Acidification of Precipitation - American Chemical Society

1 Acidification of Precipitation Β. Ottar

Downloaded by 80.82.77.83 on May 22, 2018 | https://pubs.acs.org 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

Baboian; Materials Degradation Caused by Acid Rain ACS Symposium Series; American Chemical Society: Washington, DC, 1986.


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Acidification of Precipitation

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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.


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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 .


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


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Acidification of Precipitation

T a b l e 1. Example of exchange of s u l p h u r p o l l u t a n t s between European countries (2). S

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Acidification of Precipitation - American Chemical Society

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