Sources of Airborne Calcium in Rural Central Illinois - ACS Publications

17 Sources of Airborne Calcium in Rural

Downloaded by UNIV OF MASSACHUSETTS AMHERST on May 26, 2018 | https://pubs.acs.org Publication Date: October 13, 1981 | doi: 10.1021/bk-1981-0167.ch017

Central Illinois DONALD F. GATZ, G A R Y J. STENSLAND, and MICHAEL V . MILLER Atmospheric Chemistry Section, Illinois State Water Survey, P.O. Box 5050, Station A , Champaign, IL 61820 ALISTAIR C. D. LESLIE Department of Oceanography, Florida State University, Tallahassee, F L 32305 In a search for sources o f alkaline m a t e r i a l s i n r u r a l air and rain, we have sampled and performed multi-element analyses on ambient particulate matter and p o t e n t i a l source m a t e r i a l s . Ambient a e r o s o l s were sampled daily u s i n g s i n g l e N u c l e p o r e ™ filters or F l o r i d a State U n i v e r s i t y " s t r e a k e r s . " Samples of soil and unpaved road m a t e r i a l s were a l s o coll e c t e d and a n a l y z e d . The samples were analyzed by v a r i o u s multi-element methods, i n c l u d i n g i o n -and proton-induced X-ray emission and X-ray f l u o r escence, as w e l l as by atomic absorption s p e c t r o photometry. V i s u a l o b s e r v a t i o n s , as w e l l as airborne elemental c o n c e n t r a t i o n distributions with wind direction and elemental abundances in aerosols and source m a t e r i a l s , suggested that soil and road dust both c o n t r i b u t e to airborne Ca. F a c t o r a n a l y s i s was able to i d e n t i f y o n l y a "crustal" source, but a simple mass balance suggested that roads are the major source o f Ca in rural c e n t r a l Illinois in summer. The s o u r c e s o f p a r t i c l e s i n t h e a t m o s p h e r e a r e o f much current i n t e r e s t . T h i s i s t r u e from t h e v i e w p o i n t o f b o t h t h e g e o - a t m o s p h e r i c s c i e n t i s t and t h e p o l l u t i o n c o n t r o l specialist. For the atmospheric chemist o r geochemist, the i d e n t i t i e s and t h e r e l a t i v e c o n t r i b u t i o n s o f s o u r c e s a r e i m p o r t a n t f o r u n d e r s t a n d i n g 1) a t m o s p h e r i c e l e m e n t c y c l e s and b u d g e t s , and 2) t h e c h e m i c a l c o n t e n t o f p r e c i p i t a t i o n . The p o l l u t i o n c o n t r o l d e c i s i o n - m a k e r must know t h e r e l a t i v e c o n t r i b u t i o n s o f n a t u r a l and s p e c i f i c man-made s o u r c e s o f t o x i c m a t e r i a l s i n order to e s t a b l i s h c r i t e r i a f o r c o n t r o l regulations. The o b j e c t i v e o f t h i s work was t o i d e n t i f y c a l c i u m s o u r c e s and t h e i r r e l a t i v e c o n t r i b u t i o n s i n r u r a l c e n t r a l I l l i n o i s as a step toward understanding the r o l e o f a i r b o r n e a l k a l i n e 0097-6156/81/0167-0303$05.75/0 © 1981 A m e r i c a n C h e m i c a l Society

Macias and Hopke; Atmospheric Aerosol ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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materials i n l o c a l p r e c i p i t a t i o n chemistry. The a p p r o a c h was one o f f i e l d c o l l e c t i o n o f a m b i e n t a e r o s o l s and s o u r c e mat e r i a l s f o l l o w e d by measurement o f t h e i r c h e m i c a l c o m p o s i t i o n . The d a t a w e r e i n t e r p r e t e d u s i n g a v a r i e t y o f methods i n c l u d i n g examination of element c o n c e n t r a t i o n v a r i a t i o n s w i t h wind d i r e c t i o n , f a c t o r a n a l y s e s , and c h e m i c a l e l e m e n t b a l a n c e s .


Procedures Samples o f a m b i e n t a e r o s o l and s o u r c e m a t e r i a l s w e r e c o l l e c t e d d u r i n g t h e summer and f a l l o f 1978 a t t h e W a t e r S u r v e y ' s a t m o s p h e r i c c h e m i s t r y s a m p l i n g s i t e , 10 km s o u t h w e s t o f Champaign-Urbana, I l l i n o i s . A map o f t h e i m m e d i a t e v i c i n i t y o f t h e s a m p l i n g s i t e i s shown i n F i g u r e 1. The g r o u n d s i t e i s a g r a s s y f i e l d , m e a s u r i n g 120 χ 240 m and s u r r o u n d e d by c o r n and s o y b e a n f i e l d s . The tower u s e d f o r s a m p l i n g i s 35 m h i g h and l o c a t e d 360 m t o t h e s o u t h e a s t of the ground s i t e . A l t h o u g h t h e two s i t e s a r e n o t c o i n c i d e n t , we e x p e c t c o n d i t i o n s on t h e t o w e r t o be r e p r e s e n t a t i v e o f t h o s e 35 m above t h e g r o u n d s i t e , e x c e p t on r a r e and b r i e f o c c a s i o n s when t h e t o p o f t h e t o w e r i s i n t h e plume f r o m a t r a c t o r engaged i n t i l l i n g o r h a r v e s t i n g o p e r a t i o n s . A m b i e n t A e r o s o l s . A e r o s o l s w e r e sampled b o t h c o n t i n u o u s l y , u s i n g F l o r i d a S t a t e U n i v e r s i t y " s t r e a k e r " s a m p l e r s ( 1 ) , and on a d a i l y b a s i s . The s t r e a k e r s a m p l e r s draw a i r t h r o u g h a s t r i p o f 0.4 ym p o r e d i a m e t e r N u c l e p o r e ™ f i l t e r e x p o s e d f a c e downward. The s a m p l e r u s e s a vacuum o r i f i c e w h i c h moves t h e l e n g t h o f t h e s t r i p o f f i l t e r a t a r a t e o f 1 mm h r " ^ , t h u s p r o v i d i n g one week's sample i n a " s t r e a k " 168 mm l o n g . We o p e r a t e d one s t r e a k e r s a m p l e r a b o u t 1 m above a g r a s s y f i e l d a t o u r g r o u n d s i t e ( F i g u r e 1) and a n o t h e r on t o p o f t h e t o w e r d e s c r i b e d a b o v e . Samples w e r e a n a l y z e d i n 2-hr t i m e i n c r e m e n t s u s i n g p r o t o n i n d u c e d X - r a y e m i s s i o n ( P I X E ) (2) a t F l o r i d a State University. D a i l y 1 2 - h r f i l t e r s a m p l e s w e r e c o l l e c t e d on p r e w e i g h e d 37 mm d i a m e t e r N u c l e p o r e ™ f i l t e r s w i t h 0.8 ym p o r e d i a m e t e r s . These f i l t e r s were r e - w e i g h e d a f t e r s a m p l i n g t o o b t a i n t o t a l p a r t i c l e mass. T o t a l mass was u s e d as t h e b a s i s o f t h e e l e m e n t a l mass f r a c t i o n s d e s c r i b e d l a t e r , and i s known t o w i t h i n a few percent. One s e t o f f i l t e r s was c o l l e c t e d f a c e down u n d e r an i n v e r t e d f u n n e l r a i n s h i e l d a b o u t 1.5 m above g r a s s . Another s e t was c o l l e c t e d i n a s p e c i a l l y - m a d e d e v i c e we c a l l a v a n e sampler. I t c o n s i s t s of a p l a s t i c ( p o l y v i n y l c h l o r i d e ) t u b e w i t h a g r a d u a l 90° bend and a c o n s t r i c t e d o p e n i n g designed to provide q u a s i - i s o k i n e t i c sampling of p a r t i c l e s a t w i n d s p e e d s o f a b o u t 4 m sec""^-. I t i s p r o v i d e d w i t h a t a i l f i n and i s f r e e t o r o t a t e a b o u t a v e r t i c a l a x i s , so i t a l w a y s f a c e s i n t o t h e w i n d . E l e m e n t a l a n a l y s i s o f t h e s e f i l t e r s was performed a t Crocker Nuclear L a b o r a t o r y , U n i v e r s i t y of



GATZ E T A L .

-WASHED

Sources

of Airbourne

Calcium

in

Illinois

305

GRAVEL-

, TAR & CRUSHED

h i CLOSED BRIDGE WEAK

/ U - T A R & CRUSHED

'/X TOWER SITE

LIMESTONE

I CRUSHED

'

ONE LANE

CONCRETE

ONE LANE

BLACKTOP

LIMESTONE

.CRUSHED

L .

"T TAR & WASHED

LIMESTONE

GROUND SITEi

LIMESTONE

ONE LANE CONCRETE, ONE LANE TAR & CRUSHED LIMESTONE

GRAVELl

-ONE

MILEx

T W O

LANES CONCRETE

Figure 1. Map of the sampling site and the surrounding area showing ground and tower sampling sites and road surface characteristics. During the growing season the area is planted exclusively in corn and soybeans.


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C a l i f o r n i a - D a v i s , u s i n g i o n - e x c i t e d X-ray f l u o r e s c e n c e ( 3 , 4 ) . F u r t h e r d e t a i l s o f t h e d a i l y N u c l e p o r e ™ s a m p l i n g and a n a l y s i s p r o c e d u r e s w e r e g i v e n i n an e a r l i e r p u b l i c a t i o n ( 5 ) . H o u r l y w i n d d i r e c t i o n s w e r e o b t a i n e d f r o m measurements made by F e d e r a l A v i a t i o n A g e n c y p e r s o n n e l a t t h e U n i v e r s i t y o f I l l i n o i s W i l l a r d A i r p o r t , a b o u t 8 km e a s t o f t h e s a m p l i n g site. Source M a t e r i a l s . Two c a t e g o r i e s o f l o c a l s o u r c e m a t e r i a l s w e r e s a m p l e d - r o a d d u s t and s o i l . Samples o f b u l k s o i l w e r e removed f r o m t h e u p p e r 1 0 cm o f t h e s o i l c o l u m n a t 74 l o c a t i o n s o v e r p o r t i o n s o f t h e 1 km c e n t e r e d on t h e g r o u n d s i t e . A square g r i d s p a c i n g of 160 m ( 0 . 1 0 mi) between sampling l o c a t i o n s was u s e d . B e f o r e a n a l y s i s , the samples were a i r d r i e d , c r u s h e d , and s i e v e d t o remove t h e l a r g e r p a r t i c l e s (>53 ym d i a m e t e r ) w h i c h w o u l d n o t be l i k e l y t o be r a i s e d by t h e w i n d . Road m a t e r i a l s w e r e g a t h e r e d f r o m 9 l o c a t i o n s on u n p a v e d roads i n the v i c i n i t y of the sampling s i t e . At each l o c a t i o n , d u s t f r o m t h e r o a d b e d was s c r a p e d i n t o a p o l y e t h y l e n e s a m p l e bag f r o m 5 o r more s p o t s o v e r a 1 0 m a r e a . T h e s e m a t e r i a l s w e r e a l s o a i r d r i e d and s i e v e d i d e n t i c a l l y t o t h e s o i l m a t e r i a l s , but not crushed. V i s u a l i n s p e c t i o n s of the road s u r f a c e suggested t h a t samples from 8 of the 9 s i t e s were p r i m a r i l y c r u s h e d l i m e s t o n e r o c k . The r e m a i n i n g s i t e c o n s i s t e d p r i m a r i l y o f washed g r a v e l d e r i v e d f r o m g l a c i a l d e p o s i t s . An i n v e n t o r y o f u n p a v e d r o a d s u r f a c e m a t e r i a l s w i t h i n 5 km o f t h e s a m p l i n g s i t e i n d i c a t e d t h a t a p p r o x i m a t e l y 80% c o n s i s t e d o f c r u s h e d limestone. A n a l y s i s o f b o t h s o i l and r o a d d u s t f o r A l , S i , K, T i , and Fe was p e r f o r m e d a t t h e I l l i n o i s S t a t e G e o l o g i c a l S u r v e y , u s i n g X-ray f l u o r e s c e n c e techniques ( 6 ) . Ca and Κ w e r e d e t e r mined a t the Water Survey by a t o m i c a b s o r p t i o n s p e c t r o p h o t o m e t r y (AAS) f o l l o w i n g L 1 B O 3 f u s i o n t o d i s o l v e t h e s a m p l e Ç7, 8). The Κ a n a l y s e s e m p l o y e d a n a i r / a c e t y l e n e f l a m e , b u t i t was f o u n d n e c e s s a r y t o u s e ^ O / a c e t y l e n e f o r a c c u r a t e r e s u l t s on Ca. A s e r i e s of four standard s o i l s , which are c e r t i f i e d r e f e r e n c e m a t e r i a l s f r o m t h e Canada C e n t r e f o r M i n e r a l and E n e r g y T e c h n o l o g y , O t t a w a , was a n a l y z e d by t h e A A S / f u s i o n p r o c e d u r e t o a s s u r e t h a t i t gave s a t i s f a c t o r y r e s u l t s . Excellent a g r e e m e n t w i t h recommended v a l u e s was o b t a i n e d . I n t e r c a l i b r a t i o n o f t h e two l a b o r a t o r i e s u s e d f o r t h e s o u r c e m a t e r i a l s a n a l y s e s was a c c o m p l i s h e d b y t h e p a r a l l e l a n a l y s e s o f K. Again, e x c e l l e n t a g r e e m e n t was a c h i e v e d . 2

2

F a c t o r A n a l y s e s . A n a l y s e s were c a r r i e d o u t on e l e m e n t a l c o n c e n t r a t i o n s i n a i r (ng m~^), o r e l e m e n t a l a b u n d a n c e s ( p e r c e n t o f t o t a l mass). B o t h k i n d s o f d a t a were s t a n d a r d i z e d by sub t r a c t i n g t h e e l e m e n t mean f r o m t h e o b s e r v e d v a l u e and d i v i d i n g by t h e e l e m e n t s t a n d a r d d e v i a t i o n . Computations were c a r r i e d o u t u s i n g t h e f a c t o r a n a l y s i s p r o g r a m f r o m t h e BMDP B i o m e d i c a l



17.

GATZ E T AL.

Sources

of

Airbourne

Calcium

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307

Computer P r o g r a m s ( 9 ) . I n i t i a l f a c t o r s w e r e e x t r a c t e d u s i n g a p r i n c i p a l components s o l u t i o n . The number o f f a c t o r s t o be k e p t f o r r o t a t i o n t o a f i n a l s o l u t i o n was s e l e c t e d f r o m a p l o t o f t h e v a r i a n c e e x p l a i n e d by e a c h f a c t o r ( i t s e i g e n v a l u e ) v e r s u s i t s o r d i n a l number. U s u a l l y , f a c t o r s w i t h e i g e n v a l u e s l a r g e r t h a n a b o u t 1.0 w e r e k e p t . F i n a l s o l u t i o n s w e r e o b t a i n e d u s i n g Varimax r o t a t i o n s . R e s u l t s a r e p r e s e n t e d i n terms o f t a b l e s o f " l o a d i n g s . " L o a d i n g s a r e c o r r e l a t i o n c o e f f i c i e n t s b e t w e e n v a r i a b l e s and factors. T h u s , e l e m e n t s w i t h h i g h l o a d i n g s on t h e same f a c t o r t e n d t o v a r y i n a p a r a l l e l manner and may o f t e n be i n f e r r e d t o have common s o u r c e s . The sum, a c r o s s t h e f a c t o r s , o f t h e s q u a r e s o f t h e l o a d i n g s , i s c a l l e d t h e c o m m u n a l i t y , and i n d i c a t e s t h e f r a c t i o n o f an e l e m e n t s t o t a l v a r i a n c e t h a t i s a c c o u n t e d f o r by a l l t h e f a c t o r s . 1

Chemical Element general relationship

Balances.

The method i s b a s e d on

the

P. = Σ p.. C. ι . i j J

, (1) 1 N

w h i c h e x p r e s s e s t h e p e r c e n t a g e P^ o f any e l e m e n t i i n t h e a e r o s o l as a sum o f t e r m s i n v o l v i n g P j 4 , t h e p e r c e n t o f e l e m e n t i i n t h e p a r t i c u l a t e m a t t e r e m i t t e d by s o u r c e j , and C j , t h e f r a c t i o n o f the t o t a l a e r o s o l c o n t r i b u t e d by s o u r c e j . F o r a d d i t i o n a l d i s c u s s i o n o f t h e method, s e e ( 1 0 ) . We assume h e r e t h a t s o i l and r o a d s a r e t h e o n l y n o n - n e g l i g i b l e s o u r c e s o f Κ and Ca a t o u r r u r a l s i t e , so t h a t P

P

Ca

Ca,

soil

C

soil

+

p

Ca,

C

roads

roads

and P

K,

soil ^soil

+

P

K,

roads

C

roads

!

We h a v e measured t h e P s and t h e p ' s , so we may s o l v e t h e s i m u l taneous e q u a t i o n s f o r C ^ and C j . The p e r c e n t c o n t r i b u t i o n o f s o i l t o t h e a i r b o r n e Ca i s t h e n 100 p i i Csoil/ Ca. T h i s method, a l t h o u g h s i m p l e , i s j u s t i f i e d i n t h i s c a s e b e c a u s e the two s o u r c e s c o n s i d e r e d a r e t h e o n l y m a j o r o n e s , and b e c a u s e the a b u n d a n c e s o f Ca and Κ a r e s i m i l a r , r e q u i r i n g no n o r m a l i z a t i o n , as i s sometimes n e e d e d ( 1 0 ) . Once t h e C s h a v e b e e n computed, t h e y may be u s e d w i t h t h e m e a s u r e d p's o f o t h e r e l e m e n t s t o compute t h e P's f o r t h o s e elements. These may by compared t o o b s e r v e d v a l u e s as a c h e c k on t h e r e s u l t s . The o b s e r v e d s o u r c e c o m p o s i t i o n s ( p ' s ) u s e d i n t h e c a l c u l a t i o n s , and t h e mean e l e m e n t a l a b u n d a n c e s ( P ' s ) o f t h e 36 a e r o s o l s a m p l e s f o r w h i c h C's w e r e computed s e p a r a t e l y , a r e g i v e n i n T a b l e 1. s o i

r o a c

s

p

C a

s

o

f


ATMOSPHERIC

308 Table I .

Mean a b u n d a n c e s o f c r u s t a l e l e m e n t s i n a e r o s o l s , s o i l , and r o a d d u s t i n a r u r a l a r e a n e a r Champaign, I L . p

i

p-L,


soil

p

roads*

i 5

%

%

5.1

1.30

% Al

1.8

Si

6.7

Κ

0.78

1.75

Ca

2.2

0.70

Ti

0.24

0.42

0.08

1.3

2.2

1.29

Fe

AEROSOL

13.1

35

*Assuming a l l unpaved road

0.52 25

surfaces are crushed

limestone

Results D i s t r i b u t i o n o f C o n c e n t r a t i o n s b y Wind D i r e c t i o n . The good t i m e r e s o l u t i o n o f t h e s t r e a k e r d a t a means t h a t s i n g l e 2 - h r t i m e segments o f t e n r e p r e s e n t a v e r y n a r r o w r a n g e o f w i n d d i r e c t i o n s . This i s p o t e n t i a l l y important f o r source i d e n t i f i c a t i o n , s i n c e i t a l l o w s one t o examine v a r i a t i o n s o f c o n c e n t r a t i o n s a s a f u n c t i o n of wind d i r e c t i o n . T a b l e I I shows o v e r a l l mean c o n c e n t r a t i o n s o f t h e c r u s t a l e l e m e n t s Ca, A l , S i , and Κ f o r f o u r s a m p l i n g p e r i o d s i n 1 9 7 8 , and F i g u r e s 2 t o 5 show v a r i a t i o n s of c o n c e n t r a t i o n w i t h wind d i r e c t i o n during these p e r i o d s . F i g u r e 2 shows r e s u l t s a t t h e g r o u n d s i t e f o r a one-week p e r i o d i n J u n e , when c r o p s ( c o r n and s o y b e a n s ) w e r e s h o r t enough t o a l l o w t h e g e n e r a t i o n o f s o i l a e r o s o l s t h r o u g h c u l t i v a t i o n and w i n d e r o s i o n . F i g u r e 3 shows r e s u l t s f r o m t h e t o w e r s a m p l e r f o r a two-week p e r i o d i n J u l y when c r o p s w e r e m a t u r e . C u l t i v a t i o n s h o u l d h a v e b e e n a b s e n t , and w i n d e r o s i o n very l i m i t e d , during t h i s period. F i g u r e 4 and 5 show r e s u l t s f o r a p e r i o d d u r i n g and a f t e r h a r v e s t , i n O c t o b e r and November, 1978. G e n e r a t i o n o f s o i l a e r o s o l by t i l l i n g was o b s e r v e d , and w i n d e r o s i o n was p o s s i b l e , d u r i n g t h i s p e r i o d because o f the removal of the crop cover f r o m t h e s o i l s u r f a c e . F i g u r e 4 shows r e s u l t s o f t h r e e weeks o f s a m p l e c o l l e c t i o n f r o m t h e g r o u n d s i t e , and F i g u r e 5 shows r e s u l t s f r o m f o u r weeks o f s a m p l i n g on t h e t o w e r .


17.

GATZ

ET

Table

Sources

AL.

II.

of

Airbourne

in

Illinois

309

Mean c o n c e n t r a t i o n s o f f o u r i m p o r t a n t c r u s t a l e l e m e n t s i n f o u r a e r o s o l sample g r o u p s .

e

periods June, ground Downloaded by UNIV OF MASSACHUSETTS AMHERST on May 26, 2018 | https://pubs.acs.org Publication Date: October 13, 1981 | doi: 10.1021/bk-1981-0167.ch017

Calcium

Mean C o n c e n t r a t i o n s , ng Ca

Al

Si

m' Κ

82

1930

780

3600

730

J u l y , tower

169

640

160

810

350

Fall,

ground

249

1990

520

1850

620

Fall,

tower

332

1800

490

1420

610

N o t e i n F i g u r e 2 t h a t SSE w i n d s p r o d u c e d t h e maximum Ca c o n c e n t r a t i o n s , w i t h s m a l l e r v a l u e s f r o m t h e SSW, a t g r o u n d l e v e l i n J u n e , w h e r e a s t h e o r d e r was r e v e r s e d f o r t h e o t h e r three c r u s t a l elements. This suggests a d i f f e r e n t primary s o u r c e f o r Ca t h a n f o r A l , S i , and Κ d u r i n g t h i s p e r i o d . The l i m e s t o n e g r a v e l r o a d 1 km SE ( s e e F i g u r e 1 ) , w h i c h we observed to p r o d u c e a d e n s e w h i t e c l o u d o f l i m e s t o n e d u s t f r o m v e h i c l e t r a f f i c i n d r y w e a t h e r , i s a l i k e l y Ca s o u r c e . The l i m e s t o n e g r a v e l r o a d t o t h e w e s t i s n o t a p p a r e n t i n F i g u r e 1, p e r h a p s b e c a u s e o f l e s s t r a f f i c due t o a weak b r i d g e . The most o b v i o u s f e a t u r e o f t h e J u l y t o w e r d a t a i n F i g u r e 3 i s the o v e r a l l drop i n the c o n c e n t r a t i o n s of a l l f o u r elements. This i s c o n s i s t e n t w i t h the i d e a t h a t t a l l crops i n h i b i t wind e r o s i o n or c o l l e c t eroded m a t e r i a l w i t h i n the crop canopy. It i s a l s o c o n s i s t e n t w i t h a decrease i n concentration w i t h height, w h i c h w o u l d be e x p e c t e d f o r m a t e r i a l s h a v i n g t h e i r s o u r c e a t t h e surface. However, t h e d e c r e a s e was much more t h a n was observed b e t w e e n t h e g r o u n d and t o w e r s i t e s i n t h e f a l l ( F i g u r e s 4 and 5 ) , and t h u s w o u l d a p p e a r t o h a v e an a d d i t i o n a l c a u s e b e s i d e t h e e l e v a t i o n d i f f e r e n c e . I n J u l y ( F i g u r e 3) t h e maximum c o n c e n t r a t i o n s a p p e a r e d f r o m t h e SE ( t h e d i r e c t i o n o f t h e n e a r e s t l i m e s t o n e g r a v e l r o a d ) f o r Ca and two o f t h e o t h e r t h r e e c r u s t a l elements. (K c o n c e n t r a t i o n s w e r e q u i t e u n i f o r m a r o u n d t h e com p a s s . ) T h i s s u g g e s t s t h a t r o a d s may be an i m p o r t a n t s o u r c e o f S i and A l , as w e l l as o f Ca, when m a t u r e c r o p s a r e l i m i t i n g t h e mechanisms o f s o i l e r o s i o n ; i . e . , w i n d and tilling. F i g u r e s 4 and 5 show r e s u l t s o f s a m p l i n g o v e r a b o u t one month i n t h e f a l l : m i d - O c t o b e r t o mid-November 1978. This p e r i o d i n c l u d e d h a r v e s t a c t i v i t i e s as w e l l as p o s t - h a r v e s t p l o w i n g and o t h e r t i l l i n g o p e r a t i o n s . These a c t i v i t i e s w e r e v i s u a l l y o b s e r v e d t o m o b i l i z e a c o n s i d e r a b l e amount o f s o i l material. This i s r e f l e c t e d i n the i n c r e a s e d c o n c e n t r a t i o n s over t h o s e o f J u l y ( T a b l e I I ) . M o r e o v e r , mean c o n c e n t r a t i o n s d u r i n g t h e f a l l p e r i o d a p p r o a c h e d , and i n one c a s e e x c e e d e d , t h o s e o f J u n e , when t i l l i n g and w i n d e r o s i o n w e r e a l s o a c t i v e . F i g u r e 4 shows r e s u l t s f o r t h e g r o u n d l e v e l s a m p l e r . The maximum c o n c e n t r a t i o n s o f a l l f o u r c r u s t a l e l e m e n t a l s o c c u r r e d



310

ATMOSPHERIC

AEROSOL

Figure 2. Distribution of mean concentrations with wind direction for 4 crustal elements measured on a streaker sampler at ground level during one week in June 1978. Radial bars indicate ±1 standard error of the mean. The numbers at the end of the bars indicate the number of 2-h samples from each direction.



17.

GATZ E T AL.

Figure 3.

Sources

of

Airbourne

Calcium

in

Illinois

Same as Figure 2, except for a 2-week period on the tower during 1978.


311

July

ATMOSPHERIC

AEROSOL


312

Figure 4.

Same as Figure 2, except for 3 weeks at ground level in the fall, 1978.



17.

GATZ

Figure

ET

5.

AL.

Sources

Same as Figure

of

Airbourne

Calcium

in

Illinois

2, except for 4 weeks on the tower in the fall,


313

1978.


314

ATMOSPHERIC

AEROSOL

i n w i n d s f r o m SSE t h r o u g h W. F o r e a c h e l e m e n t t h e r e was a l s o a s e c o n d a r y peak f r o m t h e NNE. The l a c k o f a d i f f e r e n c e i n d i r e c t i o n a l d i s t r i b u t i o n b e t w e e n Ca and t h e o t h e r e l e m e n t s s u g g e s t s a common p r i m a r y s o u r c e f o r a l l , and t h i s i s c o n s i s t e n t w i t h t h e o b s e r v a t i o n s o f l a r g e amounts o f s o i l and a e r o s o l from a g r i c u l t u r a l f i e l d a c t i v i t y d u r i n g t h i s p e r i o d . C o n c e n t r a t i o n s measured on t h e t o w e r d u r i n g t h e f a l l p e r i o d a r e shown i n F i g u r e 5. Compared w i t h c o n c e n t r a t i o n s a t t h e g r o u n d , t h e s e a r e s l i g h t l y s m a l l e r ( s e e T a b l e I I ) and more u n i f o r m a r o u n d t h e compass, b u t s t i l l q u i t e s i m i l a r e l e m e n t t o element. Nothing here suggests d i f f e r e n t primary sources f o r these c r u s t a l elements, but the s e a s o n a l v a r i a t i o n s i n conc e n t r a t i o n and o c c a s i o n a l d i f f e r e n c e s i n d i r e c t i o n a l r e s p o n s e s o f t h e summer and f a l l s a m p l i n g p e r i o d s s u g g e s t t h a t b o t h r o a d s and s o i l a r e i m p o r t a n t s o u r c e s , a t l e a s t f o r Ca. Abundances. A d d i t i o n a l evidence of p o s s i b l e m u l t i p l e s o u r c e s comes f r o m an e x a m i n a t i o n o f t h e mass p e r c e n t a g e s (abundances) o f c r u s t a l elements i n a e r o s o l samples. Figures 6 t h r o u g h 11 show a b u n d a n c e s f o r A l , S i , K, Ca, T i , and F e . The f i g u r e s a l s o show measured a b u n d a n c e s i n l o c a l s o i l and road dust sources f o r comparison. Except f o r S i , the e l e m e n t a l abundances i n t h e a e r o s o l s u g g e s t a c o m b i n a t i o n o f r o a d and s o i l s o u r c e s . The Ca r e s u l t s a r e i m p o r t a n t t o t h i s o b s e r v a t i o n b e c a u s e o n l y f o r Ca were t h e a b u n d a n c e s i n a e r o s o l s c o n s i s t e n t l y l e s s than those i n road d u s t , but g r e a t e r than those i n s o i l . From t h e o t h e r e l e m e n t s , one c o u l d r e a s o n a b l y c o n c l u d e t h a t roads were the major s o u r c e . The S i a b u n d a n c e s i n t h e a e r o s o l g e n e r a l l y f a l l b e l o w t h o s e o f b o t h r o a d s and s o i l , b u t t h e y a r e much c l o s e r t o t h o s e o f r o a d s . As w i l l be shown l a t e r f r o m o t h e r e v i d e n c e , t h e r e i s r e a s o n t o b e l i e v e t h a t S i abundances a r e d i m i n i s h e d i n a e r o s o l r e l a t i v e to b u l k s u r f a c e m a t e r i a l s . This i s consistent with o u r k n o w l e d g e t h a t S i i s a m a j o r component o f t h e l a r g e r p a r t i c l e s o f o u r s o i l s a m p l e s , w h i c h a r e e i t h e r t o o b i g t o become a i r b o r n e , o r , i f r a i s e d by t h e w i n d , t e n d t o f a l l o u t q u i c k l y . F a c t o r A n a l y s e s . I n an a t t e m p t t o i d e n t i f y s o u r c e s o f t h e v a r i o u s e l e m e n t s , f a c t o r a n a l y s e s were c a r r i e d o u t s e p a r a t e l y on two d a t a s e t s r e p r e s e n t i n g 1) f i l t e r s e x p o s e d f a c e down u n d e r an i n v e r t e d f u n n e l r a i n s h i e l d , and 2) f i l t e r s e x p o s e d i n a v a n e sampler c o n t i n u o u s l y f a c i n g i n t o the wind. W i t h i n each d a t a s e t , s e p a r a t e f a c t o r a n a l y s e s w e r e p e r f o r m e d on t h e d a t a e x p r e s s e d as 1) c o n c e n t r a t i o n s i n a i r (ng m~^) and 2) a b u n d a n c e s ( p e r c e n t of t o t a l m a s s ) . R a i n amount, r a i n d u r a t i o n , and s o i l m o i s t u r e d a t a were i n c l u d e d i n e a r l y a n a l y s e s , but these parameters were l a t e r d r o p p e d f r o m t h e d a t a s e t s b e c a u s e t h e y had no s i g n i f i c a n t r e l a t i o n s h i p t o any o f t h e e l e m e n t s . Wind d i r e c t i o n f r e q u e n c i e s were i n c l u d e d i n t h e d a t a s e t s t h r o u g h o u t t h e a n a l y s e s , h o w e v e r . D i f f e r e n t r e s u l t s were o b t a i n e d f o r c o n c e n t r a t i o n d a t a



GATZ

ET

AL.

Sources

of

Airbourne

Figure 6. Frequency distributions of Al ples, summer, 1978. Source abundances bars on the source abundances indicate source

Calcium

LIMESTONE

i

Figure 7.

L6_

Illinois

315

abundances from 2 sets of aerosol samfor Al are shown for comparison. The ±1 standard deviation of an individual sample.

ROAD DUST

_J

in

8 10 12 14 ABUNDANCE, PERCENT

|,

16

'

B

RULÎ^IL U

L

K

34

S

0

I

L

,|

36

Same as Figure 6, except for Si


316

ATMOSPHERIC

LOCAL LIMESTONE ROAD DUST


AEROSOL (VANE SAMPLER)

ζ

R

2

J U L

0

AEROSOL (FUNNEL SAMPLER)

0

0.2

0.4

0.6

Figure 8.

0.8 1.0 1.2 1.4 ABUNDANCE, PERCENT

1.8

2.0

2.2

Same as Figure 6, except for Κ

LOCAL BULK SOIL L U t

1.6

L

0

C

A

L

LIMESTONE ROAD DUST

A L

1

* —

1

i 1

1

1

.

1

AEROSOL (VANE SAMPLER) Ν = 36

if

i

1

Λ

ZI

Ik

ABUNDANCE, PERCENT

Figure 9.

Same as Figure 6, except for Ca


AEROSOL

17.

GATZ E T AL.

Sources

of Air bourne

Calcium

in

Illinois

LOCAL LIMESTONE ROAD DUST

AEROSOL (VANE SAMPLERl


Τ - Π

J 0

0.05

1 0.10

0.15

Figure 10.

I, ,„..i

I

0.20 0.25 0.30 0.35 0.40 ABUNDANCE, PERCENT

L 0.45

* 0.50

* 0.55 0.60

Same as Figure 6, except for Ti

LOCAL LIMESTONE ROAD DUST BULK SOIL L

Figure 11.

0

C

A

L

Same as Figure 6, except for Fe


317


318

ATMOSPHERIC

AEROSOL

t h a n f o r abundance d a t a , b u t d i f f e r e n c e s b e t w e e n s a m p l e r s ( v a n e v s . f u n n e l ) were m i n i m a l . Therefore, the r e s u l t s presented h e r e , f o r b o t h c o n c e n t r a t i o n s and a b u n d a n c e s , a r e f o r v a n e s a m p l e s only. T a b l e I I I shows t h e l o a d i n g s t a b l e b a s e d on c o n c e n t r a t i o n s . F a c t o r 1, w h i c h e x p l a i n s 44% o f t h e v a r i a n c e , i n c l u d e s a l l t h e u s u a l c r u s t a l e l e m e n t s a t h i g h l o a d i n g s p l u s Zn and Pb a t much w e a k e r l o a d i n g s . F a c t o r 2 i n c l u d e s Pb and S, b u t o n l y a t r e l a t i v e l y weak l o a d i n g s , a s s o c i a t e d w i t h SE w i n d s . This d i r e c t i o n i s c o n s i s t e n t w i t h the l o n g range t r a n s p o r t of s u l f u r f r o m t h e O h i o V a l l e y , b u t no o b v i o u s Pb s o u r c e s a r e a p p a r e n t i n t h e SE d i r e c t i o n . N o t e t h a t Ca i s p r e s e n t on o n l y one f a c t o r , w i t h a r e l a t i v e l y high l o a d i n g (0.87). The l o a d i n g s f o r t h e d a t a e x p r e s s e d as a b u n d a n c e s a r e shown i n T a b l e I V . Now f o u r f a c t o r s a p p e a r , b u t o n l y t h e f i r s t two c o n t a i n e l e m e n t s . F a c t o r 1 i s a c o m b i n a t i o n o f c r u s t a l e l e m e n t s and S, w i t h an i n v e r s e r e l a t i o n s h i p b e t w e e n t h e two. T h i s i s r e a s o n a b l e f o r m a j o r components o f t h e mass b e c a u s e when e x p r e s s e d as a b u n d a n c e s , any e x t r e m e l y h i g h v a l u e s o f one component a u t o m a t i c a l l y d e c r e a s e t h e o t h e r . As w i t h c o n c e n t r a t i o n s , no w i n d d i r e c t i o n s a r e i m p o r t a n t on f a c t o r 1. F a c t o r 2 c o n t a i n s t h e p o l l u t a n t m e t a l s Pb, Zn, and Mn, as w e l l as Ca and Fe a t weak l o a d i n g s , and t e n d s t o o c c u r w i t h NE w i n d s . T h i s s u g g e s t s p o l l u t a n t t r a n s p o r t from Champaign-Urbana. I n t h i s c a s e we do f i n d Ca s p l i t b e t w e e n s o u r c e s , b u t n o t t h e ones e x p e c t e d . The a p p a r e n t r o a d s o u r c e t o t h e SE, suggested i n the c o n c e n t r a t i o n d i s t r i b u t i o n s w i t h wind d i r e c t i o n , does n o t a p p e a r i n t h e f a c t o r a n a l y s i s r e s u l t s , no m a t t e r w h e t h e r b a s e d on c o n c e n t r a t i o n s o r a b u n d a n c e s . T h i s r e s u l t c o n t r a s t s w i t h those presented e a r l i e r , which suggested a combination o f r o a d and s o i l s o u r c e s , a t l e a s t f o r Ca. Chemical Element B a l a n c e . To h e l p r e s o l v e t h i s d i l e m m a , t h e r e s u l t s o f a s i m p l e c h e m i c a l e l e m e n t b a l a n c e b a s e d on Ca and Κ a r e u s e f u l . The c a l c u l a t i o n s w e r e p e r f o r m e d s e p a r a t e l y f o r e a c h o f t h e 36 v a n e s a m p l e s c o l l e c t e d , so a d i s t r i b u t i o n o f t h e r e s u l t s c o u l d be p r e s e n t e d . The i n p u t d a t a f o r t h e s e c a l c u l a t i o n s i n c l u d e d t h e mean a b u n d a n c e s o f t h e e l e m e n t s i n t h e s o u r c e m a t e r i a l s ( l o c a l b u l k s o i l and r o a d d u s t ) ( T a b l e 1) and t h e a e r o s o l e l e m e n t a b u n d a n c e s m e a s u r e d i n t h e 36 i n d i v i d u a l v a n e s a m p l e s . The d i s t r i b u t i o n s o f c r u s t a l e l e m e n t a b u n d a n c e s i n a e r o s o l s w e r e shown i n F i g u r e s 6-11 a l o n g w i t h the r e s p e c t i v e abundances o f the elements i n the s o u r c e materials. The d i s t r i b u t i o n s o f t h e c o n t r i b u t i o n s o f r o a d s and s o i l t o t o t a l s u s p e n d e d p a r t i c u l a t e m a t t e r (TSP) a r e shown i n F i g u r e 12. The f i g u r e shows t h a t s o i l c o n t r i b u t e d a mean o f 39% o f t h e TSP and r o a d s 12% d u r i n g t h e summer s a m p l i n g p e r i o d i n 1978. The d i s t r i b u t i o n s show t h a t on i n d i v i d u a l d a y s s o i l c o n t r i b u t e d up t o a b o u t 70% o f t h e TSP and r o a d s up t o a b o u t 30%.


17.

GATZ

ET


Table I I I .

AL.

Sources

of

Airbourne

Calcium

in

Illinois

319

L o a d i n g s from f a c t o r a n a l y s i s o f vane sampler d a t a , b a s e d on c o n c e n t r a t i o n s . L o a d i n g s

Sources of Airborne Calcium in Rural Central Illinois - ACS Publications

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