Daily forecasting of air pollution potential

The Science of the Total Environment, 23 (1982) 97--102 Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

97

DAILY FORECASTING OF AIR POLLUTION POTENTIAL

A. JOUKOFF and L.M. MALET Royal Meteorological Institute. Uccle

(Belgium)

ABSTRACT Experimental forecasts performed at the Royal Meteorological Institute of Belgium during the winters 1979-1980 and 1980-1981 are described and analysed.

These

forecasts are b a s e d on the evaluation of an air pollution potential index which uses three important meteorological parameters : wind speed, vertical stability and temperature. These meteorological forecasts combine numerical forecasts at the 850 mbar level with a

semi-climatological scheme giving air temperatures associated with the

air mass characteristics.

The meteorological index is converted into potential

air pollution ievels by means of a relation deduced from a linear regression using SO 2 measurements from the previous winter.

The results of the two seasons of

experimental forecasts are very encouraging.

INTRODUCTION The five largest urban agglomerations of Belgium (Antwerp, Brussels, Charleroi, Ghent and Liege)

are covered by a monitoring network measuring as well air quality

as meteorological parameters.

Every minute this telemetered network issues values

of the different parameters measured by all sampling stations to a regional data reduction centre

(R.D.R.C.) where half-hourly averages are computed.

The five

R.D.R.C. 's send these half-hourly averages to a national data processing centre (N.D.P.C.).

The N.D.P.C. is divided into two parts : the first one is placed

at the Institute of Hygiene and Epidemiology of the Ministery of Public Health and the second at the Royal Meteorological Institute.

One of the principal tasks

of the latter consists in issuing daily forecasts of the air quality potential for the five regions and for the next 24 hours. and analysed in the present paper.

These forecasts are described

They have been transmitted to the public

health authorities during the winter periods 1979-1980 and 1980-1981, from november to march.

They still must be considered as experimental.

Air quality potential

is evaluated by an air pollution potential index based on meteorological parameters only.

0048-9697/82/0000--0000/$02.75

© 1982 Elsevier Scientific Publishing Company

98

THE M E T E O R O L O G I C A L In o r d e r mate

AIR POLLUTION

to a p p r e c i a t e

the air p o l l u t i o n

POTENTIAL

the d i f f u s i v e

level,

developped

combines

three o f the m o s t s i g n i f i c a n t

selected

on the basis

on a routine

are

- 24 h o u r s

ting sources,

the a t m o s p h e r i c

temperature,

and v e r t i c a l

in urban

pollutants

and to esti-

potential

of studies

meteorological

dispersion

ther d i f f i c u l t mbar

areas

parameters

reliability.

index

(refs.

(MPI)

i-5).

which

It

can be

The three p a r a m e t e r s

determines

layers,

of the p o l l u t a n t s .

of the p r e v i o u s l y This

thickness,

to a dry a d i a b a t i c

i n d e x s u s e d in p r a c t i c e

the s t r e n g t h

of d o m e s t i c

the h o r i z o n t a l

transport

hea-

of

;

to predict. layer

determines ;

v, w h i c h

of low a t m o s p h e r i c

an i n d e x s in place

according

number

a sufficient

T, w h i c h

w i n d speed,

stability

700-1OO0

basis with

dominant

average

- vertical

of a certain

of the a t m o s p h e r e

air p o l l u t i o n

:

average

- 24 hours

capacity

a meteorological

has b e e n

forecasted

INDEX

This

determines

stability

used mixing height

i n d e x is a function

H, a n d the t h i c k n e s s

lapse

is

which

rate

is c h a r a c t e r i z e d

(ref.

5) w h i c h

surface

layer

by

is ra-

of the ratio b e t w e e n H d for this

for the same

the h o r i z o n t a l

the

calculated

conditions.

The

: Hd s = I0-~-9

The MPI has

the

following

form

25 - T MPI

:

v

Such a purely accumulation Thus

meteorological

and the p o s s i b l e

it r e p r e s e n t s

METEOROLOGICAL

neity

48 a n d 72 h o u r s

the d e t e r m i n a t i o n forecasts.

model.

on the basis

w i n d speeds.

region

pollutant

to another.

level e.g.).

and further

directions

shows

air p o l l u t i o n

derive

o v e r Belgium.

of m e t e o r o l o g i c a l

The use of one m o d e l

of the i n i t i a l

Our experience

to d e s c r i b e

than the 500 m b a r

layer m e a n t e m p e r a t u r e and w i n d

the p o s s i b l e

f r o m one

of air pollution.

has b e e n p e r f o r m e d

using a m a t h e m a t i c a l

are the m o s t a d e q u a t e

dients

take i n t o a c c o u n t

of p o l l u t a n t s

due to the fact t h a t no m o d e l is p e r f e c t

as r e g a r d s

sentative

does

advection

local p o t e n t i a l

forecasting

as p r e d i c t e d

dangerous

index

s

FORECASTING

Meteorological maps

the

I/2

; however conditions

t h a t maps potential

F r o m these

maps,

only may be

it g a r a n t e e s leading

homoge-

to the

24,

at the 850 m b a r level evolution one

surface

level maps

Pressure

gradients

(more

can r e a d

repre-

7OO-10OO

giving pressure are c o n v e r t e d

gra-

into

mbar

99 Wind directions climatological

are u s e d to e s t i m a t e

method

(based on ref.

tics of the air mass.

F r o m these

extreme

temperature

by means

6) g i v i n g daily e x t r e m e s

extremes,

it is p o s s i b l e

o f a semi-

from the c a r a c t e r i s -

to e v a l u a t e

24-hours

mean

temperature. Due to the scale o f the maps, r e a d i n g a c c u r a c y is l i m i t e d to -I a b o u t I m.s for the w i n d s p e e d and to 5 degrees for the w i n d d i r e c t i o n in m o s t cases.

%~nis a c c u r a c y

account

the

r e a d i n g of H rature

During

ness

fitness.

(7OO-1OO0 m b a r

and pressure

brought

thickness)

the s e c o n d e x p e r i m e n t a l

in e v a l u a t i n g

The o u t p u t the

: revised

gives

rological

TABLE

only and does n o t take

index

s is e v a l u a t e d

forecasted

results

values

into

from d i r e c t

of surface

tempe-

some i m p r o v e m e n t s

d a t a and a c o r r e c t i o n procedure

forecasters

each

6 hours

corrections

has b e e n

implemented

work.

a n d an i n t e r a c t i v e

in the temperature.

from the c o m p a r i s o n

have b e e n

for c l o u d i -

of observed

procedure

A first correc-

and computed

va-

U.T.

are s u m m a r i z e d

i n t o account),

parameters

season,

forecasting

the

values

to i n t r o d u c e

12 hours

(taking a t o l e r a n c e

The

to facilitate

interpolated

forecasters

Forecasting

and the

forecasting

the temperature.

computer

for O, 6 and

the r e a d i n g stability

climatological

tion is p r o v i d e d b y the p r o g r a m lues

with

Vertical

(giving Hd).

to the m e t h o d

in the N.D.P.C.

allows

is a s s o c i a t e d

forecast

a n d their

in table

i, g i v i n g

underestimates

combination

the n u m b e r

and overestimates

of successes for e a c h meteo-

MPI

1

Forecastinq

results

(%1

Parameter

Tolerance

T

2°

v

2 m.s

s

O.I

MPI

: meteoroloqy

-I

5 (+)

Good a b a b a b a b

a : 1979-1980 ; b : 1980-1981. (+) 5 units MPI c o r r e s p o n d to a b o u t

Except values

for the cases w h e n

followed

the o b s e r v e d respectively.

rather well

and forecasted

66 78 73 76 75 87 71 79

Under

11 6 19 21 7 10 19 6

22 15 7 3 18 4 10 15

2 5 / ~ g . m -3 S O 2 / 2 4 h

the n u m e r i c a l the o b s e r v e d values

Over

in Brussels.

forecasting

ones.

for the MPI

Fig. during

failed,

1 gives

the

forecasted

the s c a t t e r p l o t o f

the two c o n s i d e r e d w i n t e r s

100

WINTER

1979-1980

WINTER

1980-1981

50

! 27

[

::

i

!

:: i

i

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, : ...... i ...... i ...... i ...... i...... i...... ! ~ : : : : : : :/~ i :

i :

i :

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i :

i ! ....... i ....... [ .....................

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:

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40

i i..3~/.~i.i I

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: 33

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: 39

0

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~

i

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20

30

40

PMi(F)

I. S c a t t e r plots of o b s e r v e d

(MPI) vs f o r e c a s t e d

(MPI

(F)) values of MPI

POTENTIAL AIR POLLUTION FORECASTING MPI values can be c o n v e r t e d to e x p e c t e d p o t e n t i a l air p o l l u t i o n levels in ~g.m

-3 o f SO 2 (24h mean)

"

i .....

PMI(F)

Fig.

i/:: :

i .i: !~i-"~

i i ~ ....

i ii

i

....... i ......

,o

; i i i i

,~'~"I! 'i.i

i / !/ : "/:: ....... !//{

i ...... i P: ...... " .... ~. :/ i .

21

is

.! .............

in o r d e r to give a more e x p l i c i t p i c t u r e of the s i t u a -

tion ; this can e a s i l y be u s e d by p u b l i c h e a l t h authorities. D u r i n g the first e x p e r i m e n t a l winter,

this c o n v e r s i o n has b e e n done simply

by m u l t i p l y i n g the MPI by a factor d e t e r m i n e d for each urban area from p r e v i o u s w i n t e r observations. D u r i n g the s e c o n d winter,

linear 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 p e r f o r m e d

during the first w i n t e r h a v e b e e n used.

C o m p a r i s o n b e t w e e n the f o r e c a s t e d p o t e n -

tial air p o l l u t i o n and o b s e r v e d SO 2 c o n c e n t r a t i o n s is s u m m a r i z e d in table 2. H i g h 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 success, h o w e v e r concentrations c a n n o t be f o r e c a s t e d a c c u r a t e l y due to the c o n c e p t i o n o f the MPI itself, 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 are i n c l u d e d in the method.

The p u r p o s e

of this m e t h o d is to c h a r a c t e r i z e the d i f f u s i o n conditions and only those source e f f e c t s w h i c h are due to d o m e s t i c heating.

50

101

TABLE 2 F o r e c a s t i n g results U r b a n area

(%) c o n c e n t r a t i o n s Good

Brussels

a b a b a b a b a b

Antwerp Liege Ghent Charleroi

(+ 20%) 33 37 41 39 37 55 45 49 38 51

Over

(42)(+) (46) (53) (43) (61) (70) (57) (46) (41) (54)

13 51 24 48 5 10 20 26 26 21

Under

(28) (23) (21) (23) (18) (18) (16) (23) (33) (24)

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 (+) Figures b e t w e e n 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 uslng 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 b e t w e e n o b s e r v a t i o n s for the same winter.

CONCLUSIONS The simple e s t i m a t i o n o f the p o t e n t i a l air p o l l u t i o n in B e l g i u m for two years p r o v e d to be o p e r a t i o n a l to w a r n p u b l i c h e a l t h a u t h o r i t i e s quality

for daily f o r e c a s t i n g in o r d e r

a b o u t the p o s s i b l e d e t e r i o r a t i o n o f the air

24 or 48 h o u r s in advance.

The m e t h o d o f f o r e c a s t i n g the p o t e n t i a l air

p o l l u t i o n d e v e l o p p e d at the R o y a l M e t e o r o l o g i c a l

Institute of B e l g i u m and daily

u s e d d u r i n g two w i n t e r s has given e n c o u r a g i n g results. tings w e r e correct,

When numerical

forecas-

i.e. in m o s t o f the cases, MPI was g e n e r a l l y w e l l estimated.

It appears thus p o s s i b l e

to f o r e c a s t the diffusive c a p a c i t y of the atmospher~

and to e s t i m a t e p o t e n t i a l air p o l l u t i o n available

that has b e e n e x p e r i m e n t e d

at a w e a t h e r office.

from routine s y n o p t i c forecastings

SO 2 c o n c e n t r a t i o n s

an i n d i c a t i o n of the air quality.

c o m p u t e d from. the MPI give

It is to b e n o t e d that the MPI takes o n l y into

a c c o u n t the 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 to d o m e s t i c h e a ting sources.

B a c k g r o u n d p o l l u t i o n a n d i n d u s t r i a l sources are i m p l i c i t e l y taken

into a c c o u n t b y the c o n v e r s i o n m e t h o d pollutants

; h o w e v e r t r a n s p o r t and a c c u m u l a t i o n of

are n o t i n c l u d e d in this scheme, p r i m a r i l y d e s i g n e d for urban areas.

Even w h e n 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 conditions exist, lution e p i s o d e only occurs if source s t r e n g t h is sufficient.

an air pol-

The MPI m u s t 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 tant p r o d u c t i o n due to m e t e o r o l o g i c a l c o n d i t i o n s

(heating d u r i n g very cold periods)

It 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 tool for daily f o r e c a s t i n g o f the p o t e n tial air p o l l u t i o n .

102

REFERENCES i. B, Bringfelt, Atmosph. Environ., 5 (1971) 949-972. 2. D.M. Elsom and T.J. Chandler, Atmosph. Environ., 12 (1978) 1543-1554. 3. H. van Dop, A.P. van Ulden and W.R. Raaff, Scientific report, W.R. 75-4, K.N.M.I. (1975) De Bilt. 4. M.E. Berlyand, Present Topics in atmospheric diffusion and air pollution (in russian), chap.12 (1975) Leningrad. 5. L.M. Malet and A. Joukoff, W.M.O. Symposium on boundary layer physics applied to specific problems of air pollution W.M.O. n°510 (1978) , 135-141. 6. A. Bodeux, Approche d'une esquisse climatologique des types de temps en Belgique, I.R.M., Publ. s4rie A n ° 2 (1972).