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Daily Forecasting of Air Pollution Potential
97
D A I L Y FORECASTING O F A I R POLLUTION POTENTIAL
A.
JOUKOFF and L.M.
MALET
Royal M e t e o r o l o g i c a l I n s t i t u t e . Uccle (Belgium)
ABSTRACT E x p e r i m e n t a l f o r e c a s t s p e r f o r m e d a t t h e Royal M e t e o r o l o g i c a l I n s t i t u t e o f B e l gium d u r i n g t h e w i n t e r s 1979-1980 and 1980-1981 a r e d e s c r i b e d and a n a l y s e d .
These
f o r e c a s t s are b a s e d on t h e e v a l u a t i o n o f an a i r p o l l u t i o n p o t e n t i a l i n d e x which u s e s t h r e e i m p o r t a n t m e t e o r o l o g i c a l p a r a m e t e r s : wind s p e e d , v e r t i c a l s t a b i l i t y and t e m p e r a t u r e . These m e t e o r o l o g i c a l f o r e c a s t s combine n u m e r i c a l f o r e c a s t s a t t h e 850 mbar lev e l with a semi-climatological air mass characteristics.
scheme g i v i n g a i r t e m p e r a t u r e s a s s o c i a t e d w i t h t h e
The m e t e o r o l o g i c a l i n d e x i s c o n v e r t e d i n t o p o t e n t i a l
a i r p o l l u t i o n l e v e l s by means o f a r e l a t i o n deduced from a l i n e a r r e g r e s s i o n u s i n g SO
measurements from t h e p r e v i o u s w i n t e r . The r e s u l t s o f t h e two s e a s o n s of 2 experimental f o r e c a s t s a r e very encouraging.
INTRODUCTION
The f i v e l a r g e s t urban a g g l o m e r a t i o n s o f Belgium (Antwerp, B r u s s e l s , C h a r l e r o i , Ghent and L i e g e ) are c o v e r e d by a m o n i t o r i n g network measuring a s w e l l a i r q u a l i t y a s meteorological parameters.
Every minute t h i s t e l e m e t e r e d network i s s u e s v a l u e s
o f t h e d i f f e r e n t p a r a m e t e r s measured by a l l s a m p l i n g s t a t i o n s t o a r e g i o n a l d a t a reduction c e n t r e (R.D.R.C.) R.D.R.C.'s
where h a l f - h o u r l y a v e r a g e s a r e computed.
send these half-hourly
(N.D.P.C.).
The N.D.P.C.
The f i v e
averages t o a n a t i o n a l dat a processing cent r e
i s d i v i d e d i n t o two p a r t s
:
t h e f i r s t one i s p l a c e d
a t the I n s t i t u t e o f Hygiene and Epidemiology o f t h e M i n i s t e r y of P u b l i c H e a l t h and t h e s e c o n d a t t h e Royal M e t e o r o l o g i c a l I n s t i t u t e .
One o f t h e p r i n c i p a l t a s k s
of the l a t t e r c o n s i s t s i n i s s u i n g d a i l y fo reca st s of t he a i r q u a l i t y p o t e n t i a l f o r the f i v e r e g i o n s and f o r the n e x t 24 h o u r s . and a n a l y s e d i n t h e p r e s e n t paper.
These f o r e c a s t s are d e s c r i b e d
They have been t r a n s m i t t e d t o the p u b l i c
h e a l t h a u t h o r i t i e s d u r i n g t h e w i n t e r p e r i o d s 1979-1980 and 1980-1981, b e r t o march.
They s t i l l must b e c o n s i d e r e d as e x p e r i m e n t a l .
from novem-
A i r quality potential
i s e v a l u a t e d b y a n a i r p o l l u t i o n p o t e n t i a l i n d e x b a s e d on m e t e o r o l o g i c a l p a r a meters o n l y .
98 THE METEOROLOGICAL A I R POLLUTION POTENTIAL I N D E X I n o r d e r t o a p p r e c i a t e t h e d i f f u s i v e c a p a c i t y o f t h e atmosphere and to e s t i mate t h e a i r p o l l u t i o n l e v e l , a m e t e o r o l o g i c a l a i r p o l l u t i o n p o t e n t i a l i n d e x (MPI) h a s been developped on t h e b a s i s o f a c e r t a i n number o f s t u d i e s ( r e f s . 1 - 5 ) .
It
combines t h r e e o f t h e most s i g n i f i c a n t m e t e o r o l o g i c a l p a r a m e t e r s which can b e f o r e c a s t e d on a r o u t i n e b a s i s w i t h a s u f f i c i e n t r e l i a b i l i t y .
The t h r e e p a r a m e t e r s
s e l e c t e d are :
2 4 h o u r s a v e r a g e t e m p e r a t u r e , T , which d e t e r m i n e s t h e s t r e n g t h o f d o m e s t i c heat i n g s o u r c e s , dominant i n urban a r e a s
;
2 4 h o u r s a v e r a g e wind s p e e d , v , which d e t e r m i n e s t h e h o r i z o n t a l t r a n s p o r t o f the a t m o s p h e r i c p o l l u t a n t s
:
v e r t i c a l s t a b i l i t y o f l o w a t m o s p h e r i c l a y e r s , which d e t e r m i n e s t h e h o r i z o n t a l and v e r t i c a l d i s p e r s i o n of the p o l l u t a n t s .
T h i s s t a b i l i t y i s c h a r a c t e r i z e d by
an i n d e x s i n p l a c e o f t h e p r e v i o u s l y u s e d mixjng h e i g h t ( r e f . 5 ) which i s rather d i f f i c u l t to predict.
T h i s i n d e x i s a f u n c t i o n o f t h e r a t i o between t h e
700-1000 mbar l a y e r t h i c k n e s s , H , and t h e t h i c k n e s s Hd f o r t h i s l a y e r c a l c u l a t e d according t o a dry a d i a b a t i c lapse rate f o r the s a m e sur f ace conditions.
The
index s used i n p r a c t i c e i s : H
s =
d
lo--
9
n
The MPI h a s t h e f o l l o w i n g form MPI
:
25 - T 1/2
Such a p u r e l y m e t e o r o l o g i c a l i n d e x does t a k e i n t o a c c o u n t t h e p o s s i b l e p o l l u t a n t a c c u m u l a t i o n and the p o s s i b l e a d v e c t i o n o f p o l l u t a n t s from one r e g i o n t o a n o t h e r . Thus i t r e p r e s e n t s t h e l o c a l p o t e n t i a l o f a i r p o l l u t i o n . METEOROLOGICAL FORECASTING
M e t e o r o l o g i c a l f o r e c a s t i n g h a s been p e r f o r m e d on t h e b a s i s of m e t e o r o l o g i c a l maps as p r e d i c t e d u s i n g a m a t h e m a t i c a l model.
The use of one model o n l y may b e
dangerous due t o the f a c t t h a t no model i s p e r f e c t ; however i t g a r a n t e e s homogen e i t y as r e g a r d s t h e d e t e r m i n a t i o n of t h e i n i t i a l c o n d i t i o n s l e a d i n g t o t h e 2 4 , 48 and 72 h o u r s forecasts.
Our e x p e r i e n c e shows t h a t maps a t t h e 850 mbar l e v e l
are the most a d e q u a t e t o d e s c r i b e a i r p o l l u t i o n p o t e n t i a l e v o l u t i o n (more r e p r e s e n t a t i v e t h a n t h e 500 mbar l e v e l e . g . )
.
From t h e s e maps, one can r e a d 700-1000 mbar
l a y e r mean t e m p e r a t u r e and f u r t h e r d e r i v e s u r f a c e l e v e l maps g i v i n g p r e s s u r e g r a d i e n t s and wind d i r e c t i o n s o v e r Belgium. wind s p e e d s .
P r e s s u r e g r a d i e n t s are c o n v e r t e d i n t o
99 Wind d i r e c t i o n s are used t o e s t i m a t e extreme temperature by means o f a semic l i m a t o l o g i c a l method (based on r e f . 6) giving d a i l y extremes from the c a r a c t e r i s From these extremes, i t i s p o s s i b l e t o e v a l u a t e 24-hours
t i c s of the a i r mass. mean temperature. about 1 m . s - ' cases.
Due t o t h e s c a l e of t h e maps, reading accuracy i s l i m i t e d t o
f o r t h e wind speed and t o 5 degrees f o r t h e wind d i r e c t i o n i n most
This accuracy i s a s s o c i a t e d w i t h the reading only and does n o t take i n t o
account t h e f o r e c a s t f i t n e s s .
V e r t i c a l s t a b i l i t y index s i s evaluated from d i r e c t
reading of H (700-1000 mbar t h i c k n e s s ) and the f o r e c a s t e d values of s u r f a c e temper a t u r e and p r e s s u r e ( g i v i n g Hd)
.
During the second experimental f o r e c a s t i n g season, some improvements have been brought t o t h e method
:
r e v i s e d c l i m a t o l o g i c a l d a t a and a c o r r e c t i o n f o r cloudi-
ness in e v a l u a t i n g t h e temperature.
i n the N.D.P.C.
The f o r e c a s t i n g procedure has been implemented
computer t o f a c i l i t a t e the f o r e c a s t e r s work.
The o u t p u t gives i n t e r p o l a t e d values each 6 hours and an i n t e r a c t i v e procedure allows the f o r e c a s t e r s t o introduce c o r r e c t i o n s i n t h e temperature.
A f i r s t correc-
t i o n i s provided by t h e program from t h e comparison o f observed and c o e u t e d val u e s f o r 0 , 6 and 1 2 hours U . T . Forecasting r e s u l t s a r e summarized i n t a b l e 1, giving the number of successes ( t a k i n g a t o l e r a n c e i n t o a c c o u n t ) , underestimates and overestimates f o r each meteor o l o g i c a l parameters and t h e i r combination MPI TABLE 1
Forecastina r e s u l t s ( % ) Parameter T V S
MPI
:
meteorolocw
Tolerance
20
2 m.s
-1
0.1
5 (+)
Good a b a b a b a b
66 78 73 76 75 87 71 79
Over
LJuier
11 6 19 21 7 10 19 6
22 15 7 3 18 4 10 15
a : 1979-1980 ; b : 1980-1981. (+) 5 u n i t s MPI correspond t o about 2 ~ / i g . m - SO ~ /24h i n B r u s s e l s . 2 Except f o r the cases when t h e numerical f o r e c a s t i n g f a i l e d , t h e f o r e c a s t e d values followed r a t h e r w e l l t h e observed ones.
Fig.
1 gives t h e s c a t t e r p l o t of
t h e observed and f o r e c a s t e d values f o r t h e MPI d u r i n g t h e two considered w i n t e r s respectively.
100
WINTER 1979 - 1980
WINTER 1980- 1981
50
40
30
20
10 PMI 0
Fig.
1. S c a t t e r p l o t s o f o b s e r v e d (MF'I) vs f o r e c a s t e d (MPI (F)) v a l u e s of MPI
POTENTIAL A I R POLLUTION FORECASTING MPI v a l u e s c a n be c o n v e r t e d t o e x p e c t e d p o t e n t i a l a i r p o l l u t i o n l e v e l s i n -3 o f SO2 (24h mean) i n o r d e r t o g i v e a more e x p l i c i t p i c t u r e o f the s i t u a P9.m t i o n ; t h i s c a n e a s i l y b e used by p u b l i c h e a l t h a u t h o r i t i e s . During t h e f i r s t e x p e r i m e n t a l w i n t e r , this c o n v e r s i o n h a s been done s i m p l y by m u l t i p l y i n g t h e MPI by a f a c t o r d e t e r m i n e d f o r e a c h urban area from p r e v i o u s winter observations. During t h e s e c o n d w i n t e r , l i n e a r r e g r e s s i o n s b a s e d on o b s e r v a t i o n s performed d u r i n g t h e f i r s t w i n t e r have been u s e d .
Comparison between t h e f o r e c a s t e d p o t e n -
t i a l a i r p o l l u t i o n and o b s e r v e d SO2 c o n c e n t r a t i o n s i s summarized i n t a b l e 2 .
High p o l l u t i o n p e r i o d s have been f o r e c a s t e d w i t h s u c c e s s , however c o n c e n t r a t i o n s c a n n o t b e f o r e c a s t e d a c c u r a t e l y due t o t h e c o n c e p t i o n of t h e MF'I i t s e l f , as n e i t h e r a c c u m u l a t i o n n o r t r a n s p o r t a r e i n c l u d e d i n t h e method.
The p u r p o s e
o f t h i s method i s t o c h a r a c t e r i z e t h e d i f f u s i o n c o n d i t i o n s and o n l y those s o u r c e e f f e c t s which are due t o d o m e s t i c h e a t i n g .
101 TABLE 2
Forecasting r e s u l t s Urban area
(%)
concentrations Good ( + 2 0 % )
a b a b a b a b a b
Brussels Antwerp Liege Ghen t Charler o i
33 37 41 39 37 55 45 49 38 51
Over
( 4 2 ) (+) (46) (53) (43) (61) (70) (57) (46) (41) (54)
13 51 24 48 5 10 20 26 26 21
(28) (23) (21) (23) (18) (18) (16) (23) (33) (24)
Under
54 12 35 13 58 35 35 25 37 28
(31) (31) (26) (34) (20)
(12) (27) (31) (27) (33)
a : 1979-1980 , b : 1980-1981 ( + ) F i g u r e s between b r a c k e t s r e p o r t a p o s t e r i o r i f o r e c a s t i n g u s i n g f o r e c a s t e d MPI b u t a l i n e a r r e g r e s s i o n between o b s e r v a t i o n s f o r t h e same w i n t e r .
CONCLUSIONS The s i m p l e e s t i m a t i o n o f t h e p o t e n t i a l a i r p o l l u t i o n t h a t h a s been e x p e r i m e n t e d i n Belgium f o r two y e a r s p r o v e d t o be o p e r a t i o n a l f o r d a i l y f o r e c a s t i n g i n o r d e r
t o warn p u b l i c h e a l t h a u t h o r i t i e s a b o u t t h e p o s s i b l e d e t e r i o r a t i o n o f t h e a i r quality
2 4 o r 48 h o u r s i n advance.
The method of f o r e c a s t i n g t h e p o t e n t i a l a i r
p o l l u t i o n d e v e l o p p e d a t t h e Royal M e t e o r o l o g i c a l I n s t i t u t e o f Belgium and d a i l y u s e d d u r i n g two w i n t e r s h a s g i v e n e n c o u r a g i n g r e s u l t s .
When n u m e r i c a l f o r e c a s -
t i n g s w e r e correct, i . e . i n most o f t h e cases, MPI w a s g e n e r a l l y w e l l e s t i m a t e d . I t appears thus p o s s i b l e
t o f o r e c a s t t h e d i f f u s i v e c a p a c i t y o f t h e atmosphere
and t o e s t i m a t e p o t e n t i a l a i r p o l l u t i o n from r o u t i n e s y n o p t i c f o r e c a s t i n g s a v a i l a b l e a t a weather o f f i c e .
SO
an i n d i c a t i o n o f t h e a i r q u a l i t y .
2
c o n c e n t r a t i o n s computed from t h e MPI g i v e I t i s t o b e n o t e d t h a t t h e MPI t a k e s only i n t o
a c c o u n t t h e d i s p e r s i o n c o n d i t i o n s and p o l l u t a n t p r o d u c t i o n due t o d o m e s t i c heat i n g sources.
Background p o l l u t i o n and i n d u s t r i a l s o u r c e s are i m p l i c i t e l y t a k e n
i n t o a c c o u n t by t h e c o n v e r s i o n method ; however t r a n s p o r t and a c c u m u l a t i o n o f p o l l u t a n t s are n o t i n c l u d e d i n t h i s scheme, p r i m a r i l y d e s i g n e d f o r urban areas. Even when p a r t i c u l a r y u n f a v o u r a b l e m e t e o r o l o g i c a l c o n d i t i o n s e x i s t , an a i r p o l l u t i o n e p i s o d e only occurs i f s o u r c e s t r e n g t h i s s u f f i c i e n t .
The MPI must be
c o n s i d e r e d as an i n d i c a t o r o f the a t m o s p h e r i c d i f f u s i o n c a p a b i l i t y and o f p o l l u t a n t p r o d u c t i o n due t o m e t e o r o l o g i c a l c o n d i t i o n s ( h e a t i n g d u r i n g very c o l d p e r i o d s ) . I t c o n s t i t u t e s a simple b u t e f f e c t i v e t o o l f o r d a i l y f o r e c a s t i n g o f t h e p o t e n -
t i a l air pollution.
102 REFERENCES 1 . B, B r i n g f e l t , Atmosph. E n v i r o n . , 5 (1971) 949-972. 2. D.M. Elsom a n d T . J . C h a n d l e r , Atmosph. E n v i r o n . , 12 (1978) 1543-1554. 3 . H . van Dop, A.P. van Ulden a n d W.R. R a a f f , S c i e n t i f i c r e p o r t , W.R. 75-4, K.N.M.I. (1975) D e B i l t . 4. M.E. B e r l y a n d , P r e s e n t T o p i c s i n a t m o s p h e r i c d i f f u s i o n a n d a i r p o l l u t i o n ( i n r u s s i a n ) , chap.12 (1975) L e n i n g r a d . 5. L.M. Malet a n d A. J o u k o f f , W.M.O. Symposium on boundary l a y e r p h y s i c s a p p l i e d t o s p e c i f i c p r o b l e m s o f a i r p o l l u t i o n W.M.O. n 0 5 1 0 ( 1 9 7 8 ) , 135-141. 6 . A . Bodeux, Approche d ' u n e esquisse c l i m a t o l o g i q u e d e s t y p e s d e temps e n B e l g i q u e , I.R.M., Publ. s e r i e A n o 2 ( 1 9 7 2 ) .
D A I L Y FORECASTING O F A I R POLLUTION POTENTIAL
A.
JOUKOFF and L.M.
MALET
Royal M e t e o r o l o g i c a l I n s t i t u t e . Uccle (Belgium)
ABSTRACT E x p e r i m e n t a l f o r e c a s t s p e r f o r m e d a t t h e Royal M e t e o r o l o g i c a l I n s t i t u t e o f B e l gium d u r i n g t h e w i n t e r s 1979-1980 and 1980-1981 a r e d e s c r i b e d and a n a l y s e d .
These
f o r e c a s t s are b a s e d on t h e e v a l u a t i o n o f an a i r p o l l u t i o n p o t e n t i a l i n d e x which u s e s t h r e e i m p o r t a n t m e t e o r o l o g i c a l p a r a m e t e r s : wind s p e e d , v e r t i c a l s t a b i l i t y and t e m p e r a t u r e . These m e t e o r o l o g i c a l f o r e c a s t s combine n u m e r i c a l f o r e c a s t s a t t h e 850 mbar lev e l with a semi-climatological air mass characteristics.
scheme g i v i n g a i r t e m p e r a t u r e s a s s o c i a t e d w i t h t h e
The m e t e o r o l o g i c a l i n d e x i s c o n v e r t e d i n t o p o t e n t i a l
a i r p o l l u t i o n l e v e l s by means o f a r e l a t i o n deduced from a l i n e a r r e g r e s s i o n u s i n g SO
measurements from t h e p r e v i o u s w i n t e r . The r e s u l t s o f t h e two s e a s o n s of 2 experimental f o r e c a s t s a r e very encouraging.
INTRODUCTION
The f i v e l a r g e s t urban a g g l o m e r a t i o n s o f Belgium (Antwerp, B r u s s e l s , C h a r l e r o i , Ghent and L i e g e ) are c o v e r e d by a m o n i t o r i n g network measuring a s w e l l a i r q u a l i t y a s meteorological parameters.
Every minute t h i s t e l e m e t e r e d network i s s u e s v a l u e s
o f t h e d i f f e r e n t p a r a m e t e r s measured by a l l s a m p l i n g s t a t i o n s t o a r e g i o n a l d a t a reduction c e n t r e (R.D.R.C.) R.D.R.C.'s
where h a l f - h o u r l y a v e r a g e s a r e computed.
send these half-hourly
(N.D.P.C.).
The N.D.P.C.
The f i v e
averages t o a n a t i o n a l dat a processing cent r e
i s d i v i d e d i n t o two p a r t s
:
t h e f i r s t one i s p l a c e d
a t the I n s t i t u t e o f Hygiene and Epidemiology o f t h e M i n i s t e r y of P u b l i c H e a l t h and t h e s e c o n d a t t h e Royal M e t e o r o l o g i c a l I n s t i t u t e .
One o f t h e p r i n c i p a l t a s k s
of the l a t t e r c o n s i s t s i n i s s u i n g d a i l y fo reca st s of t he a i r q u a l i t y p o t e n t i a l f o r the f i v e r e g i o n s and f o r the n e x t 24 h o u r s . and a n a l y s e d i n t h e p r e s e n t paper.
These f o r e c a s t s are d e s c r i b e d
They have been t r a n s m i t t e d t o the p u b l i c
h e a l t h a u t h o r i t i e s d u r i n g t h e w i n t e r p e r i o d s 1979-1980 and 1980-1981, b e r t o march.
They s t i l l must b e c o n s i d e r e d as e x p e r i m e n t a l .
from novem-
A i r quality potential
i s e v a l u a t e d b y a n a i r p o l l u t i o n p o t e n t i a l i n d e x b a s e d on m e t e o r o l o g i c a l p a r a meters o n l y .
98 THE METEOROLOGICAL A I R POLLUTION POTENTIAL I N D E X I n o r d e r t o a p p r e c i a t e t h e d i f f u s i v e c a p a c i t y o f t h e atmosphere and to e s t i mate t h e a i r p o l l u t i o n l e v e l , a m e t e o r o l o g i c a l a i r p o l l u t i o n p o t e n t i a l i n d e x (MPI) h a s been developped on t h e b a s i s o f a c e r t a i n number o f s t u d i e s ( r e f s . 1 - 5 ) .
It
combines t h r e e o f t h e most s i g n i f i c a n t m e t e o r o l o g i c a l p a r a m e t e r s which can b e f o r e c a s t e d on a r o u t i n e b a s i s w i t h a s u f f i c i e n t r e l i a b i l i t y .
The t h r e e p a r a m e t e r s
s e l e c t e d are :
2 4 h o u r s a v e r a g e t e m p e r a t u r e , T , which d e t e r m i n e s t h e s t r e n g t h o f d o m e s t i c heat i n g s o u r c e s , dominant i n urban a r e a s
;
2 4 h o u r s a v e r a g e wind s p e e d , v , which d e t e r m i n e s t h e h o r i z o n t a l t r a n s p o r t o f the a t m o s p h e r i c p o l l u t a n t s
:
v e r t i c a l s t a b i l i t y o f l o w a t m o s p h e r i c l a y e r s , which d e t e r m i n e s t h e h o r i z o n t a l and v e r t i c a l d i s p e r s i o n of the p o l l u t a n t s .
T h i s s t a b i l i t y i s c h a r a c t e r i z e d by
an i n d e x s i n p l a c e o f t h e p r e v i o u s l y u s e d mixjng h e i g h t ( r e f . 5 ) which i s rather d i f f i c u l t to predict.
T h i s i n d e x i s a f u n c t i o n o f t h e r a t i o between t h e
700-1000 mbar l a y e r t h i c k n e s s , H , and t h e t h i c k n e s s Hd f o r t h i s l a y e r c a l c u l a t e d according t o a dry a d i a b a t i c lapse rate f o r the s a m e sur f ace conditions.
The
index s used i n p r a c t i c e i s : H
s =
d
lo--
9
n
The MPI h a s t h e f o l l o w i n g form MPI
:
25 - T 1/2
Such a p u r e l y m e t e o r o l o g i c a l i n d e x does t a k e i n t o a c c o u n t t h e p o s s i b l e p o l l u t a n t a c c u m u l a t i o n and the p o s s i b l e a d v e c t i o n o f p o l l u t a n t s from one r e g i o n t o a n o t h e r . Thus i t r e p r e s e n t s t h e l o c a l p o t e n t i a l o f a i r p o l l u t i o n . METEOROLOGICAL FORECASTING
M e t e o r o l o g i c a l f o r e c a s t i n g h a s been p e r f o r m e d on t h e b a s i s of m e t e o r o l o g i c a l maps as p r e d i c t e d u s i n g a m a t h e m a t i c a l model.
The use of one model o n l y may b e
dangerous due t o the f a c t t h a t no model i s p e r f e c t ; however i t g a r a n t e e s homogen e i t y as r e g a r d s t h e d e t e r m i n a t i o n of t h e i n i t i a l c o n d i t i o n s l e a d i n g t o t h e 2 4 , 48 and 72 h o u r s forecasts.
Our e x p e r i e n c e shows t h a t maps a t t h e 850 mbar l e v e l
are the most a d e q u a t e t o d e s c r i b e a i r p o l l u t i o n p o t e n t i a l e v o l u t i o n (more r e p r e s e n t a t i v e t h a n t h e 500 mbar l e v e l e . g . )
.
From t h e s e maps, one can r e a d 700-1000 mbar
l a y e r mean t e m p e r a t u r e and f u r t h e r d e r i v e s u r f a c e l e v e l maps g i v i n g p r e s s u r e g r a d i e n t s and wind d i r e c t i o n s o v e r Belgium. wind s p e e d s .
P r e s s u r e g r a d i e n t s are c o n v e r t e d i n t o
99 Wind d i r e c t i o n s are used t o e s t i m a t e extreme temperature by means o f a semic l i m a t o l o g i c a l method (based on r e f . 6) giving d a i l y extremes from the c a r a c t e r i s From these extremes, i t i s p o s s i b l e t o e v a l u a t e 24-hours
t i c s of the a i r mass. mean temperature. about 1 m . s - ' cases.
Due t o t h e s c a l e of t h e maps, reading accuracy i s l i m i t e d t o
f o r t h e wind speed and t o 5 degrees f o r t h e wind d i r e c t i o n i n most
This accuracy i s a s s o c i a t e d w i t h the reading only and does n o t take i n t o
account t h e f o r e c a s t f i t n e s s .
V e r t i c a l s t a b i l i t y index s i s evaluated from d i r e c t
reading of H (700-1000 mbar t h i c k n e s s ) and the f o r e c a s t e d values of s u r f a c e temper a t u r e and p r e s s u r e ( g i v i n g Hd)
.
During the second experimental f o r e c a s t i n g season, some improvements have been brought t o t h e method
:
r e v i s e d c l i m a t o l o g i c a l d a t a and a c o r r e c t i o n f o r cloudi-
ness in e v a l u a t i n g t h e temperature.
i n the N.D.P.C.
The f o r e c a s t i n g procedure has been implemented
computer t o f a c i l i t a t e the f o r e c a s t e r s work.
The o u t p u t gives i n t e r p o l a t e d values each 6 hours and an i n t e r a c t i v e procedure allows the f o r e c a s t e r s t o introduce c o r r e c t i o n s i n t h e temperature.
A f i r s t correc-
t i o n i s provided by t h e program from t h e comparison o f observed and c o e u t e d val u e s f o r 0 , 6 and 1 2 hours U . T . Forecasting r e s u l t s a r e summarized i n t a b l e 1, giving the number of successes ( t a k i n g a t o l e r a n c e i n t o a c c o u n t ) , underestimates and overestimates f o r each meteor o l o g i c a l parameters and t h e i r combination MPI TABLE 1
Forecastina r e s u l t s ( % ) Parameter T V S
MPI
:
meteorolocw
Tolerance
20
2 m.s
-1
0.1
5 (+)
Good a b a b a b a b
66 78 73 76 75 87 71 79
Over
LJuier
11 6 19 21 7 10 19 6
22 15 7 3 18 4 10 15
a : 1979-1980 ; b : 1980-1981. (+) 5 u n i t s MPI correspond t o about 2 ~ / i g . m - SO ~ /24h i n B r u s s e l s . 2 Except f o r the cases when t h e numerical f o r e c a s t i n g f a i l e d , t h e f o r e c a s t e d values followed r a t h e r w e l l t h e observed ones.
Fig.
1 gives t h e s c a t t e r p l o t of
t h e observed and f o r e c a s t e d values f o r t h e MPI d u r i n g t h e two considered w i n t e r s respectively.
100
WINTER 1979 - 1980
WINTER 1980- 1981
50
40
30
20
10 PMI 0
Fig.
1. S c a t t e r p l o t s o f o b s e r v e d (MF'I) vs f o r e c a s t e d (MPI (F)) v a l u e s of MPI
POTENTIAL A I R POLLUTION FORECASTING MPI v a l u e s c a n be c o n v e r t e d t o e x p e c t e d p o t e n t i a l a i r p o l l u t i o n l e v e l s i n -3 o f SO2 (24h mean) i n o r d e r t o g i v e a more e x p l i c i t p i c t u r e o f the s i t u a P9.m t i o n ; t h i s c a n e a s i l y b e used by p u b l i c h e a l t h a u t h o r i t i e s . During t h e f i r s t e x p e r i m e n t a l w i n t e r , this c o n v e r s i o n h a s been done s i m p l y by m u l t i p l y i n g t h e MPI by a f a c t o r d e t e r m i n e d f o r e a c h urban area from p r e v i o u s winter observations. During t h e s e c o n d w i n t e r , l i n e a r r e g r e s s i o n s b a s e d on o b s e r v a t i o n s performed d u r i n g t h e f i r s t w i n t e r have been u s e d .
Comparison between t h e f o r e c a s t e d p o t e n -
t i a l a i r p o l l u t i o n and o b s e r v e d SO2 c o n c e n t r a t i o n s i s summarized i n t a b l e 2 .
High p o l l u t i o n p e r i o d s have been f o r e c a s t e d w i t h s u c c e s s , however c o n c e n t r a t i o n s c a n n o t b e f o r e c a s t e d a c c u r a t e l y due t o t h e c o n c e p t i o n of t h e MF'I i t s e l f , as n e i t h e r a c c u m u l a t i o n n o r t r a n s p o r t a r e i n c l u d e d i n t h e method.
The p u r p o s e
o f t h i s method i s t o c h a r a c t e r i z e t h e d i f f u s i o n c o n d i t i o n s and o n l y those s o u r c e e f f e c t s which are due t o d o m e s t i c h e a t i n g .
101 TABLE 2
Forecasting r e s u l t s Urban area
(%)
concentrations Good ( + 2 0 % )
a b a b a b a b a b
Brussels Antwerp Liege Ghen t Charler o i
33 37 41 39 37 55 45 49 38 51
Over
( 4 2 ) (+) (46) (53) (43) (61) (70) (57) (46) (41) (54)
13 51 24 48 5 10 20 26 26 21
(28) (23) (21) (23) (18) (18) (16) (23) (33) (24)
Under
54 12 35 13 58 35 35 25 37 28
(31) (31) (26) (34) (20)
(12) (27) (31) (27) (33)
a : 1979-1980 , b : 1980-1981 ( + ) F i g u r e s between b r a c k e t s r e p o r t a p o s t e r i o r i f o r e c a s t i n g u s i n g f o r e c a s t e d MPI b u t a l i n e a r r e g r e s s i o n between o b s e r v a t i o n s f o r t h e same w i n t e r .
CONCLUSIONS The s i m p l e e s t i m a t i o n o f t h e p o t e n t i a l a i r p o l l u t i o n t h a t h a s been e x p e r i m e n t e d i n Belgium f o r two y e a r s p r o v e d t o be o p e r a t i o n a l f o r d a i l y f o r e c a s t i n g i n o r d e r
t o warn p u b l i c h e a l t h a u t h o r i t i e s a b o u t t h e p o s s i b l e d e t e r i o r a t i o n o f t h e a i r quality
2 4 o r 48 h o u r s i n advance.
The method of f o r e c a s t i n g t h e p o t e n t i a l a i r
p o l l u t i o n d e v e l o p p e d a t t h e Royal M e t e o r o l o g i c a l I n s t i t u t e o f Belgium and d a i l y u s e d d u r i n g two w i n t e r s h a s g i v e n e n c o u r a g i n g r e s u l t s .
When n u m e r i c a l f o r e c a s -
t i n g s w e r e correct, i . e . i n most o f t h e cases, MPI w a s g e n e r a l l y w e l l e s t i m a t e d . I t appears thus p o s s i b l e
t o f o r e c a s t t h e d i f f u s i v e c a p a c i t y o f t h e atmosphere
and t o e s t i m a t e p o t e n t i a l a i r p o l l u t i o n from r o u t i n e s y n o p t i c f o r e c a s t i n g s a v a i l a b l e a t a weather o f f i c e .
SO
an i n d i c a t i o n o f t h e a i r q u a l i t y .
2
c o n c e n t r a t i o n s computed from t h e MPI g i v e I t i s t o b e n o t e d t h a t t h e MPI t a k e s only i n t o
a c c o u n t t h e d i s p e r s i o n c o n d i t i o n s and p o l l u t a n t p r o d u c t i o n due t o d o m e s t i c heat i n g sources.
Background p o l l u t i o n and i n d u s t r i a l s o u r c e s are i m p l i c i t e l y t a k e n
i n t o a c c o u n t by t h e c o n v e r s i o n method ; however t r a n s p o r t and a c c u m u l a t i o n o f p o l l u t a n t s are n o t i n c l u d e d i n t h i s scheme, p r i m a r i l y d e s i g n e d f o r urban areas. Even when p a r t i c u l a r y u n f a v o u r a b l e m e t e o r o l o g i c a l c o n d i t i o n s e x i s t , an a i r p o l l u t i o n e p i s o d e only occurs i f s o u r c e s t r e n g t h i s s u f f i c i e n t .
The MPI must be
c o n s i d e r e d as an i n d i c a t o r o f the a t m o s p h e r i c d i f f u s i o n c a p a b i l i t y and o f p o l l u t a n t p r o d u c t i o n due t o m e t e o r o l o g i c a l c o n d i t i o n s ( h e a t i n g d u r i n g very c o l d p e r i o d s ) . I t c o n s t i t u t e s a simple b u t e f f e c t i v e t o o l f o r d a i l y f o r e c a s t i n g o f t h e p o t e n -
t i a l air pollution.
102 REFERENCES 1 . B, B r i n g f e l t , Atmosph. E n v i r o n . , 5 (1971) 949-972. 2. D.M. Elsom a n d T . J . C h a n d l e r , Atmosph. E n v i r o n . , 12 (1978) 1543-1554. 3 . H . van Dop, A.P. van Ulden a n d W.R. R a a f f , S c i e n t i f i c r e p o r t , W.R. 75-4, K.N.M.I. (1975) D e B i l t . 4. M.E. B e r l y a n d , P r e s e n t T o p i c s i n a t m o s p h e r i c d i f f u s i o n a n d a i r p o l l u t i o n ( i n r u s s i a n ) , chap.12 (1975) L e n i n g r a d . 5. L.M. Malet a n d A. J o u k o f f , W.M.O. Symposium on boundary l a y e r p h y s i c s a p p l i e d t o s p e c i f i c p r o b l e m s o f a i r p o l l u t i o n W.M.O. n 0 5 1 0 ( 1 9 7 8 ) , 135-141. 6 . A . Bodeux, Approche d ' u n e esquisse c l i m a t o l o g i q u e d e s t y p e s d e temps e n B e l g i q u e , I.R.M., Publ. s e r i e A n o 2 ( 1 9 7 2 ) .