Chapter 17
Rainwater Chemistry near an Isolated SO Emission Source 2
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Richard J. Vong , Timothy V. Larson , William H. Zoller , David S. Covert , Robert J. Charlson , Ian Sweet, Richard Peterson , Theresa Miller , John F. O'Loughlin , and Margaret N. Stevenson 4
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Department of Civil Engineering, University of Washington FX-10, Seattle, WA 98195 Department of Environmental Health, University of Washington FX-10, Seattle, WA 98195 Department of Chemistry, University of Washington FX-10, Seattle, WA 98195 Department of Atmospheric Sciences, University of Washington FX-10, Seattle, WA 98195
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A network of 38 rainwater collection sites was established in the Seattle-Tacoma area of W a s h i n g t o n S t a t e b o t h u p w i n d and downwind o f t h e d o m i n a n t regional SO emission s o u r c e , a c o p p e r smelter. R a i n w a t e r s a m p l e s were chemically analyzed f o r p H , m a j o r i o n s and trace m e t a l s (via I N A A ) . Results a r e p r e s e n t e d f o r a precipitation e v e n t s a m p l e d by t h e n e t w o r k on F e b r u a r y 1 4 - 1 5 1 9 8 5 . Two collectors were o p e r a t e d a t e a c h site with these paired results statistically screened for potential c o n t a m i n a t i o n b a s e d on i n d p e n d e n t l y measured e x p e r i m e n t a l uncertainties. Geographical mapping o f r a i n w a t e r concentrations demonstrated a clear enhancement o f Η , e x c e s s SO =, and trace m e t a l s downwind o f t h e smelter. Principal component analysis revealed the influence of seasalt, crustal material, and a component interpreted t o r e p r e s e n t s m e l t e r SO and trace metal emissions. 2
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It is important to improve our understanding of the complex r e l a t i o n s h i p s between emissions and subsequent d e p o s i t i o n of atmospheric s u l f u r compounds. These r e l a t i o n s h i p s are d i f f i c u l t to examine i n the northeastern United States and i n c e n t r a l Europe because the r e l a t i v e c o n t r i b u t i o n s of l o c a l and d i s t a n t emissions vary. In the Puget Sound area of Washington State clean background a i r (1) moves i n l a n d from the P a c i f i c Ocean past a r e l a t i v e l y small number of emission sources. Most p r e c i p i t a t i o n f a l l s as r a i n and i s a s s o c i a t e d with c y c l o n i c f r o n t a l systems which r e s u l t i n steady southwesterly a i r flow a l o f t . The combination of a c l e a n background, very few s u l f u r sources, and c o n s i s t e n t meteorology suggests that rainwater source-receptor r e l a t i o n s h i p s may be simpler i n the Puget Sound area than elsewhere. 0097-6156/87/0349-0204$06.00/0 © 1987 American Chemical Society
Johnson et al.; The Chemistry of Acid Rain ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
17.
Rainwater
VONG ET AL.
Chemistry
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The two major S0 emission sources i n Western Washington are a copper smelter l o c a t e d i n Tacoma, WA. (4 kg/sec S0 ) and a c o a l f i r e d power p l a n t l o c a t e d near Centralia,WA. (1.7 kg/sec S 0 ) . A d d i t i o n a l S0 sources i n the Seattle-Tacoma area t o t a l about 50 percent of the s m e l t e r s S0 emissions. The approach taken to observe the impact of the copper smelter on mesoscale v a r i a t i o n s rainwater composition was to determine the s p a t i a l , temporal, and experimental components of the v a r i a b i l i t y of a number of appropriate chemical s p e c i e s i n the rainwater. This paper presents r e s u l t s f o r 1985, during smelter o p e r a t i o n , and i n c l u d e s : (1) estimates of the experimental v a r i a b i l i t y i n chemical composition, (2) an approach f o r a two step chemical and s t a t i s t i c a l screening of the data s e t , (3) the s p a t i a l v a r i a t i o n i n rainwater composition f o r a storm c o l l e c t e d on February 14-15, and (4) a p r i n c i p a l component a n a l y s i s of the rainwater concentrations to help i d e n t i f y source f a c t o r s i n f l u e n c i n g our samples. 2
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Experimental A network of 38 rainwater sampling s i t e s was e s t a b l i s h e d upwind and downwind of the copper smelter i n the Seattle-Tacoma area of Washington State. F i g u r e 1 shows the l o c a t i o n of the rainwater sampling s i t e s , the copper smelter, and urban areas of Western Washington S t a t e . Storms sampled by t h i s network were p r e - s e l e c t e d based on synoptic m e t e o r o l o g i c a l information i n an attempt to sample c y c l o n i c f r o n t a l r a i n t h a t was f a i r l y uniform over the 80 km. extent of our network. The sampling p r o t o c o l r e q u i r e d that a p e r i o d of good atmospheric v e n t i l a t i o n preceed r a i n sampling. Dry d e p o s i t i o n was not evaluated but i s expected to be small compared to wet d e p o s i t i o n due to low ambient p o l l u t a n t concentrations during r a i n y weather. Surface wind speed and d i r e c t i o n from s i x s i t e s were a v a i l a b l e at four hour i n t e r v a l s during the 24 hour sample c o l l e c t i o n . These data i n d i c a t e that surface winds i n the Tacoma-Seattle area were c o n s i s t e n t l y southwesterly at 10 knots on February 14-15. A rawindsonde confirmed southwesterly flow a l o f t . F r o n t a l p r e c i p i t a t i o n as r a i n occurred with the mean r a i n f a l l accumulation across the network of 0.5 cm. i n a 3 hour p e r i o d . Hydrogen ion was computed from measurements of pH on the u n f i l t e r e d rainwater samples. The samples were then f i l t e r e d and chemically analyzed by i n d u c t i v e l y coupled argon plasma emission spectroscopy (ICP) f o r the s o l u b l e f r a c t i o n of Na, Mg, Ca, K, Fe, and Zn, by in chromatography (IC) f o r NO^ , C l , SO^ , Na , and NH. , by flameless atomic absorption spectroscopy (AAS) f o r Pb, and by instrumental neutron a c t i v a t i o n a n a l y s i s (INAA) f o r the s o l u b l e f r a c t i o n of Na, A l , T i , Ca, Cu, V, Mn, In, Br, Sb, As, and Au. 50 ml of the f i l t e r e d =
Johnson et al.; The Chemistry of Acid Rain ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
THE CHEMISTRY OF ACID RAIN
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rainwater was f r o z e n , f r e e z e - d r i e d to r e s i d u e , r e - d i s s o l v e d i n U l t r e x HNO^ and d e i o n i z e d H 0, t r a n s f e r e d to polyethylene Bags, and again f r e e z e - d r i e d to r e s i d u e f o r INAA. I r r a d i a t i o n with thermal neutrons was performed at the Los Alamos Omega West r e a c t o r . The f i r s t i r r a d i a t i o n (shorts) was f o r 5 minutes with a f l u x of 6 * 10 n/cm /sec. Later there was a s e c o n d , i r r a d i a t i o n (longs) f o r 4 hours with a f l u x of 9.7 * 10 n/cm /sec. Shorts were counted on a Ge(Li) d e t e c t o r f o r 5 minutes a f t e r a 5 min. decay and f o r 19 min. a f t e r a 20 min. decay. Longs were counted on a Ge detector f o r 4 hours a f t e r a 3-5 day decay and 8 hours a f t e r a 30 day decay. The f i l t e r s used to remove p a r t i c u l a t e matter from the rainwater samples a l s o were analyzed by INAA to determine the i n s o l u b l e f r a c t i o n of t r a c e metal s p e c i e s . Two pre-washed (ΗΝΟ^, then repeated d i s t i l l e d , d e i o n i z i e d H 0 r i n s e s u n t i l c o n d u c t i v i t y was l e s s than 1 uS/cm) funnel and b o t t l e c o l l e c t o r s were deployed at each s i t e i n response to a weather f o r e c a s t . The s i t e s were operated by community c o l l e g e students, S e a t t l e Water Department personnel, high school teachers and students, and U n i v e r s i t y of Washington personnel. At one ' c o n t r o l s i t e which we operated ourselves a t a r e p r e s e n t a t i v e but p a r t i c u l a r l y i d e a l l o c a t i o n (behind a locked gate on a l a r g e grassy f i e l d which was w e l l removed from t r a f f i c and combustion s o u r c e s ) , ten c o - l o c a t e d samples were c o l l e c t e d to determine the uncontaminated· experimental u n c e r t a i n t i e s . These measurements q u a n t i f y the o v e r a l l experimental u n c e r t a i n t i e s due to the r a i n sampler p r e p a r a t i o n , handling, and t r a n s p o r t to the f i e l d s i t e , rainwater c o l l e c t i o n , sample f i l t r a t i o n and storage, and the a n a l y t i c a l procedures. Table 1 presents these u n c e r t a i n t i e s f o r the 10 c o - l o c a t e d samplers. For r a i n amount, H , S0 "~, As, Sb, Mg, Cl"", and NO^" the measured f i e l d c o l l e c t i o n and chemical a n a l y s i s combined u n c e r t a i n t i e s represented 4-13 percent of the measured c o n c e n t r a t i o n s . For Na , Pb, and Ca the measured u n c e r t a i n t i e s represented 22-26 percent of the measured concentrations.
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Data Screening The p a i r e d samples which were c o l l e c t e d at each s i t e were compared to the r e s u l t s of the 10 sampler experiment to d e t e c t samples of poor q u a l i t y . This procedure was u t i l i z e d to insure than experimental u n c e r t a i n t i e s d i d not c o n t r i b u t e to the observed v a r i a t i o n i n composition. The variance f o r each species l i s t e d i n Table 1 from the c o n t r o l s i t e was s t a t i s t i c a l l y compared to the variance f o r the p a i r e d samples at a l l s i t e s with an F - t e s t . One of the p a i r e d measurements at a s i t e was r e j e c t e d i f t h e i r variance was s i g n i f i c a n t l y (p
