Rainwater in Montereal Island

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A N A L Y S I S O F R A IN W A T E R Q U A L I T Y V A R I A B I L I T Y O N M E S O -

S C A L E : C A S E O F T H E M O N T R E A L I S L A N D

LA UR IE R POI SSA NT 1., P IER RE PAGI~ 2 and PAT RIC K BI~RON 3

1 A tm osp he r i c E nv i ronm e nt Se rv ic e , 100 A le x i s N ihon R oo m 300, Sa in t - Laure n t Q ue bec , Canada , H 4M 2N8

(present af f i l ia t ion)

2 Universitd d u Q udbec i t MontrOal, Dpt. o f earth scien ces

3 Universi td du Qudbec it Mo ntreal , Dpt . o f chem is try

(Received 4 March 1992; accepted 19 February 1993)

Abstract. During summer of 1989, a network for the analysis of spatial variability of rainwater qualitywas operated on Montr6al Island. Six bulk samplers distributed on the territory were used for this

purpose. A total of 97 storm-station events have been analyzed for pH, conductivity, Total Organic

Carbon, nitrate, sulphate, calcium and magnesium. A canonical discriminant analysis shows that as

a whole, there is no statistically significant discrimination between stations. However, Tukey's test for

means shows that mean pH is significantly different between downtown and peripheric stations. The

pH is higher in downtown. Finally, a variance analysis shows that variations with respect to time

are greater than those on a spatial basis. Thus, the Montr6al Island can be considered as spatially

homogeneous for most rainwater quality parameters.

I . I n t r o d u c t i o n

T h e a t m o s p h e r e is n o w r e c o g n i z e d as a m a j o r v e c t o r f o r p o l l u t a n t s ( H e i t z e n b e r g ,

1989 ; Le a i t c h a nd I sa a c , 1989). T im e r e s ide nc e o f a i r bo r ne c on ta m ina n t s in the

a t m o s p h e r e i s m o r e o r l e s s l o n g , d e p e n d i n g o n n u m e r o u s f a c t o r s s u c h a s t h e

c on ta m ina n t i t s e lf , i ts phys ic a l a nd c he m ic a l s ta t e , a nd the e nv i r onm e n ta l c ond i t ions

(wind, a tmosphere s tabi l i ty , r a infa l l in tens i ty , e tc . ) .

T a k i n g i n t o a c c o u n t t h e l a rg e f lu x o f w a t e r i n th e a t m o s p h e r e ( a b o u t 5 7 7 •

1012 m 3y -1 ) a nd a m e a n r e s ide nc e t im e o f a b ou t 11 d , t he a tm o sph e r i c wa te r p l a ys

a n im por ta n t r o l e in the a tm osphe r e c l e a ns ing ( Ac a de m y P r e ss , 1983) . I n f a c t , i t

is e s t i m a t e d t h a t t h e t w o m a j o r s c a v e n g i n g m e c h a n i s m s i n v o l v e d , r a i n o u t ( i n -c l o u d

s c a ve n g i n g) a n d w a s h o u t ( s ca v e n g in g b e l o w t h e c l o u d ) , t o g e t h e r r e t u r n a b o u t 7 5

t o 8 0 % o f t h e a tm o s p h e r i c p o l l u t a n t s f r o m t h e a t m o s p h e r e t o t h e E a r t h ( R a d k e

e t a l . , 1980 ; B e a t t i e a nd W he lpda le , 1989). H ow e ve r , th i s a m o un t i s h igh ly de pe nd e n t

o n t h e s a m p l i n g l o c a t i o n i n r e l a ti o n t o e m i s si o n s o u r c e s , th e f r e q u e n c y o f r a in

e ve n t s a nd th i s num be r m a y be va r i a b le f r om spe c ie s to spe c ie s .

T h e r a i n w a t e r q u a l i t y d i s t r ib u t i o n a t s y n o p t i c sc a le ( h u n d r e d s o f s q u a r e k i l o m e t r es )

ha s be e n c ha r a c te r i z e d by a l a rge va r i a b i l it y ( Ac a de m y P r e ss , 1983), du e to ge ogr a p h ic

sp r e a d o f sou r c e s a nd s inks . B u t a t t he m e so- sc a le ( a f e w k i lom e t r e s ) on ly a f e ws tud ie s c a n be f ou nd in the l i t er a tu r e , pa r t i c u la r ly in u r ba n a r e a s.

S o m e s t u d ie s o n c h e m i c a l c o m p o s i t i o n o f r a in w a t e r i n c it ie s (D i a z - C a n e j a e t

a l . , 1989) we r e pe r f o r m e d in the p e r spe c t ive o f i ll u s t ra t ing e f fe c t s o f c it ie s on ups t r e a m

a nd downs t r e a m r a inwa te r qua l i ty f o r a g ive n r e g ion . I n f a c t , c i t i e s a r e we l l known

Water, A ir , a nd Soi l Pol lut ion 73: 363-373, 1994.

9 1994 Klu we r Academ ic Publ ishers . Pr in ted in the Nether lands .



364 L A U R I E R P O I SS A N T E T A L .

a s s o u r c e s o f m a n y p o l l u t a n t s ( G a t z , 1 99 1). S o m e o t h e r s tu d i e s w e r e in t e r e s t e d

i n th e r a i n w a t e r q u a l i t y u n d e r u r b a n c o n d i t i o n s a n d l e a d t o d i f fe r e n t c o n c l u si o n s .

O n e s t u d y in W a s h i n g t o n , D . C . ( R a n d a l l e t a l . , 1 97 8), s h o w e d t h a t t h e c o n c e n t r a t i o n s

o b s e r v e d a t t h e v a r i o u s s t a t i o n s w e r e u n i f o r m o v e r t h e e n t i re a r e a o f o b s e r v a t i o n .

O n t h e o t h e r h a n d , a s t u d y c o n d u c t e d i n S t - L o u i s , M I , b y H a l e s e t a l . in 1979

s h o w s i s op l e th s ( c u rv e s o f s a m e c o n c e n t r a t i o n s ) w i t h t h e m a x i m u m c o n c e n t r a t i o n

t o t h e n o r t h o f th e S t - L o u i s c i ty (i .e . d o w n s t r e a m ) . V e r m e t t e e t a l . ( 1 9 8 8 ) h a v e

s h o w n e i t h e r i n th e m o s t h e a v i l y i n d u s t ri a l iz e d c i ti es in C a n a d a ( H a m i l t o n ) i s o p l e th

s u r r o u n d i n g t h e i n d u s t ri a l a r e a .

L e w i s e t a l . ( 19 8 3) w o r k e d o n s p a t i a l - t e m p o r a l v a r i a t i o n s o f s n o w f al l c h e m i s t r y

i n M o n t r 6 a l ' s r e g io n . T h e y s h o w e d t h a t t h e i m p a c t o f t h e u r b a n a r e a o n s n o w

c h e m i s t r y i n r e g i o n a l p a t t e r n w a s a p p a r e n t t h r o u g h i ts c o n c e n t r a t i o n s a n d i ts a ci d

n e u t r a l i z i n g e f f e ct s , i m p a c t r e s u l ti n g i n h i g h e r u r b a n p H v a l u e s f o r m o s t s t o r m s .

T h e i n f o r m a t i o n a b o u t t h e v a r i a b i li t y o f r a i n q u a l i t y o n a m e s o - sc a l e , s u c h a s

o n t h e M o n t rO a l I s l a n d , is i m p o r t a n t i n a fi e ld l ik e s t o r m w a t e r p o l l u t i o n m o d e l l i n g

a n d c o m b i n e d s e w e r o v e rf lo w s . I n f a ct , th e s c ie n ti fi c t r e n d a b o u t t h e n e w a p p r o a c h

o n r u n o f f q u a l i ty m o d e l s n o w c o n s i d er s r a in f a ll q u a l i t y a s a p r i m a r y s o u r c e o f

c o n t r i b u t i o n ( N g , 1 9 8 7 ) , a t l e a s t f o r s o m e q u a l i t y p a r a m e t e r s l i k e n i t r a t e , s u l p h a t e

a n d o t h e r s.

T h i s s t u d y h a s t w o m a i n p u r p o s e s . T h e f i r s t o n e i s t o e v a l u a t e t h e a b i l i t y o fa p r i m a r y s t a t i o n t o a d e q u a t e l y re p r e s e n t M o n t r 6 a l ' s c o n d i t i o n s , b y c o m p a r i n g r e s u lt s

a t th i s s t a t i o n t o th o s e o b t a i n e d a t s o m e s a t e l li t e s t a t i o n s d i s t r i b u t e d o n t h e M o n t r 6 a l

t e r r i t o r y (s p a ti a l d i m e n s i o n ) . T h e s e c o n d o b j e c t i v e is t o c o m p a r e t h e t i m e d i m e n s i o n

a n d t h e s p a ti a l d i m e n s i o n a n d t o d e t e r m i n e t h e d o m i n a n t o n e , in t h e vi e w t o g e t

b a s ic k n o w l e d g e f o r m o d e l l in g r u n o f f w a t e r q u a l it y .

2 . M e t h o d s

2.1. STATIONSLOCATIONSAND SAMPLING

W i t h a p o p u l a t i o n o f a p p r o x i m a t e l y 1 ,7 50 ,0 00 p e o p l e , t h e M o n t r 6 a l I s l a n d i s t h e

s e c o n d la r g e st u r b a n a r e a in C a n a d a . L o c a t e d b e t w e e n 7 3 ~ ' a n d 7 4000 N o r t h

a n d 4 5 01 5 a n d 4 5 0 30 W e s t , t h e I s l a n d i s a b o u t 5 0 0 k m 2 ( F ig u r e 1 ). T h i s t e r r i t o r y

is u r b a n i z e d i n a p r o p o r t i o n o f 8 0% a n d l a n d u s e t h e u r b a n i z e d f r a c t i o n is d i s t r ib u t e d

b e t w e e n r e s i d e n t i a l ( 7 0 % ) , i n d u s t r i a l ( 2 0 % ) a n d c o m m e r c i a l a n d i n s t i t u t i o n a l ( 1 0 % ) .

F r o m J u n e t h r o u g h A u g u s t 1 98 9, m o n i t o r i n g s t a t i o n s w e r e i n s t a l le d in si x l o c a t i o n s .

T h e s e l e c ti o n o f s t a t i o n l o c a t i o n w a s m a d e t o f a c il it a te o p e r a t i o n a n d t o r e p r e s e n ta s w e l l a s p o s s i b l e M o n t r 6 a l ' s s i t u a t i o n ( l ig h t a n d h e a v y u r b a n i z a t i o n ) . T h e p r i m a r y

s t a t io n ( L a f o n t a i n e ) is lo c a t e d n e a r d o w n t o w n , o n t h e r o o f o f a t w o - s t o r y b u i ld i n g

o f t h e U n i v e r s i t 6 d u Q u e b e c / a M o n t rO a l , a n d a d j a c e n t t o a la r g e p a r k , t h e L a f o n t a i n e

p a r k . A m e t e o r o l o g i c a l s ta t i o n l o c a t e d in t h e i m m e d i a t e v i c in i ty a n d o p e r a t e d b y

t h e U n i v e r s i t y w a s o n e o f t h e r e a s o n f o r t h e s e l e c t i o n o f th i s s t a t i o n f o r s u b s e q u e n t

r e s e a rc h . O f th e f i ve s a te l li te s t a t io n s , o n e ( D o w n t o w n ) is l o c a t e d d o w n t o w n o n



ANALYSIS OF RAINWATER QUALIT Y VARIABILITY ON MESO-SCALE 365

C A N A D A I M o . t r ~ a a l

iJ e s u s

I s l a n d

/ _ ~ v 6

2

M o n t r 6 a i I s l a n d

4

5

0 5 10

k m

1 : C 6 t e - S t - P a u l

2 : S t - L a u r e n t

3 ; M e r c i e r

4 : L a f o n t a i n e

5 ; D o w n t o w n

6 : P i e r r e f o n d s

Fig. 1. Loca tion of sampling stations.

t h e r o o f o f a n o t h e r U n i v e r s i t y b u i l d in g ( e i g h t - s to r y b u i ld i n g ) , t w o i n l i g h t - u r b a n i z e d

s u b u r b s ( P i e r r e f o n d s a n d S t - L a u r e n t ) a n d t w o in a d e n s e r s u b u r b s ( C 6 t e S t - P a u la n d M e r c i e r ). I t is w o r t h w h i l e t o r e c a l l th a t t h o s e s t a t i o n l o c a l is a t i o n s w e r e m a d e

t o r e p r e s e n t a s w e l l a s p o s s i b l e M o n t r e a l ' s s i t u a t i o n w i t h o u t a p p a r e n t p u n c t u a l

s o u r c e s o f p o l l u t a n t s o r b i a s a n d t o r e p r e s e n t a w e ll m i x e d a t m o s p h e r e i n re s p e c t

o f t h e s t a t e o f th e a r t . B u t it t o r e m i n d t h a t a l l s t a t i o n s a r e i n u r b a n a r e a , s o

n e a r s t r e e t s , h o u s e s a n d u r b a n f a c i l i t i e s .

S a m p l e r s w e r e m a d e o f a p o l y e t h y l e n e f u n n e l ( d i a m e t e r 2 0 .3 2 c m ) d r a i n i n g i n t o



366 LAURIER POISSANT ET AL.

a polyethylene bottle. The samplers were open to the atmosphere and collect bulk

(wet and dry) deposition. Every day, around 8 AM, collectors were washed with

a laboratory cleansing solution (DECON T M )and rinsed several times with nanopurewater. This cleansing procedure was done whether samples were collected or not.

A total of 20 rainfall events were observed but the six stations were not consistently

monitored during the whole period. Local problems, lack of personnel, human

mistakes and no precipitation at some locations in some cases explain the missing

data. All together, a maximum of 97 storm-station events were analyzed during

the sampling period.

2.2. CHEMICAL ANALYSIS

The samples were brought as soon as possible to the laboratory where analyses

were done according to the following procedures:

- pH: Fisher Accumet Model 825 MP pHmeter with a combined electrode (Fisher);

-Conductivity: Radiometer Copenhagen Model CDM 80, with an electrode

Radiometer Copenhagen CDC 104 (cell constant equal to 1.0);

- Total Organic Carbon (TOC): Dohrmann Carbon Analyzer (Series DC-30);

- Ca and Mg: atomic absorption spectrometer using flame method (Instrumentation

Laboratory aa/ae Spectrometer Model 257);

- Nitrate and sulphate: ionic chromatography (Dionex Chromatograph) using

standard bicarbonate-carbonate elution. The procedure used for anions was

successfully submitted to interlaboratory checks in 1983 (Canadian LRTPA

Program).

For pH and conductivity, analyses were performed within 4 hr and no preservation

techniques was used. For TOC, if analysis could not be done within 4 hr, samples

were preserved by acidification with ultra-pure phosphoric acid and cooling at 4 ~

For Ca and magnesium, samples were analyzed within 3 d or frozen. Finally, nitrate

and sulphate were analyzed within 3 d or stored at 4 ~

2. 3. STATISTICAL ANALYSIS

The first statistical method used to meet the objective of spatial homogeneity is

the canonical discriminant analysis. This method is a dimension-reduction technique

related to principal component analysis (PCA) and canonical correlation. This

technique derives linear combinations of quantitative variables that summarize

between-class variations in the way principal components analysis summarizes total

variation (SAS, 1988).The aims of the canonical discriminant analysis is to find linear combination

of discriminant variables, whom maximize the differences between groups and in

minimizing within group variance (Van de Geer, 1983; Legendre and Legendre, 1984).

Total variance (T) o f a network data set is share as

T=B+W (1)



A N A L Y S IS O F R A I N W A T E R Q U A L I T Y V A R I A B I L IT Y O N M E S O - S C A L E 367

w h e r e B i s t h e p o r t i o n d e p e n d e n t o n d i ff e r e nc e s b e t w e e n g r o u p s , a n d W is t h e

p o r t i o n d e p e n d e n t o n d i f f e re n c e s w i t h i n g r o u p .

T h e m a x i m i z a t i o n i s g i v e n b y t h e fo l l o w m a t r i x e q u a t i o n

(A-XhV )U h = 0 (2 )

w h e r e A is b e t w e e n g r o u p d i s p e r s io n a n d V i s t h e w i t h i n d i s p e rs i o n . T h e n o r m a l i z e d

e i g e n v e c t o r s m a t r i x w h o m g iv e t h e c a n o n i c a l d i s c r i m i n a n t s p a c e ( C ) is:

c = u ( u ' v u ) - 1 / 2 . ( 3 )

F i n a l l y , t h e o b j e c t p o s i t i o n i n t h i s s p a c e i s g i v e n b y

F = [ y - y ] ' C . (4 )

T h e p r o c e d u r e h a s b e e n p e r f o r m e d o n a m u l t i v a ri a t e o n e - w a y a n a ly s is o f v a ri a n c e

a n d s q u a r e d d i s t a n c e s b e t w e e n c l a s s m e a n s b a s e d o n t h e p o o l e d w i t h i n - c l a s s

c o v a r i a n c e m a t r i x w e r e c o m p u t e d . T h e m u l t i v a r i a t e st a ti s ti c t es t u s e d f o r i n t e r p r e t in g

r e su l ts is W i l k 's L a m b d a , w h i c h r a n g e s f r o m 0 ( m a x i m u m d i s p e r s io n o f t h e c e n t r o i d )

t h r o u g h 1 ( n o d i s p e r s io n b e t w e e n g r o u p s ).

T h e s e c o n d m e t h o d f o r s p a ti a l h o m o g e n e i t y is t h e c o m p a r i s o n o f m e a n s b y a n

A N O V A F t e st . T h a t t e s t t e ll s w h e t h e r th e m e a n s a r e s i g n i f i c a n tl y d i f f e r e n t f r o m

e a c h o t h e r , b u t i t d o e s n o t s h o w w h i c h m e a n s d i f f e r f r o m w h i c h o t h e r m e a n . T oc o m p e n s a t e a t th i s li m i t a t i o n a t h i r d m e t h o d g i v e n m o r e d e t a i l a b o u t t h e d i f fe r e n c es

a m o n g t h e m e a n s i s T u k e y ' s s t u d e n t i z e d r a n g e t e s t ( R S R T ) . T h i s t e c h n i q u e i s

r e c o m m e n d e d f o r u n b a l a n c e d s e r ie s ( S A S , 1 98 8; S c h e r r e r , 1 98 4). T R S T i n d i c a t e

f o r a s p e c i f i e d c o n f i d e n c e l e v e l ( a = 0 . 05 ) w h i c h p a i r s a r e s t a t i s t ic a l l y d i f f e r e n t .

T R S T is a m u l ti p l e c o m p a r i s o n m e t h o d o f m e a n s r e s u lt f r o m c o m p a r i s o n o n e v e r y

p a i r o f m e a n s . T h e n u l l h y p o t h e s i s t h a t t h e p o p u l a t i o n m e a n s a r e e q u a l ( i .e . u l

= u2 = u3 = u/c) if

Yi -Y jJ / s ( 1 / n i + 1 ~ n ) - I / 2 < t(c~;v) (5)

w h e r e Yi a n d y j a r e t h e m e a n s t o c o m p a r e d , n i a n d n j a r e t h e n u m b e r o f o b s e r v a t i o n

i n t h e t w o s e r i e s ( i a n d j ) , s i s t h e r o o t m e a n s q u a r e e r r o r b a s e d o n v d e g r e e s

o f f r e e d o m g i v e n b y ( n i + n f - k ) , a n d t ( a ; v ) is t h e c r i t ic a l v a l u e f r o m s t u d e n t ' s

d i s t r i b u t i o n ( S c h e r r e r , 1 9 8 4 , M i l l e r , 1 9 8 6 ) .

T h e s e c o n d o b j e c t iv e o f t h e s t u d y , t h e r e l a ti v e im p o r t a n c e o f sp a c e a n d t i m e

v a r i a t io n s , i s m e t b y a 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 (P C A ) a n d b y a n a n a l ys i s

o f t h e c o e f fi c ie n t s o f v a r i a t i o n i n t h e t i m e a n d s p a c e d i m e n s i o n s .

T h e c e n t r a l i d e a o f P C A is t o r e d u c e t h e d i m e n s i o n a l i t y o f a d a t a s e t in w h i c ht h e r e a r e a la r g e n u m b e r o f i n t e r r e l a t e d v a r i a b l e s , w h i le r e t a i n i n g a s m u c h a s p o ss i b l e

o f v a r i a t i o n p r e s e n t i n t h e d a t a s et . T h i s r e d u c t i o n i s a c h ie v e d b y t r a n s f o r m i n g

t o n e w s e t o f v a r i a b le s , t h e p r i n c i p a l c o m p o n e n t s , w h i c h a r e o r t h o g o n a l ( n o n -

c o r r e l a t e d ), a n d w h i c h a r e o r d e r e d in d e c re a s i n g o r d e r . E a c h c o m p o n e n t s v a r i a t i o n

is m e a s u r e d i n t e r m o f e ig e n v a l u e (X ) f o r a s y m m e t r i c m a t r i x ( R ) . B y u s i n g R

a n d t h e i d e n t i t y m a t r i x ( I ) o f t h e s a m e d i m e n s i o n , e i g e n v a l u es w e r e d e r i v e d t h a t



36 8 LAUR IER POISSANT ET AL.

s a ti sf ie d t h e f o l lo w i n g p o l y n o m i a l e q u a t i o n :

[R -X h I ', = O . (6)

F i n a l l y i t i s p o s s i b l e t o c o m p u t e d e i g e n v e c t o r s (u h ) w h o s e a s s o c i a t e d e i g e n v a lu e s ,

u s in g m a t r i x c o m p u t a t i o n

( R- h h I ) U u = 0 . ( 7 )

T h e e l e m e n t s o f e a c h e ig e n v e c t o r s w e r e th e n m u l t i p li e d b y t h e s q u a r e r o o t o f

a s s o c i a t e d e i g e n v a l u e t o o b t a i n t h e c o m p o n e n t l o a d i n g s . T h e s e l o a d i n g s r e p r e s e n t

t h e c o r r e l a ti o n be t w e e n th e c o m p o n e n t a n d t h e p a r a m e t e r s ( R m o d e P C A ) .

O b s e r v a t i o n s ( n ) c a n b e e x p r e s se d b y m e a n o f P C s c o re (Q m o d e P C A ) c o m p u t e d a s

w h e r e U is e i g e n v e c t o r s m a t r i x .

P C s i s c o m p u t e d w i t h p o o l e d d a t a f r o m a l l s i t e s . M a t h e m a t i c a l l y , t h e P C s c a n

b e c o m p u t e d f r o m t h e c o v a r i a n c e o r o t h e r s c r o s s p r o d u c t m a t r i x . H o w e v e r , t h e

P C s w e r e d e t e r m i n e d f r o m c o r r e l a t i o n m a t r i x b e c a u s e t h e w id e r a n g e in c o n c e n t r a t i o n

o f e l e m e n t s a n d d i f f e r e n t u n i t s ( J o l l i ff e , 1 9 86 ).

3. Resul ts and discussion

3.1. SPATIALHOMOGENEITY

T O d e t e r m i n e w h e t h e r s t a ti o n s h a v e t h e i r o w n i d e n t it i es ( f o r t he p a r a m e t e r s

c o n s i d e r e d ) o r n o t a n d t o e v a l u a t e t h e n e t w o r k , a c a n o n i c a l d i s c r i m i n a n t a n a l y s i s

h a s b e e n p e r f o r m e d . T h e t w o f i r s t c a n o n i c a l f u n c t i o n s e x p l a i n 5 9 % a n d 2 1 % o f

t h e t o t a l v a r i a n c e , r e s p e c t i v e ly , f o r a t o t a l o f 8 0 % . T h e W i l k ' s L a m b d a i s 0 .4 8

a n d t h e P - v a l u e is 0 .3 1 ( P r > F ) . T h e d i s p e r s i o n o f c l as s es ( s ta t i o n s ) s h o w s t h a t

t h e r e is n o d i s c r i m i n a t i o n b e t w e e n s t a t i o n s o n a m u l t i v a r i a t e s e n s e , i .e . b y c o n s i d e r i n g

s t a ti o n s a s a w h o l e a n d n o t o n a p a r a m e t e r b a si s.

H o w e v e r , i f s t a t i o n s a r e e q u i v a l e n t o n a g l o b a l b a s i s , t h e s i t u a t i o n i s sl i g h tl y

d i f f e r e n t w h e n c o m p a r i s o n i s m a d e o n s i n g l e p a r a m e t e r b a s i s . T a b l e I s h o w s r e s u l t s

o f c o m p a r i s o n o f m e a n s b y A N O V A ' F ' t es t. A N O V A i nd i ca t es t h a t m e a n p H s

c a n n o t b e c o n s i d e r e d t h e s a m e f o r a ll t he s t a t io n s .

F u r t h e r a n a ly s i s m a d e w i t h T S R T i n d i c a te t h a t t h is n o n - h o m o g e n e i t y is d u e t o

d i ff e re n c e s b e t w e e n s t a t io n s S t - L a u r e n t a n d D o w n t o w n a n d b e t w e e n s ta t i o n sD o w n t o w n a n d P i e r r e f o n d s .

I t i s w o r t h w h i l e t o r e c a l l t h a t t h e s e r e s u l t s a r e i n a g r e e m e n t w i t h L e w i s e t a l .

( 1 98 3 ) f o r w i n t e r t im e . T h u s , p H i s t h e o n l y p a r a m e t e r f o r w h i c h d i f f e re n c e s o f

m e a n s e x i s t , a n d s t a t i o n s f o r w h i c h t h e s e d i ff e r e n c e s a r e o b s e r v e d a r e t h e le ss

u r b a n i z e d o n e s . F u r t h e r m o r e , t h e h i g h e r p H r e c o r d e d in u r b a n s it es th a n i n

s u r r o u n d i n g a r e a s a g r e e w i t h t h e r e su l t s o f S i m o n i n ( 1 9 7 6 ) i n S t - L o u i s .



A N A L Y S IS O F R A I N W A T E R Q U A L I T Y V A R I A B I L IT Y O N M E S O - S C A L E

TABLE I

Results o f spa tial difference

Param eter ANOVA 'F ' tes t

P r > F

pH 0.008

Conductivi ty 0 .497

TOC 0.497

NO3 0.754

SO4 0.758

Ca 0.748

Mg 0.912

369

3 .2 . TIM E AND SPATIAL VARIABILITIES

T h e f i r s t t w o p r i n c i p a l c o m p o n e n t s o f t h e a b o v e m e n t i o n e d P C A e x p l a in s 8 0%

o f t h e t o t a l v a r i a n c e . T h a t d i m e n s i o n - r e d u c t i o n t e c h n i q u e c a n b e u s e d to s h o w

t i m e a n d s p a t i a l v a r i a b i l i t i e s o f M o n t r 6 a l r a i n w a t e r q u a l i t y f o r t h e p a r a m e t e r s u n d e r

i n v e s t i g a t i o n . T h e F i g u r e 2 i l l u s t r a te s t h e s e v a r i a b i l i t i e s . O n t h e f i g u re , s u b j e c t i v e

l i m i t s f o r i n d i v i d u a l s t o r m s h a v e b e e n d r a w n , a s w e l l a s a r r o w s b e t w e e n c e n t r o i d

F a c t o r 2

0

-1

- 2

_ _ L _ _ _ 3 _ L I 1 3 _

- 3 - 2 . 5 - 2 - 1 . 5 - 1 - 0 . 5 0

)

f

I l _ _ _ _ • L

0 . 5 1 1 .5 2 2 . 5 3

F a c t o r 1

Fig. 2. Rain group ing for spatia l and t ime variat ion by PCA at M ontr6al du ring summ er 1989.



37 0 LAURIER POISSANT ET AL.

of subsequent storms. As shown by this figure, most individual storms display

a common character with relatively small spatial variability except for rain 178

(Julian day) which shows a greater variability. On the other hand, when timedimension is considered, variability becomes much greater.

3.3. COMPARISONOF VARIABILITY

Figure 3 shows for each quality parameters studied the spatial variations (minima

and maxima) with respect to time.

In order to investigate more precisely comparison between spatial and time

variabilities, an analysis of coefficient of variation has been undertaken. Such analysis

requires balanced matrices. To satisfy this constraint and based on the preceding

results on homogeneity, the study will compare stations Lafontaine and Downtown,

which furthermore contain the maximum number of compatible observations. The

coefficient of variation in column 2 Table II (spatial variation) are obtained by

computing, for each quality parameter, the means for each station (time averaging)

and by calculating the coefficient of variation between the two values. Coefficients

of variation of column 3 (time variation), are obtained in a similar way in inverting the

space and time dimensions. The smallest spatial coefficient of variation is for Mg with

a value of 1.37% and the greatest is for TOC (10.85%). The variations can be ex-

plained by multiple causes like analytical or sampling errors, or true spatial differences.The variations in time dimension are also due to the analytical<and sampling

errors and to the change of environmental conditions (wind direction, stability,

sources, etc.). The smallest is for pH with 13.39%, and the greatest for nitrates

with 80.95%.

As mentioned above, the variability in either dimension includes some errors

but the rat io of the two dimensions shows variability on a relative basis. Thus,

this ratio permits to show the more important dimension, i.e. the dimension for

which variability is the greatest. The fourth column in Table II shows that the

time variations are greater than the spatial ones for each quality parameter.

T A B L E I I

C o m p a r i s o n o f c o e f fi ci e nt s o f v a r i a n c e

P a r a m e t e r S p a t ia l T i m e R a t i o

C . V . C .V . T i m e / S p a c e

(%)

p H 6 . 9 0 1 3 . 3 9 1 . 94C o n d u c t i v i t y 5 . 4 0 6 0 . 8 2 1 1 .2 6

T O C 1 0 .8 5 6 1 . 4 2 5 . 6 6

N i t r a t e s 7 . 5 2 8 0 . 9 5 1 0 . 7 6

S u l f a t e s 2 . 0 2 6 9 . 8 4 3 4 . 5 7

C a l c i u m 5 . 8 6 6 2 . 95 1 0 .7 4

M a g n e s i u m 1 .3 7 6 4 .5 2 4 7 . 00



ANALYSISO F R A I N W A T E RQ U A LITYVARIABILITYON MESO-SCALE

pH

7,00 I

6 .80

i i i l

i i i ]3 . 0 0 " June July I August

Conduutlvlty (I/S/ore)

6 0 . 0

50.0

40.0

30,0

20.0

I 0 . 0 -

0.0

I

June July August

371

10.0

8 . 0 -

6 . 0 -

4.0-

2.0-

O.O June JulyI

June July

TOC(mg/L)

12~

N i t r a t e (mg/L N)

2.0-

August

1.5-

1.0-

0.5-

0 . 0 I

/August

Fig. 3. Time series of minima and maxima concentrations recorded during the study on the meso-

scale network (Montr6al).



1 0 . 0 -

g .O 4 . 0 0 -

6 . 0 84

4 . 0

g .O

8 u l f a t u ( r a g / L ) C a l o l u m ( r a g / L }6 . 0 0 -

_ I I

J u n e J u l y A u g u s t

3 . 0 0 -

2 . 0 0 -

1 . 0 0 -

J u n e.0 .... 0. 00!

J u l y

372 LAURIER POISSANT ET AL.

A u g u s t

0 . 6 0

O,SO

0 . 4 0

0 , 3 0

0 . 2 0

M a g n e s i u m ( r a g / L )

0 . 1 0

. i l0 . 0 0 J u n e J u l y A u g u s t

Fig. 3. Tim e series of m inima and m axima concentrations recorded during the study on the meso-scalenetwork (Montreal).

4 . C o n c l u s i o n s

I n a g r e e m e n t w i th R a n d a l l e t a l , ( 19 7 8 ) i n W a s h i n g t o n , D C , a n d i n o p p o s i t i o n

w i t h H a l e s e t a l . ( 1 97 9 ) i n S t -L o u i s , M I , t h e s i t u a t i o n o f M o n t r e a l I s l a n d , w i t h

a f e w e x c e p t io n s , t e n d s t o b e s p a t i a l ly r e l a ti v e l y u n i f o r m o v e r t h e e n t i re a r e a o f

o b s e r v a t i o n . T h e o n l y e x c e p t i o n is p H , w h i c h i s h i g h e r in d o w n t o w n t h a n i n l ig h t -

u r b a n s i t e s . T h e s e h i g h e r p H v a l u e s a r e i n a g r e e m e n t w i t h L e w i s e t a l . (1983) ,



ANALYSISOF RAINWATERQUALITYVARIABILITYON MESO-SCALE 37 3

w h o f o u n d t h a t w i n t e r s t o r m s i n d o w n t o w n M o n t r 6 a l w e r e m o r e a l k a l i n e t h a n

i n s u r r o u n d i n g a r ea s . O n t h e o t h e r h a n d , i m p o r t a n c e o f t i m e v a r i a t i o n s is m u c h

g r e a t e r t h a n t h e s p a t i a l o n e . T h u s , f u t u r e r e s e a r c h w i l l f o c u s o n t i m e v a r i a t i o n s

o f r a i n w a t e r q u a l i t y ( i n t r a - a n d i n t e r - s t o r m ) a t o n l y o n e l o c a t i o n .

Acknowledgments

A u t h o r s w o u l d l i k e t o a c k n o w l e d g e N a t u r a l S c i e n c e a n d E n g i n e e r i n g R e s e a r c h

C o u n c i l o f C a n a d a ( N S E R C C ) a n d th e A t m o s p h e r i c E n v i r o n m e n t S e r v i c e ( E n -

v i r o n m e n t C a n a d a ) f o r t h e i r f i n a n c i a l s u p p o r t .

References

Acad emy Pres s: 1983 , Acid dep os i t ion a tmos p her i c p roces s es in Eas te rn N or th Am er ica - A r ev iew

of cur r en t s c ien ti fi c und er s t and ing , Na t iona l Acad emy Pres s, W as h ing ton , D.C .

Beat tie , L . B . an d W helpdale , D. M .: 1989, Wa ter, air and soi l pol lut ion, 46, 45.

Diaz-C ane ja , N . , B on e t , A . Gu t i e r rez , I . , Mar t inez , A . , and Vi l l a r, E . : 1989 , Wa ter, air and soil pollution,

4 3 , 2 7 7 .

Gatz, F . D. : 1991, Atmospheric Environment, 25b, No, 1, 1-15.

Hales , J . M. an d Da na , M . T .: 1979 , Your. o f applied meteo., 18 ,294 .

He intzenb erg, J . : 1989, Tellus, 41b, 149.

Jolt if fe , I . F . : 1986, Pr incipa l com po ne nt analys is , Spr inger-Ver lag ED S, 271p.

Leai tch, W. R. and Isaac, G . A . : 1989, Tropo spher ic aeroso l s ize dis t r ib ut ion s f rom 1982 to 1988 over

eas t e rn nor th Am er ica , ma nus cr ip t 89 /327 , Atmos phe r i c Env i ron me nt Serv ice , Downs v iew, Ont .

Lege ndre, L . and Legen dre, E: 1984, Ecologic nu m6 rique: Tom e 2 - La s t ructu re des donn6es 6cologiques .

M as s on , 335p.

Lewis , E . J . , Moore, R . T . and Enr ight , J . N. : 1983, Water, Air, and Soil Pollution, 20, 7-22.

M il ler, R . G . : 1986, Be yon d A no va , bas ics of appl ied s tatis tics. J . W iley an d Sons .

Ng , H. Y. F .: 1987 , R a inw ate r con t r ibu t ion to d i s s o lved chemis t ry o f s to rm runof f , XX I I C ongres s

of the In te rn a t ion a l As s o c ia t ion fo r H ydrau l i c R es earch .

R adke , L . F . , Ho bbs , E V. and E l tg ro th , M. W. : 1980 ,Your. o f applied meteo., 10, 715.

Ra nd al l , C . W., Helsel, D . R. , Gr izza rd, T . J . an d R. C. Ho ehn : 1978,Prog. wat. Tech., 10 ,417 .

SAS: 1988, Sa s /s ta t use r 's quide, Sas Ins t i tu te Inc.Scherrer, B . : 1984, Bios tat is t ique. Gae tan M orin ED S. 850p.

S im onin , R . G . : 1976 , Water, a i r , andsoi lpol lut ion, 6, 407.

Van de Geer , J . E : 1993 , In t rod uc t ion to mul t ivar i a t e ana lys i s fo r s oc ia l s c iences . W. H. F reem ans

a n d C o m p a g n y , 23 9p .

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