petrol saving techniques

8/13/2019 petrol saving techniques

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ergamon tmospheric EnvironmentVol. 31, No . 17, pp. 2733-2740, 1997 1997 Elsevier Sc ience LtdAll r ights reserved. Printed in Great Bri ta inP I I : S 1 3 5 2 - 2 3 1 0 ( 9 7 ) 0 0 1 0 1 - 5 1352-2310/97 17.00 + 0.00

O R I G I N A N D P A T T E R N S O F D I S T R IB U T I O N O F T R AC EE L E M E N T S IN ST RE ET D U ST U N L E A D E D P E T R O L A N D

U R B A N L E A DE D U A R D O d e M I G U E L , * J U A N F . L L A M A S , * E N R I Q U E C H A C O N , *

T O R U N N B E R G , t S T E I N A R L A R S S E N , t O D D V A R R O Y S E T ta n d M A R I T V A D S E T t

* E . T . S . M inas M adrid (M adrid School o f Mines ) , Rios Rosas 21 , E-28003 M adrid , Spa in ; andt Norw egian Ins t i tu te fo r Air Resea rch , P .O. Box 100 , N-2007 K je l le r , No rw ayFirst received 23 February 1 9 9 6 and in f inal form 29 January 1997)

Ab s trac t- -T he e lemen ta l comp os i t ion , pa t te rns o f d is t r ibu t ion and poss ib le sources o f s t ree t dus t a re no tc o m m o n to a l l u rb a n e n v i ro n m e n t s , b u t v a ry a c c o rd in g to th e p e c u l i ar i ti e s o f e a c h c ity. T h e c o m m o nfea tures and d is s imilar i tie s in the o r ig in and na tu re o f s t ree t dus t were inves t iga ted th roug h a se rie s o fs tud ies in two wide ly d if ferent c i tie s, M adrid (Spain) and Os lo (Norway), be tween 1990 and 1994. The mos tcomprehens ive sampling campaign was ca rr ied ou t in the Norwegian cap i ta l dur ing the summer o f 1994 .An a r ea o f 1 ,1 km 2, cover ing mo s t o f dow ntow n Os lo and some res iden t ia l d is t ric ts to th e nor th o f the c ity ,was d iv ided in to 1 km 2 map ping un i ts , an d 16 sampling inc rem ents o f approx im ate ly 150 g were co l lec tedfrom s t ree ts and roads in each o f them. Th e frac t ion be low 100 I~m was ac id -d iges ted and ana lysed byIC P-M S. Statis tica l analyses of the results suggest that c hem ical e lem ents in s treet dust can be classified intoth ree g roups : u rba n e lements (Ba , Cd , Co , Cu , Mg, Pb , Sb , T i , Zn) , na tu ra l e lements (AI, Ga , La , Mn,Na , Sr , Th , ' ( ) and e lements o f a mixed or ig in o r w hich have undergo ne geochem ica l changes f rom the iro r ig ina l sources (Ca , Cs, Fe , Mo, N i , Rb , Sr , U) . So i l re suspens ion and /o r m obi l isa t ion appears to be themo s t imp ortan t source o f na tu ra l e lements , whi le u rba n e lements o r ig ina te p r imar i ly f rom traff ic andf ro m th e w e a th e r in g a n d c o r ro s io n o f b u ild in g m a te ri a l s. T h e d a ta fo r P b s ee m to p ro v e th a t t h e g ra d u a lsh if t f rom leaded to un leaded pe tro l a s fue l fo r au tomobiles has resu l ted in an a lmos t p roport iona lreduc t ion in the concen tra t ion o f Pb in du s t pa r t ic les under 100 l im. Th is fac t and th e spa t ia l d is t r ibu t ion o fPb in the c i ty s t rong ly suggest tha t lead sources o the r th an t raff ic ( i .e . lead accum ula ted in u rba n so i l overthe yea rs) m ay con tr ib u te as mu ch lead , i f no t m ore , to u rban s t ree t dus t. 1997 Elsev ie r Sc ience Ltd .Ke y word index: Street dust, trace elements , urban, lead, sampling, ICP-MS.

1. INTRODUCTIONO n e o f t h e n u m e r o u s g e o c h e m i c a l f ea t ur e s o f u r b a ne n v i r o n m e n t s i s t h a t t h e y c a n b e r e g a r d e d a s s p a t i a ld o m a i n s w h e r e a s t e a d y f l o w o f i n c o m i n g t r a c e e le -m e n t s i s s u b j e c t t o c h a n g e s i n t h e i r p h y s i c o c h e m i c a ls t a t e b e f o r e b e i n g d i s p o s e d o f a n d a c c u m u l a t e d w i t h i nt h e i r l im i t s . A m o n g o t h e r p o s s ib i l it i e s, t r a c e e l e m e n t sc o n c e n t r a t e o n u r b a n s u r f a ce s a s d u s t p a r t i c l es o fa w i d e r a n g e o f si z e s ( o f t e n r e f e r r e d t o a s s t r e e t d u s t ) .T h e h e a l t h i m p l i c a t i o n s o f i n h a l a t i o n a n d / o r i n ge s -t i o n o f d u s t p a rt ic l e, s w i t h h i g h c o n c e n t r a t i o n s o f t r a c ee l e m e n t s i s t h e s u b j e c t o f i n t e n s e d e b a t e a n d t h e r e -s u i ts o f r e s e a r c h t o d a t e a r e c o n t r a d i c t o r y ( H a r v e yet a l . , 1 9 8 5 a ; M c B r i d e et al . , 1 9 8 5 ) . I t s e e m s c l e a r ,n e v e r t h e le s s , t h a t c h i l d r e n a r e t h e s e c t o r o f t h e p o p u -l a t i o n a t h i g h e s t r i s k ( R u n d l e et al . , 1 9 8 5 1 T h o m a set al., 1 9 8 5 ; H a r v e y et al . , 1 9 85 b ; B i g g i n s a n d H a r -r ison , 1980) .

T h e r e i s a c r e d i b l e n e e d , t h e r e f o r e , f o r a s s e s s i n g t h ec o n c e n t r a t i o n l e v e ls o f t r a c e e l e m e n t s i n s t r e e t d u s t .

M a p s c a n b e u s e d a s a c o n v e n i e n t t o o l t o p r e s e n t t h ei n f o r m a t i o n g a i n e d f r o m a n a l y s i s o f i n d i v i d u a l s a m -p l es a n d t o f a c i l i t at e i n t e r p r e t a t i o n o f t h e r es u l ts . T h ec h o i c e o f m a p p i n g u n i t si ze an d t h e n u m b e r a n d m a s so f t h e s a m p l i n g i n c r e m e n t s t a k e n i n e a c h o n e ( s a m p -l i n g s t r a te g y ) d e t e r m i n e s t h e a c c u r a c y a n d p r e c i s i o no f t h e f i n a l g r a p h i c d i s p l a y a n d t h e v a l i d i t y o f t h ec o n c l u s i o n s d r a w n f r o m t h e i n f o r m a t i o n c o n v e y e dt h e r e i n .

2 . MAPS OF TRACE ELEMENTS AND SAM PLINGSTRATEGIES

T h e m o s t c o m m o n a p p r o a c h t o th e p r o d u c ti o n o fg e o e h e m i c a l m a p s u s e s a r e g u l a r g r i d t o d i v i d e t h ea r e a u n d e r i n v e s t ig a t i o n i n a n u m b e r o f m a p p i n gu n i ts , a ll e q u a l i n s h a p e a n d s iz e . E a c h m a p p i n g u n i t i sr e p r e s e n t e d b y a s i n g l e c o n c e n t r a t i o n v a l u e . T h i sv a l u e r e s u l ts e i t h e r f r o m a n a l y s i s o f o n e c o m p o s i t es a m p l e m a d e u p o f a n u m b e r o f s a m p l i n g i n c r e m e n t s

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2734 E . de M I G U E L e t a l .t a k e n w i t h i n t h e m a p p i n g u n i t o r f r o m c o m p u t i n ga m e a n v a l u e o u t o f t h e a n a l y t i c a l r e su l t s o f e a c h o ft h e s a m p l i n g i n c r e m e n t s . T h e f i rs t a l t e r n a t i v e i s u s u -a l l y p r e f e r r e d s i n c e i t a l l o w s f o r r e d u c e d l a b o r a t o r ye x p e n s e s , a l t h o u g h v a l u a b l e i n f o r m a t i o n r e g a r d i n gi n t e r n a l h e t e r o g e n e i t y o f t h e m a p p i n g u n i t i s l o s t .

T h e p r e c i s i o n w i t h w h i c h t h e m e a n c o n c e n t r a t i o no f a n e l e m e n t is e s t i m a t e d f o r e a c h m a p p i n g u n i t w i l lb e d e t e r m i n e d b y t h e u n i t ' s i n t e r n a l h e t e r o g e n e i t y a sw e l l a s b y t h e s a m p l i n g s t r a t e g y a n d t h e l a b o r a t o r yp r o c e d u r e s e m p l o y e d . P r e c i s i o n c a n b e i m p r o v e d a tt h e e x p e n s e o f h i g h e r c o s t s ( h i g h e r d e n s i t y o f s a m p l i n gl o c a t i o n s , m o r e a n a l y t i c a l d e t e r m i n a t i o n s , e t c . ) . I t i st h e r e f o r e d e s i r a b l e t o e x p l o r e t h e r e l a t i o n s h i p b e -t w e e n p r e c i s io n a n d t h e d i f fe r en t p a r a m e t e r s t h a t c a na f fe c t i t b e f o r e t h e s a m p l i n g c a m p a i g n i s d e s i g n e d .

T h e s a m p l i n g c a m p a i g n c a r r i e d o u t i n O s l o w a sd e s i g n e d a c c o r d i n g t o V i s m a n ' s s a m p l i n g m e t h o d o -l o g y ( D e M i g u e l , 1 9 9 5; M e r k s , 1 9 85 ), w h i c h c o n s i d e r st h e t o t a l v a r i a n c e a s s o c i a te d w i th e a c h d e t e r m i n a t i o no f t h e m e a n c o n c e n t r a t i o n v a l u e ( v ar TO T (X )) a s t h es u m o f f o u r d i f f e r e n t t e r m s : d i s t r i b u t i o n v a r i a n c e( varD lsT), co m po s i t io n v a r ian ce ( va rcoMP), p r e pa r a t io nvar ia nce (V arpREP), and ana lys i s va r i anc e ( v a r A N A L ) :varToT ()(i) - - varcoM P, + varDIST, + varpREp + varANAL,

m x n n

w h e r e ) ~i i s t h e m e a n c o n c e n t r a t i o n o f e l e m e n t i i n t h em a p p i n g u n i t, m t h e m a s s o f s a m p l i n g i n c r e m e n t , a n dn t h e n u m b e r o f s a m p l i n g i n c r e m e n t s i n t h e m a p p i n gunit .T h e l a s t t w o t e r m s a c c o u n t f o r th e v a r i a n c e a r i s i n gf r o m a l l p r o c e s s e s c a r r i e d o u t i n t h e l a b o r a t o r y ( l a -b o r a t o r y v a r i a n c e ) , f r o m t h e f i rs t a r r i v a l o f t h e r a ws a m p l e s u n t i l t h e f i n a l a n a l y t i c a l re s u l t s a r e p r o d u c e d .T h e s u m o f th e f i rs t t w o t e r m s i s n o r m a l l y r e f e r r e d t oa s s a m p l i n g v a r i a n c e . T h e d i s t r i b u t i o n v a r i a n c ea c c o u n t s f o r t h e h e t e r o g e n e i t y i n t h e s p a t i a l d i s t r i b u -t i o n o f a n e l e m e n t ' s c o n c e n t r a t i o n ( m a s s / m a s s ) o v e rt h e m a p p i n g u n i t ; it is m a s s - i n d e p e n d e n t a n d c a n o n l yb e r e d u c e d b y i n c r e a s i n g t h e n u m b e r o f s a m p l i n gi n c r e m e n t s w i t h i n e a c h m a p p i n g u n i t. T h e c o m p o s i -t i o n v a r i a n c e q u a n t i f i e s t h e h e t e r o g e n e i t y i n t h e c o m -p o s i t i o n o f i n d i v i d u a l p a r t i c l e s o r p a r t i c l e c l u s t e r s ,a n d i s i n v e r s e l y r e l a t e d t o t h e m a s s o f th e t o t a l s a m p l ec o l l ec t e d f r o m e a c h m a p p i n g u n i t.

T h e l a b o r a t o r y v a r i a n c e c a n b e e s t i m a t e d b y d u -p l i c a t in g s a m p l e s a n d t h e d i s t r i b u t i o n a n d c o m -p o s i t i o n v a r i a n c e s c a n b e d e t e r m i n e d f r o m a p i l o ts t u d y , in w h i c h a m a p p i n g u n i t r e p r e s e n t a t i v e o f t h ew h o l e a r e a u n d e r i n v e s t i g a t i o n is s a m p l e d , a n d t w os a m p l e s , o n e a p p r o x i m a t e l y 1 0 t i m e s b i g g e r ( m a s s )t h a n t h e o t h e r , a r e c o l l e c t e d i n e a c h s a m p l i n g l o c a -t i o n . F r o m t h e s e t w o s e t s o f s a m p l e s ( b ig a n d s m a l l) ,t h e d i s t r i b u t i o n a n d c o m p o s i t i o n v a r i a n c e s ca n b ee s t i m a t e d a s f o l l o w s :

m S M A L L mm6 x [ V I ] . r SM A LL~ - - vgrm6,]V a F c O M P = / / / B IG - - m S M A L L

mSMALLX I-vftrSMALL, - vfiram,]v I ~ r D I S T~ = v a r B i G i - - /T/BIG - - m S M A L Lw h e r e v I ~ rS M A L L i s t h e v a r i a n c e o f t h e s e t o f s m a l ls a m p l i n g i n c r e m e n t s , v f i rs m t h e v a r i a n c e o f t h e s e t o f

b i g s a m p l i n g i n c r e m e n t s , m SM ALL , t h e m a s s o fs m a l l s a m p l i n g i n c re m e n t s , a n d r n m 6 t h e m a s s

o f b i g s a m p l i n g i n c re m e n t s .A p i l o t - s t u d y s i m i la r to t h e o n e m e n t i o n e da b o v e w a s c a r r i e d o u t i n M a d r i d ( L l a m a s e t a l . 1990,1 9 91 ), y i e l d i n g i n f o r m a t i o n o n t h e s i z e a n d n u m b e ro f s a m p l i n g i n c r e m e n t s t o b e c o l l e c t e d fr o m e a c hm a p p i n g u n i t i n o r d e r t o a c h i e v e a p r e d e t e r m i n e dp r e c i s io n i n t h e e s t im a t e o f t h e m e a n c o n c e n t r a t i o nf o r th a t u n i t. I n a c c o r d a n c e w i t h t h e r e s u l ts o f M a d -r i d , a n d f o r t h e s i z e (1 k m x 1 k m ) o f t h e O s l o m a p -p i n g u n i t , i t w a s d e c i d e d t h a t 1 6 s a m p l i n g i n c r e m e n t so f a m i n i m u m o f 5 0 g s h o u l d b e c o l l e c t e d fr o m e a c huni t .

T h e q u a l i t y o f t h e e l e m e n t a l m a p s p r o d u c e d f o r t h eN o r w e g i a n c a p i t a l w a s e v a l u a t e d b y t h e i r s t a b i l i t ya n d r e s o l u t i o n , a s e s t i m a t e d f r o m t h e i n t e r n a l v a r i -a b i l i t y o f t h e m a p p i n g u n i t s (v a r i a b i l it y w i t h i n ) a n dt h e v a r i a b i l i t y b e t w e e n m a p p i n g u n i t s ( D e M i g u e l ,1 9 95 ; M i e s c h , 1 9 7 6 ). T h e a v e r a g e d e g r e e o f i n s t a b i l -i t y , e x c l u d i n g t h e m a p o f B e , w a s 2 . 5 % , w i t h 2 1 o f t h e2 6 e l e m e n t a l m a p s p r o d u c e d h a v i n g d e g r e e s o f i n s t a -b i l i t y o f l e s s t h a n 1 0 % . T h e h i g h s t a b i l i t y a n d r e s o l u -t i o n a c h i e v e d e n s u re t h a t t h e p a t t e r n s o f d i s tr i b u t i o no f t r a c e e l e m e n t s , a s s h o w n i n t h e m a p s , c a n b e s a f e l yi n t e r p r e t e d q u a n t i t a t i v e l y . A m o r e d e t a i l e d d e s c r i p -t i o n o f t h e m a t h e m a t i c a l b a s is f o r t h e m a p p i n g p r o -c e d u r e i s b e y o n d t h e s c o p e o f th i s a r t i c l e a n d w i l l b ep r e s e n t e d i n a s e p a r a t e p a p e r .

3. S A M P L I N G C A M P A I G N S , S A M P L E P R E P A R A T I O N A N DA N A L Y T I C A L M E T H O D S

T w o s a m p l i n g c a m p a i g n s w e re c a r r ie d o u t i n M a d -r i d in t h e s u m m e r s o f 1 99 0 a n d 1 9 92 , a n d a t h i r d o n et o o k p l a c e in O s l o i n t h e s u m m e r o f 1 99 4. T h e N o r w e -g i a n c a p i t a l i s l o c a t e d a t t h e i n n e r m o s t e n d o f th eO s l o f j o r d , i n s o u t h e a s t e r n N o r w a y , w h i l e M a d r i d s i tsa t o p t h e p l a t e a u t h a t c o v e r s m o s t o f c e n t r a l S p a i n .T h e l a r g e d i f f e re n c e s in c l i m a t e , r e g i o n a l g e o l o g y , si z ea n d p o p u l a t i o n , t o p o g r a p h y , u r b a n l a y o u t , t r a f f i ci n t e n s it y a n d u s e o f u n l e a d e d p e t r o l b e t w e e n b o t hc i t ie s a l l o w t o e x p l o r e t h e i n f l u e n c e o f t h e s e f a c t o r s o nt h e p r o c e s s e s t h r o u g h w h i c h t r a c e e l e m e n t s a r e i n -c o r p o r a t e d i n t o t h e s t r e e t d u st .

T h e m o s t e x t e n s iv e s a m p l i n g c a m p a i g n t o o k p l a c ei n O s l o f r o m 2 t o 2 3 A u g u s t 1 9 94 ; i t e x t e n d e d o v e r a na r e a o f 1 4 k m 2 , c o v e r i n g m o s t o f d o w n t o w n O s l o a n ds o m e s u b u r b a n d i s t ri c t s t o t h e n o r t h o f t h e c i ty . F o u r -t e e n m a p p i n g u n i t s o f 1 k m 1 k m w e r e s a m p l e d . I ne a c h o n e o f t h e m , 1 6 s a m p l i n g i n c r e m e n t s o f a p p r o x .1 5 0 g w e r e c o l l e c t e d b y b r u s h i n g w i t h a s m a l l p a i n t -b r u s h t h e u r b a n s u r f a c e ( s i d e w a l k , r o a d , g u t t e r ) w h e r et h e d u s t h a d a c c u m u l a t e d . T h e s a m p l i n g in c r e m e n t s


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Trace elements in street dust 2735were then transfen'ed to air-tight plastic bags fortransportation to the laboratory.

Each sampling increment was weighed on arrival atthe laboratory, then oven-dried for 72 h at a temper-ature of 45C and weighed again. Approximately, 50 gof each of the 16 sampling increments from a givenmapping unit were mixed and sieved, in an all-plasticsieving set, through a 250 and a 100 #m mesh. Thedecision to analyse the fraction below 100/~m wasbased on the fact that particles with aerodynamicdiameters under 100 #m can be transported by sus-pension (as opposed to saltati on for particles be-tween 100 and 500p m or creep for particlesbetween 500 and 1000 pm) and the finest amon g them(


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2 73 6 E . d e M I G U E L et al.c a n b e r e g a r d e d a s t h e m e a n v a l u e o f 2 2 4 f ie l d s a m -p le s . T h e s e c o n d c o l u m n o f b o t h t a b l e s s h o w t h er e s ul t s o f t h e s t u d y c a r r i e d o u t i n M a d r i d , w h e r e f e w e rl o c a t i o n s a n d a s m a l l e r a r ea w e r e s a m p l e d ( L l a m a se t a l . , 1990, 1991).

I n o r d e r t o d e s c r i b e a n d i n t e r p r e t t h e r e s u l t s b et t e r ,a n u m b e r o f m u l t i v a r i a t e a n a l y si s t e c h n i q u e s h a v eb e e n e m p l o y e d , i .e . p r i n c i p a l c o m p o n e n t a n a l y si s , f a c-t o r a n a l y s i s a n d c l u s t e r a n a l y s i s . T h e e l e m e n t a l c o n -c e n t r a t i o n s o f B e , C d , P a n d S b h a v e n o t b e e ni n c l u d e d i n s o m e o f t h e s t a t i s t i c a l a n a l y s e s , e i t h e rb e c a u s e o f t h e i r a n o m a l o u s b e h a v i o u r ( a s in t h e c a s eo f B e - s e e d i s c u s s i o n a b o v e ) o r b e c a u s e o f t h e p r e s -e n c e o f a n u m b e r o f o b s e r v a t i o n s b e l o w t h e d e t e c t i o nl i m i t ( C d , P a n d S b ) .

P r i n c i p a l c o m p o n e n t a n a l y s is ( F i g . 1 ) a n d f a c t o ra n a l y si s ( T a b l e 3 ) h a v e b e e n r u n w i t h t h e w h o l e s e t o fd a t a a n d a l s o w i t h t h e s u b s e t w h i c h i n c l u d e s o n l y t h ee l e m e n t a l c o n c e n t r a t i o n s o f i n d i v i d u a l s a m p l i n g i n -c r e m e n t s . A l t h o u g h s m a l l d i f f e r e n c e s o c c u r , t h e r e i sa g o o d a g r e e m e n t b e t w e e n t h e r e s u l t s i n b o t h c a s e s .T h r e e f a c t o r s e x p l a i n m o s t o f t h e v a r i a b i l i t y ( 7 0 % ) o ft h e d a t a . T h e f i r s t t w o f a c t o r s s e e m t o r e f l e c t t h e

u r b a n a n d n a t u r a l s o u r c e s o f s t r e e t d u s t ; a t h i r d ,o n e w h i c h c o m p r i s e s ( C a ) , C s , ( C u ) , ( M o ) , N i , P , R ba n d U , a p p e a r s t o g r o u p t h o s e e l e m e n t s w i t h a m i x e do r i g in o r e l e m e n t s w h i c h h a v e u n d e r g o n e g e o c h e m i c a lc h a n g e s f r o m t h e i r o r i g i n a l s o u r c e s ( e l e m e n t s i np a r e n t h e s e s s h o w s i g n i f i c a n t l o a d i n g s a l s o i n o n e o ft h e f i r s t t w o f a c t o r s ) .

A v e r y s i m i l a r p a t t e r n r e s u l t s f r o m a c l u s t e r a n a l y s i so f t h e v a r i a b l e s (i .e . e l e m e n t a l c o n c e n t r a t i o n s ) . T h r e ed i s t i n c t g r o u p s c a n b e o b s e r v e d i n F i g . 2 . T h e f i r sto n e , w h i c h i n c l u d e s C d a n d S b , s e e m s t o c o r r e s p o n dt o t h e u r b a n f a c t o r ; t h e s e c o n d o n e is a l m o s t i d e n t i-c a l, w i t h t h e e x c e p t i o n o f S r, to t h e a b o v e - m e n t i o n e d

n a t u r a l f a c t o r , a n d t h e t h i r d o n e a g a i n r e f l e c ts am i x e d o r i g i n , i n c o r p o r a t i n g s o m e o f t h e v a r i a b l e sw h i c h h a d b e e n p r e v i o u s l y a s s i g n e d t o th e u r b a nf a c t o r ( C a , C u , M o ) .

P r i n c ip a l C o m p o n e n t A n a l y s is

0.0L a B a Z n.0.1 o o..0 2 ~ lV ~ a ~ ~ i C o aooMg~pbTi

-0 .3 s- 0 0 . 4

- 0 . 3 - 0 . 2 - 0 . 1 0 . 0 0 1 1 0 1 2 0 1 3rincilml C o m l x m m t I

F ig . 1 . Pr inc ipa l com pone nt analysis . P lo t o f p r inc ipa l com-ponents 1 and 2 .

Tab le 3. Fa cto r analysis (38 observa tions 22 variables).Sorted ro ta ted fac to r load ings and communal i t ie sV a r i a b le F a c to r 1 F a c to r 2 F a c to r 3 C o m m u n a l i tyMg 0 .8 90 - - - - 0 .8 5 2Ti 0 .880 - - - - 0 .878Pb 0 .876 - - - - 0 .838C o 0 .8 52 - - - - 0 .7 3 9C a 0 .7 66 - - - - 0 .5 95Z n 0 . 7 6 3 - 0 . 5 0 0 - - 0 .8 33B a 0 . 6 8 6 - 0 . 4 9 5 - - 0 .7 39Mo 0 .5 92 - - - - 0 .6 0 9C u 0 .4 9 4 - - - - 0 .5 1 9Y - - 0 .834 - - 0 .831A1 - - 0 .798 - - 0 .795N a - - 0 .7 96 - - 0 .8 08G a - - 0 .7 82 - - 0 .6 7 7Fe - - 0 .781 - - 0 .668Mn - - 0 .7 57 - - 0 .6 6 6Sr - - 0 .735 - - 0 .659Th - - 0.612 0.485 0.663L a - - 0 .6 0 0 - - 0 .5 9 9Cs - - - - 0 .767 0 .792U - - - - 0 .735 0 .678N i - - - - 0 .6 6 0 0 .5 1 9R b - - - - 0 .6 59 0 .6 0 0V a r ia n ce 6 . 4 2 78 6 . 4 1 1 8 2 . 7 1 4 7 1 5 . 5 5 4 4% Va r 29.2 29.1 12.3 70.7

T h i s c l a s si f i c at i o n i n t o t h r e e g r o u p s i s s u p p o r t e d b yt h e r e s u l ts o f p r in c i p a l c o m p o n e n t a n a l y si s , f a c t o ra n a l y si s a n d c l u s t e r o f v a r i a b l e s f o r t h e s u b s e t o fv a r i a b l e s i n c l u d i n g o n l y t r a c e e l e m e n t s .4.1. N a t u r a l e l e m e n t s

T o g e t h e r w i t h m o s t o f th e m a j o r e l e m e n t s ( e x ce p tC a a n d M g ) , t h is g r o u p o f e l e m e n t s i s c h a r a c t e r i s e d b yt h e p r e s e n c e o f G a , L a , M n , S r , T h a n d Y . T h e i r o r i g i nl i e s i n t h e s o i l p a r t i c l e s t h a t t h r o u g h t h e p r o c e s s o f s o i lr e s u sp e n s i o n o r m o b i l i s a ti o n a r e i n c o r p o r a t e d i n t ot h e s t r e e t d u s t o f t h e c i t y . F o r t h e p a r t i c l e s i z e f r a c t i o ns t u d i e d ( b e l o w 1 0 0 / ~ m ) , t h i s m e c h a n i s m s h o u l da c c o u n t f o r a l a r g e p r o p o r t i o n o f t h e t o t a l m a s s o fs t r e e t d u s t .

A l t h o u g h t h e p r o b l e m o f t h e n a t u r e a n d o r i g in o fa n u r b a n s o i l i s n o t f u l l y u n d e r s t o o d , t h e a s s o c i a t i o no f e l e m e n ts w h i c h m a k e s u p t h i s g r o u p o f n a t u r a lv a r i a b l e s is c o h e r e n t w i t h t h e a l k a l i n e c o m p o s i t i o n o fs o m e o f t h e m o s t a b u n d a n t r o c k f o r m a t i o n s a r o u n dO s l o w h i c h , d u r i n g t h e l a s t g l a ci a l e p i s o d e , c o u l d h a v eb e e n w e a t h e r e d a n d g i v e n r is e t o p a r t o f t h e t o p s o i l i na n d a r o u n d t h e N o r w e g i a n c a p i t a l ( O f t e d a h l, 1 96 0) .M o r e o v e r , t h e c o n c e n t r a t i o n o f A1, F e a n d T i a r e ,r e s p e c t i v e l y , 1 .5 , 2 .5 a n d 7 t i m e s h i g h e r i n O s l o t h a n i nM a d r i d , c o n f i r m i n g t h a t t h e c o m p o s i t i o n o f t h e b ed -r o c k f r o m w h i c h u r b a n s o i ls e v o l v e h a v e a m a r k e di n f l u en c e o n t h e c o n c e n t r a t i o n o f m a j o r e l e m e n t s i ns t r e e t d u s t .T h e a b s e n c e o f C a a n d M g f r o m t h is g r o u p o fe l e m e n t s r e f le c t s t h e f a c t t h a t a l t h o u g h b o t h e l e m e n t sa r e p r e s e n t i n t h e b u l k o f s o i l p a r t i c le s w h i c h b e c o m e


5/8

Trace elements in street dus t 2737

S i m i l a r i t

2 7 4 . 9 7

1 4 9 . 9 8

2 4 . 9 9

1 0 0 0 0

C l u s t e r of Variables 38 Observations 2 5 Variables)L inkage metho d: W ardDist. Measure: C orrelation

i

VariablesFig. 2. Clust,~r of variables, from left to r ight: urba n elements, natu ral elements, and elements witha m ixed origin o r geochemically altered.

r e s u s p e n d e d , o t h e r ~ arb an s o u rc e s o f C a a n d M g ( m o s tn o t a b l y , c e m e n t d u s t ) e x p l a i n m o s t o f t h e i r s p a t i a lv a r i a b i l it y , t h u s f o r c i n g C a a n d M g t o j o i n t h e g r o u p so f e l e m e n t s w i t h arL u r b a n o r m i x e d o r i g i n .4.2. U r b a n e l e m e ~ t s

T h e g r o u p o f u r b a n e l e m e n t s i n c l u d e s B a , C d ,( C o ) , ( C u ), M g , P b , S b , T i a n d Z n ( e l e m e n t s i n p a r e n -t h e s e s s h o w s i g n i f i c a n t a f f in i t y f o r t h e g r o u p o f e le -m e n t s w i t h a m i x e d o r ig i n ). T h e m a p s d i s p l a y i n g t h e i rs p a t i a l d i s t r ib u t i o n i n t h e s t re e t d u s t o f O s l o r e v e a la s t e a d y in c r e a s e i n c o n c e n t r a t i o n i n t h e n o r t h - s o u t hd i r e c ti o n . T h e s t e e p c o n c e n t r a t i o n g r a d i e n t f r o m t h es u b u r b a n a n d r e si d e n ti a l n o r t h t o w a r d s d o w n t o w nO s l o , t o t h e s o u t h , r e f l e c t s w i t h s u r p r i s i n g a c c u r a c yt h e i n c r e a s i n g l y u r b a n c h a r a c t e r o f t h e m a p p i n gu n i t s i n t h a t d i r e c t i o n . C o n c e n t r a t i o n s o f t h e s e e l e -m e n t s a l s o i n c r e a s e , a l t h o u g h l e s s d r a m a t i c a l l y , f r o me a s t a n d w e s t t o w a r d s t h e c e n t r e o f t h e a r e a u n d e rinves t iga t ion ( F ig . 3 ) .

W i t h i n t h is g r o u p o f u r b a n e l e m e n ts , t w o so u r c e s,a t l e a s t , c a n b e i d e n t i f ie d :

( a ) t r a f f ic , an d( b) b u i l d i n g c o n s t r u c t i o n / r e n o v a t i o n a n d w e a t h e r -i n g a n d c o r r o s i o n o f b u i l d i n g m a t er i a ls .4.2.1. T r a f f i c . T h e i n f l u e n c e o f t ra f f ic i s c h a r a c t e r -

i s ed b y Z n a n d B a , a n d t o a l e s s e r e x t e n t b y C u a n dP b . Z i n c a n d b a r i u m a r e h i g h l y c o r r e l a t e d in t h e s t r e e td u s t o f O s l o ( t h e i r P e a r s o n c o r r e l a t i o n c o e f f ic i e n t i s0 .9 73 ) a n d b o t h c a n b e t r a c e d t o a u t o m o b i l e s ( K o w a l -c z y k e t a l . , 1 9 8 2 ) . B a d i s p e r s i o n s a r e w i d e l y u s e d a sd e t e r g e n t s / d i s p e r s a n t s a n d o x i d a t i o n a n d c o r r o s i o ni n h i b i t o r s i n l u b r i c a t i n g o i ls f o r d ie s e l a n d o t h e r c o m -b u s t i o n e n g i n e s , a n d a s s m o k e s u p p r e s s a n t a d d i t i v e si n d i e s e l f u el s. T h e h i g h l y b a s i c B a d i s p e r s i o n s w h i c hh a v e b e e n u s e d a s , ; m o k e s u p p r e s s a n t a d d i t i v e s c o n -t a i n l a rg e a m o u n t s (e .g . a b o u t 2 0 % ) o f b a r i u m c o m -p o u n d s . S i m i l a rl y , z i n c c o m p o u n d s h a v e b e e ne m p l o y e d e x t e n s i v e l y a s a n t i o x i d a n t s (e .g . z i n c c a r -

b o x y l a t e c o m p l e x e s a n d z i n c s u l fo n a t e s) a n d a s d e t e r -g e n t / d i s p e r s a n t i m p r o v e r s f o r l u b r i c a t i n g o i ls ( D r e w ,1 9 75 ). T y r e w e a r h a s a l s o b e e n r e p o r t e d t o c o n t r i b u t es i g n i f i c a n t l y t o t h e Z n l o a d i n s t r e e t d u s t , e s p e c i a l l y i nt h e f o r m o f c o a r s e d u s t p a r t i c l e s (S t i g li a n i a n d A n d e r -be r g , 1991; F r ied lander , 1973) .

O x i d a t i o n o f l u b r ic a t i n g o il s u p o n e x p o s u r e t o a i ra t h i g h t e m p e r a t u r e s r e s u l t s i n t h e f o r m a t i o n o f o r -g a n i c a c i d s , a l c o h o l s , k e t o n e s , a l d e h y d e s a n d o t h e ro r g a n i c c o m p o u n d s w h i c h a r e c o r r o s i v e t o m e t a l .T h i s c o r r o s i v e a c t io n c a u s e s w e a r o f th o s e m e t a l p a r t sw h i c h c o m e i n t o c o n t a c t w i t h t h e o i l a n d w h i c h i nm a n y c a s e s c o n si s t o f z i n c, c o p p e r a n d c a d m i u m - b e a r -i n g a l l o y s ( D r e w , 1 9 75 ) o r , a s i n t h e c a s e o f s i n t e r i s e dm a t e r i a l s u s e d i n t h e a u t o m o b i l e s ' o i l p u m p , o f N i , C ua n d M o . T h i s p r o c e s s re s u l t s u l t i m a t e l y i n t h e r e l e a s eo f t h o s e m e t a l s t o t h e u r b a n e n v i r o n m e n t a n d t h e i ra c c u m u l a t i o n i n t h e s t re e t d u s t. A l t h o u g h C u s e e m s too r i g i n a t e f r o m m o r e t h a n o n e s o u r c e , t h e h i g h c o p p e rc o n c e n t r a t i o n s i n s a m p l e s c o l l e c te d c l o se t o b u s yr o a d s a n d t h e h i g h c o r r e l a t io n b e tw e e n C u a n d P b i nt h e s t r e e t d u s t o f M a d r i d ( P e a r s o n c o r r e l a t i o n c o ef fi c-i e n t : 0 .9 4 7) s u g g e s t t h a t t h e m e c h a n i s m j u s t d e s c r i b e dh a s a s p e c i a l s i g n i f ic a n c e f o r t h i s e l e m e n t .

H i s t o r i c a l l y , l e a d h a s b e e n t h e m o s t r e l i a b l e t r a c e ro f t ra f fi c a n d m u c h w o r k h a s b e e n d o n e o n t h e g e n e r a -t i o n , d i s t r i b u t i o n a n d s iz e a n d c h e m i c a l c o m p o s i t i o no f l e a d - b e a r i n g e x h a u s t p a r t i c l e s , a s w e l l a s o n t h e i rh e a l t h i m p l i c a t i o n s . H o w e v e r , t h e g r a d u a l s h if t f ro ml e a d e d t o u n l e a d e d p e t r o l a s f u e l f o r a u t o m o b i l e s h a sr e d u c e d t r a ff i c e m i s s i o n s o f th i s e l e m e n t t o s u c h a ne x t e n t t h a t i t i s h i g h l y d e b a t a b l e w h e t h e r e x h a u s tp a r t i c l e s a r e s t i l l t h e m a j o r s o u r c e o f P b i n t h e s t r e e td u s t o f s o m e a r e a s o f t h e c i t y .

I n t h i s r e g a rd , i t m u s t b e n o t e d t h a t t h e d i s c r e p a n c yb e t w e e n t h e f i g u re s fo r l e a d i n M a d r i d a n d O s l o ( 1 0 :1 )r e f le c t s w i t h e x t r a o r d i n a r y a c c u r a c y t h e d i f f e r e n c e b e -t w e e n t h e a v e r a g e l e a d c o n t e n t o f th e p e t r o l b u r n t i nt h o s e t w o c i t i e s a t t h e t i m e o f b o t h s t u d i e s . T h ep e r c e n t a g e o f l e a d e d p e t r o l u s e d i n M a d r i d i n 1 99 0


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2738 E. de MIGUEL et al.

Fig. 3. Map of isoconcentrations of Cu (ppm, dry wt) in the city of Oslo. The concentration gradienttowards downtown Oslo marks the increasing urban character of the mapping units in that direction.

and in Oslo in 1993 was, respectively, 100 and 25%,with lead content s of 0.40 and 0.15 g t'-1 . These fig-ures yield an average lead-in-petrol concentration of0.4 g - 1 for Madrid and 0.0375 g ~- 1 for Oslo, aga inten times higher in the Spanish capital, as is the casefor the average lead-in-street dust concentration. Al-though the difference in traffic int ensit ies mus t alsoplay a significant role, this finding supports the in tu-itive idea that the gradual shift from leaded to un-leaded petrol results in an almost proportionalreduction in the concentratio n of lead in dust particlesunder 100/~m in urb an environments.

Furthermore, the average lead-in-street dust con-centra tion in Oslo (Table 2) is fairly close, for thesame particle size (< 100 #m), to the m ean Pb conten tof urban soils in Madrid, of 160 ppm (De Miguel,1995). If the average Pb concentration in the urbansoil of Oslo were of the same magnitude, soil particleswould account for a large proportion of Pb in streetdust and the influence of vehicle emissions would onlybe significantly noticed at locations with high-densit ytraffic. Elsewhere, lead sources of a different kindcould be of similar or higher importance.

As a matter of fact, the m ap of lead concentr ation inOslo shows that, although this element follows thegeneral trend for urban elements, the highest valueis reached in the vicin ity of a smelter and some asso-ciated industries, which were closed down a few yearsago. This fact supports the assumption that soil par-

ticles are one of the major sources of lead in streetdust: since direct emissions from the smelter and/orthe nearby factories have ceased for some years now,the origin of the lead in the street dust of this particu-lar mapping unit should be found in the lead thataccumulated over the years in the soil around theabove ment ioned indus trial facilities.

4.2.2. Bu i ld in g co n s t ru c t i o n ~ren o va t i o n a n d me ta lcorrosion . The samples collected in the proximity ofbuildings which were being renovated show high con-centrations of Ca and a ratio Mg/Ca of 0.14 (Kowal-czyk et al. 1982), suggesting that cement dust isa major component of street dust in these locations.Some of these samples also show the highest concen-trations for most of the trace elements analysed. Paintflakes from the facade are very likely responsible forthe unusual ly high lead content, while corrosion ofmetal structures can explain the anomaly for some ofthe other trace elements.

The contri bution of metal corrosion to the Z n a ndCd load in street dust, although limited in spatialreach, is of great significance. Corrosion of gal-vanised-metal structures exposed to the u rban atmo-sphere should be responsible for concent ratio ns of upto 1.2% of Zn an d 12 ppm of Cd in the street dustaround buildings undergoing renovation (Cd, as animpurity of Zn, is found in significant amounts ingalvanised metals). Even h igher concen trati ons (4.4%


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Trace elements in street dus t 2739o f Z n a n d 2 0 ppn~L o f C d ) w e r e f o u n d i n t h e d u s tc o l l e c t e d f r o m u n d e .r t h e m e t a l l e d g e s a n d b a l c o n i e s o fo l d b u i l d i n g s .

T h e c o r r o s i v e a c t i o n e x e r t e d b y u r b a n a t m o s p h e r e sc a n b e l i n k e d to t h e a c i d n a t u r e o f u r b a n r a i n w a t e r(with p H va lue s we'.Llb e l o w 4 .0 i n m a n y c a s es ). I ts r o l ea s a s o u r c e o f t r a c e e l e m e n t s is p a r t i c u l a r l y im p o r t a n ti n c o a s t a l c i t i e s, ~ h e r e t h e i n f l u e n c e o f t h e m a r i n ea e r o s o l e n h a n c e s t h e c o r r o s i v e n a t u r e o f t h e u r b a na t m o s p h e r e .

T h e o r i g i n o f C o a n d S b i s l e ss c l e a r . B o t h e l e m e n t sa r e e n r i c h e d i n t h e f l y -a s h f r o m c o a l c o m b u s t i o n , b u tt h i s i s a n u n l i k e l y s o u r c e o f d u s t p a r t i c l e s i n t h es u m m e r t im e , w h e n t h e s a m p l i n g c a m p a i g n t o o kp l a c e . I t i s a l so d o u b t f u l t h a t r e fu s e i n c i n e r a t i o n , a n -o t h e r s o u r c e o f S b i :a u r b a n e n v i r o n m e n t s , w o u l d h a v ea s i g n i f i c a n t i n f l u e n c e i n t h e N o r w e g i a n c a p i t a l . A n t i -m o n y i s a s s o c i a t e d w i t h n o n - f e r r o u s o r e s , e s p e c i a l l yC u o r es , a n d C o i s f o u n d i n N i , P b , C u a n d F e o r e s( A d r i a n o , 1 98 6 ). D u r i n g t h e s m e l t i n g o f t h e s e o r e s , C oa n d S b a r e r e l e as e d to t h e a t m o s p h e r e a s s t a c k d u s tp a r t i c l e s w h i c h c a n t r a v e l l o n g d i s t a n c e s f r o m t h ee m i s s i o n p o i n t . A l t h o u g h t h e c o n c e n t r a t i o n s o f S bf o u n d i n s o u t h e r n N o r w a y h a v e b e e n r e l a t e d t o l o n g -r a n g e a e r i a l t r a n s p o r t ( B e rg et al . 1994) , i t i s deba t -a b l e w h e t h e r t h i s c ,3 u ld a l s o b e t h e s o u r c e o f S b a n dC o i n t h e s tr e e t d u s t o f O s l o .4.3. E l e m e n t s w i t h a m i x e d o r i g i n o r 9 e o c h e m i c a l l ya l t e red

T h i s g r o u p o f el e m e n t s in c l u d e s C s, N i , R b a n d U ,w i t h C a , C u , F e , M , ~ a n d S r s h o w i n g s o m e a f f i n i ty f o ri t. A l l t h e s e e l e m e n t s l i e s o m e w h e r e i n b e t w e e n t h et w o g r o u p s p r e v i o u s l y d e s c r ib e d . S o m e o f t h e md i s p l a y b o t h ch a r a c t e rs , u r b a n a n d n a t u r a l , a n dt h e i r o r i g i n i s t o b e f o u n d n o t o n l y i n t h e p r o c e s s o fs o i l r e s u s p e n s i o n b u t a l s o i n t y p i c a l l y u r b a n s o u r ce s ,i .e . c e m e n t d u s t , f o r C a a n d a c c o m p a n y i n g S r ; tr a ff ic ,f o r C u a n d , p r o b a b l y , M o ; a n d m e t a l c o r r o s i o n ,f or Fe .

T h e s e p a r a t i o n o f C s , R b , S r a n d U f r o m t h e g r o u po f n a t u r a l e l e m e n t s i s v e r y l i k e ly d u e t o a p r o c e s s o fg e o c h e m i c a l d i f f e r e n t i a t i o n f r o m t h e o r i g i n a l s o u r c eo f t h e s e e l e m e n t s . T h i s p r o c e s s i s b e s t i l l u s t r a t e d b yt h e b e h a v i o u r o f U a n d T h . B o t h e l e m e n t s h a v e s im -i l a r e l e c t r o n c o n f i g u r a t io n s a n d o c c u r i n n a t u r e i n t h et e t r a v a l e n t o x i d a t i c , n s ta t e , w h i l e th e i r i o n s h a v e s i m -i l a r r a d i i a n d c a n s u b s t i t u t e e x t e n s i v e l y f o r e a c h o t h e r .U r a n i u m a n d t h o r i u m a r e i n c o r p o r a t e d i n t o s t r e e td u s t t h r o u g h t h e p r o c e s s o f s o i l r e s u s p e n s i o n a n d ,c o n s e q u e n t l y , b o t h w o u l d b e e x p e c t e d t o b e i n c l u d e di n t h e g r o u p o f n a t u r a l e l em e n t s . U n d e r o x i d i s in gc o n d i t i o n s , h o w e v e r , u r a n i u m f o r m s t h e u r a n y li o n ( U O ~ , o x i d a t i o n s t a t e + 6 ) w h o s e c o m -p o u n d s a r e s o l u b l e in w a t e r. T h e r e fo r e , u n d e r t h ec o n d i t i o n s t h a t p r e v a i l i n u r b a n s o i ls a n d s t re e t d u s t,u r a n i u m b e h a v e s ~Ls a m o b i l e e l e m e n t a n d c a n b es e p a r a t e d f r o m t h o r i u m , w h i c h e x i s t s o n l y i n t h et e t r a v a l e n t o x i d a t i o n s t a t e a n d w h o s e c o m p o u n d sa r e g e n e r a l l y i n s o l u b l e . T h i s f a c t c o u l d e x p l a i n t h e

s e p a r a t i o n o f u r a n i u m f r o m t h e g r o u p o f n a t u r a le l e m e n t s .

5. CONCLUSIONSA c o m b i n a t i o n o f s t a t is t i c a l t e c h n i q u e s ( V i s m a n ' s

m e t h o d o l o g y a n d A n a l y s i s o f V a r i a n c e) p r o v e d t o b ea r e l i a b l e t o o l i n t h e d e s i g n o f a s a m p l i n g c a m p a i g nf o r p a r t i c u l a t e m a t e r i a l s , w h e n t h e f i n a l a i m i s t op r o d u c e m a p s w i t h a p r e d e t e r m i n e d d e g r e e o f p r e -c i s i o n , r e s o l u t i o n a n d s t a b i l i t y . T h e s e m a p s o f 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 s t re e t d u s t r e v e a l t h e c h a n g i n gn a t u r e ( i .e . f r o m r e s i d e n t i a l t o t y p i c a l l y u r b a n ) o f t h ed i f f e r e n t d i s t r i c t s w i t h i n t h e c i t y u n d e r i n v e s t i g a t i o na n d h e l p l o c a t e a r e a s w o r t h y o f f u rt h e r, m o r e d e t a i l e ds t u d y .

T h e s t a t i s t i c a l a n a l y s i s o f t h e r e s u l t s r e v e a l e d t h r e ed i s t in c t g r o u p s o f e l e m e n ts , a c c o r d i n g t o t h e n a t u r e o ft h e i r s o u r c e s :

( 1) N a t u r a l e l e m e n t s ( c h a r a c t e r i s e d b y t h e p r e s -e n c e o f G a , L a , M n , S r , T h a n d Y ), w h o s e o r i g i n s e e m st o l i e i n t h e s o i l p a r t i c l e s t h a t t h r o u g h t h e p r o c e s s o fs o i l r e s u s p e n s i o n a r e i n c o r p o r a t e d i n t o t h e s t r e e t d u s to f t h e c i t y . T h e c o n c e n t r a t i o n o f th e s e e l e m e n t s i n t h es t re e t d u s t is h e a v il y d e p e n d e n t u p o n t h e c o m p o s i t i o no f t h e g e o l o g i c a l m a t e r i a l f r o m w h i c h t h e u r b a n s o i lsa r e d e r i v e d .

( 2) U r b a n e l e m e n t s ( B a , C d , [ -C o ] , [ C u ] , M g , P b ,S b , T i a n d Z n ) , a r e m o s t l y a n t h r o p o g e n i c , t h e m a i ns o u r c e s a p p e a r i n g t o b e t r a f f i c , b u i l d i n g c o n s t r u c -t i o n / r e n o v a t i o n , a n d w e a t h e r i n g a n d c o r r o s i o n o fb u i l d i n g m a t e r i a l s .

T h e o r i g i n o f t h o s e t r a c e e l e m e n t s a s s o c i a t e d w i t ht r a ff i c ( e x c l u d i n g l e a d ) l ie s p r i m a r i l y i n t h e c o m -p o u n d s u s e d a s a d d i t i v e s in l u b r i c a t i n g o i ls a n d d i e se lf ue ls , a n d i n t h e m e t a l w e a r c a u s e d b y t h e o x i d a t i o np r o d u c t s o f l u b r i c a ti n g o i l s. C o r r o s i o n o f g a l v a n i s e d -m e t a l s t r u c t u r e s e x p o s e d t o t h e u r b a n a t m o s p h e r e i sr e s p o n s i b l e f o r th e v e r y h i g h c o n c e n t r a t i o n o f Z n a n dC d f o u n d i n t h e v i c i n i t y o f o l d b u i l d i n g s .

( 3) E l e m e n t s ( [- C a ], C s , [ F e ] , [ M o ] , N i , R b , [ S r ] ,a n d U ) w h i c h h a v e a m i x e d ( a n t h r o p i c a n d n a t u r a l )o r i g i n o r h a v e u n d e r g o n e g e o c h e m i c a l c h a n g e s fr o mt h e i r o r i g i n a l s o u r c e s .

T h e r a t i o o f th e m e a n l e a d c o n c e n t r a t i o n i n t h es t r e e t d u s t o f O s l o t o t h a t o f M a d r i d ( 1 : 1 0 ) i s a l m o s ti d e n t i c a l t o t h e r a t i o o f t h e a v e r a g e l e a d c o n t e n t o f t h ep e t r o l b u r n t i n t h e N o r w e g i a n c a p i t a l t o t h a t o f t h ep e t r o l b u r n t i n t h e S p a n i s h o n e a t t h e t i m e o f b o t hs t u d i e s . T h i s f i n d i n g s u p p o r t s t h e i n t u i t i v e i d e a t h a tt h e g r a d u a l s h if t f ro m l e a d e d t o u n l e a d e d p e t r o l h a sr e s u l t e d in a s i g n i f i c a n t r e d u c t i o n i n t h e c o n c e n t r a t i o no f l e a d i n d u s t p a r t i c l e s u n d e r 1 0 0 # m i n u r b a n e n v i -r o n m e n t s . T h e f a c t t h a t t h e h i g h e s t P b c o n c e n t r a t i o ni n t h e s t r e e t d u s t o f O s l o i s fo u n d i n t h e s u r r o u n d i n g so f a s m e l t e r sh u t d o w n y e a r s a g o s u g g e s ts t h a t P bs o u r c e s o t h e r t h a n t r a ff i c ( i.e . t h e P b a c c u m u l a t e di n t h e u r b a n s o il o v e r t h e y e a r s ) m a y c o n t r i b u t e


8/8

2 74 0 E . d e M I G U E L et al.n o w a d a y s a s m u c h P b t o t h e u r b a n s t r e e t d u s t a st r a f f i c d o e s .

R E F E R E N E S

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