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The Overlay Technique — A Simple Approach to the Topography Problem: 1 Long Term Concentrations
Atmospheric Pollution 1978, Proceedings of the 13th International Colloquium, Paris, France, April 25-28, 1978, M.M. Benarie (Ed.), Studies in Environmental Science, Volume 1 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
193
THE OVERLAY TECHNIQUE - A SIMPLE APPROACH TO THE TOPOGRAPHY PROBLEM: 1 LONG TERM CONCENTRATIONS
James W. S. Young, Ph.D. Beak C o n s u l t a n t s L i m i t e d , Toronto, Canada
AE5STRACT Most two d i m e n s i o n a l a i r p o l l u t i o n d i s p e r s i o n models i n u s e today a r e a p p l i e d t o a r e a s h a v i n g s i g n i f i c a n t topography o r land-sea e f f e c t s .
To model t h e s e t y p e s o f
areas more r e a l i s t i c a l l y i n v o l v e s t h e n u m e r i c a l s o l u t i o n of t h e c l a s s i c a l t h r e e dimensional equations.
T h i s r e q u i r e s , however, t h e complete s p e c i f i c a t i o n of t h e
flow f i e l d , e i t h e r e x p e r i m e n t a l l y o r t h e o r e t i c a l l y , which i s a d i f f i c u l t and expensive p r o p o s i t i o n f o r t h e c a s u a l model u s e r . T h i s paper p r e s e n t s a s i m p l e o v e r l a y t e c h n i q u e , t h a t can b e a p p l i e d to t h e s t a n d a r d long-term Gaussian f l a t p l a i n m o d e l l i n g o u t p u t , t o g i v e a s p a t i a l l y improved p r e d i c t i o n . The method p r e s e n t e d i s a p p l i e d t o t h e p r e d i c t i o n of t h e long-term concent r a t i o n s of suspended p a r t i c u l a t e m a t t e r from b o t h area and p o i n t s o u r c e s around an iron ore processing f a c i l i t y .
INTRODUCTION
Methods abound i n t h e l i t e r a t u r e f o r t h e p r e d i c t i o n of d i s p e r s i o n from s t a t i o n a r y s o u r c e s i n complex t e r r a i n .
D i s p e r s i o n estimates have been improved by
(1) a l t e r i n g t h e s t a b i l i t y p a r a m e t e r s , ( 2 ) by u s i n g t u r b u l e n c e measurements t o
s p e c i f y d i f f u s i o n c o e f f i c i e n t s o r ( 3 ) by s o l v i n g t h e complete three-dimensional flow f i e l d . The major problems w i t h t h e e x i s t i n g a p p r o a c h e s , from a u s e r s p o i n t of view, are t h a t (1) d e t a i l e d measurements a r e r e q u i r e d i n e a c h area t o b e modelled, ( 2 ) nont u r b u l e n t p r o c e s s e s can i n f l u e n c e plume d i s p e r s i o n , ( 3 ) t h e c o s t of r u n n i n g t h e computer model i s h i g h , and ( 4 ) t h e c a s u a l u s e r may n o t have a s u f f i c i e n t understandi n g of t h e i n t e r a c t i o n s t o a v o i d n o n - r e a l i s t i c s c e n a r i o s a n d / o r programming b i a s e s c a u s i n g anomalous o u t p u t . The b a s i c p r e m i s e s f o r t h e work p r e s e n t e d h e r e were:
(1) t h a t e x i s t i n g two-dimen-
s i o n a l models must b e used ( h e r e t h e C l i m a t o l o g i c a l D i s p e r s i o n Model ( R e f . 1 ) ; ( 2 ) t h a t t h e method b e s i m p l e t o u s e and n o t c o s t l y ; and ( 3 ) t h a t a s i g n i f i c a n t l y improved o u t p u t b e r e a l i z e d i n areas of moderate t o p o g r a p h i c a l i n f l u e n c e .
194 ASSUMPTIONS The f o l l o w i n g assumptions were made i n t h e development of t h i s t e c h n i q u e : ( 1 ) 100 p e r c e n t t e r r a i n r i s e w a s assumed w i t h a t e r r a i n - f o l l o w i n g
streamline.
There are t h r e e models (Ref. 2 ) i n g e n e r a l use i n t h e United S t a t e s today. One i s t h e Half-Height T e r r a i n Model which assumes t h a t t h e s t r e a m l i n e through a plume from a t a l l s t a c k i s i n t e r m e d i a t e between a t e r r a i n - f o l l o w i n g streamline p a r a l l e l t o the sea-level plane. t h i s is v a l i d f o r near-neutral
s t r e a m l i n e and a
Wind t u n n e l s i m u l a t i o n s s u g g e s t t h a t
atmospheric conditions.
The second model i s t h e V a l l e y Model which i s used f o r s t a b l e c o n d i t i o n s and i t assumes t h a t t h e plume s t r e a m l i n e , a t e f f e c t i v e plume h e i g h t , i s p a r a l l e l t o t h e sea-level plane. The t h i r d model i s t h e LAPPES Model which assumes a 65 t o 100% t e r r a i n r i s e depending upon t h e f l o w regime - 65% w i t h moderate t o s t r o n g winds and 100% with l i g h t winds. I t s h o u l d b e n o t e d h e r e t h a t a l l of t h e s e models a r e s h o r t term models and a r e used t o estimate t h e w o r s t c a s e 1 t o 24 hour a v e r a g e c o n c e n t r a t i o n s .
(2)
The e f f e c t i v e plume h e i g h t r e l a t i v e t o a f i x e d datum i s used as i n p u t t o
t h e model.
T h i s h e i g h t i s m o d i f i e d by changing t h e v a l u e i n p u t f o r t h e i n d i v i d u a l
stack heights. The s t a n d a r d Gaussian models a l l assume t h a t two i d e n t i c a l e m i t t e r s , one i n a v a l l e y and t h e o t h e r on t o p of a h i l l , i n f l u e n c e t h e downwind r e c e p t o r s e q u a l l y . I n t h i s t e c h n i q u e , t h e plumes a r e more r e a l i s t i c a l l y d i s t r i b u t e d s p a t i a l l y .
(3)
P l u m e s t h a t a r e below a r e c e p t o r ' s h o r i z o n do n o t i n f l u e n c e t h e concentration
a t that receptor. On t h e l o n g t e r m a t l e a s t h a l f of t h e c o n d i t i o n s t o b e modelled o c c u r when t h e r e
i s no s u r f a c e h e a t i n g .
I n areas w i t h topography, downslope o r k a t a b a t i c winds
o c c u r d u r i n g t h e s e p e r i o d s and p o l l u t i o n o c c u r r i n g on h i l l s i d e s i s c a r r i e d i n t o v a l l e y s below (Ref. 3 ) . i s t r a p p e d i n t h i s flow.
A l s o p o l l u t i o n e m i t t e d a t a low l e v e l ( n e a r t h e ground) I t i s w e l l known t h a t t h e o n l y way t o e n s u r e t h a t e f f l u e n t
i s n o t t r a p p e d i n a v a l l e y i s t o p l a c e t h e l e v e l of emission above, o r a t t h e very
l e a s t o n l y a v e r y s m a l l d i s t a n c e below, t h e l e v e l of t h e s u r r o u n d i n g h i l l s .
(4)
P o l l u t a n t s e m i t t e d a t a given e l e v a t i o n w i l l f i n d t h e i r way t o a l l receptors
a t that elevation.
T h i s i s t h e same a s assuming mass c o n t i n u i t y f o r each two-
d i m e n s i o n a l e l e v a t i o n l a y e r , a r b i t r a r i l y s e l e c t e d a s 30.5 m t h i c k i n t h i s technique.
DATA SET The d a t a s e t used c o n s i s t s of t h e f o l l o w i n g 4 components: (1) t h e m e t e o r o l o g i c a l i n f o r m a t i o n , ( 2 ) t h e p o i n t s o u r c e i n f o r m a t i o n , ( 3 ) t h e observed c o n c e n t r a t i o n s a t ground l e v e l and ( 4 ) t h e estimates of e m i s s i o n s from a r e a s o u r c e s .
195 THE METEOROLOGICAL INFORMATION
The climate of n o r t h e r n O n t a r i o may b e c l a s s i f i e d as m o d i f i e d c o n t i n e n t a l , t h e m o d i f i c a t i o n b e i n g mainly due t o t h e p r e s e n c e of t h e Great Lakes on t h e s o u t h and t o a minor e x t e n t , t o Hudson Bay on t h e n o r t h . The m e t e o r o l o g i c a l d a t a s e t used w a s t h e Day-Night STAR j o i n t f r e q u e n c y d i s t r i b u t i o n f o r t h e Atikokan a i r p o r t .
This gives
t h e j o i n t f r e q u e n c y of o c c u r r e n c e of a wind d i r e c t i o n s e c t o r , a wind speed c l a s s and a s t a b i l i t y c a t e g o r y and w a s p r e p a r e d f o r t h e 10 y e a r p e r i o d 1967-1976. s t a t i o n i s a t an e l e v a t i o n of 427m.
This
The a v e r a g e a f t e r n o o n mixing h e i g h t used w a s
1 0 2 1 m and t h e a v e r a g e n o c t u r n a l mixing h e i g h t used w a s 1 2 5 m.
The mean atmospheric
t e m p e r a t u r e used w a s 1.7"C.
THE POINT SOURCES
Twenty-three (23) p o i n t s o u r c e s w e r e d e f i n e d f o r t h i s area.
F o u r t e e n ( 1 4 ) of
them had e x c e l l e n t i n f o r m a t i o n on e m i s s i o n r a t e s based on s t a c k t e s t i n g and m a t e r i a l balances.
The remaining n i n e (9) are b e s t estimates from t h e O n t a r i o M i n i s t r y of
t h e Environment e n g i n e e r i n g s t a f f .
All v a l u e s used a s model i n p u t s w e r e c a l c u l a t e d
t o b e e q u i v a l e n t t o long-term a v e r a g e e m i s s i o n r a t e s .
THE AREA SOURCES
E i g h t (8) area s o u r c e s w e r e d e f i n e d f o r i n p u t t o t h i s model.
One of t h e s e w a s
a n estimate o f e m i s s i o n s from s o u r c e s i n t h e town and i s f e l t t o be q u i t e good b u t t h e r e m a i n i n g seven a r e e m i s s i o n s from open p i t mines and t a i l i n g s a r e a s and are f e l t t o b e o n l y f i r s t h i g h estimates of t h e a c t u a l e m i s s i o n s .
Three b a s i c c a l c u l a -
t i o n methods were a p p l i e d which gave e m i s s i o n s (from t h e p i t w i t h t h e most informat i o n ) r a n g i n g from 100 t o 790 g / s . The a c t u a l r a t e used f o r t h i s p i t was 366 g / s b a s e d on t h e method of Cowherd and Hendriks ( R e f . 4 ) .
I t i s f e l t t h a t t h e emission
r a t e s used may b e t o o h i g h by a f a c t o r of 50 p e r c e n t .
IXE OBSERVED SUSPENDED PARTICULATE MATTER CONCENTRATIONS
Suspended p a r t i c u l a t e matter h a s been monitored i n t h i s a r e a s i n c e 1966.
The
v a l u e s used f o r c a l i b r a t i o n of t h e model are from 1 2 m o n i t o r s l o c a t e d w i t h i n a 7 km r a d i u s of t h e major s o u r c e s .
The a v e r a g e c o n c e n t r a t i o n s used r e p r e s e n t v a r y i n g
l e n g t h s of r e c o r d from 1 t o 9 y e a r s w i t h s t a n d a r d d e v i a t i o n s r a n g i n g from 8 t o over 90 p e r c e n t of t h e a v e r a g e long-term v a l u e s .
The observed long-term v a l u e s of SPM
a t t h e s e s t a t i o n s i s given i n Table 1. T h i s d a t a i s t y p i c a l of t h e q u a l i t y of i n f o r m a t i o n from s o u r c e m o n i t o r i n g programs, and a v a i l a b l e f o r e n v i r o n m e n t a l impact a s s e s s m e n t s .
196 TABLE TABLE 31 Long-term Long-term Suspended S u s p e n d e d PP aa rr tt ii cc uu ll aa tt ee Matter Matter (SPM) (SPM) C C oo nn cc ee nn tt rr aa tt ii oo nn ss ii nn ug/rn3 ug/rn3
XX
R R ee cceeppttoorr
L L ooccaatt ii oo nn
153.5 153.5 1155 44 .. 77 152.7 152.7 115 2 . 8 150.0 150.0 150.9 150.9 150.6 150.6 148.6 148.6 148.5 148.5 115 0 . 8 1144 99 .. 77 152.2 152.2
1 1 22 33 44 55 66 77 88 99 1100 1 11 1 11 22
YY
Observed Observed
46.9 46.9 49.2 49.2 48.2 48.2 40.8 40.8 47.6 47.6 47.a 47.a 50.4 50.4 48.2 48.2 46.5 46.5 44.6 44.6 4488 .. 33 4488..11
50 50 120 120 98 98 42 42 194 194 162 162 54 54 46 46 40 40 331 1 118 118 222 222
C C aa ll cc uu ll aa tt ee dd SS t a n d a r d O Ov e r l a y CDM Technique CDM Technique 506. 506. 272. 272. 1354. 1354. 101. 101. 549. 549. 938. 938. 315. 315. 317. 317. 282. 282. 505. 505. 574. 574. 1587.
448. 448. 84. 84. 170. 170. 95. 95. 422. 422. 761. 761. 29. 29. 36. 36. 40. 40. 41. 41. 368. 368. 1144 66 00 ..
METHOD METHOD The C l i m a t o l o g i c a l D i s p e r s i o n Model (CDM) d e t e r m i n e s l o n g - t e r m p o l l u t a n t concent r a t i o n s a t any g r o u n d - l e v e l
r e c e p t o r u s i n g a v e r a g e e m i s s i o n s r a t e s from p o i n t and
area s o u r c e s and a j o i n t f r e q u e n c y d i s t r i b u t i o n o f wind d i r e c t i o n s and s p e e d , and
s t a b i l i t y f o r t h e same p e r i o d . ground-level
(Ref.
1).
The c o n c e n t r a t i o n s a r e o u t p u t a t t h e
r e c e p t o r s f o r which o b s e r v a t i o n s e x i s t and a s t r a i g h t l i n e e q u a t i o n
of t h e form: Observed = A
+ B*(Calculated)
i s f i t t o c a l i b r a t e t h e model o u t p u t . F o r
t h e test d a t a used, t h e c o e f f i c i e n t of determination ( r 2 ) i s 0.43, with c o r r e l a t i o n c o e f f i c i e n t s A = 40.9 a n d B = 0.0940.
The model o u t p u t d a t a used f o r t h i s c a l i b -
r a t i o n a r e g i v e n i n T a b l e 1 under " S t a n d a r d CDM".
The c a l i b r a t e d s t a n d a r d r u n o u t -
p u t i s shown i n F i g u r e 1 f o r t h e whole area.
55
-
.................. .. \
50 50 -
-
\ I
45 45
i
/
-
i ..............
/
/
cc ll
/
-40 40
,,
II
,,
II
11
11
11
11
1145 45 1150 50 155 1160 I 155 FFiigg.. 1. a t t e r -- SSttaa nn d a r d C 1. Ground Ground LL ee vv e l Suspended S u s p e n d e d PP aa rr t i c u l a t e M Matter Caalliibbrraatteedd CDM CDM O 80 g/m Ouuttppuutt (-120, (-120, 8 0 and--60 and--60 g/m ))
197 For t h e o v e r l a y t e c h n i q u e , e a c h r e q u i r e d r e c e p t o r - h e i g h t
(here the centre point
of each s q u a r e k i l o m e t r e ) i s c l a s s i f i e d i n t o a topography l a y e r .
The l o w e s t ( o r b a s e )
l e v e l used i n t h i s l o c a t i o n w a s 366 m - t h a t b e i n g t h e approximate e l e v a t i o n of t h e
area s o u r c e e m i s s i o n s .
The mid-point
topography w a s c a t e g o r i z e d i n t o 30.5 m l a y e r s
so t h a t e a c h r e c e p t o r f e l l i n t o t h e 366 (366 - 396 m), t h e 396 (396 - 427 m), t h e
427 ( 4 2 7
-
4 5 7 m) o r t h e 4 5 7 m e t r e l a y e r ( 4 5 7 + ) .
The r e l a t i v e v e r t i c a l p o s i t i o n s
of a l l s o u r c e s ( p o i n t and a r e a ) w e r e r e f e r r e d i n i t i a l l y t o t h e 366 m datum and t h e i n p u t s t a c k h e i g h t s w e r e modified t o s u i t . 366 m u n c a l i b r a t e d o v e r l a y .
The CDM run f o r t h i s c a s e p r o v i d e s t h e
The i n p u t s t a c k h e i g h t s were t h e n reduced t o model a
30.5 m t e r r a i n r i s e (by s u b t r a c t i n g 30.5 m from t h e s t a c k h e i g h t s used i n t h e 366 m o v e r l a y ) .
Any s t a c k h e i g h t s t h a t became n e g a t i v e ( s o u r c e s below t h i s t e r r a i n
h e i g h t ) were o m i t t e d and t h i s modified d a t a set produced t h e 396 m o v e r l a y o u t p u t . This p r o c e d u r e w a s c o n t i n u e d f o r t h e remaining two 30.5 m t o p o g r a p h i c l a y e r s producing t h e 427 and 457 m o v e r l a y s .
By u s i n g t h e r e c e p t o r - h e i g h t c l a s s i f i c a t i o n one can
then e x t r a c t t h e u n c a l i b r a t e d c o n c e n t r a t i o n s f o r each r e c e p t o r , and c a l i b r a t i o n p o i n t s from t h e a p p r o p r i a t e o v e r l a y .
For example, a r e c e p t o r a t 404 m i s i n t h e 396 - 427 m
l a y e r and t h e g r o u n d - l e v e l c o n c e n t r a t i o n i s b e s t r e p r e s e n t e d by t h e 396 m o v e r l a y . Using t h e d a t a from t h e o v e r l a y t e c h n i q u e ( T a b l e 1 ) and t h e observed d a t a t o produce a c a l i b r a t i o n e q u a t i o n , a s b e f o r e , w e f i n d t h a t t h e c o e f f i c i e n t o f determinat i o n ( r 2 ) i s 0 . 6 4 , w i t h c o r r e l a t i o n c o e f f i c i e n t s of A
=
5 7 . 3 and B = 0 . 1 2 4 .
The composite model o u t p u t can now be c a l i b r a t e d t o g i v e t h e o u t p u t shown i n Figure 2 .
145
150
155
F i g . 2 . Ground L e v e l Suspended P a r t i c u l a t e Matter i n ug/m3 C a l i b r a t e d Overlay Technique
160
145
150
155
10
F i g . 3. 427 Metre E l e v a t i o n Contour ( d a r k a r e a s a r e above and l i g h t areas are below 4 2 7 m)
198 OBSERVATIONS When one compares t h e c o n c e n t r a t i o n s ( F i g u r e 2 ) t o t h e a c t u a l topography, one o b s e r v e s t h a t t h e h i g h SPM v a l u e s o c c u r i n t h e p i t a r e a s and n o t on t h e h i g h ground s u r r o u n d i n g them as i n t h e s t a n d a r d CDM o u t p u t , t h a t i s , t h e method a p p e a r s t o g i v e a b e t t e r s p a t i a l l y defined output. Some anomolies do a p p e a r , however, such a s an i n c r e a s e d g e n e r a l background l e v e l (57 v s 4 1 pg/m3) and some u n i q u e l y h i g h ground l e v e l v a l u e s . good example, a t x = 154 and y
=
One s t a n d s o u t a s a
45 we have a ground l e v e l c o n c e n t r a t i o n of 97 ug/m3.
This p o i n t i s i n a v a l l e y ( F i g u r e 3) w i t h a b a s e e l e v a t i o n o f about 366 m.
The
r e c e p t o r s c l o s e s t t o i t , a l o n g t h e v a l l e y , (mid-points of a s q u a r e k i l o m e t r e ) , j u s t happen t o f a l l h a l f way up t h e v a l l e y w a l l ( i n t h e n e x t t o p o g r a p h i c l a y e r ) and t h e c o n c e n t r a t i o n s are, t h e r e f o r e , c o r r e s p o n d i n g l y l o w e r .
This points o u t t h a t a user
must c a r e f u l l y choose h i s o u t p u t p o i n t s because t h e model i s o n l y two-dimensional i n a s p e c i f i c l a y e r and c a n n o t make t h e c h o i c e s f o r t h e u s e r . This p a r t i c u l a r anomaly r e p r e s e n t s w e l l t h e normal s p a t i a l v a r i a b i l i t y observed i n n a t u r e . r u n n i n g t h i s model i s v e r y r e a s o n a b l e
-
p e r h a p s , i n g e n e r a l , o n l y t w i c e t h a t of t h e
s t a n d a r d CDM r u n s i n c e s o u r c e s d i s a p p e a r as t h e t e r r a i n r i s e s . tion
The c o s t of
If t h e a c t u a l eleva-
of a r e c e p t o r p o i n t i s used t o i n t e r p o l a t e a c o n c e n t r a t i o n , t h e c o e f f i c i e n t
of d e t e r m i n a t i o n i s n o t as good ( r 2 = 0 . 6 0 ) a n d , t h e r e f o r e , n o t worth t h e e f f o r t i n volved.
The method d e s c r i b e d rounds a l l e l e v a t i o n s down t o t h e n e a r e s t 3 0 . 5 m.
If
one rounds up, t h e c o e f f i c i e n t o f d e t e r m i n a t i o n a g a i n i s n o t a s good ( r 2 = 0.60) s u g g e s t i n g t h a t l e s s than a 100% t e r r a i n rise may be b e n e f i c i a l .
CONCLUSION The o v e r l a y t e c h n i q u e g i v e s a n improved c o r r e l a t i o n between model o u t p u t and obs e r v e d ground l e v e l c o n c e n t r a t i o n s .
I t a l s o g i v e s a s p a t i a l l y improved p r e d i c t i o n i n
an area with s i g n i f i c a n t topographical influences.
The t e c h n i q u e u s e s a n e x i s t i n g
long-term model (CDM) and i s b o t h s i m p l e t o a p p l y and c o s t e f f e c t i v e .
The o u t p u t
a p p e a r s t o r e p r e s e n t t h e observed n a t u r a l v a r i a b i l i t y b e t t e r t h a n most two-dimensional models, ACKNOWLEDGEMENTS The a u t h o r i s i n d e b t e d t o S t e e p Rock I r o n Mines L i m i t e d f o r l e t t i n g him u s e t h e emissions d a t a f o r t h i s paper.
REFERENCES
1. A.D. Busse and J . R . Zimmerman, EPA-R4-73-024, (1973) 2. A . A . Slowik, J . M . A u s t i n and G . N . P i c a , P a p e r 77-29.1, p r e s e n t e d a t t h e 7 0 t h Annual Meeting o f t h e AF'CA, (1977) 3 . R. S c o r e r , A i r P o l l u t i o n . Pergamon P r e s s 1968, 1 5 1 pp. 4 . C. Cowherd and R.V. H e n d r i k s , P a p e r No. 77 - 6.2 p r e s e n t e d a t t h e 70th Annual Meeting of t h e APCA, (1977)
193
THE OVERLAY TECHNIQUE - A SIMPLE APPROACH TO THE TOPOGRAPHY PROBLEM: 1 LONG TERM CONCENTRATIONS
James W. S. Young, Ph.D. Beak C o n s u l t a n t s L i m i t e d , Toronto, Canada
AE5STRACT Most two d i m e n s i o n a l a i r p o l l u t i o n d i s p e r s i o n models i n u s e today a r e a p p l i e d t o a r e a s h a v i n g s i g n i f i c a n t topography o r land-sea e f f e c t s .
To model t h e s e t y p e s o f
areas more r e a l i s t i c a l l y i n v o l v e s t h e n u m e r i c a l s o l u t i o n of t h e c l a s s i c a l t h r e e dimensional equations.
T h i s r e q u i r e s , however, t h e complete s p e c i f i c a t i o n of t h e
flow f i e l d , e i t h e r e x p e r i m e n t a l l y o r t h e o r e t i c a l l y , which i s a d i f f i c u l t and expensive p r o p o s i t i o n f o r t h e c a s u a l model u s e r . T h i s paper p r e s e n t s a s i m p l e o v e r l a y t e c h n i q u e , t h a t can b e a p p l i e d to t h e s t a n d a r d long-term Gaussian f l a t p l a i n m o d e l l i n g o u t p u t , t o g i v e a s p a t i a l l y improved p r e d i c t i o n . The method p r e s e n t e d i s a p p l i e d t o t h e p r e d i c t i o n of t h e long-term concent r a t i o n s of suspended p a r t i c u l a t e m a t t e r from b o t h area and p o i n t s o u r c e s around an iron ore processing f a c i l i t y .
INTRODUCTION
Methods abound i n t h e l i t e r a t u r e f o r t h e p r e d i c t i o n of d i s p e r s i o n from s t a t i o n a r y s o u r c e s i n complex t e r r a i n .
D i s p e r s i o n estimates have been improved by
(1) a l t e r i n g t h e s t a b i l i t y p a r a m e t e r s , ( 2 ) by u s i n g t u r b u l e n c e measurements t o
s p e c i f y d i f f u s i o n c o e f f i c i e n t s o r ( 3 ) by s o l v i n g t h e complete three-dimensional flow f i e l d . The major problems w i t h t h e e x i s t i n g a p p r o a c h e s , from a u s e r s p o i n t of view, are t h a t (1) d e t a i l e d measurements a r e r e q u i r e d i n e a c h area t o b e modelled, ( 2 ) nont u r b u l e n t p r o c e s s e s can i n f l u e n c e plume d i s p e r s i o n , ( 3 ) t h e c o s t of r u n n i n g t h e computer model i s h i g h , and ( 4 ) t h e c a s u a l u s e r may n o t have a s u f f i c i e n t understandi n g of t h e i n t e r a c t i o n s t o a v o i d n o n - r e a l i s t i c s c e n a r i o s a n d / o r programming b i a s e s c a u s i n g anomalous o u t p u t . The b a s i c p r e m i s e s f o r t h e work p r e s e n t e d h e r e were:
(1) t h a t e x i s t i n g two-dimen-
s i o n a l models must b e used ( h e r e t h e C l i m a t o l o g i c a l D i s p e r s i o n Model ( R e f . 1 ) ; ( 2 ) t h a t t h e method b e s i m p l e t o u s e and n o t c o s t l y ; and ( 3 ) t h a t a s i g n i f i c a n t l y improved o u t p u t b e r e a l i z e d i n areas of moderate t o p o g r a p h i c a l i n f l u e n c e .
194 ASSUMPTIONS The f o l l o w i n g assumptions were made i n t h e development of t h i s t e c h n i q u e : ( 1 ) 100 p e r c e n t t e r r a i n r i s e w a s assumed w i t h a t e r r a i n - f o l l o w i n g
streamline.
There are t h r e e models (Ref. 2 ) i n g e n e r a l use i n t h e United S t a t e s today. One i s t h e Half-Height T e r r a i n Model which assumes t h a t t h e s t r e a m l i n e through a plume from a t a l l s t a c k i s i n t e r m e d i a t e between a t e r r a i n - f o l l o w i n g streamline p a r a l l e l t o the sea-level plane. t h i s is v a l i d f o r near-neutral
s t r e a m l i n e and a
Wind t u n n e l s i m u l a t i o n s s u g g e s t t h a t
atmospheric conditions.
The second model i s t h e V a l l e y Model which i s used f o r s t a b l e c o n d i t i o n s and i t assumes t h a t t h e plume s t r e a m l i n e , a t e f f e c t i v e plume h e i g h t , i s p a r a l l e l t o t h e sea-level plane. The t h i r d model i s t h e LAPPES Model which assumes a 65 t o 100% t e r r a i n r i s e depending upon t h e f l o w regime - 65% w i t h moderate t o s t r o n g winds and 100% with l i g h t winds. I t s h o u l d b e n o t e d h e r e t h a t a l l of t h e s e models a r e s h o r t term models and a r e used t o estimate t h e w o r s t c a s e 1 t o 24 hour a v e r a g e c o n c e n t r a t i o n s .
(2)
The e f f e c t i v e plume h e i g h t r e l a t i v e t o a f i x e d datum i s used as i n p u t t o
t h e model.
T h i s h e i g h t i s m o d i f i e d by changing t h e v a l u e i n p u t f o r t h e i n d i v i d u a l
stack heights. The s t a n d a r d Gaussian models a l l assume t h a t two i d e n t i c a l e m i t t e r s , one i n a v a l l e y and t h e o t h e r on t o p of a h i l l , i n f l u e n c e t h e downwind r e c e p t o r s e q u a l l y . I n t h i s t e c h n i q u e , t h e plumes a r e more r e a l i s t i c a l l y d i s t r i b u t e d s p a t i a l l y .
(3)
P l u m e s t h a t a r e below a r e c e p t o r ' s h o r i z o n do n o t i n f l u e n c e t h e concentration
a t that receptor. On t h e l o n g t e r m a t l e a s t h a l f of t h e c o n d i t i o n s t o b e modelled o c c u r when t h e r e
i s no s u r f a c e h e a t i n g .
I n areas w i t h topography, downslope o r k a t a b a t i c winds
o c c u r d u r i n g t h e s e p e r i o d s and p o l l u t i o n o c c u r r i n g on h i l l s i d e s i s c a r r i e d i n t o v a l l e y s below (Ref. 3 ) . i s t r a p p e d i n t h i s flow.
A l s o p o l l u t i o n e m i t t e d a t a low l e v e l ( n e a r t h e ground) I t i s w e l l known t h a t t h e o n l y way t o e n s u r e t h a t e f f l u e n t
i s n o t t r a p p e d i n a v a l l e y i s t o p l a c e t h e l e v e l of emission above, o r a t t h e very
l e a s t o n l y a v e r y s m a l l d i s t a n c e below, t h e l e v e l of t h e s u r r o u n d i n g h i l l s .
(4)
P o l l u t a n t s e m i t t e d a t a given e l e v a t i o n w i l l f i n d t h e i r way t o a l l receptors
a t that elevation.
T h i s i s t h e same a s assuming mass c o n t i n u i t y f o r each two-
d i m e n s i o n a l e l e v a t i o n l a y e r , a r b i t r a r i l y s e l e c t e d a s 30.5 m t h i c k i n t h i s technique.
DATA SET The d a t a s e t used c o n s i s t s of t h e f o l l o w i n g 4 components: (1) t h e m e t e o r o l o g i c a l i n f o r m a t i o n , ( 2 ) t h e p o i n t s o u r c e i n f o r m a t i o n , ( 3 ) t h e observed c o n c e n t r a t i o n s a t ground l e v e l and ( 4 ) t h e estimates of e m i s s i o n s from a r e a s o u r c e s .
195 THE METEOROLOGICAL INFORMATION
The climate of n o r t h e r n O n t a r i o may b e c l a s s i f i e d as m o d i f i e d c o n t i n e n t a l , t h e m o d i f i c a t i o n b e i n g mainly due t o t h e p r e s e n c e of t h e Great Lakes on t h e s o u t h and t o a minor e x t e n t , t o Hudson Bay on t h e n o r t h . The m e t e o r o l o g i c a l d a t a s e t used w a s t h e Day-Night STAR j o i n t f r e q u e n c y d i s t r i b u t i o n f o r t h e Atikokan a i r p o r t .
This gives
t h e j o i n t f r e q u e n c y of o c c u r r e n c e of a wind d i r e c t i o n s e c t o r , a wind speed c l a s s and a s t a b i l i t y c a t e g o r y and w a s p r e p a r e d f o r t h e 10 y e a r p e r i o d 1967-1976. s t a t i o n i s a t an e l e v a t i o n of 427m.
This
The a v e r a g e a f t e r n o o n mixing h e i g h t used w a s
1 0 2 1 m and t h e a v e r a g e n o c t u r n a l mixing h e i g h t used w a s 1 2 5 m.
The mean atmospheric
t e m p e r a t u r e used w a s 1.7"C.
THE POINT SOURCES
Twenty-three (23) p o i n t s o u r c e s w e r e d e f i n e d f o r t h i s area.
F o u r t e e n ( 1 4 ) of
them had e x c e l l e n t i n f o r m a t i o n on e m i s s i o n r a t e s based on s t a c k t e s t i n g and m a t e r i a l balances.
The remaining n i n e (9) are b e s t estimates from t h e O n t a r i o M i n i s t r y of
t h e Environment e n g i n e e r i n g s t a f f .
All v a l u e s used a s model i n p u t s w e r e c a l c u l a t e d
t o b e e q u i v a l e n t t o long-term a v e r a g e e m i s s i o n r a t e s .
THE AREA SOURCES
E i g h t (8) area s o u r c e s w e r e d e f i n e d f o r i n p u t t o t h i s model.
One of t h e s e w a s
a n estimate o f e m i s s i o n s from s o u r c e s i n t h e town and i s f e l t t o be q u i t e good b u t t h e r e m a i n i n g seven a r e e m i s s i o n s from open p i t mines and t a i l i n g s a r e a s and are f e l t t o b e o n l y f i r s t h i g h estimates of t h e a c t u a l e m i s s i o n s .
Three b a s i c c a l c u l a -
t i o n methods were a p p l i e d which gave e m i s s i o n s (from t h e p i t w i t h t h e most informat i o n ) r a n g i n g from 100 t o 790 g / s . The a c t u a l r a t e used f o r t h i s p i t was 366 g / s b a s e d on t h e method of Cowherd and Hendriks ( R e f . 4 ) .
I t i s f e l t t h a t t h e emission
r a t e s used may b e t o o h i g h by a f a c t o r of 50 p e r c e n t .
IXE OBSERVED SUSPENDED PARTICULATE MATTER CONCENTRATIONS
Suspended p a r t i c u l a t e matter h a s been monitored i n t h i s a r e a s i n c e 1966.
The
v a l u e s used f o r c a l i b r a t i o n of t h e model are from 1 2 m o n i t o r s l o c a t e d w i t h i n a 7 km r a d i u s of t h e major s o u r c e s .
The a v e r a g e c o n c e n t r a t i o n s used r e p r e s e n t v a r y i n g
l e n g t h s of r e c o r d from 1 t o 9 y e a r s w i t h s t a n d a r d d e v i a t i o n s r a n g i n g from 8 t o over 90 p e r c e n t of t h e a v e r a g e long-term v a l u e s .
The observed long-term v a l u e s of SPM
a t t h e s e s t a t i o n s i s given i n Table 1. T h i s d a t a i s t y p i c a l of t h e q u a l i t y of i n f o r m a t i o n from s o u r c e m o n i t o r i n g programs, and a v a i l a b l e f o r e n v i r o n m e n t a l impact a s s e s s m e n t s .
196 TABLE TABLE 31 Long-term Long-term Suspended S u s p e n d e d PP aa rr tt ii cc uu ll aa tt ee Matter Matter (SPM) (SPM) C C oo nn cc ee nn tt rr aa tt ii oo nn ss ii nn ug/rn3 ug/rn3
XX
R R ee cceeppttoorr
L L ooccaatt ii oo nn
153.5 153.5 1155 44 .. 77 152.7 152.7 115 2 . 8 150.0 150.0 150.9 150.9 150.6 150.6 148.6 148.6 148.5 148.5 115 0 . 8 1144 99 .. 77 152.2 152.2
1 1 22 33 44 55 66 77 88 99 1100 1 11 1 11 22
YY
Observed Observed
46.9 46.9 49.2 49.2 48.2 48.2 40.8 40.8 47.6 47.6 47.a 47.a 50.4 50.4 48.2 48.2 46.5 46.5 44.6 44.6 4488 .. 33 4488..11
50 50 120 120 98 98 42 42 194 194 162 162 54 54 46 46 40 40 331 1 118 118 222 222
C C aa ll cc uu ll aa tt ee dd SS t a n d a r d O Ov e r l a y CDM Technique CDM Technique 506. 506. 272. 272. 1354. 1354. 101. 101. 549. 549. 938. 938. 315. 315. 317. 317. 282. 282. 505. 505. 574. 574. 1587.
448. 448. 84. 84. 170. 170. 95. 95. 422. 422. 761. 761. 29. 29. 36. 36. 40. 40. 41. 41. 368. 368. 1144 66 00 ..
METHOD METHOD The C l i m a t o l o g i c a l D i s p e r s i o n Model (CDM) d e t e r m i n e s l o n g - t e r m p o l l u t a n t concent r a t i o n s a t any g r o u n d - l e v e l
r e c e p t o r u s i n g a v e r a g e e m i s s i o n s r a t e s from p o i n t and
area s o u r c e s and a j o i n t f r e q u e n c y d i s t r i b u t i o n o f wind d i r e c t i o n s and s p e e d , and
s t a b i l i t y f o r t h e same p e r i o d . ground-level
(Ref.
1).
The c o n c e n t r a t i o n s a r e o u t p u t a t t h e
r e c e p t o r s f o r which o b s e r v a t i o n s e x i s t and a s t r a i g h t l i n e e q u a t i o n
of t h e form: Observed = A
+ B*(Calculated)
i s f i t t o c a l i b r a t e t h e model o u t p u t . F o r
t h e test d a t a used, t h e c o e f f i c i e n t of determination ( r 2 ) i s 0.43, with c o r r e l a t i o n c o e f f i c i e n t s A = 40.9 a n d B = 0.0940.
The model o u t p u t d a t a used f o r t h i s c a l i b -
r a t i o n a r e g i v e n i n T a b l e 1 under " S t a n d a r d CDM".
The c a l i b r a t e d s t a n d a r d r u n o u t -
p u t i s shown i n F i g u r e 1 f o r t h e whole area.
55
-
.................. .. \
50 50 -
-
\ I
45 45
i
/
-
i ..............
/
/
cc ll
/
-40 40
,,
II
,,
II
11
11
11
11
1145 45 1150 50 155 1160 I 155 FFiigg.. 1. a t t e r -- SSttaa nn d a r d C 1. Ground Ground LL ee vv e l Suspended S u s p e n d e d PP aa rr t i c u l a t e M Matter Caalliibbrraatteedd CDM CDM O 80 g/m Ouuttppuutt (-120, (-120, 8 0 and--60 and--60 g/m ))
197 For t h e o v e r l a y t e c h n i q u e , e a c h r e q u i r e d r e c e p t o r - h e i g h t
(here the centre point
of each s q u a r e k i l o m e t r e ) i s c l a s s i f i e d i n t o a topography l a y e r .
The l o w e s t ( o r b a s e )
l e v e l used i n t h i s l o c a t i o n w a s 366 m - t h a t b e i n g t h e approximate e l e v a t i o n of t h e
area s o u r c e e m i s s i o n s .
The mid-point
topography w a s c a t e g o r i z e d i n t o 30.5 m l a y e r s
so t h a t e a c h r e c e p t o r f e l l i n t o t h e 366 (366 - 396 m), t h e 396 (396 - 427 m), t h e
427 ( 4 2 7
-
4 5 7 m) o r t h e 4 5 7 m e t r e l a y e r ( 4 5 7 + ) .
The r e l a t i v e v e r t i c a l p o s i t i o n s
of a l l s o u r c e s ( p o i n t and a r e a ) w e r e r e f e r r e d i n i t i a l l y t o t h e 366 m datum and t h e i n p u t s t a c k h e i g h t s w e r e modified t o s u i t . 366 m u n c a l i b r a t e d o v e r l a y .
The CDM run f o r t h i s c a s e p r o v i d e s t h e
The i n p u t s t a c k h e i g h t s were t h e n reduced t o model a
30.5 m t e r r a i n r i s e (by s u b t r a c t i n g 30.5 m from t h e s t a c k h e i g h t s used i n t h e 366 m o v e r l a y ) .
Any s t a c k h e i g h t s t h a t became n e g a t i v e ( s o u r c e s below t h i s t e r r a i n
h e i g h t ) were o m i t t e d and t h i s modified d a t a set produced t h e 396 m o v e r l a y o u t p u t . This p r o c e d u r e w a s c o n t i n u e d f o r t h e remaining two 30.5 m t o p o g r a p h i c l a y e r s producing t h e 427 and 457 m o v e r l a y s .
By u s i n g t h e r e c e p t o r - h e i g h t c l a s s i f i c a t i o n one can
then e x t r a c t t h e u n c a l i b r a t e d c o n c e n t r a t i o n s f o r each r e c e p t o r , and c a l i b r a t i o n p o i n t s from t h e a p p r o p r i a t e o v e r l a y .
For example, a r e c e p t o r a t 404 m i s i n t h e 396 - 427 m
l a y e r and t h e g r o u n d - l e v e l c o n c e n t r a t i o n i s b e s t r e p r e s e n t e d by t h e 396 m o v e r l a y . Using t h e d a t a from t h e o v e r l a y t e c h n i q u e ( T a b l e 1 ) and t h e observed d a t a t o produce a c a l i b r a t i o n e q u a t i o n , a s b e f o r e , w e f i n d t h a t t h e c o e f f i c i e n t o f determinat i o n ( r 2 ) i s 0 . 6 4 , w i t h c o r r e l a t i o n c o e f f i c i e n t s of A
=
5 7 . 3 and B = 0 . 1 2 4 .
The composite model o u t p u t can now be c a l i b r a t e d t o g i v e t h e o u t p u t shown i n Figure 2 .
145
150
155
F i g . 2 . Ground L e v e l Suspended P a r t i c u l a t e Matter i n ug/m3 C a l i b r a t e d Overlay Technique
160
145
150
155
10
F i g . 3. 427 Metre E l e v a t i o n Contour ( d a r k a r e a s a r e above and l i g h t areas are below 4 2 7 m)
198 OBSERVATIONS When one compares t h e c o n c e n t r a t i o n s ( F i g u r e 2 ) t o t h e a c t u a l topography, one o b s e r v e s t h a t t h e h i g h SPM v a l u e s o c c u r i n t h e p i t a r e a s and n o t on t h e h i g h ground s u r r o u n d i n g them as i n t h e s t a n d a r d CDM o u t p u t , t h a t i s , t h e method a p p e a r s t o g i v e a b e t t e r s p a t i a l l y defined output. Some anomolies do a p p e a r , however, such a s an i n c r e a s e d g e n e r a l background l e v e l (57 v s 4 1 pg/m3) and some u n i q u e l y h i g h ground l e v e l v a l u e s . good example, a t x = 154 and y
=
One s t a n d s o u t a s a
45 we have a ground l e v e l c o n c e n t r a t i o n of 97 ug/m3.
This p o i n t i s i n a v a l l e y ( F i g u r e 3) w i t h a b a s e e l e v a t i o n o f about 366 m.
The
r e c e p t o r s c l o s e s t t o i t , a l o n g t h e v a l l e y , (mid-points of a s q u a r e k i l o m e t r e ) , j u s t happen t o f a l l h a l f way up t h e v a l l e y w a l l ( i n t h e n e x t t o p o g r a p h i c l a y e r ) and t h e c o n c e n t r a t i o n s are, t h e r e f o r e , c o r r e s p o n d i n g l y l o w e r .
This points o u t t h a t a user
must c a r e f u l l y choose h i s o u t p u t p o i n t s because t h e model i s o n l y two-dimensional i n a s p e c i f i c l a y e r and c a n n o t make t h e c h o i c e s f o r t h e u s e r . This p a r t i c u l a r anomaly r e p r e s e n t s w e l l t h e normal s p a t i a l v a r i a b i l i t y observed i n n a t u r e . r u n n i n g t h i s model i s v e r y r e a s o n a b l e
-
p e r h a p s , i n g e n e r a l , o n l y t w i c e t h a t of t h e
s t a n d a r d CDM r u n s i n c e s o u r c e s d i s a p p e a r as t h e t e r r a i n r i s e s . tion
The c o s t of
If t h e a c t u a l eleva-
of a r e c e p t o r p o i n t i s used t o i n t e r p o l a t e a c o n c e n t r a t i o n , t h e c o e f f i c i e n t
of d e t e r m i n a t i o n i s n o t as good ( r 2 = 0 . 6 0 ) a n d , t h e r e f o r e , n o t worth t h e e f f o r t i n volved.
The method d e s c r i b e d rounds a l l e l e v a t i o n s down t o t h e n e a r e s t 3 0 . 5 m.
If
one rounds up, t h e c o e f f i c i e n t o f d e t e r m i n a t i o n a g a i n i s n o t a s good ( r 2 = 0.60) s u g g e s t i n g t h a t l e s s than a 100% t e r r a i n rise may be b e n e f i c i a l .
CONCLUSION The o v e r l a y t e c h n i q u e g i v e s a n improved c o r r e l a t i o n between model o u t p u t and obs e r v e d ground l e v e l c o n c e n t r a t i o n s .
I t a l s o g i v e s a s p a t i a l l y improved p r e d i c t i o n i n
an area with s i g n i f i c a n t topographical influences.
The t e c h n i q u e u s e s a n e x i s t i n g
long-term model (CDM) and i s b o t h s i m p l e t o a p p l y and c o s t e f f e c t i v e .
The o u t p u t
a p p e a r s t o r e p r e s e n t t h e observed n a t u r a l v a r i a b i l i t y b e t t e r t h a n most two-dimensional models, ACKNOWLEDGEMENTS The a u t h o r i s i n d e b t e d t o S t e e p Rock I r o n Mines L i m i t e d f o r l e t t i n g him u s e t h e emissions d a t a f o r t h i s paper.
REFERENCES
1. A.D. Busse and J . R . Zimmerman, EPA-R4-73-024, (1973) 2. A . A . Slowik, J . M . A u s t i n and G . N . P i c a , P a p e r 77-29.1, p r e s e n t e d a t t h e 7 0 t h Annual Meeting o f t h e AF'CA, (1977) 3 . R. S c o r e r , A i r P o l l u t i o n . Pergamon P r e s s 1968, 1 5 1 pp. 4 . C. Cowherd and R.V. H e n d r i k s , P a p e r No. 77 - 6.2 p r e s e n t e d a t t h e 70th Annual Meeting of t h e APCA, (1977)