

N02"

0.03

0.5

HNO3

Ν03"

2.0(0.7)*

0.5

HCHO

CH00-

0.6

0.5

-

0.5

S02

S03 ,S0ïr

NO2

HCH0+S02

=

HCHOHSO3-

* The v a l u e i n p a r e n t h e s e s i s based on t h e d e p o s i t i o n o b t a i n e d a f t e r s u b t r a c t i n g t h e H N O 3 s a t u r a t i o n s u r f a c e d e n s i t y from t h e d e p o s i t i o n o b t a i n e d by dew a n a l y s i s .

190

M A T E R I A L S D E G R A D A T I O N C A U S E D BY A C I D R A I N

c o r r o s i o n p r o d u c t s ' w i l l be used t o denote the Zn(0H)2 t h a t comprise the p r o t e c t i v e l a y e r .

compounds ZnC03

and

Formulation of Corrosion Model. The c o r r o s i o n p r o d u c t s formed on g a l v a n i z e d s t e e l c o n s i s t o f i n s o l u b l e compounds (Zn(0H>2, ZnC03, e t c . ) and s o l u b l e compounds (ZnSOlj, Zn(N03)2, e t c . ) . F i r s t , the time e v o l u t i o n o f the i n s o l u b l e component w i l l be a d d r e s s e d . The c o r r o s i o n w i l l be e x p r e s s e d i n terms o f change i n s u r f a c e t h i c k n e s s due t o c o r r o s i o n p r o d u c t f o r m a t i o n .

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch010

As discussed p r e v i o u s l y , under c l e a n a i r c o n d i t i o n s , a protective layer w i l l form on the s u r f a c e inhibiting further corrosion. The time development o f the p r o t e c t i v e i n s o l u b l e c o r r o s i o n p r o d u c t l a y e r can be described by the following d i f f e r e n t i a l equation:

1

dt Τ where Τ = the t h i c k n e s s o f the i n s o l u b l e c o r r o s i o n p r o d u c t layer, f = the f r a c t i o n a l time o f wetness, and « = a diffusion coefficient. The parameter / i s i n t r o d u c e d t o t a k e i n t o account the f a c t t h a t c o r r o s i o n o n l y t a k e s p l a c e when the s u r f a c e i s wet. The s o l u t i o n t o E q u a t i o n 12 i s as f o l l o w s :

T(t) = V2^fT where t i s the t o t a l exposure time. Τ i s a p a r a b o l i c f u n c t i o n of the exposure time c o n t r o l l e d by the value o f the d i f f u s i o n c o e f f i c i e n t «,whose v a l u e i s not known, but i s l i k e l y t o be r e l a t e d t o the d i f f u s i o n c o e f f i c i e n t s t h a t d e s c r i b e m o l e c u l a r transport through the s o l i d p r o t e c t i v e l a y e r . The r e s u l t s o f the e x p e r i m e n t s r e p o r t e d h e r e a r e c o n s i s t e n t w i t h a model i n which a c i d i c components i n the r a i n and dew react w i t h the i n s o l u b l e c o r r o s i o n p r o d u c t s . I f i t i s assumed t h a t a l l deposited compounds r e a c t stoichiometrically with the layer compound, E q u a t i o n 12 can be r e - e x p r e s s e d as E q u a t i o n 14:

— = Ι/_β dt

Τ '

( 1 4 ) μ

where Ν

β=Α

+

di

[x.] + /(o.5[/r ] + s)

and Ν

the number o f gas phase s p e c i e s t h a t d e p o s i t s o n t o the s u r f a c e and p a r t i c i p a t e s i n c o r r o s i o n ; the gas phase c o n c e n t r a t i o n o f a i r p o l l u t a n t i; the dry d e p o s i t i o n v e l o c i t y o f a i r p o l l u t a n t i;

(15)

10.

E D N E Y ET AL.

7j

SO ,

x

and Oxidants on Galvanized Steel

x

191

=

I [H+ S A

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch010

Impact of NO ,

the stoichiometric coefficient for the reaction between the d i s s o l v e d a i r p o l l u t a n t i and the l a y e r compound ; = the amount o f r a i n per u n i t time; ] = the r a i n c o n c e n t r a t i o n o f H+; = s o l u b i l i t y o f ZnCC>3; = a constant that converts the l o s s o f m a t e r i a l i n moles per u n i t a r e a t o change i n t h i c k n e s s . a

n

d

The wet d e p o s i t i o n component o f β has been d i v i d e d i n t o a " c l e a n " r a i n c o n t r i b u t i o n and a term t h a t r e p r e s e n t s the c o r r o s i o n induced by the a c i d i c components o f the r a i n . The l a t t e r component i s e x p r e s s e d i n terms o f H+ c o n c e n t r a t i o n i n the r a i n and assumes t h a t i t t a k e s two H+ i o n s t o c o r r o d e one Zn atom. T h i s mechanism i s e s s e n t i a l l y i d e n t i c a l t o the one proposed f o r the p r o d u c t i o n of soluble Zn corrosion products by deposition of acidifying air pollutants i n t o the dew. The "clean" rain term c o n t a i n s the c o n t r i b u t i o n due t o the s o l u b i l i t y o f ZnC03 i n H2O. This type o f term has not been i n c l u d e d f o r dry d e p o s i t i o n because, a t l e a s t t o a first a p p r o x i m a t i o n , the volumes o f dew produced under ambient c o n d i t i o n s , as opposed t o t h a t produced i n the p r e s e n t l a b o r a t o r y , would be small. Therefore, the c l e a n dew c o n t r i b u t i o n can be ignored relative t o t h a t o f the dew acids. More r e s e a r c h is r e q u i r e d t o e s t a b l i s h t h i s assumption. In a d d i t i o n , i t has been assumed that the two contributions to wet deposition-induced c o r r o s i o n are a d d i t i v e . T h i s may be an o v e r - s i m p l i f i c a t i o n o f what a c t u a l l y o c c u r s under ambient c o n d i t i o n s . The

s o l u t i o n to Equation

T(t) = Τ

1

—

14

i s as

follows:

, where Τ = β

exp

(16)

and i s the s t e a d y s t a t e t h i c k n e s s o f the i n s o l u b l e c o r r o s i o n p r o d u c t layer. The total corrosion C(t) i s obtained by adding the c o n t r i b u t i o n o f the s o l u b l e c o r r o s i o n p r o d u c t s t o T(t), i.e.,

C(t) = Τ

1

—

exp

(τω+βί)

+ β*

(17)

E q u a t i o n 16 i s a t r a n s c e n d e n t a l e q u a t i o n t h a t must be solved iteratively. The c o r r o s i o n a t exposure time t i s the sum o f the soluble and insoluble components; however, the insoluble c o n t r i b u t i o n depends on the amount o f s o l u b l e p r o d u c t s produced v i a i t s dependence on βί. The d e v e l o p e d model d i f f e r s s i g n i f i c a n t l y from the l i n e a r model represented by E q u a t i o n 3. Analysis of galvanized s t e e l corrosion f i e l d d a t a shows t h a t , i n g e n e r a l , the c o r r o s i o n i s not a l i n e a r f u n c t i o n o f exposure t i m e , p a r t i c u l a r l y f o r s h o r t exposure t i m e s (5). The development o f the steady s t a t e p r o t e c t i v e l a y e r i s n o n l i n e a r i n time, and o n l y a f t e r t h i s l a y e r i s e s t a b l i s h e d w i l l the corrosion appear to increase linearly. The thickness of the p r o t e c t i v e l a y e r depends on the e n v i r o n m e n t a l c o n d i t i o n . Under c l e a n a i r c o n d i t i o n s a t h i c k p r o t e c t i v e l a y e r w i l l form; however, under h i g h l y p o l l u t e d c o n d i t i o n s ( l a r g e β ) , Γ„ w i l l be s m a l l and the

192

MATERIALS DEGRADATION CAUSED BYACID RAIN

corrosion w i l l be dominated by the s o l u b l e c o n t r i b u t i o n to Equation 17. The proposed model represents a f i r s t step i n the development of a corrosion model f o r galvanized s t e e l . To v a l i d a t e the model, d e t a i l e d t e s t i n g o f model predictions versus r e s u l t s o f f i e l d exposure studies i s required. Such an e f f o r t i s presently being conducted i n our laboratory.

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch010

Disclaimer

Although the research described i n t h i s a r t i c l e has been funded wholly or i n part by the United States Environmental Protection Agency through c o n t r a c t 68-02-4033 t o Northrop Services, Inc. - Environmental Sciences, i t has not been subjected to the Agency's required peer and p o l i c y review and therefore does not necessarily r e f l e c t the views of the Agency, and no o f f i c i a l endorsement should be i n f e r r e d .

Literature Cited 1. Atteraas L.; Haagenrud, S. In "Atmospheric Corrosion"; Ailor, W.E., Ed.; J. Wiley and Sons: New York, 1982; pp. 873-891. 2. Legault, R.A. In "Atmospheric Corrosion"; Ailor, W.E., Ed.; J. Wiley and Sons: New York, 1982; pp. 607-614. 3. Mikhailvosky, V.N. In "Atmospheric Corrosion"; Ailor, W.E., Ed.; J. Wiley and Sons: New York, 1982; pp. 85-105. 4. Knotkova, D.; Barton, K.; Cerny, M. In "Atmospheric Corrosion"; Ailor, W.E., Ed.; New York: J. Wiley and Sons, 1982; pp. 991-1014. 5. Spence, J.W.; Haynie, F.H.; Edney, E.O.; Stiles, D.C. A Field Study for Determining the Effects of Dry and Wet Deposition on Materials. Presented at State of the Art Symposium on Degradation of Materials due to Acid Rain; Arlington, VA; 1985. 6. Flinn, D.R.; Cramer, S.D.; Carter, J.P.; Spence, J.W. Mat. Perform. Submitted. 7. Haynie, F.H.; Upham, J.B. Mat. Perform. 1970, 9:35. 8. Benarie, M. Metallic Corrosion as Functions of Atmospheric Pollutant Concentrations and Rain pH. BNL 35668. Upton, NY: Brookhaven National Laboratory. 9. Lipfert, F.W.; Benarie, M.; Dawn, M.L. Derivation of Metallic Corrosion Damage Functions for Use in Environmental Assessment. Draft Report. Brookhaven National Laboratory: Upton, NY; 1985. 10. Mansfield, F.B. Effects of Airborne Sulfur Pollutants on Materials. EPA-600/4-80-007. U.S. Environmental Protection Agency: Research Triangle Park, NC; 1980. 11. Haynie, F.H. In "Durability of Building Materials and Components"; Sereda,P.J.; Litran, G.G., Eds.; American Society for Testing and Materials, 1980; pp. 157-175. 12. Edney, E.O.; Stiles, D.C.; Spence; J.W.; Haynie, F.H.; Wilson, W.E. Atmos. Environ. Submitted. 13. Barton, K. In "Protection Against Atmospheric Corrosion"; Wiley-Interscience, 1976; Chap. 3. 14. In "Handbook of Chemistry and Physics, 63rd Edition"; Weast, R.C., Ed; The Chemical Rubber Co.: Cleveland, OH, 1982.

10.

15. 16. 17. 18. 19.

20.

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch010

21. 22.

EDNEY ET AL.

Impact ofNO ,SO ,and Oxidants on Galvanized Steel x

x

Barton, K.; Beranek, E. Werkst. Dorros. 1959, 10:377. Kuntz, R.; Lonneman, W.A.; Namie, G.R.; Hull, L.A. Anal. Lett. 1980, 13:409. Lonneman, W.A.; Bufalini, J.J.; Namie, G.R. Environ. Sci. Technol. 1982, 16:655. Lee, Y.N.; Schwartz; S.E. J.Geophys.Res. 1981, 86:11971. Judeikis, H.S.; Siegel, S.; Stewart, T.B.; Hedgpeth, H.R.; Wren, A.G. In "Nitrogeneous Air Pollutants: Chemical and Biological Implications"; Grosjean, D., Ed.; Ann Arbor Science: Ann Arbor, MI, 1979; pp. 83-110. Ten Brink, H.M.; Bontje, J.Α.; Spoelstra, H.; Van DeVate, J.F. In "Atmospheric Corrosion"; Benarie, M., Ed.; Amsterdam: Elsevier, 1978; pp. 239-244. Knotkova, D.; Vlckova, J . Werkst. Korros. 1970, 21:16. Munger, J.W.; Jacob, D.J.; Hoffmann, M.R. J. of Atmos. Chem. 1984, 1:335.

RECEIVED January 13, 1986

19

11 A Field Experiment to Partition the Effects of Dry and Wet Deposition on Metallic Materials 1

1

2

2

John W. Spence , Fred H . Haynie , Edward O. Edney , and David C. Stiles 1

Atmospheric Sciences Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch011

2

Northrop Services, Inc., Research Triangle Park, NC 27709

One of the major research objectives of Task Group G, Effects on Materials and Cultural Resources, within the National Acid Precipitation Assessment Program is to derive material damage functions that relate the effects of dry and wet acid deposition on materials degradation. At an exposure site located at the Research Triangle Park, NC site, the Environmental Protection Agency has installed an automatic covering device to partition the effects of dry and wet acid deposition on the exposed materials. The device automatically covers the materials only during the rain event. Materials are exposed to both dry and wet deposition (uncovered exposure) and dry deposi­ tion (covered exposure). Corrosion data collected over a two year period for galvanized and weathering steels will be presented. The contributing effects of dry and wet deposition on the corrosion of these steels will be discussed. At a m a t e r i a l exposure s i t e l o c a t e d a t t h e R e s e a r c h T r i a n g l e Park, N.C., t h e E n v i r o n m e n t a l P r o t e c t i o n Agency began i n O c t o b e r 1982 a s t u d y t o p a r t i t i o n t h e e f f e c t s o f d r y and wet d e p o s i t i o n on g a l v a ­ n i z e d s t e e l and C o r t e n A w e a t h e r i n g s t e e l . I n t h i s study a mobile d e v i c e c o v e r s a s e t o f t h e m e t a l l i c m a t e r i a l s d u r i n g each r a i n e v e n t . A n o t h e r s e t o f t h e m e t a l s i s b o l d l y exposed ( u n c o v e r e d ) a t the s i t e . The r e s u l t s o f t h e two-year exposure o f t h e s e two m e t a l s i s presented. Experimental Procedures P a n e l s (10 χ 15 cm) o f 20 gauge g a l v a n i z e d s t e e l and C o r t e n A wea­ t h e r i n g s t e e l were p r e p a r e d . E a c h p a n e l was i d e n t i f i e d by a code s t e n c i l e d l i g h t l y on t h e ground exposed s i d e o f t h e p a n e l . P r i o r t o f i e l d exposure t h e g a l v a n i z e d p a n e l s were c l e a n e d by immersion f o r 2 minutes i n 10% by weight o f ammonium c h l o r i d e s o l u t i o n a t a temperature o f 60-80°C ( J J . The w e a t h e r i n g s t e e l p a n e l s were 0097-6156/86/0318-0194S06.00/ 0 © 1986 American Chemical Society

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch011

11.

SPENCEETAL.

Effects of Dry and Wet Deposition

195

c l e a n e d by immersion i n C l a r k ' s s o l u t i o n ( J J . A l l p a n e l s were r i n s e d i n d e i o n i z e d water and then w i t h methanol t o remove m o i s t u r e , and weighed to 0.1 mg. The p a n e l s were exposed a t 30° between c e r a m i c i n s u l a t o r s f a c i n g s o u t h a t the s i t e ( 2 ) . P a n e l s of each m e t a l were exposed i n t r i p l i c a t e f o r p e r i o d s of 6, 12, and 24 months. The six-month p a n e l s were c o n t i n u a l l y r e p l a c e d w i t h c l e a n e d p a n e l s i n o r d e r t o s t u d y the c o r r o s i o n d u r i n g w i n t e r and summer e x p o s u r e s . Two s e t s of each m e t a l p a n e l s were exposed a t the s i t e . An a u t o m a t i c d e v i c e which i s t r i g g e r e d by a s e n s o r on a r a i n bucket c o l l e c t o r c o v e r e d one s e t of p a n e l s o n l y d u r i n g each r a i n e v e n t . T h i s s e t of p a n e l s i s exposed p r i m a r i l y t o d r y d e p o s i t i o n . The r e m a i n i n g s e t of p a n e l s was exposed uncovered t o wet and dry d e p o s i t i o n . A f t e r each exposure p e r i o d the p a n e l s were removed, t h e n c l e a n e d a c c o r d i n g t o the p r o c e d u r e e s t a b l i s h e d p r i o r t o the exposure and reweighed to 0.1 mg. Results W e i g h t - l o s s d a t a f o r the g a l v a n i z e d and w e a t h e r i n g s t e e l f o r the c o v e r e d and uncovered c o n d i t i o n s a r e shown i n T a b l e 1 f o r each exposure p e r i o d . The d i f f e r e n c e s i n w e i g h t - l o s s ( A l o s s ) f o r covered and uncovered c o n d i t i o n s a r e a l s o shown i n the t a b l e . A f t e r the i n i t i a l six-month exposure p e r i o d , the i d e n t i t y code of the w e a t h e r i n g s t e e l p a n e l s was not r e a d a b l e and new p a n e l s were p r e p a r e d and exposed. The w e i g h t - l o s s of the u n i d e n t i f i e d p a n e l s was determined as the d i f f e r e n c e of the combined weight of the t r i p l i c a t e p a n e l s f o r each exposure p e r i o d . T h i s d a t a i s r e p o r t e d i n T a b l e 1 w i t h o u t computation of a s t a n d a r d d e v i a t i o n . A f t e r two y e a r s of exposure the w e i g h t - l o s s of the g a l v a n i z e d s t e e l f o r the uncovered exposure i s n e a r l y t w i c e the w e i g h t - l o s s r e c o r d e d f o r the c o v e r e d c o n d i t i o n . Whereas, f o r the w e a t h e r i n g s t e e l , the w e i g h t - l o s s f o r the c o v e r e d exposure i s g r e a t e r than the uncovered e x p o s u r e . Discussion D u r i n g exposure, g a l v a n i z e d s t e e l and w e a t h e r i n g s t e e l a r e e x p e c t e d to c o r r o d e by f o r m i n g a p r o t e c t i v e s u r f a c e f i l m t h a t r e t a r d s c o r r o sion. The r a t e of c o r r o s i o n would then be d i f f u s i o n c o n t r o l l e d and depend upon the t h i c k n e s s of the f i l m . Many of the c o r r o s i o n p r o d u c t s , p a r t i c u l a r l y the c a r b o n a t e s , h y d r o x i d e s , e t c . w i t h i n the f i l m are s o l u b l e i n a c i d s o l u t i o n s . I n environments where i n c r e a s e d a c i d i t y i s p r e s e n t , d i s s o l u t i o n of the p r o t e c t i v e f i l m i s a competing mechanism t h a t a c c e l e r a t e s the r a t e o f c o r r o s i o n of m e t a l s . P r e v i o u s exposure s t u d i e s of t h e s e m e t a l s have shown t h a t time-of-wetness and SO2 c o n c e n t r a t i o n s c o n t r i b u t e t o the a c c e l e r a t e d corrosion (3)(4). At the R e s e a r c h T r i a n g l e Park, NC exposure s i t e , the ambient c o n c e n t r a t i o n of SO2 i s below the d e t e c t a b l e l i m i t ( 5 ppb) of a i r m o n i t o r i n g i n s t r u m e n t a t i o n and i s not s i g n i f i c a n t l y d i f f e r e n t from z e r o . At t h e s e l e v e l s d r y d e p o s i t i o n o f SO2 i s not e x p e c t e d t o be an i m p o r t a n t f a c t o r i n the c o r r o s i o n of t h e s e m e t a l s . Time-of-wetness r e s u l t s from b o t h the f o r m a t i o n of dew and r a i n . W i t h v e r y low SO2 l e v e l s , the dew i s not e x p e c t e d t o be v e r y a c i d i c .

196

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318

M A T E R I A L S D E G R A D A T I O N C A U S E D BY A C I D R A I N

d e p o s i t i o n i n t e r a c t s w i t h m o i s t u r e and a f f e c t s p a i n t e d wood i s unknown a t t h i s t i m e . D i m e n s i o n a l changes are a f u n c t i o n o f d e n s i t y ; t h e r e f o r e the h i g h e r d e n s i t y latewood changes more t h a n the lower d e n s i t y e a r l y wood. Thus the l a r g e areas o f latewood i n f l a t - g r a i n e d lumber h o l d p a i n t p o o r l y ( F i g u r e 3 ) . T h i s i s p a r t i c u l a r l y t r u e o f the l a r g e latewood bands o f t e n found i n plywood. M i n i u t t i ( 4 , 5) r e p o r t e d d i f f e r e n t s w e l l i n g o f earlywood and latewood i n v e r t i c a l - g r a i n lumber. He a l s o showed t h a t the d i f f e r e n t i a l s w e l l i n g o f p o o r l y machined f l a t g r a i n s i d i n g developed severe s t r a i n s i n the c o a t i n g over t h e s e areas ( F i g u r e 4 ) . T h i s r a i s e d g r a i n developed c r a c k s over the latewood p o r t i o n s o f the s w e l l e d wood ( F i g u r e 5 ) .

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch022

A c i d D e p o s i t i o n E f f e c t s on C o a t i n g s A comprehensive r e v i e w o f the e f f e c t s o f p o l l u t i o n on c o a t i n g s a p p l i e d t o wood and many o t h e r m a t e r i a l s was p u b l i s h e d i n 1979 (6) and i t i s not my i n t e n t t o d u p l i c a t e t h i s e f f o r t . I w i l l however, r e v i e w some o f the work t h a t impacts d i r e c t l y on wood and wood finishing. Of f i n i s h e s used o u t s i d e , the polymers t h a t can o f f e r the b e s t p r o t e c t i o n a g a i n s t a c i d d e p o s i t i o n are those not c o n t a i n i n g a c i d s e n s i t i v e groups such as e s t e r s . I n c l u s i o n of a c i d r e s i s t a n t p a i n t b i n d e r s such as v i n y l s , u r e t h a n e , and e p o x i e s would produce a c i d r e s i s t a n c e o n l y i f the o t h e r components are a l s o a c i d r e s i s t a n t . S a p o n i f i c a t i o n o f e s t e r s c a t a l y z e d by h y d r o x y l s formed d u r i n g c o r r o s i o n o f s t e e l s u b s t r a t e s may a l s o degrade p o l y e s t e r s ( 7 ) . V i r t u a l l y a l l o f the r e s e a r c h on a c i d d e p o s i t i o n e f f e c t s on f i n i s h e s has d e a l t w i t h c o a t i n g d e g r a d a t i o n and d i d not i n c l u d e the e f f e c t on the s u b s t r a t e . I n e a r l y l a b o r a t o r y experiments o f SO^ e f f e c t s on p a i n t , Holbrow (8) showed t h a t some o i l - b a s e d p a i n t s d r i e d more s l o w l y i n a SO^ contaminated atmosphere. The e f f e c t was dependent upon SO^ c o n c e n t r a t i o n , type o f o i l , and pigment.

Paints

based on l i n s e e d o i l , b o d i e d dehydrated c a s t o r o i l s , and tung o i l , w i t h t i t a n i u m d i o x i d e p i g m e n t s , were more s u s c e p t i b l e t o d r y i n g r e t a r d a t i o n t h a n unbodied dehydrated c a s t o r o i l and b a s i c pigments such as w h i t e l e a d o r z i n c o x i d e . The g r e a t e s t e f f e c t o c c u r r e d w i t h i n the f i r s t day o r two o f cure and the e f f e c t was more pronounced under m o i s t u r e condensing c o n d i t i o n s . The SO^ exposure d u r i n g the e a r l y s t a g e s o f o i l cure rendered the f i l m s m o i s t u r e s e n s i t i v e and t h e y w r i n k l e d under f u r t h e r exposure t o m o i s t c o n d i t i o n s . The d r y i n g o f l a t e x p a i n t s has n o t been e v a l u a t e d . The s o i l i n g o f p a i n t s by v a r i o u s p a r t i c u l a t e s has been documented. These p a r t i c u l a t e s i n c l u d e s u l f a t e s and c h l o r i d e s o f i r o n , c a l c i u m , and z i n c (8) as w e l l as dust from a l k a l i n e mortar ( 9 ) . Spence and Haynie (10) d i s c u s s e d two s u r v e y s by M i c h e l s o n and T o u r i n , and Booz e t a l . i n which an attempt was made t o c o r r e l a t e c o n c e n t r a t i o n o f a t m o s p h e r i c p a r t i c u l a t e m a t t e r w i t h the frequency of r e p a i n t i n g . A l t h o u g h t h e s e s u r v e y s showed a c o r r e l a t i o n , t h e r e are many unanswered q u e s t i o n s . The e f f e c t s o f o t h e r p o l l u t a n t s , the t y p e o f p a i n t u s e d , and the s o c i a l and economic f a c t o r s a f f e c t i n g p a i n t i n g frequency were not t a k e n i n t o a c c o u n t .

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch022

22.

WILLIAMS

Effects of Acid Rain on Painted Wood Surfaces

F i g u r e 3 . - - P a i n t f a i l u r e over latewood o f f l a t - g r a i n e d (30). (M147 211-12)

319

siding

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320

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F i g u r e 4 . — E n l a r g e d view o f t h e end g r a i n o f p a i n t e d wood b e f o r e ( t o p ) and a f t e r (bottom) s w e l l i n g w i t h water. The p a i n t i s one t h i c k c o a t o f s o l v e n t - b o r n e p r i m e r . (Upper): Dry. (Lower): Wet (4). (M121 550)

F i g u r e 5 . - - E n l a r g e d views o f t h e p a i n t e d f a c e ( t o p ) and end g r a i n (bottom) o f a p i e c e o f wood s i m i l a r t o t h a t i n F i g u r e 4. The c r a c k i n t h e t h i c k c o a t o f s o l v e n t - b o r n e p r i m e r i s over t h e earlywoodlatewood j u n c t i o n and developed a f t e r water was p l a c e d on t h e end g r a i n t o s w e l l t h e crushed springwood c e l l s beneath t h e band o f latewood ( 4 ) . (M121 551)

22.

WILLIAMS

Effects of Acid Rain on Painted Wood Surfaces

321

G u t f r e u n d ( H ) used exposure o f p a i n t f i l m s t o 0^ as a means o f

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch022

p r e d i c t i n g p a i n t performance. H i g h e r grades o f p a i n t e m b r i t t l e d l e s s d u r i n g exposure t o t h i s p o l l u t a n t . I n the e a r l y 1970's a s e r i e s o f experiments were begun by Campbell, Spence, S c h u r r , and o t h e r c o l l a b o r a t o r s t o a s s e s s t h e e f f e c t s o f a c i d d e p o s i t i o n on p a i n t f i l m s . The work was a l o g i c a l c o n t i n u a t i o n o f p r e v i o u s work by Holbrow, T i c e , and G u t f r e u n d . I n the f i r s t o f t h e s e e x p e r i m e n t s , u s i n g s t a i n l e s s s t e e l s u b s t r a t e s , the a c c e l e r a t e d e r o s i o n o f t h e p a i n t s u r f a c e by SO^ and 0^ was e v a l uated by a t t e n u a t e d t o t a l r e f l e c t a n c e i n f r a r e d s p e c t r o s c o p y (ATR I R ) , s c a n n i n g e l e c t r o n m i c r o s c o p y (SEM), and by measuring p a i n t e r o s i o n or l o s s g r a v i m e t r i c a l l y . I n subsequent work, t h e p a n e l s were e v a l uated o n l y g r a v i m e t r i c a l l y . A 1974 s t u d y by Campbell e t a l . (12) i n v o l v e d b o t h l a b o r a t o r y and f i e l d exposure o f f i v e c o a t i n g systems on s t a i n l e s s s t e e l panels: o i l - b a s e d house p a i n t ; l a t e x house p a i n t ; i n d u s t r i a l maintenance p a i n t ; c o i l - c o a t i n g p a i n t ; and n i t r o c e l l u l o s e / a c r y l i c a u t o motive p a i n t . The f o u r f i e l d exposure s i t e s were n o r t h c e n t r a l N o r t h Dakota; Los A n g e l e s , C a l i f o r n i a ; C h i c a g o , I l l i n o i s ; and V a l p a r a i s o , Indiana. The r e s e a r c h f o c u s e d on a c c e l e r a t e d e f f e c t s o f p o l l u t i o n on e r o s i o n , t h e normal d e g r a d a t i v e mechanism f o r a good p a i n t system, and d i d n o t i n c l u d e c a t a s t r o p h i c f a i l u r e s caused by l o s s o f p a i n t a d h e s i o n . The w e i g h t l o s s o f specimens a t low S0^ c o n c e n t r a t i o n s seemed t o c o r r e l a t e w e l l w i t h t h e p a i n t s h a v i n g CaCO^ e x t e n d e r p^g_ ments (Table

I I I ) . A t h i g h e r l e v e l s o f SO^ (1.0 ppm), t h e e r o s i o n

r a t e s were s u b s t a n t i a l l y h i g h e r . The g r e a t e s t i n c r e a s e i n e r o s i o n r a t e o c c u r r e d w i t h o i l - b a s e d house p a i n t h a v i n g CaCO^ e x t e n d e r pigments. ATR IR s p e c t r o s c o p y e v a l u a t i o n o f t h e s u r f a c e showed more r a p i d breakdown o f t h e b i n d e r i n t h e o i l / a l k y d p a i n t s t h a n i n t h e a c r y l i c - b a s e d l a t e x p a i n t s . Shaded specimens showed s i m i l a r t r e n d s but l e s s d e g r a d a t i o n . S u r f a c e e v a l u a t i o n u s i n g SEM s u b s t a n t i a t e d the r e s u l t s from t h e weight l o s s measurement. ATR IR s p e c t r o s c o p y showed t h a t o i l - b a s e d house p a i n t s have t h e g r e a t e s t s u r f a c e degradat i o n . L a t e x house p a i n t s a l s o showed severe s u r f a c e d e g r a d a t i o n . The r e s u l t s w i t h 0^ were l e s s c l e a r a l t h o u g h t h e o i l - b a s e d p a i n t was more s e v e r e l y a f f e c t e d than t h e l a t e x p a i n t . R e s u l t s o f l a b o r a t o r y exposure t o S0^ c o r r e l a t e d w e l l w i t h t h e outdoor exposure; t h e highest erosion rate occurred f o r coatings having a c i d - s e n s i t i v e e x t e n d e r pigments ( m a i n l y CaCO^) i n a r e a s o f h i g h p o l l u t i o n . The l a b o r a t o r y exposure v a l u e s o b t a i n e d f o r unshaded specimens were g e n e r a l l y h i g h e r than f o r t h e low c o n c e n t r a t i o n S0^ (0.1 ppm) and almost as h i g h as t h e h i g h c o n c e n t r a t i o n

S0^ (1.0 ppm).

based house p a i n t c o n t a i n i n g CaCO^ was an e x c e p t i o n , h a v i n g

Oiltwice

as h i g h an e r o s i o n r a t e f o r 1.0 ppm SO^ exposure (shaded) as f o r t h e 0.1 ppm S0^ (unshaded).

I n most cases t h e e f f e c t o f l i g h t and SO^

appeared a d d i t i v e e x c e p t f o r t h e o i l - b a s e d house p a i n t . Here t h e e r o s i o n was more t h a n t w i c e as f a s t as t h e sum o f S 0 and l i g h t 9

1 ± 2.2

2 ± 2.2

1 ± 1.3

1 ± 1.8

3 ± 5.4

9 ± 4.3

3 ± 1.9

0 ± 6.4

Oil

11 ±

Coil

I n d u s t r i a l maintenance

± 9.4

refinish

0

ppm

47 ± 10.6 99%

19 ± 10.5 99%

13 ± 2.9 50%

8 ± 2 99%

3 ± 1.4 95%

SHADED

1.0

concentration

0.1 ppm

SO^

ppm

Controls

4.6

Latex

Automotive

Coating

21 ± 15 87% 4 ± 4.2 55%

6 ± 8.*

6.1

6.8

1 ±

±

11 ± 3 30%

2 ± 1.6 95%

3 ± 1.4 96%

ppm

2 ± 4.4

1 ± 2.3

1.0

concentration

0.1 ppm

0^

T a b l e I I I . S l o p e o f E r o s i o n Data ( m i l s l o s s χ 1θ" / h r w i t h 95% c o n f i d e n c e l i m i t s ) Accompanied by a T - t e s t P r o b a b i l i t y (%) t h a t a S t a t i s t i c a l D i f f e r e n c e E x i s t s Between the R e s p e c t i v e S l o p e f o r a G i v e n P o l l u t a n t Type and L e v e l v s . the Zero P o l l u t a n t L e v e l , Based on A c c e l e r a t e d Weathering Data C o l l e c t e d a t 400, 700, and 1,000 Hours Only (used, w i t h p e r m i s s i o n , from Campbell e t a l . (12))

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch022

22 ± 2

20 = 7.2

Oil

141 ± 19 99%

34 ± 4.7 99%

22 ± 7 66%

12 ± 3.3

9 ± 1.7

11 ± 1 99%

3 ± 13.4

12 ± 2 . 3

3 ± 2.6 75%

4 ± 5

Coil

1.5

4 ±

5.1

OA

2 ±

ppm

UNSHADED

1.0

concentration

0.1 ppm

SO^

19 ±

refinish

0 ppm

Controls

I n d u s t r i a l maintenance

Latex

Automotive

Coating

28 ± 14 85% 15 ± 2.5 94% 45 ± 10.5 99%

10 ± 14.1

6 ± 3.3

22 ± 17.2

2 ±

± 5.< 93%

5 ± 1.3 99%

ppm

0.3

2 ± 1.7

1.0

concentration

0.1 ppm

0^

T a b l e I I I . S l o p e o f E r o s i o n Data ( m i l s l o s s χ ΙΟ" / h r w i t h 95% c o n f i d e n c e l i m i t s ) Accompanied by a T - t e s t P r o b a b i l i t y (%) t h a t a S t a t i s t i c a l D i f f e r e n c e E x i s t s Between the R e s p e c t i v e S l o p e f o r a G i v e n P o l l u t a n t Type and L e v e l v s . the Zero P o l l u t a n t L e v e l , Based on A c c e l e r a t e d Weathering Data C o l l e c t e d a t 400, 700, and 1,000 Hours Only (used, w i t h p e r m i s s i o n , from Campbell e t a l . ( 1 2 ) )

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch022

>

ο SX.

S*

S' ο

«s

in

M A T E R I A L S D E G R A D A T I O N C A U S E D BY A C I D R A I N

324

exposure. A l t h o u g h t h i s r e s u l t might suggest some s y n e r g i s m between t h e s e two e f f e c t s w i t h t h e o i l - b a s e d house p a i n t , t h e data do n o t s u p p o r t e x t e n d i n g t h i s t o o t h e r p a i n t s . I t i s l i k e l y an i s o l a t e d e f f e c t caused by combining a h i g h l y U V - s e n s i t i v e b i n d e r w i t h CaCO^ e x t e n d e r pigments. The r e s u l t s from t h e s e experiments should be viewed w i t h some c a u t i o n because o f p o s s i b l e c o m p l i c a t i o n s i n measu r i n g w e i g h t l o s s . A d d i t i o n o r c o n d e n s a t i o n type r e a c t i o n s o f p o l l u t a n t s w i t h p a i n t components, d i f f u s i o n o f p o l l u t a n t s i n t o t h e f i l m , o u t g a s s i n g o f t h e p a i n t , and a c c u m u l a t i o n o f d i r t ( p a r t i c u l a r l y i n t h e f i e l d e x p o s u r e s ) can a l l b i a s t h e w e i g h t - l o s s measurements. I n a l a t e r s t u d y (1^3) , a c o n t r o l l e d environment chamber was used to i d e n t i f y d i r e c t and p o s s i b l e s y n e r g i s t i c e f f e c t s o f SO^, NO^, and

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch022

0^ on an o i l - b a s e d house p a i n t , an a c r y l i c l a t e x house p a i n t , a v i n y l c o i l c o a t i n g , and an a c r y l i c c o i l c o a t i n g , a l l on aluminum s u b s t r a t e s . V a r i a b l e s i n chamber c o n d i t i o n s i n c l u d e d t e m p e r a t u r e , r e l a t i v e humidi t y (RH), p o l l u t a n t s ( S 0 , N 0 , and 0 ) , dew, and l i g h t . The chamber 2

2

3

was c o n s t r u c t e d such t h a t t h e p a i n t s u r f a c e s were s u b j e c t e d t o m o i s t u r e - c o n d e n s i n g c o n d i t i o n s . The r e s u l t o f t h e s t u d y , based o n l y on w e i g h t l o s s , i n d i c a t e d t h a t o i l - b a s e d house p a i n t s h a v i n g s i l i c a t e e x t e n d e r s were a f f e c t e d by SO^ and RH. D e g r a d a t i o n t o t h e a c r y l i c and v i n y l c o i l c o a t i n g s was v e r y s l i g h t . I t i s s i g n i f i c a n t that the l a t e x house p a i n t f a i l e d because o f c o r r o s i o n o f t h e aluminum substrate. I n t h e case o f porous f i l m s such as l a t e x p a i n t s , t h e d i f f u s i o n o f SO^ t h r o u g h t h e f i l m was s u f f i c i e n t t o b r i n g about catastrophic paint f a i l u r e . I n a more r e c e n t 30-month outdoor exposure s t u d y i n v o l v i n g n i n e s i t e s i n t h e S t . L o u i s , M i s s o u r i , a r e a , t h e performance o f goodq u a l i t y o i l - and l a t e x - b a s e d house p a i n t s on s t a i n l e s s s t e e l were e v a l u a t e d by w e i g h t - l o s s measurements (14). The p a i n t s d i d n o t c o n t a i n CaCO^ e x t e n d e r pigments. Spencer and Haynie r e p o r t e d no e f f e c t s caused by SO^, b u t e r o s i o n r a t e s were a f u n c t i o n o f time o f w e t n e s s , t e m p e r a t u r e , and s u n l i g h t . No e x p l a n a t i o n was g i v e n f o r change i n SO^ e f f e c t s i n comparison w i t h t h e e a r l i e r i n v e s t i g a t i o n s . Because t h e p a i n t s t h a t performed p o o r l y i n t h e e a r l i e r s t u d i e s contained a c i d s e n s i t i v e extenders, the higher r e s i s t a n c e of the p a i n t s used i n t h e l a t e r s t u d y may be a t t r i b u t e d t o t h e l a c k o f t h e s e e x t e n d e r s . Spence and Haynie r e p o r t e d s i g n i f i c a n t l y lower e r o s i o n r a t e s f o r o i l - v e r s u s l a t e x - b a s e d p a i n t s . However, e r o s i o n r a t e s a l o n e may n o t be a good c r i t e r i a f o r e v a l u a t i n g l a t e x - v e r s u s o i l based p a i n t s . The major cause o f p a i n t f a i l u r e on wood i s n o t e r o s i o n b u t c a t a s t r o p h i c f a i l u r e o f t h e wood-paint i n t e r f a c e and subsequent p e e l i n g o f t h e p a i n t . R e d u c t i o n s i n e r o s i o n r a t e s t h r o u g h f o r m u l a t i n g h i g h l y c r o s s l i n k e d p a i n t s may be c o u n t e r p r o d u c t i v e . A c i d D e p o s i t i o n E f f e c t s on Wood and C e l l u l o s i c M a t e r i a l s The e f f e c t s on wood and o t h e r c e l l u l o s i c m a t e r i a l s o f a c i d r a i n and the o x i d e s o f n i t r o g e n and s u l f u r have been r e p o r t e d . Raczkowski (3) found t h a t e x p o s i n g s t r i p s o f microtomed spruce ( P i c e a a b i e s K a r s t . ) t o s u n l i g h t , wind, and r a i n r e s u l t e d i n de-

22.

WILLIAMS

Effects of Acid Rain on Painted Wood Surfaces

325

creased t e n s i l e s t r e n g t h compared w i t h unexposed c o n t r o l s . Twelve s e t s o f specimens were exposed f o r 1-month p e r i o d s over 1 y e a r . The l o s s i n t e n s i l e s t r e n g t h a l o n g the g r a i n was g e n e r a l l y d i r e c t l y r e l a t e d t o the amount of s u n l i g h t d u r i n g the summer and f a l l ( F i g u r e 6 ) ; however, the l o s s i n s t r e n g t h f o r w i n t e r and s p r i n g seemed h i g h e r t h a n c o u l d be accounted f o r on the b a s i s of s u n l i g h t alone. The a c i d i t y of the r a i n and SO^ l e v e l s were h i g h e r d u r i n g

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch022

the w i n t e r and s p r i n g , and t h i s h i g h e r l o s s was a t t r i b u t e d t o t h e s e higher a c i d i t y l e v e l s . I n i t i a l i n s p e c t i o n of the data i n d i c a t e d t h a t the main e f f e c t was caused by s u n l i g h t and t h a t t h e r e may be an a c i d e f f e c t p a r t i c u l a r l y d u r i n g the w i n t e r months. However the summer a c i d l e v e l s seem r a t h e r low. The pHs ranged from 6 t o 7.5 ( F i g u r e 7 ) . The pH of r a i n caused o n l y by atmospheric CO^ s h o u l d be 5.6. I f the study had i n c l u d e d another c o n t r o l t h a t was exposed t o s u n l i g h t but not t o a c i d c o n d i t i o n s , i t might have been p o s s i b l e t o s e p a r a t e t h e s e two e f f e c t s . I n a s e r i e s of t h r e e p a p e r s , A r n d t and Gross (15-17) r e p o r t e d on c o l o r and weight changes caused by outdoor exposure and a c c e l e r a t e d w e a t h e r i n g of wood. I n one of the p a p e r s , p a i n t e d s t e e l was a l s o evaluated. I n b o t h the wood and p a i n t e d s t e e l , o n l y c o l o r changes c o u l d be observed f o l l o w i n g outdoor and a c c e l e r a t e d w e a t h e r i n g . C o n c l u s i o n s based on c o l o r change must be viewed w i t h some c a u t i o n because, i n the case of p a i n t , minor pigment i n s t a b i l i t y c o u l d show c o l o r change w i t h o u t s e r i o u s l y a f f e c t i n g the b i n d e r i n t e g r i t y . With most wood, c o l o r changes are r e l a t e d t o the i n s t a b i l i t y of e x t r a c t i v e s , which have l i t t l e t o do w i t h the i n t e g r i t y of the wood. I n a d d i t i o n , the g r a v i m e t r i c measure of w e a t h e r i n g was c o m p l i c a t e d by s e v e r a l c o v a r i a b l e s ; the changes i n SO^ l e v e l s i n d i f f e r e n t l o c a t i o n s a l s o had d i f f e r e n t m o i s t u r e exposure, s o l a r exposure, and dry d e p o s i tion rates. The d e g r a d a t i o n of wood s u r f a c e s by ozone (0^) was a l s o s t u d i e d ( 1 8 ) . Exposure of wood a t two m o i s t u r e c o n t e n t s ( 6 % and s a t u r a t e d ) t o 0^ c o n c e n t r a t i o n s of 0.5, 1.0, and 1.5% r e s u l t e d i n a weight l o s s o f wood. However, the specimens showed no l o s s o f c r y s t a l l i n i t y or s t r e n g t h p a r a l l e l t o the g r a i n . I t appeared t h a t the l o s s i n w e i g h t was caused by d e g r a d a t i o n of the e a s i l y a c c e s s i b l e h e m i c e l l u l o s e s . The c r y s t a l l i n e c e l l u l o s e was not degraded and t h e r e f o r e the s t r e n g t h was u n a l t e r e d . Evans and Banks (19) exposed microtomed s e c t i o n s of Lime ( T i l i a v u l g a r i s ) and C o r s i c a n p i n e ( P i n u s n i g r a ) t o d i l u t e s u l f u r i c , s u l f u r o u s , n i t r i c , a c e t i c , and f o r m i c a c i d s , pH 2.0 t o 6.0, f o r up t o 12 months a t 40°C. C o n t r o l s were soaked i n water a t the same tempera t u r e . A t a pH of 2.0, a l l a c i d t r e a t m e n t s caused g r e a t e r l o s s of s t r e n g t h and toughness compared w i t h the c o n t r o l s . The amount of s t r e n g t h l o s s was pH dependent. The most i n t e r e s t i n g r e s u l t , however, was t h a t the s t r e n g t h l o s s caused by s u l f u r o u s a c i d was g r e a t e r than a l l o t h e r a c i d s a t s i m i l a r pHs. They noted t h a t the s t r e n g t h l o s s e s may be caused by a c o m b i n a t i o n of b o t h h y d r o l y t i c d e g r a d a t i o n of the h e m i c e l l u l o s e s and a s u l f o n a t i o n r e a c t i o n of the lignin. Scanning e l e c t r o n m i c r o s c o p y (SEM) data showing f a i l u r e a t the l i g n i n - r i c h m i d d l e l a m e l l a f u r t h e r s u p p o r t e d the s p e c u l a t i o n t h a t l i g n i n d e g r a d a t i o n i s p a r t i a l l y r e s p o n s i b l e f o r the decrease i n s t r e n g t h and toughness.

M A T E R I A L S D E G R A D A T I O N C A U S E D BY A C I D R A I N

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80

A

M

J

J A 1977

S

O

N

D

J

F

M 1978

F i g u r e 6.—The l o s s o f t e n s i l e s t r e n g t h o f spruce m i c r o s e c t i o n s , t h e mean monthly i n s o l a t i o n , and t h e a c i d i t y o f t h e r a i n w a t e r ( 3 ) . (ML85 5193) 10

Γ

A

M

J

J

A S 1977

O

N

D

J

F

M 1978

F i g u r e 7.—Mean monthly pH o f r a i n w a t e r and s u l p h u r d i o x i d e c o n c e n t r a t i o n i n t h e a i r ( 3 ) . (ML85 5192)

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22.

WILLIAMS

Effects of Acid Rain on Painted Wood Surfaces

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F e i s t (20) and W i l l i a m s (21) have used xenon a r c a c c e l e r a t e d w e a t h e r i n g t o determine the e f f i c a c y of s u r f a c e t r e a t m e n t s o f wood. The d e g r a d a t i o n o f the s u r f a c e i s m a n i f e s t as e r o s i o n and can be measured m i c r o s c o p i c a l l y ( 2 ) . I n r e c e n t work a t the F o r e s t P r o d u c t s L a b o r a t o r y ( 2 2 ) , these t e c h n i q u e s were used t o determine the e f f e c t o f a c i d treatment on the e r o s i o n r a t e of w e s t e r n redcedar (Thuja p l i c a t a Donn ex D. Don). F i v e r e p l i c a t e specimens o f w e s t e r n redcedar and t h e i r l o n g i t u d i n a l l y end-matched c o n t r o l s were a r t i f i c i a l l y weathered (xenon a r c Weather-Ometer, a p p r o x i m a t e l y 24-h l i g h t and 4-h d e i o n i z e d water spray d a i l y ) . The Weather-Ometer was shut down f o r about 1 h Monday t h r o u g h F r i d a y i n o r d e r t o soak the specimens i n d i l u t e a c i d f o r 15 min. S i x types of a c i d soaks were used: n i t r i c and s u l f u r i c a c i d s a t pHs o f 3.0, 3.5, and 4.0. I found s i m i l a r r e s u l t s w i t h b o t h a c i d s . Compared w i t h the unsoaked c o n t r o l s , the 3.0 pH a c i d caused a 10% i n c r e a s e i n e r o s i o n r a t e . At a pH o f 3.5 the e f f e c t was a 4% i n c r e a s e due t o the a c i d , and no e f f e c t was found a t a pH o f 4.0. A l t h o u g h o n l y a l i m i t e d amount of work has been done on a i r p o l l u t i o n e f f e c t s on wood, the e f f e c t s on o t h e r c e l l u l o s i c m a t e r i a l , such as c o t t o n y a r n and f a b r i c , have been s t u d i e d by s e v e r a l groups (23-28). With minor d i f f e r e n c e s as t o the importance o f n i t r o g e n o x i d e s , the g e n e r a l r e s u l t s of these s t u d i e s showed t h a t t h e r e was an a c c e l e r a t e d d e g r a d a t i o n e f f e c t caused by p o l l u t i o n . These s t u d i e s compared the s t r e n g t h of f a b r i c f o l l o w i n g v a r i o u s exposures o f c o t t o n c l o t h t o outdoor environments h a v i n g v a r y i n g amounts o f p o l l u t i o n . The r e s u l t s i n d i c a t e d a s t r o n g c o r r e l a t i o n between s t r e n g t h l o s s and SO^ c o n c e n t r a t i o n , w i t h s o i l i n g a l s o h a v i n g an impact. A l s o as p o i n t e d out by these r e s e a r c h e r s , the s o l a r e f f e c t s cannot be negl e c t e d , p a r t i c u l a r l y d u r i n g the summer months. As f o r the mechanism o f d e g r a d a t i o n o r the i n t e r a c t i o n s of the v a r i o u s f a c t o r s , (SO^, s o i l i n g , and l i g h t ) , these a s p e c t s o f the problem have not been a d d r e s s e d . I n a d d i t i o n , the e f f e c t o f wet d e p o s i t i o n v e r s u s d r y d e p o s i t i o n has not been a d e q u a t e l y a d d r e s s e d . The work showing the e f f e c t o f s o i l i n g covers o n l y one a s p e c t o f the dry d e p o s i t i o n problem. The r e s u l t s o f the work w i t h c e l l u l o s e c l e a r l y demonstrate an e f f e c t o f a c i d d e p o s i t i o n . F u r t h e r work i s needed t o d e l i n e a t e the v a r i o u s f a c t o r s and the r e l a t i o n s h i p of the v a r i o u s f a c t o r s w i t h one another. F i n a l Comments There are s e v e r a l avenues f o r f u t u r e r e s e a r c h i n the r e s i s t a n c e o f wood and wood c o a t i n g s t o d e g r a d a t i o n by a c i d r a i n . P r e v i o u s r e s e a r c h on a c i d d e p o s i t i o n e f f e c t s on wood c o a t i n g s d i d not t a k e i n t o account the e f f e c t of the s u b s t r a t e but l i n k e d poor performance i n a c i d environments t o the extenders i n the p a i n t . I t s h o u l d be r e l a t i v e l y easy t o f o r m u l a t e p a i n t s t o overcome t h i s e r o s i o n problem. However, i n wood i t i s c a t a s t r o p h i c f a i l u r e t h a t causes most p o o r - p a i n t performance. Thus, the e f f e c t of a c i d s on t h i s i n t e r f a c e f a i l u r e s h o u l d be addressed i n f u t u r e work. I t i s i m p o r t a n t t o t e s t c o a t i n g s on the s u b s t r a t e f o r w h i c h they are designed. R e s e a r c h on p a i n t e d s t e e l w i l l not l i k e l y be a p p l i c a b l e t o p a i n t e d wood because the p r o p e r t i e s o f the p a i n t must be d i f f e r e n t i n o r d e r t o accommodate the v a s t l y d i f f e r e n t p r o p e r t i e s

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328

of s t e e l and wood. A h i g h l y c r o s s - l i n k e d m o i s t u r e b a r r i e r a p p l i c a b l e t o s t e e l w i l l a c t u a l l y t r a p m o i s t u r e a t the wood-paint i n t e r f a c e and c o u l d cause p e e l i n g . These c o a t i n g s are b r i t t l e and are prone to c r a c k i n g , which l e a d s to f u r t h e r m o i s t u r e p e n e t r a t i o n . Paints for wood p r o d u c t s s h o u l d be more f l e x i b l e and porous. I n the r e s e a r c h done so f a r , specimens have not u s u a l l y been exposed t o the s p e c i f i c l o c a t i o n s where a c i d d e p o s i t i o n i s most l i k e l y t o o c c u r on a p a i n t e d s t r u c t u r e - - p r o t e c t e d areas such as under eaves and s o f f i t s . I n f a c t , i n t e r c o a t p e e l i n g of z i n c - c o n t a i n i n g p a i n t s under eaves has been l i n k e d to the f o r m a t i o n of m o i s t u r e s e n s i t i v e s a l t s t h r o u g h the a c t i o n of p o l l u t a n t s (j^2). The l i n k i s r a t h e r c i r c u m s t a n t i a l and f u r t h e r r e s e a r c h i s needed. The d i s c o l o r a t i o n or " f r o s t i n g " of l a t e x p a i n t s i s r e p o r t e d to be caused by the c o n c e n t r a t i o n of p o l l u t a n t s such as SO^, NO^, or Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch022

H^S

i n protected

areas such as under eaves and

soffits

(12,

29)•

When t h e s e p o l l u t a n t s are absorbed by p a i n t f i l m s under m o i s t cond e n s i n g c o n d i t i o n s , the a c i d s t h a t form may p e n e t r a t e the f i l m and r e a c t w i t h some pigments. The s a l t s formed by t h i s r e a c t i o n l e a v e a g r a y i s h - w h i t e d e p o s i t on the p a i n t a f t e r the water evapo r a t e s . The problem i s more n o t i c e a b l e w i t h d a r k e r c o l o r s . I t i s c o n c e i v a b l e t h a t a c i d or SO^ would d i f f u s e through the f i l m over an extended p e r i o d of time and thus have an impact on the wood-paint i n t e r f a c e . I t s h o u l d be k e p t i n mind, however, t h a t the pH o f most wood s p e c i e s i s a l r e a d y i n the range of w e t - a c i d d e p o s i t i o n . Under dry d e p o s i t i o n c o n d i t i o n s , h i g h e r b u i l d u p o f a c i d (SO^) may o c c u r a t t h i s i n t e r f a c e . I t would be w o r t h w h i l e t o d e s i g n an experiment t o measure the a c i d c o n d i t i o n s under the f i l m . F u t u r e r e s e a r c h on a c i d d e g r a d a t i o n s h o u l d determine which components o f wood are most a f f e c t e d by a c i d and what e f f e c t t h i s d e g r a d a t i o n has on p a i n t performance. Assuming t h e r e i s an a c i d environment a t the wood-paint i n t e r f a c e , some h y d r o l y s i s of the h e m i c e l l u l o s e s i s p r o b a b l e . I t i s a l s o l i k e l y t h a t amorphous c e l l u l o s e would be h y d r o l y z e d . Recent work by Banks (19) l i n k e d l i g n i n d e g r a d a t i o n t o s u l f u r o u s a c i d . C r y s t a l l i n e c e l l u l o s e s h o u l d remain u n a l t e r e d ; but i f h y d r o l y s i s of the h e m i c e l l u l o s e s does o c c u r , i t i s not n e c e s s a r i l y a s u f f i c i e n t l y s e r i o u s c o n d i t i o n t o weaken the p a i n t a d h e s i o n . We know from r e c e n t work a t the F o r e s t P r o d u c t s L a b o r a t o r y t h a t b r i e f exposure o f wood t o u l t r a v i o l e t l i g h t ( n a t u r a l s u n l i g h t ) p r i o r to p a i n t i n g d r a s t i c a l l y decreases p a i n t adhesion. T h i s exposure a f f e c t s m a i n l y the l i g n i n . Thus, i t seems t h a t of the t h r e e main c o n s t i t u e n t s o f wood ( c e l l u l o s e , h e m i c e l l u l o s e , and l i g n i n ) , l i g n i n i s the most c r i t i c a l f o r p a i n t a d h e s i o n . Evaluating l i g n i n s u s c e p t i b i l i t y to d e g r a d a t i o n by a c i d d e p o s i t i o n may be the key t o u n d e r s t a n d i n g the e f f e c t s o f a c i d d e p o s i t i o n on wood and f i n i s h e d wood. Disclaimer

Notice

The use of t r a d e , f i r m , or c o r p o r a t i o n names i n t h i s p u b l i c a t i o n i s f o r the i n f o r m a t i o n and convenience o f the r e a d e r . Such use does not c o n s t i t u t e an o f f i c i a l endorsement o r a p p r o v a l by the U.S. Department o f A g r i c u l t u r e o f any p r o d u c t or s e r v i c e t o the e x c l u s i o n o f o t h e r s t h a t may be s u i t a b l e .

22.

WILLIAMS

Literature 1.

2. 3. 4. 5. 6.

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7.

8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

20.

21. 22. 23. 24. 25. 26. 27. 28.

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329

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Feist, W. C.; Hon, D. N.-S. In "Chemistry of Solid Wood;" Rowell, R. M., Ed.; ADVANCES IN CHEMISTRY SERIES No. 207, American Chemical Society: Washington, DC, 1984; pp 401-51. Feist, W. C.; Mraz, E. A. Forest Prod. J. 1978, 28(3), 38-42. Raczkowski, J. Holz als Roh-und Werkstoff 1980, 38(6), 231-34. Miniutti, V. P. Offical Digest 1963, 35(460), 451-71. Miniutti, V. P. Forest Prod. J. 1964, 571-76. Gross, H. Effects of air pollution on surface finishes and similar coatings," Erich Schmidt Verlag, Berlin, 1979. Wicks, Z. W., Jr. In "Corrosion Control by Coatings," Leidheiser, Η., Jr., Ed.; Science Press: Princeton, 1979; p. 29-34. Holbrow, G. L. J. Oil Colour Chemists' Assoc. 1962, 45(10), 701-18. Tice, E. A. J. Air Pollution Control Assoc. 1962, 12, 533. Spence, J. W.; Haynie, F. H. J. Paint Technol. 1972, 44(574), 70-74. Gutfreund, K. J. Paint Technol. 1966, 38(503), 732-39. Campbell, G. G.; Schurr, G. G.; Slawikowski, D. E.; Spence, J. W. J. Paint Tech. 1974, 46(593), 59-71. Spence, J. W.; Haynie, F.; Upham, J. B. J. Paint Technol. 1975, 47(609), 57-63. Haynie, F. H.; Spence, J. W. J. Air Pollution Control Assoc. 1984, 34, 941-44. Arndt, U.; Gross, U. Staub Reinhaltung der Luft. 1974, 34(6), 225-27. Arndt, U.; Gross, U. Staub Reinhaltung der Luft. 1976, 36(10), 405-10. Arndt, U.; Gross, U. Staub Reinhaltung der Luft. 1977, 37(2), 53-55. Dick, J. L.; Murphey, W. K. Research Briefs. 1972, 6(2), 4-6. Evans, P. D.; Banks, W. B. The International Research Group on Wood Preservation, Working Group III, Preservatives and Methods of Treatment, Sixteenth Annu. Meet., Brazil, 12-17 May 1985. Document No: IRG/WP/3326, 21 Feb. 1985. Feist, W. C. "Protection of wood surfaces with chromium trioxide;" Res. Pap. FPL 339, Madison, WI, U.S. Department of Agriculture, Forest Service, Forest Products Laboratory; 1979. Williams, R. S. J. Appl. Polym. Sci. 1983, 28, 2093-103. Williams, R. S. Unpublished. Race, E. J. Soc. Dryers Colourists 1949, 65, 55-63. Bogaty, H.; Campbell, K. S.; Appel, W. D. Textile Res. J. 1952, 22, 81-83. Morris, Μ. Α.; Young, Μ. Α.; Molig, T. A. Textile Res. J. 1964, 34, 563-64. Brysson, R. J.; Trask, B. J.; Upham, J. B.; Booras, S. G. J. Air Pollution Control Assoc. 1967, 17(5), 294-98. Brysson, R. J.; Trask, B. J.; Cooper, A. S., Jr. Am. Dyestuff Rep. 1968, 57, 512-17. Brysson, R. J., Walker, A. M.; Cooper, A. S., Jr. Textile Res. J. 1975, 45, 154-59.

330

MATERIALS

DEGRADATION

CAUSED BY ACID RAIN

29. Olympic Stain, A division of Clorox Company. Olympic Technical Information Bulletin No. 14, Bellevue, WA; 1977. 30. Forest Products Laboratory. Wood Handbook: Wood as an engineering material; Agric. Handb. 72, rev., Washington, DC; U.S. Department of Agriculture; 1974. 31. Feist, W. C.; Oviatt, A. E. "Wood siding--installing, finishing, maintaining," Home and Garden Bull. 203, Washington, DC; U.S. Department of Agriculture; 1983. 23 p.

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch022

G l o s s a r y ( E x t r a c t e d from the F o r e s t P r o d u c t s Wood Handbook, 1974.)

Laboratory,

ANNUAL GROWTH RING. The l a y e r o f wood growth put on a t r e e d u r i n g a s i n g l e growing season. I n the temperature zone the annual growth r i n g s o f many s p e c i e s ( e . g . , oaks and p i n e s ) a r e r e a d i l y d i s t i n g u i s h e d because o f d i f f e r e n c e s i n the c e l l s formed d u r i n g the e a r l y and l a t e p a r t s o f the season. I n some temperate zone s p e c i e s ( b l a c k gum and sweetgum) and many t r o p i c a l s p e c i e s , annual growth r i n g s are n o t e a s i l y r e c o g n i z e d . CELLULOSE. The c a r b o h y d r a t e t h a t i s the p r i n c i p a l c o n s t i t u e n t o f wood and forms t h e framework o f the wood c e l l s . DECAY. The d e c o m p o s i t i o n o f wood substance by f u n g i . Advanced ( o r t y p i c a l ) decay. The o l d e r stage o f decay i n w h i c h the d e s t r u c t i o n i s r e a d i l y r e c o g n i z e d because the wood has become punky, s o f t and spongy, s t r i n g y , r i n g s h a k e d , p i t t e d , or crumbly. Decided d i s c o l o r a t i o n o r b l e a c h i n g o f the r o t t e d wood i s o f t e n apparent. I n c i p i e n t decay. The e a r l y stage o f decay t h a t has not p r o ceeded f a r enough t o s o f t e n o r o t h e r w i s e p e r c e p t i b l y i m p a i r t h e hardness o f the wood. I t i s u s u a l l y accompanied by a s l i g h t d i s c o l o r a t i o n o r b l e a c h i n g o f the wood. DIMENSIONAL STABILIZATION. S p e c i a l t r e a t m e n t o f wood t o reduce t h e s w e l l i n g and s h r i n k i n g t h a t i s caused by changes i n i t s m o i s t u r e c o n t e n t w i t h changes i n r e l a t i v e h u m i d i t y . EARLYWOOD. The p o r t i o n o f the annual growth r i n g t h a t i s formed d u r i n g the the e a r l y p a r t o f the growing season. I t i s u s u a l l y l e s s dense and weaker m e c h a n i c a l l y t h a n latewood. EDGE-GRAIN LUMBER. Another term f o r v e r t i c a l - g r a i n lumber. EXTRACTIVE. Substances i n wood, n o t an i n t e g r a l p a r t o f the c e l l u l a r s t r u c t u r e , t h a t can be removed by s o l u t i on i n hot o r c o l d w a t e r , e t h e r , benzene, o r o t h e r s o l v e n t s t h a t do not r e a c t c h e m i c a l l y w i t h wood components. FIBER SATURATION POINT. The s t a g e i n the d r y i n g o r w e t t i n g o f wood a t which the c e l l w a l l s a r e s a t u r a t e d and the c e l l c a v i t i e s f r e e from water. I t a p p l i e s t o an i n d i v i d u a l c e l l o r group o f c e l l s , not t o whole b o a r d s . I t i s u s u a l l y t a k e n as a p p r o x i m a t e l y 30 p e r c e n t m o i s t u r e c o n t e n t , based on ovendry w e i g h t . FINISH (FINISHING). Wood p r o d u c t s such as d o o r s , s t a i r s , and o t h e r f i n e work r e q u i r e d t o complete a b u i l d i n g , e s p e c i a l l y t h e i n t e r i o r . A l s o , c o a t i n g s o f p a i n t , v a r n i s h , l a c q u e r , wax, e t c . , a p p l i e d t o wood s u r f a c e s t o p r o t e c t and enhance t h e i r d u r a b i l i t y or appearance. FLAT-GRAINED WOOD. Lumber t h a t has been sawed p a r a l l e l t o the p i t h and a p p r o x i m a t e l y tangent t o the growth r i n g s . Lumber i s

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch022

22.

WILLIAMS

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c o n s i d e r e d f l a t g r a i n e d when the a n n u a l growth r i n g s make an a n g l e o f l e s s t h a n 45° w i t h the s u r f a c e o f the p i e c e . HEARTWOOD. The wood e x t e n d i n g from the p i t h t o the sapwood, the c e l l s o f which no l o n g e r p a r t i c i p a t e i n the l i f e p r o c e s s e s o f the t r e e . Heartwood may c o n t a i n p h e n o l i c compounds, gums, r e s i n s , and o t h e r m a t e r i a l s t h a t u s u a l l y make i t d a r k e r and more decay r e s i s t a n t t h a n sapwood. HEMICELLULOSE. A c e l l u l o s e l i k e m a t e r i a l ( i n wood) t h a t i s e a s i l y decomposable as by d i l u t e a c i d , y i e l d i n g s e v e r a l d i f f e r e n t simple sugars. LATEWOOD. The p o r t i o n o f the annual growth r i n g t h a t i s formed a f t e r the earlywood f o r m a t i o n has ceased. I t i s u s u a l l y denser and s t r o n g e r m e c h a n i c a l l y t h a n earlywood. LIGNIN. The second most abundant c o n s t i t u e n t o f wood, l o c a t e d p r i n c i p a l l y i n the secondary w a l l and t h e m i d d l e l a m e l l a , which i s the t h i n cementing l a y e r between wood c e l l s . Chemicallyi t i s an i r r e g u l a r polymer o f s u b s t i t u t e d p r o p y l p h e n o l groups, and thus no s i m p l e c h e m i c a l f o r m u l a can be w r i t t e n f o r i t . LUMEN. I n wood anatomy, the c e l l c a v i t y . MOISTURE CONTENT. The amount o f water c o n t a i n e d i n the wood, u s u a l l y e x p r e s s e d as a p e r c e n t a g e of the w e i g h t o f the ovendry wood. RADIAL. C o i n c i d e n t w i t h a r a d i u s from the a x i s o f the t r e e o r l o g t o the c i r c u m f e r e n c e . A r a d i a l s e c t i o n i s a l e n g t h w i s e s e c t i o n i n a p l a n e t h a t passes t h r o u g h the c e n t e r l i n e o f t h e t r e e t r u n k . QUARTERSAWED LUMBER. Another term f o r v e r t i c a l - g r a i n e d lumber. RELATIVE HUMIDITY. R a t i o o f the amount o f water vapor p r e s e n t i n the a i r t o t h a t which the a i r would h o l d a t s a t u r a t i o n a t the same t e m p e r a t u r e . I t i s u s u a l l y c o n s i d e r e d on the b a s i s o f the w e i g h t o f the vapor b u t , f o r a c c u r a c y , s h o u l d be c o n s i d e r e d on the b a s i s o f vapor p r e s s u r e s . SAPWOOD. The wood of p a l e c o l o r near the o u t s i d e o f the l o g . Under most c o n d i t i o n s the sapwood i s more s u s c e p t i b l e t o decay t h a n heartwood. SPRINGWOOD. (See EARLYWOOD.) SUMMERWOOD. (See LATEWOOD.) TANGENTIAL. S t r i c t l y , c o i n c i d e n t w i t h a t a n g e n t a t the c i r c u m f e r e n c e o f a t r e e o r l o g , or p a r a l l e l t o such a t a n g e n t . I n p r a c t i c e , however, i t o f t e n means r o u g h l y c o i n c i d e n t w i t h a growth r i n g . A t a n g e n t i a l s e c t i o n i s a l o n g i t u d i n a l s e c t i o n through a tree or l i m b p e r p e n d i c u l a r t o a r a d i u s . F l a t - g r a i n e d lumber i s sawed tangentially. VERTICAL-GRAINED LUMBER. Lumber t h a t has been sawed so t h a t the wide s u r f a c e s extend a p p r o x i m a t e l y a t r i g h t a n g l e s t o the annual growth r i n g s . Lumber i s c o n s i d e r e d v e r t i c a l - g r a i n e d when the r i n g s form an a n g l e o f 45° t o 90°with the wide s u r f a c e o f the piece. WEATHERING. The m e c h a n i c a l o r c h e m i c a l d i s i n t e g r a t i o n and d i s c o l o r a t i o n o f the s u r f a c e o f wood caused by exposure t o l i g h t , the a c t i o n o f d u s t and sand c a r r i e d by w i n d s , and the a l t e r n a t e s h r i n k i n g and s w e l l i n g . RECEIVED

January 2, 1986

23 Effect of Acid Rain on Woody Plants and Their Products Ellen T. Paparozzi

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch023

Department of Horticulture, University of Nebraska, Lincoln, NE 68583-0724 Acid rain has been shown to effect woody plants at all stages of their development. Seedlings, imma­ ture through older, fully expanded leaves and needles, as well as annual rings of woody plants have been shown to be injured by simulated acid rain. There has been research that suggests that the growth of trees could be affected if acid rain has a long term acidifying effect on soils. The ultimate implication of the effects of this pollutant as it impacts tree growth will be in terms of tree produc­ tivity and wood quality. This could influence products such as paper and wood for furniture, blight our landscape and affect roofs, decks, telephone poles, and fences. Little work has been done on the effect of acid rain on wood products. However, work on wood chemistry indicates that acid rain has the potential and the characteristics needed to be a destructive force to these materials.

Of a l l t h e o r g a n i c m a t e r i a l s mentioned d u r i n g t h i s c o n f e r e n c e , t r e e s a r e one o f t h e most m u l t i d i m e n s i o n a l . They impact o u r l i v e s v i s u a l l y , as w e l l as p h y s i c a l l y . They a r e a source o f r e c r e a t i o n , the k e y t o a v i t a l i n d u s t r y employing over a m i l l i o n p e o p l e , and p r o v i d e a haven and/or food source f o r w i l d l i f e * Until recently t r e e s have been taken f o r g r a n t e d i n o u r everyday l i v e s * The renewed p u b l i c i n t e r e s t i n woody p l a n t s , p a r t i c u l a r l y t r e e s , i s l a r g e l y due t o atmospheric p o l l u t a n t s , o f w h i c h a c i d r a i n i s one, w h i c h have been c a u s i n g s t r e s s and damage t o f o r e s t s here and i n Europe. A c i d p r e c i p i t a t i o n i s composed of b o t h d r y and wet d e p o s i t i o n . As d r y d e p o s i t i o n i s d i f f i c u l t t o measure, most c o l l e c t i o n s t u d i e s have c e n t e r e d on the wet d e p o s i t i o n . Q u a n t i t y , e l e m e n t a l p o s i t i o n and pH a r e r o u t i n e l y recorded by weather s t a t i o n s p a r t i c i p a t i n g i n t h e N a t i o n a l Atmospheric D e p o s i t i o n Program. R a i n i s made a c i d i c b y the a d d i t i o n o f C 0 , S 0 and Ν 0 , w i t h t h e S 0 and Ν Ο components b e i n g of g r e a t e s t concern. The p r o p o r t i o n s of S 0 t o Ν 0 v a r y a c r o s s t h e U n i t e d S t a t e s and a r e p r o j e c t e d t o f a v o r t h e i n c r e a s i n g of t h e Ν 0 component o f a c i d r a i n i n t h e f u t u r e . 2

2

χ

2

χ

2

χ

0097-6156/ 86/ 0318-0332S06.00/ 0 © 1986 American Chemical Society

χ

23.

PAPAROZZI

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Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch023

Trees can be impacted by a c i d r a i n i n any number of ways and these e f f e c t s can be c l a s s i f i e d as e i t h e r d i r e c t o r i n d i r e c t ( l j . The f o l l o w i n g d i s c u s s i o n w i l l p r e s e n t an o v e r v i e w of the many ways a c i d r a i n c o u l d a f f e c t woody p l a n t s s p e c i f i c a l l y as w e l l as u n f i n ished wood p r o d u c t s . POLLEN GERMINATION AND POLLEN TUBE GROWTH P o l l e n of n i n e f o r e s t t r e e s was c o l l e c t e d and c u l t u r e d on a medium t h a t had been a d j u s t e d , u s i n g d i l u t e s u l p h u r i c a c i d t o pH l e v e l s as low as 2.6. A r e d u c t i o n i n p o l l e n tube l e n g t h was observed i n sugar maple ( A c e r saccharutn) and quaking aspen ( Populus t r e m u l o i d e s c l o n e I I I ) a t a medium pH l e v e l of 4.0. At pH 3.6 and below sugar maple, a l l t h r e e c l o n e s of quaking aspen and paper b i r c h ( B e t u l a p a p y r i f e r a ) showed a d e c r e a s e i n p o l l e n g e r m i n a t i o n as w e l l as a r e d u c t i o n i n p o l l e n tube l e n g t h , w h i l e w h i t e p i n e ( P i n u s s t r o b u s ) showed o n l y a d e c r e a s e i n p o l l e n g e r m i n a t i o n . At pH 3.0, p o l l e n tube l e n g t h of w h i t e p i n e and Canadian hemlock (Tsuga c a n a d e n s i s ) was d e c r e a s e d , w i t h a l l s p e c i e s ( i n c l u d i n g Prunus pennsvlvanica» P i n u s r e s i n o s a % P i c ea m a r i a n a . and P i n u s b a n k s i a n a ) showing reduced p o l l e n g e r m i n a t i o n and p o l l e n tube growth ( 2 ) . Sidhu (3) found t h a t s i m u l a t e d a c i d r a i n of pH 3.6 c o u l d i n h i b i t p o l l e n g e r m i n a t i o n of w h i t e spruce by up t o 30% as w e l l as p o l l e n tube growth. In a f i e l d study i t was found t h a t , w h i l e s i m u l a t e d a c i d r a i n a t pH 2.5 damaged ' E m p i r e ' a p p l e b l s s o m s and r e d u c e d pollen g e r m i n a t i o n , i t d i d not i n f l u e n c e f r u i t s e t ( 4 ) . WOODY PLANT SEED GERMINATION G e r m i n a t i o n of woody p l a n t seed has been found t o be i n h i b i t e d o r s t i m u l a t e d by s i m u l a t e d a c i d r a i n . I n h i b i t i o n of red maple ( A c e r rubrum) seed g e r m i n a t i o n was found a t pH 4.0 and 3.0, w h i l e s t a g h o r n sumac (Rhus t v p h i n a ) seed g e r m i n a t i o n was i n h i b i t e d a t pH 3.0 ( 5 ) . However, seed from f l o w e r i n g dogwood (Cornus f l o r i d a ) . sugar maple ( Ac e r saccharum), red a l d e r ( Alnus r u b r a ) , American beech (Fagus grand i f o l i a ) . t u l i p - p o p l a r ( L i r i o d e n d r o n t u l i p i f e r a ) , and shagbark hickory (Carva ova t a ) d i d n o t g e r m i n a t e any d i f f e r e n t l y when exposed to pH l e v e l s of 3.0, 3.5, 4.0 o r 5.7 ( 5 ) . Raynal et a l . (6) a l s o found t h a t w h i l e seed g e r m i n a t i o n o v e r a l l was u n a f f e c t e d , when seeds were exposed t o pH 3.0 s i m u l a t e d a c i d r a i n , r a d i c a l e l o n g a t i o n was r e d u c e d , m o s t l y due t o b a c t e r i a l i n f e c t i o n . G e r m i n a t i o n of w h i t e p i n e ( P i n u s s t r o b u s ) ( 5_, 7 ) , E a s t e r n red c e d a r ( J u n i p e r u s v i r g i n i a n a ) and Douglas f i r (Pseudotsuga m e n z i e n s i i ) was s t i m u l a t e d by pK l e v e l s of 3.5 and 3.0 s i m u l a t e d a c i d rain (5). SYMPTOMS OF INJURY S e v e r a l woody p l a n t s p e c i e s w i l l r e a c t t o exposure of s i m u l a t e d a c i d r a i n by forming f o l i a r l e s i o n s . W h i l e the pH l e v e l of s i m u l a t e d a c i d r a i n t h a t p r o d u c e d t h e s e l e s i o n s v a r i e s from s p e c i e s t o s p e c i e s , t h e l e s i o n s t h e m s e l v e s a r e g e n e r a l l y y e l l o w t o brown n e c r o t i c s p o t s o r r e g i o n s ( s e e T a b l e 1)· A d d i t i o n a l l y , on two c l o n e s of p o p l a r , g a l l s were formed i n response t o s i m u l a t e d a c i d rain. S u r f a c e c h a r a c t e r i s t i c s such as s t o m a t a l presence and dens i t y , t r i c h o m e d e n s i t y , type and amount of e p i c u t i c u l a r wax, l e a f s u r f a c e w e t t a b i l i t y and b u f f e r i n g c a p a c i t y have a l l been shown t o i n f l u e n c e f o l i a r i n j u r y by s i m u l a t e d a c i d r a i n . However, i t may be

M A T E R I A L S D E G R A D A T I O N C A U S E D BY A C I D R A I N

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch023

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t h e i n t e r a c t i o n of any o r a l l of these f a c t o r s , i n a d d i t i o n t o l e a f / n e e d l e age t h a t d e t e r m i n e s the i n d i v i d u a l response by s p e c i e s t o pH l e v e l s of s i m u l a t e d a c i d r a i n ( 8 , 9, 10., 11 ) » L e a f i n j u r y d u r i n g one growing season may not be as c r i t i c a l t o d e c i d u o u s s p e c i e s as i t i s t o c o n i f e r o u s s p e c i e s * Paparozzi (12) f o u n d t h a t , d e s p i t e e x t e n s i v e l e a f i n j u r y t o young b i r c h t r e e s from s i m u l a t e d a c i d r a i n of pH 2.8 and 3.2, the r a t e of a b s c i s s i o n of i n j u r e d l e a v e s was not a c c e l e r a t e d . The f o l l o w i n g s p r i n g , the same p r e v i o u s l y i n j u r e d p l a n t s l e a f e d out and grew comparably t o the c o n t r o l p l a n t s and p l a n t s , w h i c h had r e c e i v e d s i m u l a t e d a c i d r a i n of pH 4.0 and 5.6. C o n i f e r o u s o r e v e r g r e e n s p e c i e s , however, w h i c h would hold t h e i r i n j u r e d n e e d l e s f o r up t o t h r e e y e a r s c o u l d show a g r a d u a l d e c l i n e i n growth due t o a r e d u c t i o n i n p h o t o s y n t h e s i s . The p r e v i o u s s t u d i e s and almost a l l of the s i m u l a t e d a c i d r a i n e x p e r i m e n t s d i s c u s s e d h e r e i n w e r e d e s i g n e d t o q u i c k l y produce symptoms and o b t a i n t h r e s h h o l d s f o r p l a n t i n j u r y . To d a t e t h e r e has been no documented f i e l d i d e n t i f i c a t i o n of ambient a c i d r a i n i n j u r y t o f o r e s t t r e e s or woody p l a n t s ( 8 ) . Among many p o t e n t i a l r e a s o n s , t h i s may be due e i t h e r t o the f a c t t h a t ambient a c i d r a i n i s o f t e n accompanied by o t h e r atmospheric p o l l u t a n t s , thus i n j u r y symptoms are d i f f e r e n t , or t h a t changes are o c c u r r i n g s u b t l y over time.

TABLE 1.

A p a r t i a l l i s t of woody p l a n t s w h i c h developed f o l i a r l e s i o n s a f t e r exposure t o s i m u l a t e d a c i d r a i n .

PLANT

CITATION

PH

A c e r saccharum Marsh A c e r rubrum L. Betula alleshaniensis B r i t t . Carva i l l i n o e n s i s (Wane.) Κ. K a l t Cornus f l o r i d a L. Liriodendron t u l i p i f e r a Malus h v p e h e n s i s (Pamp*) Pinus s t r o b u s L. Populus SPD* h y b r i d s Ouercus p h e l l o s Ouercus p r i n u s L. Ouercus r u b r a L. Rhododendron SPP. R o b i n i a p s e u d o a c a c i a L.

3.0 2.0 3.0 2.0

(13.) (14)

2.0 2.0 3.25 1.0 3.1 3.2 2.0 2.8 2.8 2.0

(14) (14) (16) (16) (II) (18) (14) (11) (19) (14)

(14)

LEACHING OF ELEMENTS FROM FOLIAGE Rain and m i s t , a c i d or o t h e r w i s e , have been shown t o l e a c h n u t r i e n t s from the f o l i a g e of woody p l a n t s (19)· Wood & Bormann (13) found t h a t when sugar maple s e e d l n g s were exposed to pH 3.0 ( l e a f i n j u r y ) , 3.3, and 4.0 of s i m u l a t e d a c i d r a i n , t h e r e were s i g n i f i c a n t i n c r e a s e s i n l e a c h i n g of K , Mg and Ca* i o n s * Cronan (21.) found t h a t i n c o n i f e r o u s t h r o u g h f a l l which was exposed t o ambient r a i n of pH 4*0, t h e r e was an i n c r e a s e i n H , Ca+, Mg , K+, Mn , S0^~» N0^~ and C I " as compared t o b u l k p r e c i p i t a t i o n . In c o n t r a s t , t h r o u g h f a l l +

+

+

+

+

PAPAROZZI

23.

+

+

from hardwoods showed i n c r e a s e s i n C a , Mg"*", K , SO^, NO^""; no change i n Mn+ and Cl"and a d e c r e a s e i n H compared t o b u l k p r e c i p i t ­ ation. W h i l e the exact i o n c o n c e n t r a t i o n s d i f f e r e d , g e n e r a l l y o t h e r r e s e a r c h e r s ( 2 2 , 2£, 2 4 ) , a l s o made s i m i l a r o b s e r v a t i o n s i n t h e i r f i e l d studies. S c h e r b a t s k o y and K l e i n ( 2 5 ) u s i n g s i m u l a t e d a c i d m i s t , found t h a t , i n a d d i t i o n t o l e a c h i n g o f K , C a and ΝΟβ~, amino a c i d s w e r e a l s o l e a c h e d a t pH 2.8. L e a c h i n g of c h l o r o p h y l l , 2 4"*» and c a r b o h y d r a t e s was n o t a f f e c t e d by v a r y i n g t h e m i s t pH l e v e l . A d d i t i o n a l l y , i t was found pH 4.3 s i m u l a t e d a c i d m i s t , a f t e r i t passed through y e l l o w b i r c h and w h i t e spruce t r e e s , became more acidic. They suggested t h a t t h i s may be due t o removal of d r y a c i d i c d e p o s i t s f r o m t h e l e a v e s . A l c o c k and M o r t o n (26.) a l s o found a d e c r e a s e i n the pH l e v e l of r a i n f a l l as i t passed through f i e l d s i t e s o f E u r o p e a n b i r c h ( E e t u l a pendula) and Scotch p i n e ( P i n u s s v l v e s t r i s ) . However, they suggest t h a t , i n a d d i t i o n t o the p r e v i o u s e x p l a n a t i o n , the i n c r e a s e i n a c i d i t y c o u l d be r e l a t e d t o t h e l e a c h i n g o f o r g a n i c a c i d s from t h e l e a v e s . Direct nutrient a v a i l a b i l i t y from l e a v e s t o t h e t r e e t e r m i n a t e s when l e a v e s a b s c i s e . H o w e v e r , l e a f l i t t e r around t h e base o f t h e t r e e c a n c o n t r i b u t e n u t r i e n t s back t o t h e s o i l as t h e l i t t e r decomposes. Hovland e t a l . (27.) used a c i d i f i e d w a t e r on Norway spruce n e e d l e s t o t e s t i t s e f f e c t on n u t r i e n t l e a c h i n g . They found t h a t K l e a c h i n g was i n c r e a s e d as w a t e r q u a n t i t y i n c r e a s e d the l e a c h i n g , w h i l e Mg + , Mn+ and Ca+ l e a c h i n g was i n c r e a s e d b y u s i n g w a t e r s o l u t i o n s of i n c r e a s e d a c i d i t y . A c i d i f i e d water decreased phosphate l e a c h i n g d u r i n g t h e f i r s t f o u r t e e n weeks of t h e e x p e r i m e n t , b u t then i n c r e a s e d l e a c h i n g a f t e r t h a t time. Hagvar and K j o n d a l (28) u s i n g w h i t e b i r c h ( B e t u l a v e r r u c o s a ) l e a v e s , a l s o found t h a t Ca+, M g and Mn were e f f e c t i v e l y removed from l e a f l i t t e r as t h e a c i d i t y o f t h e water s o l u t i o n increased. I n i t i a l l y , pH 3.0 and 2.0 i n c r e a s e d t h e decomposition r a t e . However, l a t e r i n t h e experiment i t was found t h a t t h e d e c o m p o s i t i o n r a t e was reduced a t pH 2.0. Both groups of r e s e a r c h e r s commented t h a t l e a c h i n g may be dependent on the sub­ s t a n c e t h a t i s b e i n g decomposed a t t h a t time and t h a t t h i s w i l l change over time as the l i t t e r decomposes. A d d i t i o n a l i n f o r m a t i o n on how l e a f l i t t e r p o t e n t i a l l y i n t e r a c t s w i t h a c i d r a i n was c o n t r i b u t e d by Lee & Weber ( 2 9 ) . In t h e i r e x p e r i m e n t s , a c i d r a i n was s i m u l a t e d i n a f i e l d s i t u a t i o n on sugar maple and r e d a l d e r . R a i n as t h r o u g h f a l l was a l l o w e d t o i n t e r a c t w i t h l e a f l i t t e r and the l e a c h a t e was c o l l e c t e d . L i t t e r leachate was found t o be h i g h e r i n SO^"", Ca+ and Mg + , and t h e pH was found t o have i n c r e a s e d . Thus, they h y p o t h e s i z e d t h a t t h e l i t t e r was n e u t r a l i z i n g the simulated a c i d r a i n , with red a l d e r l i t t e r being more e f f e c t i v e than sugar maple. +

H

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+

P0

+

+

+

SOIL EFFECTS The e f f e c t of a c i d r a i n on l e a f l i t t e r should be viewed i n c o n j u n c ­ t i o n w i t h t h e e f f e c t o f a c i d r a i n on t h e u n d e r l y i n g s o i l s . I f t h e c h e m i s t r y of s o i l s i s a f f e c t e d by a c i d r a i n d i r e c t l y o r through i n t e r a c t i o n w i t h t h e l e a f l i t t e r , this i n turn w i l l affect e l e m e n t s a v a i l a b l e t o woody p l a n t s . Of most c o n c e r n a r e t h e m a c r o n u t r i e n t s Ν, Ρ, Κ, S, Mg and Ca, as w e l l as elements t h a t may be t o x i c t o p l a n t s , such as A l . A c c o r d i n g t o Krug and F r i n k (30 %31 ) t h e r e a r e many m i s c o n c e p t i o n s about s o i l a c i d i t y . One o f these i s t h a t a c i d r a i n w i l l i n c r e a s e t h e a c i d i f i c a t i o n o f s o i l and w a t e r .

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T h i s comment c o n c u r s w i t h the o b s e r v a t i o n s of R i c h t e r et a l . (32) i n two f o r e s t ecosystems. They found at b o t h s i t e s t h a t s t r o n g a c i d s i n b u l k p r e c i p i t a t i o n were n e u t r a l i z e d by f o r e s t c a n o p i e s and the surface s o i l layers. T a b a t a b a i ( 3 ? ) t a g r e e i n g t h a t a d d i t i o n s of a c i d r a i n to s o i l s are probably i n s i g n i f i c a n t , notes t h a t s o i l f o r m a t i o n i s an a c i d i f y i n g p r o c e s s . S o i l s a l o n e produce sources of a c i d i t y by m i n e r a l i z a t i o n of o r g a n i c Ν & S, c a r b o n i c a c i d f o r m a t i o n and n i t r o g e n f i x a t i o n . S o i l s a l s o r e c e i v e sources of a c i d i t y i n the form of o r g a n i c a c i d s from l i t t e r d e c o m p o s i t i o n . Johnson et a l . ( 3 4 ) i n t h e i r review on c a t i o n l e a c h i n g by n a t u r a l p r o c e s s e s and a c i d d e p o s i t i o n , s t a t e t h a t i t d i d not appear t h a t a t m o s p h e r i c i n p u t s caused s i g n i f i c a n t l o s s e s of base c a t i o n s . This i s p r o b a b l y due t o the f a c t t h a t many s o i l s have a s u b s t a n t i a l buffering capacity. I f t h a t b u f f e r i n g c a p a c i t y i s exceeded by a c i d i n p u t s and i f l e a c h i n g l o s s e s of c a t i o n s are g r e a t e r than those p r o d u c e d by t h e w e a t h e r i n g of m i n e r a l s , then t h e r e w i l l be an i n c r e a s e i n s o i l a c i d i f i c a t i o n and w e a t h e r i n g . However, though t h i s occurrence may be r a r e , an example where i t c o u l d o c c u r would be p o o r l y b u f f e r e d s o i l s r e c e i v i n g l a r g e i n p u t s of a c i d d e p o s i t i o n

(21).

H o w e v e r , as K r u g and F r i n k (31.) and J o h n s o n e t a l . (34) r e s p e c t i v e l y p o i n t o u t , t h e i n f l u e n c e of changing land use and s u c c e s s i v e v e g e t a t i o n and f o r e s t management p r a c t i c e s w i l l need t o be a c c o u n t e d f o r . J o h n s o n e t a l . ( 3 5 ) go on t o s u g g e s t t h a t g e n e r a l i z a t i o n s about a c i d r a i n e f f e c t s w i l l have l i t t l e meaning. S i t e c o n d i t i o n s , amounts and types of i n p u t s w i l l v a r y and the r e s u l t may be a p o s i t i v e , n e g a t i v e or no e f f e c t on the f o r e s t ecosystem. An e x t e n s i v e r e v i e w of t h i s a r e a and i n t e r e s t i n g r e a d i n g i s found i n Evans et a l . (36)· ACID RAIN AND WOODY PLANT DISEASES AND INSECTS There i s l i t t l e p u b l i s h e d work on the r e l a t i o n s h i p between a c i d r a i n and i n s e c t s . However, Smith e t a l . (37) p o i n t out t h a t a number of damaging f o r e s t i n s e c t s d e t e c t and respond t o t r e e s under s t r e s s . E n v i r o n m e n t a l changes such as a c i d r a i n c o u l d cause t r e e s t r e s s . The i n s e c t s t h a t would b e a r o b s e r v a t i o n would be those t h a t spend a l l or p a r t of t h e i r l i f e c y c l e s on l e a v e s o r n e e d l e s , as t h a t i s where i n j u r y occurs and s u b s t a n c e s are l e a c h e d , or m i c r o a r t h r o p o d s i n h a b i t l e a f l i t t e r and s o i l . Research a d d r e s s i n g the e f f e c t of s i m u l a t e d a c i d r a i n on woody h o s t i d i s e a s e pathogen i n t e r a c t i o n s i s a l s o l i m i t e d . S h r i n e r (3 8) found t h a t oak t r e e s exposed t o pH 3.2 s i m u l a t e d a c i d r a i n had 84% l e s s t e l i a , produced by the oak-pine r u s t pathogens, compared t o the c o n t r o l . Bruck & Shafer (39) exposed l o b l o l l y p i n e ( P i n u s taeda) t o s i m u l a t e d a c i d r a i n of pH 5.6 to 2.4 and i n o c u l a t e d p l a n t s w i t h fusiform rust. Needle n e c r o s i s o c c u r r e d , w i t h n e c r o s i s formed on 60% of n e e d l e s exposed t o pH 2.4 as compared t o no n e e d l e n e c r o s e s a t pH 5.6. S i x months l a t e r they found s i g n i f i c a n t l y fewer r u s t g a l l s on n e e d l e s exposed t o the low pH l e v e l . They noted t h a t the b a s i d i o s p o r e o f f u s i f o r m r u s t p e n e t r a t e s through h e a l t h y n e e d l e tissue. W i t h f e w e r a r e a s of t h e n e e d l e l e f t a l i v e due t o the exposure t o s i m u l a t e d a c i d r a i n of pH 2.4, i n f e c t i o n was l e s s and t h u s , fewer r u s t g a l l s . T h e s e few experiments are not enough, however, t o d e f i n e the e f f e c t s of s i m u l a t e d a c i d r a i n on the woody h o s t i d i s e a s e pathogen

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PAPAROZZI

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interaction. As Evans ( 8 ) p o i n t s o u t , as y e t t h e r e a r e no e x p e r i m e n t a l f i e l d d a t a t h a t show t h a t the host:pathogen i n t e r a c t i o n s i g n i f i c a n t l y c h a n g e s p l a n t s u r v i v a l or p r o d u c t i v i t y . C e r t a i n l y , t h i s i s one of the more complex study a r e a s w i t h the i n t e r a c t i o n by the l e a f , the pathogen and the r a i n f a l l a l l b e i n g m u l t i d i m e n s i o n a l and ever c h a n g i n g , depending on the type of p l a n t and pathogen, stage of pathogen i n f e c t i o n , the l e a f s u r f a c e , the l e s i o n produced and the e l e m e n t a l l e a c h i n g from the l e a f by a c i d r a i n . Woody p l a n t s o f t e n a l s o have a s y m b i o t i c r e l a t i o n s h i p w i t h a m y c o r r h i z a l f u n g u s . M y c o r r h i z a e , of w h i c h t h e r e are two g e n e r a l t y p e s ; endomycorrhizae and e c t o m y c o r r h i z a e , are thought t o enhance n u t r i e n t u p t a k e , p a r t i c u l a r l y phosphorus. P r e l i m i n a r y work u s i n g l o b l o l l y p i n e s e e d l i n g s growing i n sand, e x p l o r e d the e f f e c t of s i m u l a t e d a c i d r a i n on the i n f e c t i o n of r o o t s by ec t o m y c o r r h i z a e . Shafer et a l . (40) found t h a t s i m u l a t e d a c i d r a i n of pH 4.0 and 3.2 was i n h i b i t i n g e c t o m y c o r r h i z a l i n f e c t i o n when compared t o r o o t s exposed t o pH 5.6. At pH 2.4 t h e r e appeared t o be s t i m u l a t o r y e f f e c t s on i n f e c t i o n . The a u t h o r s s u g g e s t e d t h a t i n c r e a s e d s o i l a c i d i t y was the cause of the enhanced e c t o m y c o r r h i z a l i n f e c t i o n , as o t h e r experiments have shown t h a t , i f s u b s t r a t e a c i d i t y i s i n c r e a s e d , so w i l l i n f e c t i o n . The a u t h o r s d i d c a u t i o n , however, t h a t t h i s s h o r t term greenhouse study was j u s t p r e l i m i n a r y . ACID RAIN AS A STIMULATOR AND INHIBITOR OF GROWTH Some r e s e a r c h e r s have r e p o r t e d t h a t , d e s p i t e n e e d l e o r l e a f i n j u r y a t low l e v e l s of s i m u l a t e d a c i d r a i n , growth of the p l a n t o c c u r r e d . Wood and Bormann (T) exposed w h i t e p i n e s e e d l i n g s t o s i m u l a t e d a c i d r a i n of pH 2.3, 3.0, 4.0 and 5.6. P l a n t s exposed to pH 3.0 and 4.0 had g r e a t e r t o t a l p l a n t and n e e d l e w e i g h t s than p l a n t s exposed t o pH 5.6. P l a n t s e x p o s e d t o pH 2.3 showed needle n e c r o s e s but had s i g n i f i c a n t l y g r e a t e r t o t a l p l a n t and n e e d l e w e i g h t s than any o t h e r treatment. R a y n a l et a l . (41.) found t h a t sugar maple s e e d l i n g s u n d e r n u t r i e n t - l i m i t e d c o n d i t i o n s showed f o l i a r damage and growth s t i m u l a t i o n at pH 3.0. B o t h groups suggest t h a t the N0^~ component may be r e s p o n s i b l e f o r g r o w t h s t i m u l a t i o n . H o w e v e r , t h i s i s q u e s t i o n a b l e , as Wood & Bormann p o i n t e d o u t , growth was a l s o accompanied by l e a c h i n g of K , Mg and C a . One would expect t h a t , f o r growth t o o c c u r , these e s s e n t i a l m a c r o n u t r i e n t s would need to be readily available. T v e i t e and Abraham (42) a l s o observed a s t i m u l a t i o n i n h e i g h t and d i a m e t e r of Scots p i n e s a p l i n g s when pH l e v e l s 2, 2.5 and 3.0 of s i m u l a t e d a c i d r a i n were s u p p l i e d . There were no e f f e c t s on Norway spruce or lodgepole pine. The authors suggested t h a t the growth of S c o t c h p i n e may be due t o i n c r e a s e d uptake of n i t r o g e n from the soil. The u l t i m a t e aim of a l l the a c i d r a i n r e s e a r c h was, and i s , to h e l p i d e n t i f y and c h a r a c t e r i z e a c i d r a i n i n j u r y so i t can be used t o a s s e s s i n j u r y t o woody p l a n t s i n f o r e s t s . This process has begun. U n f o r t u n a t e l y , we need the key now. The P i n e l a n d s of New J e r s e y , and the f o r e s t s i n the n o r t h e a s t e r n and s o u t h e a s t e r n U.S. and i n C e n t r a l Europe have shown a problem r e f e r r e d t o as a d e c l i n e . I n t h e P i n e B a r r e n s , J o h n s o n and co-workers (43.) found t h a t t w o - t h i r d s of the s h o r t l e a f , l o b l o l l y and p i t c h p i n e t r e e s sampled showed e i t h e r a n o t i c e a b l y abnormal or d r a m a t i c d e c r e a s e i n r i n g increment s i z e . T h i s d e c r e a s e d growth +

+

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occurred i n young and o l d t r e e s . P e s t s , ozone and w i l d f i r e were a b s e n t . U n f o r t u n a t e l y , when d a t a were a n a l y z e d , pH was s i g n i f i c a n t l y c o r r e l a t e d w i t h g r o w t h when c o m b i n e d w i t h many of the independent v a r i a b l e s . Thus, i t was d i f f i c u l t to s i n g l e out any one factor. However, the a u t h o r s f e l t t h a t summer d r o u g h t , a v a r i a b l e t h a t was f r e q u e n t l y c o r r e l a t e d w i t h growth and pH, c o u l d be e x a c e r b a t e d by a c i d r a i n . They f u r t h e r p o i n t e d out t h a t t h e r e was a c l e a r r e l a t i o n s h i p between stream pH and growth r a t e . Thus, a c i d r a i n should s t i l l be c o n s i d e r e d when e v a l u a t i n g t h i s s i t u a t i o n . In the n o r t h e r n A p p a l a c h i a n s , l a r g e numbers of red spruce have been d y i n g . T h i s has been o c c u r r i n g over the l a s t twenty y e a r s w i t h o u t any o b v i o u s p r o v o c a t i o n . Here a g a i n , Johnson and Siccama (44) found t h a t t h e r e was a d r a m a t i c d e c r e a s e i n t r e e r i n g increment s i z e i n the mid I960's i n 40% of the t r e e s sampled. They suggested t h a t t h i s r a t h e r abrupt s h i f t to narrow increments i s an i n d i c a t i o n of red spruce d e c l i n e . The a u t h o r s f e l t t h a t a c i d r a i n may be but one of s e v e r a l s t r e s s e s , p r o b a b l y p r e d i s p o s i n g the p l a n t to drought stress. Others s t r e s s e s t h a t c o u l d be i n v o l v e d i n c l u d e ozone, S O 2 , l o n g - t e r m change i n c l i m a t e , heavy m e t a l s and d r o u g h t . They a l s o noted t h a t drought i s one common f a c t o r i n the t r e e growth d e c l i n e s i n the Pine B a r r e n s , the n o r t h e r n A p p a l a c h i a n s and the German forests. In c e n t r a l Europe the f o r e s t d e c l i n e i s c a l l e d the 'Waldsterben' syndrome. The W a l d s t e r b e n syndrome i s of g r e a t c o n c e r n to the f o r e s t r y i n d u s t r y and the p u b l i c , e s p e c i a l l y i n West Germany ( 4 j ) . The f o r e s t e d a r e a t h a t i t has a f f e c t e d has i n c r e a s e d from about 8% i n 1982 t o 50% i n 1984. As S c h u t t and Cowling (46) n o t e d , t h i s phenomenon p o s s e s s e s s e v e r a l f e a t u r e s t h a t were d i f f e r e n t than the d e c l i n e i n the U.S., such as the f a c t t h a t i t a f f e c t s s i m u l t a n e o u s l y b o t h deciduous and c o n i f e r o u s t r e e s and t h a t a r a p i d d e c r e a s e i n h e a l t h and v i g o r o c c u r s o v e r a w i d e r a n g e o f e n v i r o n m e n t a l conditions. Symptoms i n c l u d e t h a t of w a t e r s t r e s s , growth d e c r e a s e and abnormal growth. The s t r e s s f a c t o r s i n d u c i n g the syndrome are unknown, but a c i d r a i n may be one. ACID RAIN EFFECTS ON UNFINISHED WOOD PRODUCTS M i l l i o n s of t r e e s are h a r v e s t e d a n n u a l l y and p r o c e s s e d i n t o v a r y i n g types of wood p r o d u c t s from paper to lumber. U n f i n i s h e d or raw wood p r o d u c t s no l o n g e r possess the p r o t e c t i v e o u t e r l a y e r , the b a r k , t h a t the t r e e does. Thus, the wood w h i c h i s n o r m a l l y p r o t e c t e d from a c i d r a i n i n the f o r e s t , now, as a wood p r o d u c t , w i l l be d i r e c t l y exposed t o the environment. T h e r e f o r e , i t i s i m p o r t a n t to c o n s i d e r the d i r e c t e f f e c t of a c i d r a i n on wood p r o d u c t s such as t e l e p h o n e p o l e s , f e n c e s , wood s i d i n g and s h i n g l e s . There was l i t t l e r e s e a r c h a v a i l a b l e i n the l i t e r a t u r e on the e f f e c t s of a c i d r a i n on wood p r o d u c t s . L e t t e r s to various u t i l i t y companies a l s o i n d i c a t e d t h a t t h e r e was l i t t l e work done i n t h i s area. However, the a v a i l a b l e l i t e r a t u r e w i l l be c i t e d and i n t e g r a t e d w i t h c u r r e n t knowledge i n the a r e a of wood s c i e n c e . E x t e n s i v e r e s e a r c h has been conducted u t i l i z i n g a c i d h y d r o l y s i s on wood i n o r d e r to i n v e s t i g a t e the c h e m i s t r y of wood and c o n v e r t wood to c e l l u l o s e and even f u r t h e r to g l u c o s e f o r t e c h n o l o g i c a l u t i l i z a t i o n ( 4 7 ) . However, c o n c e n t r a t i o n s of a c i d u s e d , even i n d i l u t e a c i d p r o c e d u r e s , are g e n e r a l l y much h i g h e r than found i n a c i d rain.

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch023

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H o v l a n d and A b r a h a m s e n ( i n 28) exposed c e l l u l o s e s h e e t s and s m a l l p i e c e s o f a s p e n wood ( P o p u l u s tremula) t o a r t i f i c i a l a c i d " r a i n " t o determine i t s e f f e c t on d e c o m p o s i t i o n . These m a t e r i a l s were p l a c e d on the l e a f l i t t e r i n t h r e e c o n i f e r o u s f o r e s t s i t e s . The o n l y r e s u l t was t h a t a p p l i c a t i o n of pH 2.5 w a t e r reduced the d e c o m p o s i t i o n r a t e of c e l l u l o s e i n one o f the s i t e s . Hon (48) i s c u r r e n t l y w o r k i n g on t h e d e g r e d a t i v e e f f e c t of a c i d r a i n on the s u r f a c e q u a l i t y of wood and has found t h a t a c i d r a i n does d e t e r i o r a t e wood. The e f f e c t s o f a c i d r a i n were f u r t h e r pronounced by the p r e s e n c e of UV l i g h t and m o i s t u r e , t h u s , a s y n e r g i s m . Hon has observed t h a t t h e s e f a c t o r s t o g e t h e r appear t o a f f e c t the exposed s u r f a c e b y c h a n g i n g t h e c o l o r of t h e wood, i t s u l t r a s t r u c t u r e , t e n s i l e s t r e n g t h and c h e m i c a l c o m p o s i t i o n . Banks e t a l . ( 4 9 ) * u s i n g t h i n and t h i c k s e c t i o n s of p i n e ( P i n u s s y l v e s t r i s ) and l i n d e n ( T i l i a v u l g a r i s ) . found s i g n i f i c a n t s t r e n g t h l o s s e s when 100 um l o n g i t u d i n a l s e c t i o n s were exposed t o d i l u t e a c i d s o l u t i o n s , p a r t i c u l a r l y s u l f u r o u s a c i d s o l u t i o n s . Using l a r g e r , transverse sections s i g n i f i c a n t l o s s i n mechanical propert i e s o c c u r r e d o n l y t o a d e p t h of about 0.5 mm. Thus, t h e wood s u r f a c e may be m o d i f i e d and t h i s c o u l d i n f l u e n c e the s u s c e p t i b i l i t y of s u r f a c e s . When a raw wood s u r f a c e i s exposed t o the environment, i t w i l l weather. W e a t h e r i n g , w h i c h c o n s i s t s of the wood t u r n i n g c o l o r and the g r a d u a l breakdown of t h e c e l l s and s u r f a c e of t h e wood, r e s u l t s f r o m t h e i n t e r a c t i o n o f f a c t o r s such as l i g h t ( p a r t i c u l a r l y UV) , water and w i n d . T h i s p r o c e s s i s not c o n s i d e r e d d e t r i m e n t a l and o f t e n wood s i d i n g on b u i l d i n g s remains u n t r e a t e d i n o r d e r t o a c h i e v e a g r a y , n a t u r a l l o o k (50)· However, t h e p o t e n t i a l of n o r m a l w e a t h e r i n g i n c o m b i n a t i o n w i t h a c i d r a i n a c c e l e r a t i n g the exposure of wood s u r f a c e s t o i n s e c t s and d i s e a s e s should not be overlooked. Under e n v i r o n m e n t a l c o n d i t i o n s , s o f t - r o t fungi w i l l slowly, g r a d u a l l y and p r o g r e s s i v e l y decay wood s u r f a c e s . A d d i t i o n a l l y , some f u n g i grow b e s t around pH 4.0 t o 6.0 w i t h some f u n g i apparently b e i n g a b l e t o change t h e pH of the wood s l i g h t l y as they grow ( 50). Thus, i t i s p o s s i b l e t h a t a c i d r a i n may i n f l u e n c e t h e i n v a s i o n of wood s u r f a c e s by some f u n g i , b u t t h i s w i l l a l s o depend on the type of wood. Not a l ] woods ty show a p r e d i s p o s i t i o n t o i n v a s i o n by d i s e a s e pathogens and i n s e c t s . As S c h e f f e r and Cowling (51.) p o i n t e d o u t , woods do v a r y i n t h e e x t e n t t o which they w i l l i n h e r e n t l y r e s i s t heartwood decay. C e r t a i n types of oak and redwood a r e r e s i s t a n t t o decay w h i l e some p i n e s , b i r c h e s and h i c k o r i e s a r e s l i g h t l y o r not r e s i s t a n t t o heartwood decay. Two of t h e members of t h i s s l i g h t l y o r not r e s i s t a n t decay c a t e g o r y d i d show s u r f a c e d e t e r i o r a t i o n i n work done by Banks et a l . ( 4 9 ) . I t seems f e a s i b l e t h a t wood from t h e s e t r e e s c o u l d b e a f f e c t e d by a c i d r a i n and p o s s i b l y o t h e r p o l l u t a n t s i n c o m b i n a t i o n w i t h l i g h t and w a t e r . The r e s u l t of t h i s m u l t i p l e f a c t o r i n t e r a c t i o n may then be impacted by i n s e c t s o r diseases. Whether wood p r o d u c t s made from t r e e s w h i c h have been i n j u r e d by a t m o s p h e r i c d e p o s i t i o n ( i n c l u d i n g d e c l i n e ) w i l l show reduced wood s t r e n g t h and d u r a b i l i t y t o t h e above f a c t o r s i s unknown. However, an i n f o r m a l w o r k i n g p a r t y w i t h i n the I n t e r n a t i o n a l A s s o c i a t i o n o f Wood A n a t o m i s t s has been formed t o h e l p address t h i s t o p i c . Baas

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Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch023

( 52) n o t e s t h a t r e s e a r c h i n t h i s a r e a s h o u l d i n c r e a s e i n t h e f u t u r e . As t r e e g r o w t h i n r e l a t i o n t o wood s t r u c t u r e i s a v e r y complex a r e a , i t i s i m p o r t a n t t h a t experienced researchers g e t i n v o l v e d so t h a t r a s h o r m i s l e a d i n g c o n c l u s i o n s a r e not the r e s u l t . The f i r s t endeavor of t h i s working p a r t y was t o c o m p i l e an annotated l i s t of s c i e n t i s t s working on a c i d r a i n and wood s t r u c t u r e . This e f f o r t w i l l c e r t a i n l y h e l p b r i n g t o g e t h e r i n t e r e s t e d s c i e n t i s t s and f u r t h e r focus research i n t h i s area. ASSESSMENT The r e s e a r c h a v a i l a b l e t o d a t e p r e s e n t s a p a r t i a l view of t h e impacts of a c i d r a i n on woody p l a n t s . Many o f t h e impacts a r e s t i l l o n l y ' p o t e n t i a l ' i m p a c t s , as s i m u l a t i o n s t u d i e s v e r s u s f i e l d s t u d i e s p r e s e n t a c o n f l i c t i n g view. However, one t h i n g appears q u i t e c l e a r - more r e s e a r c h i s needed. As many r e s e a r c h e r s have found, the e f f e c t of a c i d r a i n i s n o t g o i n g t o be one of s i m p l e cause and e f f e c t , b u t r a t h e r one of a m u l t i p l e f a c t o r i n t e r a c t i o n . Thus, f u t u r e work s h o u l d be s t a t i s t i c a l l y designed t o t e s t t h e i n t e r a c t i o n ( s ) r a t h e r than main e f f e c t s . Work needs t o be done over b o t h t h e s h o r t and long term t o a s s e s s i n j u r y . Basic physiological work a c r o s s d i s c i p l i n e s w i t h t h e s t a n d a r d i z a t i o n o f t e c h n i q u e s used ( e . g . one s e t type o f s i m u l a t o r f o r a l l r e s e a r c h e r s t o produce s i m u l a t e d a c i d r a i n ) must b e e m p l o y e d i n o r d e r f o r d i f f e r e n t e x p e r i m e n t a l r e s u l t s t o be comparable. I f we c a n d i s c o v e r how p l a n t s w i l l r e a c t t o g i v e n c o m b i n a t i o n s o f s t r e s s e s , o n l y then w i l l we be a b l e t o propose an a p p r o p r i a t e c o u r s e of a c t i o n . P u b l i s h e d a s P a p e r Number A g r i c u l t u r a l Experiment S t a t i o n .

7838,

Journal

Series,

Nebraska

LITERATURE CITED 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.

Tamm, C.O.; Cowling, E.B. Water, Air, Soil 1977, 503-512. Cox, R.M. New Phytol. 1983, 95, 269-276. Sidhu, S.S. Can. J. Botany 1983, 61, 3095-3099. Forsline, P.L.; Musselman, R.C.; Kender, W.J.; Dee, R.J. J. Amer. Hort. Sci. 1983, 108, 70-74. Lee, J.J.; Weber, D.E. Forest Sci. 1979, 25, 393-398. Raynal D.J.; Roman, J.R.; Eichenlaub, W. Environ. Exp. Bot. 1982, 22, 385-392. Wood, T.; Bormann, F.H. Water, Air, Soil 1977, 7, 479-488. Evans, L.S. Ann. Rev. Phytopath. 1984, 22, 397-420. Evans, L.S. Botan. Rev. 1984, 50, 449-490. Craker, L.E.; Bernstein, D. Environ. Poll. Ser. A. 1984, 36, 375-381. Paparozzi, E.T.; Tukey, H.B. Jr. J. Amer. Soc. Hort. Sci. 1983, 108, 890-898. Paparozzi, E.T. Ph.D. Thesis. Cornell University, Ithaca, NY. 1981. Wood, T.; Bormann, F.H. Ambio 1975, 4, 169-171. Haines, B.; Stefani, M; Hendrix, F. Water, Air, Soil 1980, 14, 403-407. Wood, T.; Bormann, F.H. Environ. Pollut. 1974, 7, 259-267. Forsline, P.L.; Dee, R.J.; Melios, R.E. J. Amer.Hort. Sci. 1983, 108, 70-74.

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch023

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341

17. Evans, L.S.; Gmur, N.F.; Da Costa, F. Phytopath. 1978, 68, 847-855. 18. Shriner, D.S. Water, Air, Soil 1977, 8, 9-14. 19. Keever, G.J. Ph.D. Thesis. Cornell University, Ithaca, N.Y., 1982. 20. Tukey, H.B. Jr. Ann. Rev. Plant Physiol. 1970, 21, 305-324. 21. Cronan, C.S. In "Indirect Effects of Acidic Deposition on Vegetation"; Teasley, J. Ed.; Acid Precip. Ser. 1984, 5, 65-79. 22. Eaton, J.S.; Likens, G.E.; Bormann, F.H. J. Ecol. 1973, 61, 495-508. 23. Hoffman, W.A. Jr.; Lindberg, S.E.; Turner, R.R. J. Environ. Qual. 1980, 9, 35-100. 24. Mollitor, A.V.; Raynal, D.J. Soil Sci. Soc. Amer.J. 1982, 46, 137-141. 25. Scherbatskoy, T.; Klein, R.M. J. Environ. Qual. 1983, 12, 189-195. 26. Alcock, M.R.; Morton, A.J. J. Appl. Ecol. 1981, 18, 835-839. 27. Hovland, J.; Abrahamsen, G.; Ogner, G. Plant and Soil 1980, 56, 365-378. 28. Hagvar, S.; Kjondal, B. Pediobio. 1981, 22, 232-245. 29. Lee, J.J.; Weber, D.E. J. Environ. Qual. 1982, 11, 57-64. 30. Krug, E.C.; Frink, C.R. Bulletin 811. The Conn. Ag. Exp. Station. 1983. 31. Krug, E.C.; Frink, C.R. Science 1983, 221, 520-525. 32. Richter, D.D.; Johnson, D.W.; Todd, D.E. J.Environ. Qual. 1983, 12, 263-270. 33. Tabatabai, M.A. Environ. Control 1985, 15, 65-110. 34. Johnson, D.W.; Richter, D.D.; Van Miegroet, H.; Cole, D. J. Air Poll. Con. Assc.1983. 3, 1036-1041. 35. Johnson, D.W.; Turner, J.; Kelly, J.M. Water Res. Res. 1982, 18, 449-461. 36. Evans, L.S.; Hendrey, G.R.; Stensland, G.J.; Johnson, D.W.; Francis, A.J. Water, Air, Soil 1981, 16, 469-509. 37. Smith, W.H.; Gebballe, G.; Fuhrer, J. In "Indirect and Indirect Effects of Acidic Deposition on Vegetation"; Teasley, J., Ed.; Acid Precip. Ser.1984, 5, 33-34. 38. Shriner, D.S., Phytopath. 1978, 68, 213-218. 39. Bruck, R.I.; Shafer, S.R. In "Indirect Effects of Acidic Deposition on Vegetation"; Teasley, J., Ed.; Acid Precip. Ser. 1984, 5, 19-32. 40. Shafer, S.R., Grand, L.F.; Bruck, R.I.; Heagle, A.S. Can. J. For. Res. 1984, 15, 66-71. 41. Raynal, D.J.; Roman, J.R.; Eichenlaub, W. Environ. Exp. Bot. 1982, 22, 385-392. 42. Tveite, B.; Abrahamsen, G. SNSF-contribution FA 29/78. 1978. 43. Johnson, A.H.; Siccama, T.C.; Wang, D.; Turner, R.S.; Barringer, T.H. Environ. Qual. 1981, 10, 427-430. 44. Johnson, A.H.; Siccama, T.G. Tappi J. 1984, 67, 68-72. 45. Steinbeck, K. Forestry 1984, 81, 719-720. 46. Schutt, P.; Cowling, E.B. Plant Disease 1985, 69, 1-9. 47. Wenzl, H.F.J. "The Chemical Technology of Wood"; Academic Press, NY. 1970. 48. Hon, D.N.-S. Amer. Chem. Soc. Abstr. 1985, Cell 0007, 0009. 49. Banks, W.B.; Evans, P.D. Amer. Chem. Soc. Abstr. 1985, Cell 0010.

342

MATERIALS

50. Haygreen, Science"; 51. Scheffer, 147-170. 52. Baas, P.

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch023

RECEIVED

DEGRADATION

CAUSED

BY ACID RAIN

J.G.; Bowyer, J.F. "Forest Products and Wood Iowa State Univ. Press, Ames, Iowa, 1982. T.C.; Cowling, E.B. Ann. Rev. Phytopath. 1966, 4, IAWA Bulletin

January 2, 1986

1984, 5, 316.

24 Acid Rain Degradation of Nylon 1

Karen E. Kyllo and Christine M . Ladisch

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch024

Textile Science, Consumer Sciences and Retailing Department, Purdue University, West Lafayette, IN 47907

Nylon 6,6 fabric exposed to simulated acid rain in light and darkness conditions showed polymer damage particularly when acids of pH 2.0 and 3.0 were used. This study reports the effects of sunlight, aqueous acid, heat and humidity (acid rain conditions) on spun delustered nylon 6,6 fabric. Untreated nylon and nylon treated with sulfuric acid pH 2.0, 3.0 and 4.4 were exposed to light in an Atlas Xenon-arc fadeometer at 63°C and 65% RH for up to 640 AATCC Fading Units. The untreated and acid treated fabrics were also exposed to similar temperature and humidity conditions without light. Nylon degradation was determined by changes in breaking strength, elongation, molecular weight and amine end group analysis. Physical damage was assessed using SEM.

Acidic precipitation is a growing environmental problem. Acid rain, snow or fog is formed when oxides of sulfur and nitrogen from fossil fuel combustion are oxidized in the atmosphere by ultra-violet light and ozone to give sulfuric and nitric acids. These acids then mix with atmospheric water to form acidic precipitation. Since the normal pH of atmospheric water is 5.6-5.7, precipitation having a pH below 5.6 is termed "acid rain" (J., 2). The pH values of acid rain have steadily dropped over the last 25 years. Areas east of the Mississippi River Valley which once had precipitation of pH 5.0 are now subject to precipita1

Current address: Department of Merchandising, Consumer Studies and Design, University of Vermont, Burlington, VT 05405 0097-6156/86/0318-0343$06.00/ 0 © 1986 American Chemical Society

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch024

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t i o n w i t h an average pH of 4.4-4-2. S i n g l e i n c i d e n t s of p r e c i p i t a t i o n w i t h pH's as low as 2.1 have a l s o been recorded (2-4). The d e l e t e r i o u s e f f e c t o f a c i d r a i n on l a k e s , aquatic ecosystems, and v e g e t a t i o n has been w i d e l y p u b l i c i z e d and i s undergoing c o n t i n u a l s t u d y Ç2, 4_, _5). Damage t o b u i l d i n g s and s y n t h e t i c m a t e r i a l s i s a l s o thought t o be s i g n i f i c a n t but i s not as w e l l documented. D e t e r i o r a t i o n of outdoor t e x t i l e s by a c i d r a i n i s r e f l e c t e d by reduced t e n s i l e and t e a r s t r e n g t h s and d i s c o l o r a t i o n o r s p o t t i n g (6,_7)· E v i d e n c e o f a c i d r a i n damage to t e x t i l e s i s c o m p l i c a t e d by the s y n e r g i s t i c e f f e c t s of o t h e r e n v i r o n m e n t a l f a c t o r s such as s u n l i g h t and h e a t . N y l o n f i b e r s a r e used e x t e n s i v e l y i n outdoor t e x t i l e s and as a r e s u l t a r e s u b j e c t t o s u n l i g h t , v a r y i n g temperatures and a c i d precipitation. The d e g r a d a t i o n of n y l o n by l i g h t , heat, h u m i d i t y and a i r p o l l u t e d w i t h s u l f u r d i o x i d e has been w i d e l y studied (8-13). However, l i t t l e d a t a i s a v a i l a b l e on the e f f e c t of aqueous a c i d on n y l o n i n the presence of h e a t , l i g h t and m o i s t u r e ( i . e . a c i d r a i n c o n d i t i o n s ) . T h e r e f o r e , the purpose of t h i s work was t o determine the e f f e c t o f a c i d r a i n c o n d i t i o n s on nylon. The s y n e r g i s t i c e f f e c t s of aqueous a c i d , l i g h t and heat on n y l o n were a l s o examined. Weathering o f N y l o n T e x t i l e s N y l o n i s r e a d i l y degraded by u l t r a v i o l e t r a d i a t i o n from s u n l i g h t (10, 14-15). A b s o r p t i o n of l i g h t i n the 270-280 and 300-340 nm r e g i o n of the e l e c t r o m a g n e t i c spectrum i s r e s p o n s i b l e f o r the m a j o r i t y o f the d e g r a d a t i o n of n y l o n 6,6 ( 1 5 ) . Exposure t o wavelengths o f r a d i a t i o n below 300 nm r e s u l t s i n p h o t o l y s i s and and exposure t o wavelengths o f r a d i a t i o n above 300 nm r e s u l t s i n photooxidation. The f r e e r a d i c a l r e a c t i o n s o f p h o t o l y s i s can r e s u l t i n c h a i n s c i s s i o n a t t h e amide l i n k a g e of the n y l o n polymer or c r o s s l i n k i n g between p o l y m e r i c c h a i n s ( 15, 1 7 ) . D e g r a d a t i o n o f n y l o n by p h o t o l y s i s i s independent o f oxygen, h e a t , m o i s t u r e o r additives. P h o t o o x i d a t i o n r e a c t i o n s o n l y take p l a c e i n the presence o f oxygen (15, 1 7 ) . These r e a c t i o n s a r e the p r i m a r y source o f most of the s u n l i g h t damage t o t e x t i l e s . P h o t o o x i d a t i o n of n y l o n and model compounds have shown t h a t oxidative attack usually produces f r e e r a d i c a l s , p e r o x i d e s , and u l t i m a t e l y polymer c h a i n s c i s s i o n . T h i s r e s u l t s i n lower t e n s i l e s t r e n g t h and u l t i m a t e l y a s h o r t e r u s e f u l l i f e t i m e of the t e x t i l e p r o d u c t . Heat, h u m i d i t y , a t m o s p h e r i c p o l l u t a n t s and d e l u s t r a n t s such as t i t a n i u m d i o x i d e a l s o h i g h l y i n f l u e n c e p h o t o o x i d a t i o n ( 9 , 15, 18). S t u d i e s on UV l i g h t - e x p o s e d n y l o n showed a decrease i n t e n s i l e s t r e n g h as the r e l a t i v e h u m i d i t y was i n c r e a s e d ( 19) and as the temperature was i n c r e a s e d ( 8 ) . D e l u s t e r e d n y l o n showed a g r e a t e r degree o f s t r e n g t h l o s s than n o n - d e l u s t e r e d n y l o n ( 10). E x p o s u r e o f n y l o n 6,6 f a b r i c t o 0.2 ppm SO^ g a s ( t h e c o n c e n t r a t i o n r e p r e s e n t a t i v e o f SO^ i n a p o l l u t e d atmosphere) also r e s u l t e d i n t e n s i l e strength l o s s (20).

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch024

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A l l of these a c c e l e r a t i n g e f f e c t s were found t o o c c u r o n l y i n the presence of l i g h t . S i n c e a c i d alone i s a l s o known t o degrade n y l o n ( 1 2 , 13) i t i s r e a s o n a b l e t o s u s p e c t a s y n e r g i s t i c a c t i o n by l i g h t , h u m i d i t y , h e a t , and aqueous a c i d ( i . e . a c i d r a i n c o n d i t i o n s ) on t h e c h e m i c a l and p h y s i c a l p r o p e r t i e s o f the nylon f a b r i c . One r e s e a r c h e r examined the r e s i s t a n c e o f n y l o n t o a c i d h y d r o l y s i s ( 1 5 % HC1 f o r 16 hours a t 50 C) a f t e r exposure t o l i g h t , heat and h u m i d i t y ( 1 3 ) . A c i d h y d r o l y s i s r e s u l t e d i n p o l y m e r i c damage comparable t o t h a t found i n n y l o n exposed t o l i g h t and 0.2 ppm SO under s i m i l a r c o n d i t i o n s . The amino end group c o n c e n t r a t i o n Π Ν Η ^ ] ) ( an i n d i c a t o r o f c l e a v a g e o f the amide l i n k a g e i n the n y l o n polymer) o f the a c i d h y d r o l y z e d n y l o n was, however, h i g h e r than t h a t o f the n y l o n exposed t o l i g h t and SO^» I t was concluded t h a t exposure t o S0^ gas i n the presence of l i g h t i n a humid atmosphere d i d not cause a c i d h y d r o l y s i s and t h a t the SO^ may not have been c o n v e r t e d t o 2 ^ 4 d u r i n g exposure p e r i o d . Another s t u d y i n d i c a t e d t h a t n y l o n 6,6 exposed t o l i g h t and SO^-contaminated a i r showed a 13% s t r e n g t h l o s s a f t e r 168 hours of exposure a t 40% h u m i d i t y . The s t r e n g t h l o s s was 39% when an 18 minute water spray e v e r y 2 hours was added t o the c o n d i t i o n s . Exposure w i t h 0.2 ppm SO^ r e s u l t e d i n 41% s t r e n g t h l o s s w i t h o u t water s p r a y and 68% w i t h water s p r a y , i n d i c a t i n g the s i g n i f i c a n t r o l e of SO^ and water i n the d e g r a d a t i o n p r o c e s s . SO^ i s thought t o Form s u l f u r i c a c i d i n the presence o f water and thus may c a t a l y z e c h a i n s c i s s i o n o f the n y l o n polymer (J3, 1 0 ) . I n an e f f o r t t o determine the e f f e c t o f aqueous a c i d on n y l o n i n the presence of l i g h t , Z e r o n i o n e t a l (12) submerged n y l o n f a b r i c i n 20% s u l f u r i c a c i d a t 50 C i n a f l i n t g l a s s j a r and exposed i t t o i r r a d i a t i o n from a 275 watt sunlamp a t a d i s t a n c e o f 6 i n c h e s from the f a b r i c . The n y l o n showed more polymer c h a i n s c i s s i o n and g r e a t e r [NH^] than n y l o n degraded by l i g h t and SO^ gas b o t h w i t h and w i t h o u t a water s p r a y . From these e x p e r i m e n t s , i t was concluded t h a t i f s u l f u r i c a c i d was p r e s e n t i n the atmosphere, i t s a t t a c k on n y l o n was a c c e l e r a t e d by the presence of l i g h t . Scanning e l e c t r o n m i s c r o s c o p y o f t h e f i b e r s exposed t o SO^, s u l f u r i c a c i d and l i g h t r e v e a l e d t h a t p h o t o d e g r a d a t i o n w i t h S0~ produced p i t t i n g of the f i b e r s u r f a c e . Combined a c i d and l i g h t c o n d i t i o n s a l s o r e s u l t e d i n f i b e r s u r f a c e p i t t i n g and roughness, whereas a c i d h y d r o l y s i s a l o n e d i d n o t produce p i t t i n g . I t was concluded t h a t the mode of d e g r a d a t i o n i n the presence o f s u l f u r i c a c i d and l i g h t was d i f f e r e n t from the a t t a c k by a c i d o r l i g h t alone U 2 , 2 1 ) . The purpose of t h i s s t u d y was t o examine the e f f e c t s o f l i g h t , h e a t , h u m i d i t y and aqueous a c i d on d e l u s t e r e d n y l o n 6,6. The d e g r a d a t i o n r e s u l t i n g from s e p a r a t e exposure t o l i g h t , h e a t , humidity and aqueous acid was compared with degradation r e s u l t i n g from combined exposure t o l i g h t , h e a t , h u m i d i t y and aqueous a c i d . The exposed n y l o n was e v a l u a t e d f o r d e g r a d a t i o n by measuring b r e a k i n g s t r e n g t h , v i s c o s i t y and [ΝΗ^]· Scanning e l e c t r o n microscopy was a l s o used t o c h a r a c t e r i z e the p h y s i c a l d e g r a d a t i o n i n the f i b e r . H

t n e

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M a t e r i a l s and Methods F a b r i c . A p l a i n weave f a b r i c ( T e s t f a b r i c s #361) made from spun, d e l u s t e r e d n y l o n 6,6 was used i n t h i s s t u d y . The f a b r i c was chosen because i t was r e p r e s e n t a t i v e of the type of n y l o n f i b e r u s e d o u t d o o r s and t h e t y p e o f f a b r i c u s e d i n previous p h o t o d e g r a d a t i o n s t u d i e s (21-23). The n y l o n f a b r i c was t r e a t e d w i t h s u l f u r i c a c i d because o f i t s n o n v o l a t i l e n a t u r e and because i t i s c o n s i d e r e d t o be a major c o n t r i b u t o r t o r a i n a c i d i t y ( p . F a b r i c samples measuring 27 c m ^ w a r p ) by 36 c m _ Ç f i l l ) were t r e a t e d w i t h 7.4 χ 10 , 0.9 χ 10 and 0.2 χ 10 p e r c e n t H S0^ s o l u t i o n s . These a c i d concentrations r e p r e s e n t pH v a l u e s o f 2.0, 3.0 and 4.4, r e s p e c t i v e l y , and a r e r e p r e s e n t a t i v e o f the range o f a c i d r a i n pH v a l u e s found i n the U.S. e a s t o f the M i s s i s s i p p i R i v e r ( 2 ) . The a c i d s o l u t i o n s were padded onto the f a b r i c w i t h a 50:1 l i q u o r - t o - g o o d s r a t i o t o produce a 78% wet p i c k - u p .

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch024

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Exposure t o Heat, L i g h t and H u m i d i t y . The a c i d - t r e a t e d and u n t r e a t e d c o n t r o l f a b r i c s were a t t a c h e d t o a T e f l o n screen (280u f i l a m e n t s , 33 f i l a m e n t s / i n c h , Tekco, I n c . , N.Y.), which was then c l i p p e d t o the specimen r a c k i n an A t l a s Xenon-arc Fadeometer model 25-FT. White cardboard was wrapped around the o u t s i d e c i r c u m f e r e n c e of the specimen rack to s e r v e as a s o l i d w h i t e , r e f l e c t i v e b a c k i n g f o r the samples. The s c r e e n and the cardboard d i d n o t touch one a n o t h e r . The Fadeometer was equipped w i t h a 2500 watt xenon-arc lamp and borosilicate i n n e r and o u t e r f i l t e r s . Conditions of exposure were 63 +3 C and 65 _+ 5% R.H. The f a b r i c s were exposed to l i g h t f o r 40, 80, 160, 320 and 640 AATCC F a d i n g U n i t s (AFU), as measured by AATCC B l u e Wool L i g h t f a s t n e s s Standards L - 5 , L-6, L-7, L-8 and L-9, r e s p e c t i v e l y . The f a b r i c s were padded w i t h a c i d i m m e d i a t e l y p r i o r t o each 40 AFU of l i g h t exposure. For example, f a b r i c s exposed f o r 80 AFU were padded w i t h a c i d a t o t a l o f 2 t i m e s ; f a b r i c s exposed t o 160 AFU were padded w i t h acid 4 times. N y l o n f a b r i c was a l s o exposed i n darkness t o the same temperature, h u m i d i t y and a c i d c o n d i t i o n s d e s c r i b e d above. The f a b r i c s were p l a c e d i n an A t l a s Gas Exposure C a b i n e t model GE-1RC. F i l t e r e d a i r was a l l o w e d t o f l o w through the c a b i n e t . For each t r e a t m e n t , f a b r i c s were exposed t o l i g h t and darkness s i m u l t a n e o u s l y t o i n s u r e e q u a l amounts of exposure. Following exposure, a l l fabrics were r i n s e d in distilled water, n e u t r a l i z e d i n 1.0% sodium c a r b o n a t e , r i n s e d a g a i n i n d i s t i l l e d water and a i r d r i e d . The f a b r i c s were then s t o r e d a t 21 + 1 C and 65 + 1% R.H. f o r a t l e a s t 24 hours.

E v a l u a t i o n o f F i b e r and F a b r i c P r o p e r t i e s . Breaking strengths of t h e c o n t r o l and t r e a t e d f a b r i c s were determined a c c o r d i n g t o ASTM D 1682, r a v e l l e d s t r i p method (24) u s i n g an I n s t r o n model 1130 equipped w i t h a 1,000 pound l o a d c e l l and a gear r a t i o of 1:1. F i v e c o n d i t i o n e d warp s t r i p s from each of two r e p l i c a t e s were t e s t e d f o r each e x p e r i m e n t a l c o n d i t i o n .

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Two r e p l i c a t e s from each o f the e x p e r i m e n t a l t r e a t m e n t s were e v a l u a t e d f o r changes i n v i s c o s i t y . Dilute solutions (0.10, 0.20, 0.30, 0.40 and 0.50 g/100ml) of n y l o n 6,6 d i s s o l v e d i n 90% f o r m i c a c i d were made. V i s c o s i t i e s of the d i l u t e polymer s o l u t i o n s were determined a t 25 +_ 0.1°C u s i n g a s i z e 75 Cannon-Fenske c a p i l l a r y v i s c o m e t e r . Flow time measurements were repeated f o r each s o l u t i o n and f o r the pure s o l v e n t u n t i l t h r e e c o n s e c u t i v e r e a d i n g s w i t h i n 0.2 seconds o r 0.1% o f the mean were o b t a i n e d ( 2 4 ) . The average o f the t h r e e c o n s e c u t i v e f l o w times was used t o determine the r e l a t i v e v i s c o s i t y f o r each s o l u t i o n . From the r e l a t i v e v i s c o s i t y , the reduced and i n h e r e n t v i s c o s i t i e s were c a l c u l a t e d and p l o t t e d a g a i n s t c o n c e n t r a t i o n . The l i n e o f b e s t f i t through each s e t o f p o i n t s was e x t r a p o l a t e d to z e r o t o determine the i n t r i n s i c v i s c o s i t y [ η]. The m o l e c u l a r weight (M) of the n y l o n was then c a l c u l a t e d a c c o r d i n g t o the Mark-Houwink e q u a t i o n , [η] = KM , where Κ = 3.5 χ 10 and a = 0.786. Amino end group c o n c e n t r a t i o n of the e x p e r i m e n t a l f a b r i c s was determined u s i n g t h e n i n h y d r i n method ( 2 5 ) . Three samples from each of the two r e p l i c a t e s f o r each e x p e r i m e n t a l c o n d i t i o n were a n a l y z e d . S u r f a c e c h a r a c t e r i s t i c s of the n y l o n 6,6 f i b e r s exposed t o acid rain c o n d i t i o n s were examined by s c a n n i n g electron microscopy (SEM). Nylon f a b r i c samples were a t t a c h e d t o an SEM mounting s t u b u s i n g c o n d u c t i v e silver paint. The mounted samples were sprayed w i t h an a n t i - s t a t i c s p r a y and a l l o w e d t o dry thoroughly. The samples were then s p u t t e r c o a t e d w i t h g o l d , a f t e r which the a n t i - s t a t i c spray was r e a p p l i e d and a l l o w e d t o dry. M i c r o g r a p h s were taken u s i n g a JSM-U3 SEM a t 10 KV a t m a g n i f i c a t i o n s o f 1000 and 3000 w i t h a P o l a r o i d camera. S t a t i s t i c a l Analyses. A n a l y s i s o f v a r i a n c e i n a nested f a c t o r i a l d e s i g n (BMDP) was used t o determine the i n f l u e n c e o f the type o f a c i d treatment and l e v e l o f exposure on the measured variables. T - t e s t s were a l s o used t o determine i f d i f f e r e n c e s e x i s t e d between l i g h t and dark exposed samples a t a g i v e n exposure l e v e l and a c i d t r e a t m e n t . A l l s t a t i s t i c a l evaluations were c a r r i e d o u t a t Ρ = 0.05. R e s u l t s And D i s c u s s i o n Breaking Strength. The b r e a k i n g s t r e n g t h o f the n y l o n was n o t significantly a f f e c t e d by e x p o s u r e to l i g h t o r by t h e c o m b i n a t i o n o f l i g h t and a c i d t r e a t m e n t s u n t i l a f t e r 80 AFU ( F i g u r e 1 ) . The l i g h t exposed c o n t r o l f a b r i c showed a l o s s i n b r e a k i n g s t r e n g t h of 2% a t 80 AFU, 8% a t 160 AFU and 13% a t 640 AFU. Thus, b r e a k i n g s t r e n g t h l o s s f o r the c o n t r o l f a b r i c was not as severe as expected from p r e v i o u s s t u d i e s ( 9 , 2 1 ) . B r e a k i n g s t r e n g t h l o s s e s between 39-75% have r e s u l t e d from l i g h t exposure a t 40% h u m i d i t y w i t h and w i t h o u t water s p r a y s ( 1 2 ) . The h i g h e r h u m i d i t y o f 65% i n t h i s study and the padding o f water on the f a b r i c a f t e r each 40 AFU of exposure s h o u l d have resulted i n larger strength losses according to a v a i l a b l e literature. The h i g h h u m i d i t y and e x t r a water may have been

American Chemical Society Library 1155 16th st N. nr. Wfi8hip«;:3P.

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r e s p o n s i b l e f o r observed i n c r e a s e s i n f a b r i c compactness due t o f i b e r s w e l l i n g and t h e r e f o r e lower s t r e n g t h l o s s e s . Light exposure and t r e a t m e n t of the n y l o n w i t h pH 4.4 and 3.0 ^SO^ a l s o produced r e l a t i v e l y s m a l l l o s s e s i n b r e a k i n g s t r e n g t h . The s t r e n g t h l o s s e s f o r the pH 4.4 and 3.0 a c i d t r e a t m e n t s a t 640 AFU were 14 and 6%, respectively. S t a t i s t i c a l a n a l y s i s of f a b r i c s t r e n g t h l o s s e s a f t e r 640 AFU i n d i c a t e d no s i g n i f i c a n t d i f f e r e n c e s among t h e c o n t r o l , pH 3.0 and pH 4.4 acid treatments. A f t e r 80 AFU of e x p o s u r e , the l o s s i n b r e a k i n g s t r e n g t h of the pH 2.0 t r e a t e d f a b r i c was g r e a t l y a c c e l e r a t e d . A f t e r 80 AFU of e x p o s u r e , the pH 2.0 o ^4 treatment significantly accelerated the l o s s i n breaking strength. The breaking s t r e n g t h l o s s e s of 16% at 160 AFU, 35% a t 320 AFU and 75% at 640 AFU r e s u l t e d i n an almost l i n e a r r e l a t i o n s h i p between amount of exposure and l o s s of s t r e n g t h . These s t r e n g t h l o s s e s were significantly greater than those observed for a l l other treatments. The r e l a t i v e l y steep s l o p e of the pH 2.0 s t r e n g t h l o s s c u r v e i s i n d i c a t i v e of c o n t i n u e d d e g r a d a t i o n beyond 640 AFU. The combined e f f e c t of a c i d , h e a t , and h u m i d i t y without l i g h t on the b r e a k i n g s t r e n g t h of n y l o n f a b r i c i s presented i n F i g u r e 2. The c o n t r o l and the a c i d t r e a t e d f a b r i c s exposed t o darkness w i t h heat and h u m i d i t y showed s t r e n g t h i n c r e a s e s . The s t r e n g t h of the pH 4.4, 3.0, 2.0 and c o n t r o l f a b r i c s i n c r e a s e d 0, 3, 7 and 15%, r e s p e c t i v e l y , a f t e r 640 hours of exposure. The i n c r e a s e , r a t h e r than a d e c r e a s e , i n b r e a k i n g s t r e n g t h over 640 AFU of exposure may have been due t o s h r i n k a g e brought about by the presence of m o i s t u r e r e s u l t i n g i n b u l k i e r , thus stronger yarns. The s h r i n k a g e of the yarns would r e s u l t i n a more compact f a b r i c and thus a g a i n i n b r e a k i n g s t r e n g t h . The e x t r a m o i s t u r e which would c o n t r i b u t e to f i b e r s w e l l i n g and hence s h r i n k a g e of the f a b r i c s t r u c t u r e would not be p r e s e n t t o the same degree i n the l i g h t exposed f a b r i c due to h i g h e r f a b r i c s u r f a c e temperature which would d r i v e o f f some of the m o i s t u r e . The e f f e c t of the h u m i d i t y on the b r e a k i n g s t r e n g t h of the fabrics exposed to dark c o n d i t i o n s was observed p r i m a r i l y between 40 and 160 u n i t s of exposure. The most d r a m a t i c d i f f e r e n c e s i n s t r e n g t h l o s s between the l i g h t and dark exposed samples o c c u r r e d i n the pH 2.0 samples and the c o n t r o l s ( F i g u r e 3 ) . From t h i s d a t a , i t i s e v i d e n t t h a t the a c i d t r e a t m e n t , even a t pH 2.0, had l i t t l e e f f e c t under darkness c o n d i t i o n s on the b r e a k i n g s t r e n g t h of n y l o n f a b r i c . The g a i n i n s t r e n g t h i n the darkness c o n d i t i o n s may be due t o s w e l l i n g of the f i b e r l e a d i n g to an i n c r e a s e i n b u l k and compactness of the f a b r i c w h i c h c o u l d r e s u l t i n the apparent s t r e n g t h i n c r e a s e s . However, the s y n e r g i s t i c e f f e c t of l i g h t on the h y d r o l y t i c a c t i o n of a c i d on n y l o n i s c l e a r l y i n d i c a t e d by the d i f f e r e n c e i n s t r e n g t h l o s s between the l i g h t and dark exposed pH 2.0 t r e a t e d f a b r i c s a f t e r 640 AFU. The a n t i c i p a t e d l o s s i n b r e a k i n g s t r e n g t h due to the a d d i t i v e e f f e c t of l i g h t and a c i d can be c a l c u l a t e d by adding the l o s s due t o l i g h t ( l i g h t c o n t r o l ) at 640 AFU and the l o s s due t o a c i d alone (dark pH 2.0 - dark c o n t r o l ) at 640 AFU. The a n t i c i p a t e d a d d i t i v e

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch024

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Acid Rain Degradation of Nylon

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch024

KYLLO A N D LADISCH

320 EXPOSURE UNITS

F i g u r e 2.

P e r c e n t change i n b r e a k i n g s t r e n g t h as a f u n c t i o n dark exposure. X Ι­ Ο Ζ LU OC Ι­ Ο) Ο Ζ

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no a d d , light Ρ. 2.0. light no acid, dark PH 2.0, dark 1

40 80

1

160

1

320

640

FA01NG UNITS

F i g u r e 3.

P e r c e n t change i n b r e a k i n g s t r e n g t h as a f u n c t i o n exposure.

350

M A T E R I A L S D E G R A D A T I O N C A U S E D BY A C I D RAIN

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch024

l o s s i n b r e a k i n g s t r e n g t h f o r the pH 2.0 t r e a t e d n y l o n a t 640 AFU was 22%. The a c t u a l l o s s a t 640 AFU was 75%. This i n d i c a t e d t h a t 53% o f the l o s s i n b r e a k i n g s t r e n g t h was due t o the s y n e r g i s t i c e f f e c t o f l i g h t on the h y d r o l y t i c a c t i o n of acid. M o l e c u l a r Weight. The p e r c e n t change i n m o l e c u l a r weight o f the n y l o n as a f u n c t i o n of l i g h t exposure i s p r e s e n t e d i n F i g u r e 4. A l l of the c o n t r o l and a c i d t r e a t e d n y l o n f a b r i c s e x h i b i t e d a s i g n i f i c a n t decrease i n m o l e c u l a r w e i g h t , p a r t i c u l a r l y a f t e r 80 AFU exposure. The r a t e of m o l e c u l a r weight l o s s up t o 640 AFU was s i m i l a r f o r the c o n t r o l , pH 3.0 and 4.4 f a b r i c s . The 28 and 21% d e c r e a s e s i n D.P. observed a f t e r 640 AFU f o r the pH 3.0 and 4.4 f a b r i c s , r e s p e c t i v e l y were n o t s i g n i f i c a n t l y d i f f e r e n t from one a n o t h e r . The pH 2.0 t r e a t e d sample e x h i b i t e d a much h i g h e r r a t e o f molecular weight loss as a f u n c t i o n of l i g h t exposure, p a r t i c u l a r l y a f t e r 80 AFU. As seen i n F i g u r e 4, the pH 2.0 sample had a 58% d e c r e a s e i n m o l e c u l a r weight a f t e r 640 AFU, which was 31% g r e a t e r than t h a t o f the c o n t r o l . For most p o l y m e r s , b r e a k i n g s t r e n g t h i s a f u n c t i o n of molecular weight. T h i s r e l a t i o n s h i p i s c l e a r l y i l l u s t r a t e d by comparison of F i g u r e s 1 (breaking strength loss) and 4 ( m o l e c u l a r weight l o s s ) . The r a t e and r e l a t i v e e x t e n t of b r e a k i n g s t r e n g t h and m o l e c u l a r weight l o s s e s due t o l i g h t exposure a r e almost i d e n t i c a l . M o l e c u l a r weight l o s s of the n y l o n was a l s o determined f o l l o w i n g exposure t o a c i d under darkness c o n d i t i o n s ( F i g u r e 5 ) . L i t t l e m o l e c u l a r weight l o s s o c c u r r e d i n the c o n t r o l , pH 3.0 and 4.4 t r e a t e d f a b r i c s up t o 640 exposure u n i t s . M o l e c u l a r weight l o s s of 19% f o r the pH 2.0 f a b r i c a t 640 exposure u n i t s was the o n l y s i g n i f i c a n t change observed i n the d a r k exposed f a b r i c s a t 640 exposure u n i t s . The r a t e and r e l a t i v e e x t e n t o f b r e a k i n g s t r e n g t h and m o l e c u l a r weight l o s s e s due t o darkness exposure were not h i g h l y c o r r e l a t e d . The h i g h h u m i d i t y produced a p h y s i c a l change i n the f a b r i c which a f f e c t e d the breaking s t r e n g t h of the f a b r i c but not the change i n m o l e c u l a r weight due t o c h a i n s c i s s i o n . The p e r c e n t m o l e c u l a r weight l o s s e s observed f o r the c o n t r o l and pH 2.0 t r e a t e d f a b r i c as a f u n c t i o n o f l i g h t and d a r k exposure a r e p r e s e n t e d i n F i g u r e 6. The change i n m o l e c u l a r weight o f the c o n t r o l a f t e r 640 AFU exposure was 1% i n the d a r k and 27% i n the l i g h t . Under the same 640 u n i t s of d a r k and l i g h t c o n d i t i o n s , the pH 2.0 t r e a t e d samples had 19 and 58% decreases i n molecular weight, r e s p e c t i v e l y . I f the e f f e c t s of l i g h t and a c i d on n y l o n were p u r e l y a d d i t i v e , a 45% m o l e c u l a r weight l o s s would be e x p e c t e d . However, a 58% m o l e c u l a r weight l o s s was o b s e r v e d , l e a d i n g t o the c o n c l u s i o n t h a t l i g h t a c t s s y n e r g i s t i c a l l y w i t h the a c i d t o degrade the n y l o n and was r e s p o n s i b l e f o r the 13% d i f f e r e n c e between the a c t u a l and a d d i t i v e m o l e c u l a r weight changes. Amino End Group C o n c e n t r a t i o n . P r e v i o u s work on the d e g r a d a t i o n of n y l o n has shown t h a t the [ΝΗ ] o f n y l o n d e c r e a s e d i f the ?

Acid Rain Degradation of Nylon

KYLLO AND LADISCH

320

Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch024

FADING UNITS

F i g u r e 4.

P e r c e n t change i n m o l e c u l a r weight as a f u n c t i o n o f l i g h t exposure.

10

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