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Air Pollution Modeling by the “Smeared Concentration Approximation”
143
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
A I R POLLUTION MODELING BY THE "SMEARED CONCENTRATION APPROXIMATION" Robin L. Dennis I n t e r n a t i o n a l I n s t i t u t e f o r A p p l i e d Systems A n a l y s i s
ABSTRACT T h i s paper d e s c r i b e s a s i m p l i f i e d method, t h e Smeared C o n c e n t r a t i o n Approximation, developed t o c h a r a c t e r i z e a i r p o l l u t i o n d i s p e r s i o n f o r use i n models concerned w i t h long-term p o l i c y analysis a t t h e regional level. around t h e urban s c a l e .
The methodology c e n t e r s
The main assumptions behind t h e a p p r o x i m a t i o n a r e d e s c r i b e d
and t h e SCA U i s p e r s i o n Parameter i s d e f i n e d .
Development o f t h e SCA D i s p e r s i o n
parameter, u s i n g d e t a i l e d a i r p o l l u t i o n d e s p e r s i o n models, i s d e s c r i b e d .
Illustra-
t i o n s of t h e use o f t h i s methodology i n r e g i o n a l energylenvironment a n a l y s i s a r e p r e s e n t e d and some c o n c l u s i o n s c o n c e r n i n g t h e use o f t h e method a r e g i v e n .
INTRODUCTION The purpose o f t h e paper i s t o d e s c r i b e a methodology t h a t has been developed a t I I A S A t o a l l o w the i n c l u s i o n o f a i r p o l l u t i o n dispersion i n large-scale, i n t e r d i s c i p l i n a r y r e g i o n a l and n a t i o n a l modeling e f f o r t s [ l ] . The methodology bypasses t h e d i r e c t need o f complex and l a r g e a i r p o l l u t i o n d i s p e r s i o n models.
The work
was s p e c i f i c a l l y designed t o be most r e l e v a n t f o r a n a l y s i s o f l o n g - t e r m s t r a t e g i e s and p o l i c y o p t i o n s c o n c e r n i n g a i r p o l l u t i o n a t t h e r e g i o n a l l e v e l .
The methodology
c e n t e r s around d i s p e r s i o n a t t h e urban o r m e t r o p o l i t a n s c a l e ; t h e e f f e c t o f an urban area on i t s e l f . By l a r g e - s c a l e ,
i n t e r d i s c i p l i n a r y modeling i s meant modeling e f f o r t s where a i r
p o l l u t i o n i s j u s t one o f many f a c t o r s considered, a l b e i t an i m p o r t a n t one.
Examples
o f t h e s e t y p e s o f models a r e t h e Brookhaven Energy Systems O p t i m i z a t i o n Model (BESOM) [ 2 ] ,
t h e K c o n s i n Energy Model (WISE) [3], and an Economic Environmental
P l a n n i n g Model o f t h e U n i v e r s i t y o f Maryland [ 4 ] . I f concern i s about e n v i r o n m e n t a l impacts, t h e emissions o f a i r p o l l u t a n t s a r e a poor p r o x y f o r an impact a n a l y s i s .
What m a t t e r s i s what happens t o those emis-
s i o n s ; a damage o r impact assessment i s d e s i r e d .
Accounting f o r d i s p e r s i o n i s
r e q u i r e d , even f o r long-range p o l i c y a n a l y s i s ; b u t t h i s i s n o t easy s i n c e d i s p e r s i o n models themselves a r e u s u a l l y l a r g e and d a t a i n t e n s i v e . What i s needed i s a s i m p l e method t h a t i s e a s i l y useable by a range o f models and modelers w o r k i n g on l a r g e i n t e r d i s c i p l i n a r y models aimed a t l o n g - t e r m p o l i c y
144 analysis.
The method s h o u l d c o n t a i n t h e e s s e n t i a l f e a t u r e s o f d i s p e r s i o n , y e t
r e s u l t i n a simple, useable a l g o r i t h m .
The Smeared C o n c e n t r a t i o n Approximation
method was developed w i t h t h i s need i n mind:
The SCA method c o n c e n t r a t e s on t h e
urban a r e a because t h i s i s where most o f t h e human h e a l t h impact f r o m a i r p o l l u t i o n occurs.
Main assumotions The b a s i c assumption i s t h a t an annual average g r o u n d - l e v e l c o n c e n t r a t i o n averaged o v e r t h e e n t i r e urban area i s a s u f f i c i e n t l y p r e c i s e i n d i c a t o r f o r l o n g t e r m impact a n a l y s i s .
People a r e good i n t e g r a t o r s o f a i r p o l l u t i o n ; t h e i r m o b i l i t y
i s h i g h r e l a t i v e t o t h e s p a t i a l v a r i a t i o n o f t h e p o l l u t i o n concentration.
This
average i n t e g r a t e d exposure i s t h e c o l l e c t i v e dose t o t h e urban area, o r t h e average dose an average person r e c e i v e s i n t h e urban a r e a .
Thus a s i n g l e exposure i s
a s s o c i a t e d w i t h each urban a r e a . T h i s average i n t e g r a t e d annual exposure n o r m a l i z e d by t h e t o t a l annual emissions f r o m t h e urban area i s d e f i n e d as t h e Smeared C o n c e n t r a t i o n D i s p e r s i o n Parameter, D. C h a r a c t e r i z a t i o n o f t h e e s s e n t i a l f e a t u r e s o f a i r p o l l u t i o n d i s p e r s i o n i s achieved by d e f i n i n g a s e t o f D ' s ; t h e d i s a g g r e g a t i o n o f t h i s s e t i s determined by b o t h d i s p e r s i o n and p o l i c y c o n s i d e r a t i o n s . F i r s t , t h r e e c l a s s e s o f composite SCA d i s p e r s i o n parameters, Dk, a r e d e f i n e d f o r each o f t h r e e c l a s s e s o f e m i s s i o n sources: D1:
D2:
SCA d i s p e r s i o n parameter f o r l o w - l e v e l o r area sources
SCA d i s p e r s i o n parameter f o r medium-level p o i n t sources
SCA d i s p e r s i o n parameter f o r h i g h - l e v e l p o i n t sources D3: The d i s p e r s i o n c h a r a c t e r i s t i c s o f t h e s e t h r e e c l a s s e s o f sources are, i n general,
d i s t i n c t l y d i f f e r e n t ; t h e d i f f e r e n c e s w i t h i n a c l a s s a r e smaller than d i f f e r e n c e s between c l a s s e s .
Broad p o l i c y o p t i o n s can be d e f i n e d i n terms o f t h e s e t h r e e
c l a s s e s o f e m i s s i o n sources.
The p o l i c y o p t i o n s can be q u i t e d i f f e r e n t between
t h e t h r e e c l a s s e s ; t h u s many p o l i c y s t r a t e g i e s can be analyzed by t h i s d i v i s i o n o f e m i s s i o n sources. Second, each Dk i s d e f i n e d as a composite o f a b a s i c s e t , Dkj,
d e f i n e d i n terms
Each D i s an SCA d i s p e r s i o n parameter kj d e f i n e d f o r a p a r t i c u l a r atmospheric s t a b i l i t y c o n d i t i o n and a p a r t i c u l a r wind
o f wind speed and atmospheric s t a b i l i t y . speed.
Experience has deemed t h a t t h r e e atmospheric s t a b i l i t i e s and f o u r wind
speeds i s an adequate d i s a g g r e g a t i o n t o c h a r a c t e r i z e t h e d i s p e r s i o n .
Differences
i n m e t e o r o l o g y can be accounted f o r w i t h t h i s s e t .
SCA D I S P E R S I O N PARAMETER DEVELOPMENT The area source SCA d i s p e r s i o n parameters were developed from computer
145 c a l c u l a t i o n s made w i t h a g r a d i e n t d i f f u s i o n a i r p o l l u t i o n model w i t h e x p l i c i t l y modeled wind and d i f f u s i v i t y p r o f i l e s . U n i v e r s i t y o f Wisconsin [ 5 ] .
T h i s numerical model was developed a t t h e
The p o i n t source SCA d i s p e r s i o n parameters were
developed u s i n g a Gaussian plume d i s p e r s i o n model, a v a i l a b l e a t Wisconsin and I I A S A [61.
Both models have been approved by t h e USEPA.
The SCA d i s p e r s i o n parameter,
a g a i n , i s d e f i n e d as t h e average g r o u n d - l e v e l c o n c e n t r a t i o n c a l c u l a t e d f o r t h e e n t i r e urban a r e a d i v i d e d b y t h e t o t a l emissions f r o m t h e urban area.
Ihe e s s e n t i a l f e a t u r s s
o f t h e SCA d i s p e r s i o n parameters were d e f i n e d w i t h t h e h e l p of t h e computer models.
Area Sources:
D1
The main d i s p e r s i o n f e a t u r e s o f t h e area source d i s p e r s i o n parameter, D1,
1.
are:
D1 i s n o t s e n s i t i v e t o t h e d i s t r i b u t i o n o f emissions i n a n urban a r e a .
2. D1 i s n o t s e n s i t i v e t o t h e roughness o f t h e urban a r e a . 3.
D1 i s a f u n c t i o n o f t h e average r a d i u s o f t h e urban area.
Several model c i t i e s were d e f i n e d w i t h d i f f e r i n g emissions d e n s i t y .
The d i f -
f e r e n c e s were b o t h w i t h r e s p e c t t o t h e r a t i o o f t h e maximum t o t h e minimum emission d e n s i t y and w i t h r e s p e c t t o t h e s p a t i a l d i s t r i b u t i o n o f t h e e m i s s i o n d e n s i t i e s . F i v e model c i t i e s a r e shown i n F i g u r e 1. Model c i t y A has a max-minimum emission d e n s i t y r a t i o o f 82, model c i t y 3, 29.8, model c i t y C, 82.3, model c i t y 0, 1.0 Model C i t y ( u n i f o r m ) , and model c i t y E ( a model c i t y o f Vienna, A u s t r i a ) , 38.5.
E i s shown as a c r o s s s e c t i o n t h r o u g h t h e c e n t e r . The r e s u l t o f c a l c u l a t i n g D
Ij
f o r t h e f i v e model c i t i e s w i t h a g i v e n atmospheric
s t a b i l i t y and g e o s t r o p h i c wind i s shown i n F i i u r e 2 .
For t h e l a r g e d i f f e r e n c e s i n
between t h e 5 1j The d i f f e r e n c e i s on t h e o r d e r o f + 10 p e r c e n t around t h e average o f f o r t h e model c i t i e s . I n t e r e s t i n g l y , t h e r a t i o o f t h e maximum concentra-
t h e p a t t e r n s o f emissions, t h e r e was o n l y a s m a l l change i n each D model c i t i e s . each D
1j
t i o n t o t h e urban average c o n c e n t r a t i o n was t h e same f o r model c i t y A and "Vienna", w h i l e t h e i r max-minimum e m i s s i o n d e n s i t y r a t i o was q u i t e d i f f e r e n t and Vienna's
Dlj
i s v e r y c l o s e t o t h e u n i f o r m c i t y Dlj.
The main c o n c l u s i o n i s t h a t t h e 0
are i n s e n s i t i v e t o the d e t a i l s o f the emission d e n s i t i e s .
1j
's
A s i m i l a r s e t o f c a l c u l a t i o n s was c a r r i e d o u t t o i n v e s t i g a t e s u r f a c e roughness. S i m i l a r r e s u l t s were o b t a i n e d as above. what g r e a t e r spread o f D
S u r f a c e roughness e f f e c t s produced a some-
f o r a l l p o s s i b l e combinations, b u t t h e c o n c l u s i o n i s
ij t h e same, s u r f a c e roughness d i f f e r e n c e s can be i g n o r e d .
The f a c t t h a t one does n o t
need t o w o r r y about t h e d e t a i l s o f t h e urban area i s an i m p o r t a n t f e a t u r e o f t h e SCA method; d a t a needs a r e reduced t o a minimum. The SCA d i s p e r s i o n parameter 0 i s a f u n c t i o n o f t h e s i z e of t h e urban a r e a . lj The average r a d i u s o f t h e urban area i s used as t h e parameter t o r e p r e s e n t i t s s i z e . F i g u r e 3 shows D
Ij
as a f u n c t i o n o f t h e average c i t y r a d i u s f o r one wind speed and
t h r e e atmospheric s t a b i l i t i e s .
The r e s u l t s f o r t h e o t h e r m e t e o r o l o g i c a l combinations
146
R=lOkm NEUTRAL STABILITY
Up = 10 m/s
km FROM URBAN CENTER
F i g . 1: Emission D e n s i t y CrossS e c t i o n f o r t h e F i v e Model C i t i e s
F i g . 2. SCA D i s p e r s i o n Parameter, D l j , C a l c u l a t e d f o r t h e F i v e Model C i t i e s
The f u n c t i o n a l f o r m o f t h e i n d i v i d u a l D ' s i s -b 1j a power l a w w i t h r e s p e c t t o t h e average r a d i u s , i . e . D . ( R ) = a.R j. a r e i d e n t i c a l i n f o r m t o F i g u r e 3.
15
P o i n t Sources:
J
D2 and D3
The main d i s p e r s i o n f e a t u r e s o f t h e o o i n t source d i s p e r s i o n parameters, D2 and D3 a r e :
1. D2 i s n o t s e n s i t i v e t o t h e l o c a t i o n o f t h e p o i n t sources i n t h e urban a r e a .
2.
D2 and D3 a r e n o t v e r y s e n s i t i v e t o t h e roughness o f t h e urban area.
3.
D2 and D3 a r e f u n c t i o n s o f t h e average r a d i u s o f t h e urban area.
These t h r e e c o n c l u s i o n s f o l l o w f r o m t h e p o i n t source c a l c u l a t i o n s as e a r l i e r i l l u s t r a t e d f o r t h e area sources.
The medium-level p o i n t sources show more response
t o s t r o n g changes i n s u r f a c e roughness t h a n t h e area sources; n e v e r t h e l e s s , changes due t o s u r f a c e roughness a r e n o t s i g n i f i c a n t .
F i g u r e 4 shows D
2j
as a f u n c t i o n o f
average c i t y r a d i i f o r v e r y l o w wind speeds and t h r e e atmospheric s t a b i l i t i e s . The v e r y low wind speeds emphasize t h e d i f f e r e n c e s between D
lj
and DZj;
r a d i i t h e plume i s r e a c h i n g t h e ground more and more o u t s i d e t h e c i t y .
f o r decreasing For h i g h
wind speeds, DZj as a f u n c t i o n o f average c i t y r a d i u s i s a s t r a i g h t l i n e on t h e l o g - l o g graph f o r a l l s t a b i l i t i e s , j u s t l i k e D l j .
The f u n c t i o n a l f o r m o f t h e
147
UNSTABLE
VERY LOW WINO SPEEDS
5.0
+ 2
2
1
10 20 30 40 URBAN RADIUS (km)
2
3 4 5
F i g . 3. SCA D i s p e r s i o n Parameter D a F u n c t i o n o f Average City Radius
2J
.
F i g . 4. SCA D i s p e r s i o n Parameter D as a 23 F u n c t i o n o f Average City Radius
I s and D . I s a r e o n l y power laws w i t h r e s p e c t t o R f o r l a r g e urban 33
individual D radii
'Jas
Forminq t h e composite SCA D ' s The composite d i s p e r s i o n parameters, an urban c o l l e c t i v e exposure.
Dk, a r e t h e parameters needed t o c a l c u l a t e
These parameters a r e d e r i v e d f r o m t h e Dkjls.
Each
f u n c t i o n D .(R) i s m u l t i p l i e d by t h e f r e q u e n c y o f occurance o f i t s combination
kJ
o f wind speed and atmospheric s t a b i l i t y .
The f u n c t i o n s a r e combined i n t h i s
weighted manner t o b u i l d a composite f u n c t i o n Dk(R) t h a t r e f l e c t s t h e r e g i o n a l meteorology.
F o r t h e m e t e o r o l o g i c a l f r e q u e n c y f a c t o r s o f M i l w a u k i e , Wisconsin,
the resulting
D (R) i s
D1 = 690
R-'03'
kj
(10-4pg/m3/ton)
.
(1)
F o r comparative pusposes, i f we o n l y c o n s i d e r t h e power l a w p a r t f o r D2(R > 5km),
148 the resulting D2 = 32.3
-
D2(R) i s
R-Oa8'
(10-4~g/m3/ton)
.
Equations 1 and 2 i l l u s t r a t e t h r e e i m p o r t a n t p o i n t s .
The f i r s t p o i n t i s t h a t
t h e c o e f f i c i e n t i n f r o n t o f R f o r D2, E q u a t i o n 2, i s more t h a n an o r d e r o f magnit u d e s m a l l e r t h a n t h e c o e f f i c i e n t f o r D1,
E q u a t i o n 1.
The c o e f f i c i e n t f o r D3 w i l l
be more t h a n two o r d e r s o f magnitude l o w e r t h a n t h e c o e f f i c i e n t f o r depending on s t a c k h e i g h t .
D1, o r l o w e r
These c o e f f i c i e n t s show t h e r e l a t i v e c o n t r i b u t i o n a
u n i t o f emissions f r o m each e m i s s i o n c l a s s w i l l have on t h e c a l c u l a t e d urban exposure, t h e l a r g e s t c o n t r i b u t o r b e i n g D1,
a r e a sources.
The second p o i n t i s t h a t
t h e f u n c t i o n a l dependence on R i s d i f f e r e n t f o r t h e d i f f e r e n t e m i s s i o n c l a s s e s ; t h u s t h e r e l a t i v e c o n t r i b u t i o n each c l a s s o f emissions makes t o t h e exposure w i l l change w i t h community s i z e .
The t h i r d D o i n t i s t h a t f o r a l l emission c l a s s e s ,
t h e urban s i z e makes a d i f f e r e n c e i n t h e D ' s .
Thus t h e D ' s change w i t h d i f f e r e n t
urban p a t t e r n s ; t h e s e may be d i f f e r e n t growth, f o r m o r d e n s i t y p a t t e r n s . The composite SCA d i s p e r s i o n parameters express t h e e s s e n t i a l f e a t u r e s o f urban a i r p o l l u t i o n d i s p e r s i o n f o r l o n g - t e r m p o l i c y a n a l y s i s ; d i f f e r e n c e s between m a j o r e m i s s i o n c l a s s e s a r e d e s c r i b e d , and t h e main urban s i z e dependence i s c h a r a c t e r i z e d . A minimum o f emissions d e t a i l i s r e q u i r e d f o r use o f t h e SCA method due t o t h e f e a t u r e s o f t h e SCA d i s p e r s i o n parameters.
By b u i l d i n g up f r o m a base s e t o f SCA
d i s p e r s i o n parameters, d i f f e r e n c e s can be accounted f o r i n r e g i o n a l meteorology. VALIDATION AND USE The SCA method has been v a l i d a t e d i n s e v e r a l c i t i e s where d e t a i l e d emissions i n v e n t o r i e s were r e a d i l y a v a i l a b l e , namely I l i l w a u k e e and Madison, Wisconsin and Vienna, A u s t r i a .
F o r these c i t i e s , t h e c a l c u l a t e d exposure was w i t h i n 10-20% o f
t h e expected exposure based on m o n i t o r i n g d a t a and, f o r Wisconsin, d e t a i l e d i s o p l e t h s f r o m c a l i b r a t e d d i s p e r s i o n models.
F o r s e v e r a l o t h e r c i t i e s i n Europe,
g e n e r a l checks have been made and c a l c u l a t e d SCA exposures appear t o be i n reasonable agreement w i t h d a t a . The SCA method has been used i n r e g i o n a l s t u d i e s o f energy and environmental management.
The most r e c e n t i s an A u s t r i a n case s t u d y [ 7 ] .
A s e n s i t i v i t y study
i s p r e s e n t e d f r o m t h e A u s t r i a n s t u d y t o i l l u s t r a t e t h e use o f t h e SCA method.
A
h e a l t h model 181 was used t o c o n v e r t SO2 exposure t o a h e a l t h impact, expressed as Person-Days-Lost (PDL).
The s e n s i t i v i t y l o o k s a t t h e e f f e c t i v e n e s s o f t h e SO2
e m i s s i o n s t a n d a r d s assumed i n t h e s c e n a r i o s developed f o r A u s t r i a . a r e shown g r a p h i c a l l y i n F i g u r e s 5 and 6 . have a s i g n i f i c a n t e f f e c t on t h e
The r e s u l t s
While each o f t h e e m i s s i o n standards
SO2 emissions, o n l y t h e p e t r o l e u m d e s u l f u r i z a t i o n
has a s i g n i f i c a n t e f f e c t on h e a l t h impact.
T h i s i s because t h e r e s i d e n t i a l and
c o m m e r c i a l - s e r v i c e emissions ( a r e a sources) were o n l y a f f e c t e d by t h e o i l
149
s1
s1 s1 s1 S1 '' , With Desulfurization S1
1971
u I-
With Desulfurization + Present Emission Standards , With Desulfurization + Anticipated New US Emission Standards
1980
1990
2000
.5 E 5:
N
2010
2020
F i g . 5. S e n s i t i v i t y o f SO Emissions t o SO2 R e g u l a t i o n s f o r Scgnario SI, Austria desulfurization.
19171
1980
1990
2000
2010
2020
F i g . 6. S e n s i t i v i t y o f A i r P o l l u t i o n P u b l i c H e a l t h t o S O p R e g u l a t i o n s f o r Scenario 1, Austria
W i t h d e s u l f u r i z a t i o n , t h e area sources were a l r e a d y a t t h e p r e s e n t
U.S. Standard, and t h e new U.S. s t a n d a r d was assumed t o o n l y a f f e c t p o i n t sources. The c o n c l u s i o n i s t h a t t h e e f f e c t i v e n e s s o f each new SO2 r e d u c t i o n i s l e s s t h a n t h e p r e c e e d i n g one i n terms o f h e a l t h impact.
A word o f c a u t i o n must be expressed;
l o n g - r a n g e t r a n s p o r t o f s u l f a t e s i s n o t i n c l u d e d here, t h u s t h e standards would a c t u a l l y be more e f f e c t i v e t h a n i n d i c a t e d h e r e . CONCLUSION The SCA method i s a b l e t o c h a r a c t e r i z e urban a i r p o l l u t i o n d i s p e r s i o n a t t h e urban l e v e l and i t r e q u i r e s a minimum o f emissions d e t a i l .
The method has been
shown t o g i v e v a l u a b l e i n s i g h t i n t o p o l i c y a n a l y s i s i n a c t u a l s t u d i e s ; i t p r o v i d e s a "first-cut"
a n a l y s i s f o r long-range p l a n n i n g and s t r a t e g y o p t i o n a n a l y s i s .
The
SCA method p r e s e n t s o n l y one s i d e o f t h e a i r p o l l u t i o n impact p i c t u r e , t h e s h o r t range u r b a n i m p a c t .
When t h e c a u s a l a g e n t s o f t h e impacts a r e chemical r e a c t i o n
p r o d u c t s , t h e n t h e SCA method must be supplemented by a long-range t r a n s p o r t method t o balance t h e a n a l y s i s o f p o l i c y o p t i o n s .
The SCA method i s a u s e f u l and useable
150 t o o l f o r a i r p o l l u t i o n impact a n a l y s i s f o r long-range s t u d i e s when used i n t h e proper context.
REFERENCES
1 R.L. Dennis, The Smeared C o n c e n t r a t i o n A p p r o x i m a t i o n Method: A S i m p l i f i e d A i r P o l l u t i o n D i s p e r s i o n Methodology, Research Report, I n t e r n a t i o n a l I n s t i t u t e f o r A p p l i e d Systems A n a l y s i s , Laxenburg, A u s t r i a , " i n p r e s s " , (1978). 2 W.K. F o e l l , J.W M i t c h e l l , and J.L. Pappas, I h e WISconsin Regional Energy Model: A Systems Approach t o Regional Energy A n a l y s i s , R e p o r t 56, I n s t i t u t e f o r Environmental S t u d i e s , U n i v e r s i t y o f Wisconsin Energy Systems and P o l i c y Research Group, 1975. 3 E.A.
Cherniavsky, Brookhaven t n e r g y Systems O p t i m i z a t i o n Model, Brookhaven N a t i o n a l
L a b o r a t o r y , BNL-19569, December 1974. 4 J.H. Cumberland and A.J.
Krupnick, An Economic Environmental P l a n n i n g Manual f o r
C o u n t r i e s , S t a t e s and M e t r o p o l i t a n Areas, Bureau o f Business and Economic Research, U n i v e r s i t y o f Maryland, BBER-HP-1,
(1977).
5 K.W. Ragland, R.L. Dennis, and K.W.
W i l k e n i n g , Boundary-Layer Model f o r T r a n s p o r t
o f Urban A i r P o l l u t a n t s , i n D.W. Cooper (ed.), Houston Conference, March 16-20,
A.1.Ch.E.
A i r S e r i e s , Proc. A.1.Ch.E.
1975, Houston, Texas, (1976).
6 K.W.
Ragland, " p e r s o n a l communication".
7 W.K.
F o e l l , K.L. Dennis, L . Hervey, A. H o e l z l , M. Hanson, E. P o e n i t z , and
J . Peerenboom, The I I A S A A u s t r i a n Regional Energy/Environment Study, I n t e r n a t i o n a l I n s t i t u t e f o r A p p l i e d Systems A n a l y s i s , Laxenburg, A u s t r i a , " i n p r e s s " , (1978). 8 W.A.
Buehring, R.L. Dennis, and A. H o e l z l , E v a l u a t i o n o f H e a l t h E f f e c t s f r o m
S u l f u r D i o x i d e Emissions f o r a Reference C o a l - F i r e d Power P l a n t , RM-76-23, t i o n a l I n s t i t u t e f o r A p p l i e d Systems A n a l y s i s , Laxenburg, A u s t r i a , (1976).
Interna-
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
A I R POLLUTION MODELING BY THE "SMEARED CONCENTRATION APPROXIMATION" Robin L. Dennis I n t e r n a t i o n a l I n s t i t u t e f o r A p p l i e d Systems A n a l y s i s
ABSTRACT T h i s paper d e s c r i b e s a s i m p l i f i e d method, t h e Smeared C o n c e n t r a t i o n Approximation, developed t o c h a r a c t e r i z e a i r p o l l u t i o n d i s p e r s i o n f o r use i n models concerned w i t h long-term p o l i c y analysis a t t h e regional level. around t h e urban s c a l e .
The methodology c e n t e r s
The main assumptions behind t h e a p p r o x i m a t i o n a r e d e s c r i b e d
and t h e SCA U i s p e r s i o n Parameter i s d e f i n e d .
Development o f t h e SCA D i s p e r s i o n
parameter, u s i n g d e t a i l e d a i r p o l l u t i o n d e s p e r s i o n models, i s d e s c r i b e d .
Illustra-
t i o n s of t h e use o f t h i s methodology i n r e g i o n a l energylenvironment a n a l y s i s a r e p r e s e n t e d and some c o n c l u s i o n s c o n c e r n i n g t h e use o f t h e method a r e g i v e n .
INTRODUCTION The purpose o f t h e paper i s t o d e s c r i b e a methodology t h a t has been developed a t I I A S A t o a l l o w the i n c l u s i o n o f a i r p o l l u t i o n dispersion i n large-scale, i n t e r d i s c i p l i n a r y r e g i o n a l and n a t i o n a l modeling e f f o r t s [ l ] . The methodology bypasses t h e d i r e c t need o f complex and l a r g e a i r p o l l u t i o n d i s p e r s i o n models.
The work
was s p e c i f i c a l l y designed t o be most r e l e v a n t f o r a n a l y s i s o f l o n g - t e r m s t r a t e g i e s and p o l i c y o p t i o n s c o n c e r n i n g a i r p o l l u t i o n a t t h e r e g i o n a l l e v e l .
The methodology
c e n t e r s around d i s p e r s i o n a t t h e urban o r m e t r o p o l i t a n s c a l e ; t h e e f f e c t o f an urban area on i t s e l f . By l a r g e - s c a l e ,
i n t e r d i s c i p l i n a r y modeling i s meant modeling e f f o r t s where a i r
p o l l u t i o n i s j u s t one o f many f a c t o r s considered, a l b e i t an i m p o r t a n t one.
Examples
o f t h e s e t y p e s o f models a r e t h e Brookhaven Energy Systems O p t i m i z a t i o n Model (BESOM) [ 2 ] ,
t h e K c o n s i n Energy Model (WISE) [3], and an Economic Environmental
P l a n n i n g Model o f t h e U n i v e r s i t y o f Maryland [ 4 ] . I f concern i s about e n v i r o n m e n t a l impacts, t h e emissions o f a i r p o l l u t a n t s a r e a poor p r o x y f o r an impact a n a l y s i s .
What m a t t e r s i s what happens t o those emis-
s i o n s ; a damage o r impact assessment i s d e s i r e d .
Accounting f o r d i s p e r s i o n i s
r e q u i r e d , even f o r long-range p o l i c y a n a l y s i s ; b u t t h i s i s n o t easy s i n c e d i s p e r s i o n models themselves a r e u s u a l l y l a r g e and d a t a i n t e n s i v e . What i s needed i s a s i m p l e method t h a t i s e a s i l y useable by a range o f models and modelers w o r k i n g on l a r g e i n t e r d i s c i p l i n a r y models aimed a t l o n g - t e r m p o l i c y
144 analysis.
The method s h o u l d c o n t a i n t h e e s s e n t i a l f e a t u r e s o f d i s p e r s i o n , y e t
r e s u l t i n a simple, useable a l g o r i t h m .
The Smeared C o n c e n t r a t i o n Approximation
method was developed w i t h t h i s need i n mind:
The SCA method c o n c e n t r a t e s on t h e
urban a r e a because t h i s i s where most o f t h e human h e a l t h impact f r o m a i r p o l l u t i o n occurs.
Main assumotions The b a s i c assumption i s t h a t an annual average g r o u n d - l e v e l c o n c e n t r a t i o n averaged o v e r t h e e n t i r e urban area i s a s u f f i c i e n t l y p r e c i s e i n d i c a t o r f o r l o n g t e r m impact a n a l y s i s .
People a r e good i n t e g r a t o r s o f a i r p o l l u t i o n ; t h e i r m o b i l i t y
i s h i g h r e l a t i v e t o t h e s p a t i a l v a r i a t i o n o f t h e p o l l u t i o n concentration.
This
average i n t e g r a t e d exposure i s t h e c o l l e c t i v e dose t o t h e urban area, o r t h e average dose an average person r e c e i v e s i n t h e urban a r e a .
Thus a s i n g l e exposure i s
a s s o c i a t e d w i t h each urban a r e a . T h i s average i n t e g r a t e d annual exposure n o r m a l i z e d by t h e t o t a l annual emissions f r o m t h e urban area i s d e f i n e d as t h e Smeared C o n c e n t r a t i o n D i s p e r s i o n Parameter, D. C h a r a c t e r i z a t i o n o f t h e e s s e n t i a l f e a t u r e s o f a i r p o l l u t i o n d i s p e r s i o n i s achieved by d e f i n i n g a s e t o f D ' s ; t h e d i s a g g r e g a t i o n o f t h i s s e t i s determined by b o t h d i s p e r s i o n and p o l i c y c o n s i d e r a t i o n s . F i r s t , t h r e e c l a s s e s o f composite SCA d i s p e r s i o n parameters, Dk, a r e d e f i n e d f o r each o f t h r e e c l a s s e s o f e m i s s i o n sources: D1:
D2:
SCA d i s p e r s i o n parameter f o r l o w - l e v e l o r area sources
SCA d i s p e r s i o n parameter f o r medium-level p o i n t sources
SCA d i s p e r s i o n parameter f o r h i g h - l e v e l p o i n t sources D3: The d i s p e r s i o n c h a r a c t e r i s t i c s o f t h e s e t h r e e c l a s s e s o f sources are, i n general,
d i s t i n c t l y d i f f e r e n t ; t h e d i f f e r e n c e s w i t h i n a c l a s s a r e smaller than d i f f e r e n c e s between c l a s s e s .
Broad p o l i c y o p t i o n s can be d e f i n e d i n terms o f t h e s e t h r e e
c l a s s e s o f e m i s s i o n sources.
The p o l i c y o p t i o n s can be q u i t e d i f f e r e n t between
t h e t h r e e c l a s s e s ; t h u s many p o l i c y s t r a t e g i e s can be analyzed by t h i s d i v i s i o n o f e m i s s i o n sources. Second, each Dk i s d e f i n e d as a composite o f a b a s i c s e t , Dkj,
d e f i n e d i n terms
Each D i s an SCA d i s p e r s i o n parameter kj d e f i n e d f o r a p a r t i c u l a r atmospheric s t a b i l i t y c o n d i t i o n and a p a r t i c u l a r wind
o f wind speed and atmospheric s t a b i l i t y . speed.
Experience has deemed t h a t t h r e e atmospheric s t a b i l i t i e s and f o u r wind
speeds i s an adequate d i s a g g r e g a t i o n t o c h a r a c t e r i z e t h e d i s p e r s i o n .
Differences
i n m e t e o r o l o g y can be accounted f o r w i t h t h i s s e t .
SCA D I S P E R S I O N PARAMETER DEVELOPMENT The area source SCA d i s p e r s i o n parameters were developed from computer
145 c a l c u l a t i o n s made w i t h a g r a d i e n t d i f f u s i o n a i r p o l l u t i o n model w i t h e x p l i c i t l y modeled wind and d i f f u s i v i t y p r o f i l e s . U n i v e r s i t y o f Wisconsin [ 5 ] .
T h i s numerical model was developed a t t h e
The p o i n t source SCA d i s p e r s i o n parameters were
developed u s i n g a Gaussian plume d i s p e r s i o n model, a v a i l a b l e a t Wisconsin and I I A S A [61.
Both models have been approved by t h e USEPA.
The SCA d i s p e r s i o n parameter,
a g a i n , i s d e f i n e d as t h e average g r o u n d - l e v e l c o n c e n t r a t i o n c a l c u l a t e d f o r t h e e n t i r e urban a r e a d i v i d e d b y t h e t o t a l emissions f r o m t h e urban area.
Ihe e s s e n t i a l f e a t u r s s
o f t h e SCA d i s p e r s i o n parameters were d e f i n e d w i t h t h e h e l p of t h e computer models.
Area Sources:
D1
The main d i s p e r s i o n f e a t u r e s o f t h e area source d i s p e r s i o n parameter, D1,
1.
are:
D1 i s n o t s e n s i t i v e t o t h e d i s t r i b u t i o n o f emissions i n a n urban a r e a .
2. D1 i s n o t s e n s i t i v e t o t h e roughness o f t h e urban a r e a . 3.
D1 i s a f u n c t i o n o f t h e average r a d i u s o f t h e urban area.
Several model c i t i e s were d e f i n e d w i t h d i f f e r i n g emissions d e n s i t y .
The d i f -
f e r e n c e s were b o t h w i t h r e s p e c t t o t h e r a t i o o f t h e maximum t o t h e minimum emission d e n s i t y and w i t h r e s p e c t t o t h e s p a t i a l d i s t r i b u t i o n o f t h e e m i s s i o n d e n s i t i e s . F i v e model c i t i e s a r e shown i n F i g u r e 1. Model c i t y A has a max-minimum emission d e n s i t y r a t i o o f 82, model c i t y 3, 29.8, model c i t y C, 82.3, model c i t y 0, 1.0 Model C i t y ( u n i f o r m ) , and model c i t y E ( a model c i t y o f Vienna, A u s t r i a ) , 38.5.
E i s shown as a c r o s s s e c t i o n t h r o u g h t h e c e n t e r . The r e s u l t o f c a l c u l a t i n g D
Ij
f o r t h e f i v e model c i t i e s w i t h a g i v e n atmospheric
s t a b i l i t y and g e o s t r o p h i c wind i s shown i n F i i u r e 2 .
For t h e l a r g e d i f f e r e n c e s i n
between t h e 5 1j The d i f f e r e n c e i s on t h e o r d e r o f + 10 p e r c e n t around t h e average o f f o r t h e model c i t i e s . I n t e r e s t i n g l y , t h e r a t i o o f t h e maximum concentra-
t h e p a t t e r n s o f emissions, t h e r e was o n l y a s m a l l change i n each D model c i t i e s . each D
1j
t i o n t o t h e urban average c o n c e n t r a t i o n was t h e same f o r model c i t y A and "Vienna", w h i l e t h e i r max-minimum e m i s s i o n d e n s i t y r a t i o was q u i t e d i f f e r e n t and Vienna's
Dlj
i s v e r y c l o s e t o t h e u n i f o r m c i t y Dlj.
The main c o n c l u s i o n i s t h a t t h e 0
are i n s e n s i t i v e t o the d e t a i l s o f the emission d e n s i t i e s .
1j
's
A s i m i l a r s e t o f c a l c u l a t i o n s was c a r r i e d o u t t o i n v e s t i g a t e s u r f a c e roughness. S i m i l a r r e s u l t s were o b t a i n e d as above. what g r e a t e r spread o f D
S u r f a c e roughness e f f e c t s produced a some-
f o r a l l p o s s i b l e combinations, b u t t h e c o n c l u s i o n i s
ij t h e same, s u r f a c e roughness d i f f e r e n c e s can be i g n o r e d .
The f a c t t h a t one does n o t
need t o w o r r y about t h e d e t a i l s o f t h e urban area i s an i m p o r t a n t f e a t u r e o f t h e SCA method; d a t a needs a r e reduced t o a minimum. The SCA d i s p e r s i o n parameter 0 i s a f u n c t i o n o f t h e s i z e of t h e urban a r e a . lj The average r a d i u s o f t h e urban area i s used as t h e parameter t o r e p r e s e n t i t s s i z e . F i g u r e 3 shows D
Ij
as a f u n c t i o n o f t h e average c i t y r a d i u s f o r one wind speed and
t h r e e atmospheric s t a b i l i t i e s .
The r e s u l t s f o r t h e o t h e r m e t e o r o l o g i c a l combinations
146
R=lOkm NEUTRAL STABILITY
Up = 10 m/s
km FROM URBAN CENTER
F i g . 1: Emission D e n s i t y CrossS e c t i o n f o r t h e F i v e Model C i t i e s
F i g . 2. SCA D i s p e r s i o n Parameter, D l j , C a l c u l a t e d f o r t h e F i v e Model C i t i e s
The f u n c t i o n a l f o r m o f t h e i n d i v i d u a l D ' s i s -b 1j a power l a w w i t h r e s p e c t t o t h e average r a d i u s , i . e . D . ( R ) = a.R j. a r e i d e n t i c a l i n f o r m t o F i g u r e 3.
15
P o i n t Sources:
J
D2 and D3
The main d i s p e r s i o n f e a t u r e s o f t h e o o i n t source d i s p e r s i o n parameters, D2 and D3 a r e :
1. D2 i s n o t s e n s i t i v e t o t h e l o c a t i o n o f t h e p o i n t sources i n t h e urban a r e a .
2.
D2 and D3 a r e n o t v e r y s e n s i t i v e t o t h e roughness o f t h e urban area.
3.
D2 and D3 a r e f u n c t i o n s o f t h e average r a d i u s o f t h e urban area.
These t h r e e c o n c l u s i o n s f o l l o w f r o m t h e p o i n t source c a l c u l a t i o n s as e a r l i e r i l l u s t r a t e d f o r t h e area sources.
The medium-level p o i n t sources show more response
t o s t r o n g changes i n s u r f a c e roughness t h a n t h e area sources; n e v e r t h e l e s s , changes due t o s u r f a c e roughness a r e n o t s i g n i f i c a n t .
F i g u r e 4 shows D
2j
as a f u n c t i o n o f
average c i t y r a d i i f o r v e r y l o w wind speeds and t h r e e atmospheric s t a b i l i t i e s . The v e r y low wind speeds emphasize t h e d i f f e r e n c e s between D
lj
and DZj;
r a d i i t h e plume i s r e a c h i n g t h e ground more and more o u t s i d e t h e c i t y .
f o r decreasing For h i g h
wind speeds, DZj as a f u n c t i o n o f average c i t y r a d i u s i s a s t r a i g h t l i n e on t h e l o g - l o g graph f o r a l l s t a b i l i t i e s , j u s t l i k e D l j .
The f u n c t i o n a l f o r m o f t h e
147
UNSTABLE
VERY LOW WINO SPEEDS
5.0
+ 2
2
1
10 20 30 40 URBAN RADIUS (km)
2
3 4 5
F i g . 3. SCA D i s p e r s i o n Parameter D a F u n c t i o n o f Average City Radius
2J
.
F i g . 4. SCA D i s p e r s i o n Parameter D as a 23 F u n c t i o n o f Average City Radius
I s and D . I s a r e o n l y power laws w i t h r e s p e c t t o R f o r l a r g e urban 33
individual D radii
'Jas
Forminq t h e composite SCA D ' s The composite d i s p e r s i o n parameters, an urban c o l l e c t i v e exposure.
Dk, a r e t h e parameters needed t o c a l c u l a t e
These parameters a r e d e r i v e d f r o m t h e Dkjls.
Each
f u n c t i o n D .(R) i s m u l t i p l i e d by t h e f r e q u e n c y o f occurance o f i t s combination
kJ
o f wind speed and atmospheric s t a b i l i t y .
The f u n c t i o n s a r e combined i n t h i s
weighted manner t o b u i l d a composite f u n c t i o n Dk(R) t h a t r e f l e c t s t h e r e g i o n a l meteorology.
F o r t h e m e t e o r o l o g i c a l f r e q u e n c y f a c t o r s o f M i l w a u k i e , Wisconsin,
the resulting
D (R) i s
D1 = 690
R-'03'
kj
(10-4pg/m3/ton)
.
(1)
F o r comparative pusposes, i f we o n l y c o n s i d e r t h e power l a w p a r t f o r D2(R > 5km),
148 the resulting D2 = 32.3
-
D2(R) i s
R-Oa8'
(10-4~g/m3/ton)
.
Equations 1 and 2 i l l u s t r a t e t h r e e i m p o r t a n t p o i n t s .
The f i r s t p o i n t i s t h a t
t h e c o e f f i c i e n t i n f r o n t o f R f o r D2, E q u a t i o n 2, i s more t h a n an o r d e r o f magnit u d e s m a l l e r t h a n t h e c o e f f i c i e n t f o r D1,
E q u a t i o n 1.
The c o e f f i c i e n t f o r D3 w i l l
be more t h a n two o r d e r s o f magnitude l o w e r t h a n t h e c o e f f i c i e n t f o r depending on s t a c k h e i g h t .
D1, o r l o w e r
These c o e f f i c i e n t s show t h e r e l a t i v e c o n t r i b u t i o n a
u n i t o f emissions f r o m each e m i s s i o n c l a s s w i l l have on t h e c a l c u l a t e d urban exposure, t h e l a r g e s t c o n t r i b u t o r b e i n g D1,
a r e a sources.
The second p o i n t i s t h a t
t h e f u n c t i o n a l dependence on R i s d i f f e r e n t f o r t h e d i f f e r e n t e m i s s i o n c l a s s e s ; t h u s t h e r e l a t i v e c o n t r i b u t i o n each c l a s s o f emissions makes t o t h e exposure w i l l change w i t h community s i z e .
The t h i r d D o i n t i s t h a t f o r a l l emission c l a s s e s ,
t h e urban s i z e makes a d i f f e r e n c e i n t h e D ' s .
Thus t h e D ' s change w i t h d i f f e r e n t
urban p a t t e r n s ; t h e s e may be d i f f e r e n t growth, f o r m o r d e n s i t y p a t t e r n s . The composite SCA d i s p e r s i o n parameters express t h e e s s e n t i a l f e a t u r e s o f urban a i r p o l l u t i o n d i s p e r s i o n f o r l o n g - t e r m p o l i c y a n a l y s i s ; d i f f e r e n c e s between m a j o r e m i s s i o n c l a s s e s a r e d e s c r i b e d , and t h e main urban s i z e dependence i s c h a r a c t e r i z e d . A minimum o f emissions d e t a i l i s r e q u i r e d f o r use o f t h e SCA method due t o t h e f e a t u r e s o f t h e SCA d i s p e r s i o n parameters.
By b u i l d i n g up f r o m a base s e t o f SCA
d i s p e r s i o n parameters, d i f f e r e n c e s can be accounted f o r i n r e g i o n a l meteorology. VALIDATION AND USE The SCA method has been v a l i d a t e d i n s e v e r a l c i t i e s where d e t a i l e d emissions i n v e n t o r i e s were r e a d i l y a v a i l a b l e , namely I l i l w a u k e e and Madison, Wisconsin and Vienna, A u s t r i a .
F o r these c i t i e s , t h e c a l c u l a t e d exposure was w i t h i n 10-20% o f
t h e expected exposure based on m o n i t o r i n g d a t a and, f o r Wisconsin, d e t a i l e d i s o p l e t h s f r o m c a l i b r a t e d d i s p e r s i o n models.
F o r s e v e r a l o t h e r c i t i e s i n Europe,
g e n e r a l checks have been made and c a l c u l a t e d SCA exposures appear t o be i n reasonable agreement w i t h d a t a . The SCA method has been used i n r e g i o n a l s t u d i e s o f energy and environmental management.
The most r e c e n t i s an A u s t r i a n case s t u d y [ 7 ] .
A s e n s i t i v i t y study
i s p r e s e n t e d f r o m t h e A u s t r i a n s t u d y t o i l l u s t r a t e t h e use o f t h e SCA method.
A
h e a l t h model 181 was used t o c o n v e r t SO2 exposure t o a h e a l t h impact, expressed as Person-Days-Lost (PDL).
The s e n s i t i v i t y l o o k s a t t h e e f f e c t i v e n e s s o f t h e SO2
e m i s s i o n s t a n d a r d s assumed i n t h e s c e n a r i o s developed f o r A u s t r i a . a r e shown g r a p h i c a l l y i n F i g u r e s 5 and 6 . have a s i g n i f i c a n t e f f e c t on t h e
The r e s u l t s
While each o f t h e e m i s s i o n standards
SO2 emissions, o n l y t h e p e t r o l e u m d e s u l f u r i z a t i o n
has a s i g n i f i c a n t e f f e c t on h e a l t h impact.
T h i s i s because t h e r e s i d e n t i a l and
c o m m e r c i a l - s e r v i c e emissions ( a r e a sources) were o n l y a f f e c t e d by t h e o i l
149
s1
s1 s1 s1 S1 '' , With Desulfurization S1
1971
u I-
With Desulfurization + Present Emission Standards , With Desulfurization + Anticipated New US Emission Standards
1980
1990
2000
.5 E 5:
N
2010
2020
F i g . 5. S e n s i t i v i t y o f SO Emissions t o SO2 R e g u l a t i o n s f o r Scgnario SI, Austria desulfurization.
19171
1980
1990
2000
2010
2020
F i g . 6. S e n s i t i v i t y o f A i r P o l l u t i o n P u b l i c H e a l t h t o S O p R e g u l a t i o n s f o r Scenario 1, Austria
W i t h d e s u l f u r i z a t i o n , t h e area sources were a l r e a d y a t t h e p r e s e n t
U.S. Standard, and t h e new U.S. s t a n d a r d was assumed t o o n l y a f f e c t p o i n t sources. The c o n c l u s i o n i s t h a t t h e e f f e c t i v e n e s s o f each new SO2 r e d u c t i o n i s l e s s t h a n t h e p r e c e e d i n g one i n terms o f h e a l t h impact.
A word o f c a u t i o n must be expressed;
l o n g - r a n g e t r a n s p o r t o f s u l f a t e s i s n o t i n c l u d e d here, t h u s t h e standards would a c t u a l l y be more e f f e c t i v e t h a n i n d i c a t e d h e r e . CONCLUSION The SCA method i s a b l e t o c h a r a c t e r i z e urban a i r p o l l u t i o n d i s p e r s i o n a t t h e urban l e v e l and i t r e q u i r e s a minimum o f emissions d e t a i l .
The method has been
shown t o g i v e v a l u a b l e i n s i g h t i n t o p o l i c y a n a l y s i s i n a c t u a l s t u d i e s ; i t p r o v i d e s a "first-cut"
a n a l y s i s f o r long-range p l a n n i n g and s t r a t e g y o p t i o n a n a l y s i s .
The
SCA method p r e s e n t s o n l y one s i d e o f t h e a i r p o l l u t i o n impact p i c t u r e , t h e s h o r t range u r b a n i m p a c t .
When t h e c a u s a l a g e n t s o f t h e impacts a r e chemical r e a c t i o n
p r o d u c t s , t h e n t h e SCA method must be supplemented by a long-range t r a n s p o r t method t o balance t h e a n a l y s i s o f p o l i c y o p t i o n s .
The SCA method i s a u s e f u l and useable
150 t o o l f o r a i r p o l l u t i o n impact a n a l y s i s f o r long-range s t u d i e s when used i n t h e proper context.
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