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LAGRANGI DATA

A CONCENTRA Tl~~SERVA TIONS AND PRECIPITATION

SULPHUR DEPOSITION PATTERNS OVER EUROPE ESTIMATED USING A LAGRANGIAN DISPERSION MODEL, CONCENTRATION DATA AND

PRECIPITATION OBSERVATIONS

ANTON ELIASSEN AND JØRGEN SALTBONES

KJELLER, 4TH DECEMBER 1975

NORWEGIAN INSTITUTE FOR AIR RESEARCH P.O. BOX 115, 2007 KJELLER

NORWAY

SULPHUR DEPOSITION PATTERNS OVER EUROPE ESTIMATED USING A LAGRANGIAN DISPERSION MODEL, CONCENTRATION DATA AND

PRECIPITATION OBSERVATIONS

l INTRODUCTION

In the following an estimated sulphur wet deposition pattern for Europe is presented, covering the period 13th December 1973 to 1st April 1975. The wet deposition pattern is based on precipitation data from the meteorological stations net- work, calculated S02 air concentrations from a Lagrangian dispersion model, and an empirical relationship established between mean calculated S02-concentrations in air and mean measured sulphate concentrations in precipitation.

Using the Lagrangian dispersion model, a S02 dry deposition pattern has been calculated for the same period. Half-year S02 dry deposition patterns for the period July 1972 - July 1975 are presented elsewhere (Eliassen and Saltbones 1975), together with a discussion of the model and some other results.

The total amounts of sulphur emitted and deposited within the area considered during the period have been estimated using S02 emission data for Europe and the two calculated deposition patterns.

2 THE SULPHATE WET DEPOSITION PATTERN 2.1 Calculation

The total sulphate wet deposition Sper unit area at any place within the region considered is:

S

=

1: p.c.

=

^Pc

. l l

l

( 1)

where p. is the amount of precipitation fallen and c. is

l l

the concentration of sulphate in precipitation at day no. i, c is the mean (weighted) sulphate concentration and Pis the total amount of precipitation fallen during the period. +he quantities pi and P may be evaluated using data from the net- work of meteorological stations. This network covers Europe

fairly well. Every day observations of precipitation from 500-1000 stations have been employed to construct daily pre- cipitation fields in a 127 km grid. A method of objective analysis has been employed, with a "distance of influence"

of 300 km over the sea and 100 km over land. Over the sea, the precipitation probably is underestimated in some areas due to lack of data. Figure 1 shows the field of total precipitation P during the period, obtained by adding all the daily precipitation fields.

Values of both p. and c. throughout the period are available

l l

at 50 LRTAP sampling sites. To calculate the wet deposition of sulphate in the large areas not covered by these sites, estimated values of sulphate concentrations in precipitation are needed. For this purpose, some relation is sought between the mean sulphate concentration~ and calculated air concen- trations from the Lagrangian dispersion model. At 26 of the LRTAP sampling sites, calculated daily S02 air concentrations q. from the Lagrangian dispersion model are available together

l

with p. and c .. Figure 2 shows the yearly mean 1973 concen-

l l

trations cat these stations plotted against the yearly weighted mean S02-concentrations

q,

defined by:

Pq-

=

Z: p. q.

. 'l. l l

( 2)

Values of c,

q

and Pat the various sites for 1973 and 1974 are given in Table 1. The measurements of sulphate concen- trations in precipitation at Danish stations are not con- sidered reliable during the second half of 1974. From Table 1 it is seen that

c

has increased by large amounts from 1973 to 1974 at the Danish sites. A corresponding increase

has not taken place at other sites. This increase in mean values at the Danish sites is accompanied by a significant increase in standard deviations.

From Figure 2 it is seen that there is a fairly good relation- ship between cand

q.

The relationship is obviously not

linear, and a curve is drawn by hand to fit the data.

It should be mentioned that the Lagrangian model used to calculate the S02 air concentrations q. does not include _i

any specific description of the removal of S02 by precipitation.

In the model calculations, S02 is assumed to have a constant half-life of 19 hours.

Since p. and q. are available for all grid elements in the

i i

127 km grid, a value of

q

may be calculated for each ele- ment, and an estimate of the mean sulphate concentration

c

may be obtained by assuming that the empirical relationship of Figure 2 is valid everywhere. The total sulphate wet deposition Sat the grid element is found by multiplication with the total amount P of precipitation. The resulting sulphate wet deposition pattern is shown on Figure 3. The measured sulphate wet deposition at LRTAP sites are shown on Figure 4.

2.2 Discussion

The sulphate wet deposition pattern of Figure 3 shows maxima in the Ruhr region, in Southern Germany, in Southern

Scotland and in Southern Norway. Although the wet deposition pattern largely resembles the precipitation distribution

of Figure 1, some differences are clearly visible. In Northern Norway, North-Western Scotland and Ireland, large values of Pare not reflected by large values of sulphate wet deposition.

The reason for this is obviously that the estimated sulphate concentration in rain is low in these areas. For the same reason, the maximum zone of precipitation in Southern Norway

is found along the west coast, whereas the maximum sulphate wet deposition is found on the southeastern slope of the mountains. Here, the estimated sulphate concentration in the rain is higher, because on rainy days the air has usually passed some of the large S02-emission areas in western or central Europe.

Assuming that the measured depositions of Figure 4 are

representative for the surrounding regions, it is seen that the estimated deposition level of Figure 3 is somewhat high in Great Britain and sanewhat low in France, but that the estimated and measured depositions may reflect the same geo- graphical distribution. In the other regions, there is a good agreement between estimated and measured depositions.

Calculated patterns of sulphur wet deposition have been presented earlier by Bolin and Persson (1973). They used a statistical formulation of the transport equation, and cal- culated the horizontal-dispersion of sulphur on the basis

of the statistical properties of a large number of trajectories initiated from different points in Europe. As a first

approximation, the processes of dry and wet deposition of sulphur were described using constant deposition rates.

The main difference between the wet deposition patterns of Bolin and Persson, and the patterns presented here, is that the wet deposition maximum in Southern Norway does not

appear in their calculations. There are two main reasons for the existence of this maximum: ~) When a low pressure cell, to which precipitation is associated, approaches Southern Norway from the west, a southerly airstrearn is set up flowing

from areas with large S02-emissions towards Scandinavia, b) When winds are southerly, there is a high probability for precipitation to occur in Southern Norway due to orographic effects. These effects cannot be described by a wet deposition rate independent of position and wind direction.

3 BUDGET CONSIDERATIONS

The SO2 emission field in this work is shown on Figure 5.

This emission field is mainly an extension of the field employed earlier by Eliassen and Saltbones (1975b) to a larger area. The yearly emission data are believed to be within ±20% of the actual figures, but may be more uncertain

for the eastern european countries. Natural sources of SO2 have not been taken into account· In the region considered they are probably negligible compared to the anthropogenic ones.

The SO2 dry deposition pattern for the period is shown on Figure 6. Mean SO2-concentrations are calculated using the Lagrangian dispersion model mentioned earlier, and a constant deposition velocity of 8 mms-¹ is employed. A description of the dispersion model, and dry deposition maps for other

periods are presented elsewhere (Eliassen and Saltbones 1975).

It should be mentioned, however, that the dry deposition values may be too small in the major emission areas. When calculating the dry deposition, the computed mean concen- trations are adjusted by comparing with measured mean concen- trations at LRTAP sampling sites. To avoid that the influence of long range transport is masked by contributions from local emissions, these sites are placed in rural areas and may

therefore not be representative for the ground level concen- tration of a grid element. The importance of this effect depends upon the distribution of the ground level concen- tration inside the grid elements. Information on such distri- butions are n9t readily available, thus the evaluation of this effect would require extensive additional investigations on the sub-grid scale, taking into consideration that a

significant part of the emissions are warm emissions from tall stacks, and that urban plumes may be lifted from the surface by thermal effects.

Figure 7 shows the total sulphur deposition pattern, obtained by adding the dry deposition of SO2 and the wet deposition of sulphate. The dry deposition of particulate sulphate is probably less than 10% of the SO2 dry deposition in the region considered, and are neglected in the budget considerations.

The reason for this is that the deposition velocity of sul- phate particles, which have diameters typically in the

0.1 - l µm range, is an order of magnitude lower than the

value of about l cms-¹ established for SO2 (Chamberlain, 1966), (Owers and Powell, 1975), (Shepherd, 1975), (Garland et al.

1975), and the measured particulate sulphate concentrations in air is generally lower than the measured SO2-concentra- tions.

From the emission field, the total emission of SO2 during the period (13.12.73 to 1.4.75, 474 days) is 6.8 • 10⁷ metric tonnes. The total dry deposition of SO2 is 3.0 • 10⁷ tonnes, or 44% of the emitted amount. The total wet deposition of sulphate is 1.5 • 10⁷ tonnes (22%). The total flux of sulphur out of the region is 2.3 • 10⁷ tonnes (34%), estimated as a difference between total emissions and total deposition.

(All numbers in tonnes of SO2.)

Figure 8 shows the difference between the total deposition and the emission of sulphur for each grid element during the period. Positive numbers signify a net import of sul- phur, and negative numbers a net export. The main export regions are confined to the industrialized regions of Central Europe and Great Britain.

Table 2 shows.the total emission and estimated total depo- sition for each country. As one should expect, most countries in western Europe are net exporters of sulphur. According to these estimates, Norway imports a large amount of sulphur compared to its own emissions.

4 CONCLUSIONS

Even though the sulphur deposition patterns presented here are valid for the period 13.12.73 to 1.4.75, they show some traits which may be more generally valid when con- sidering time periods of a year or more. Within the

region considered, the dry deposition of SO2 is about twice as large as the wet deposition of sulphate (in SO2 mass units).

In regions with large emissions of SO2, dry deposition of SO2 is the most important deposition process. Some regions with small emissions, however, are located in such a way

that when precipitation is released, there is a high probability that the air masses have passed over areas

with large emissions of SO2. In such regions, the wet depo- sition of sulphate may outweigh the dry deposition of SO2.

Typical examples are Southern Norway, and to some extent Southern Scotland, and the northward and southward slopes of the Alps. In Southern Norway, the wet deposition is three times as high as the dry deposition, and in the other

regions mentioned the wet and dry depositions are of about the same magnitude.

REFERENCES

Bolin, Bert and Persson, Christer (1975)

"Regional dispersion and deposition of atmospheric pollu- tants with particular application to sulfur pollution over Western Europ~_".

Tellus ']2, ^281-310.

Chamberlain, A.C. (1966)

"Transport of Lycopodium spores and other small particles to rough surfaces".

Proc. Roy. Soc. A. 296, 45-70.

Eliassen, Anton and Saltbones, Jørgen (1975)

"Sulphur transport and dry deposition over Europe described by a simple Lagrangian dispersion model". LRTAP - 22/75.

Eliassen, Anton and Saltbones, JØrgen (1975b)

"Decay and transformation rates of S02, as estimated from emission data, trajectories and measured air concentrations".

Atmospheric Environ.ment 2_, 4 2 5- 4 2 9 •

Garland, J.A., Atkins, D.H.F., Readings, C.J. and Caughey, S.J. (1974)

"Deposition of gaseous sulphur dioxide to the ground".

Atmospheric Environment ~, 7 5-79.

Owers, S.J. and Powell, A.W. (1974)

"Deposition velocity of sulphur dioxide on land and water surfaces using a ³⁵S tracer method".

Atmospheric Environment ~, 63-67.

Shepherd, J . G. ( 19 7 4 )

"Measurements of the direct deposition of sulphur dioxide onto grass and water surfaces by the profile method".

Atmospheric Environment ~, 6 9- 7 4 .

- _(mgQ,-1) - _(iJgrn-3)

P (mm)

C q

1973 1974 1973 1974 1973 1974

A 1 14.7

-

^41.9

-

^{104 -}

A 2 7.3 10.2 38.4 38.0 127 J 03

D 3

-

^3.6

-

^{18.0 - 170}

DK2 4.2 9.4 8.7 10.8 423 706

DK3 3.4 15.2 10.9 12.l 480 613

DK4 3.7 8.9 16.7 19.8 390 552

DKS 4.5 7.0 19.0 16.9 264 402

DK6 5.8 9.1 19.3 17.l 381 4CJ7

F 1 5.5 5.7 15.3 17.4 529 650

N l 3.3 3.4 11.5 12.1 1030 1550

N 3 2.3 2.6 9.1 10.4 1160 1640

N 9 l. 7 1.6 3.7 4.8 2020 1780

N22 3.9 3.4 10.3 12.l 493 682

N23 3.9 4.0 12.l 11.6 678 808

NLl 6.0 5.8 29.6 27.3 601 788

NL2 3.5 4.2 23.5 25.8 733 810

NL3 4.9 3.8 20.7 20.0 507 796

NL4 - 5.6

-

^{25.9 - 727}

SFl 3.0 2.9 7.9 11.l 560 766

SF2 3.5 2.8 10.5 11.0 533 614

SF3 2.8 3.8 8.1 11. 3 522 849

SF4 2.7 2.0 6.6 8.4 613 701

SPS 1.5 1.5 2.7 3.4 344 541

s ^{3 3.7 4.2 11.0 14.9 469 689}

S 4 3.3 3.4 9.3 11.3 473 578

s ^{5 1.5 1.9 3.5 4.8 669 876}

UKl 4.8 3.7 38.3 36.3 440 688

UK2 2.6 1.9 10. 3 9.8 792 1120

Table 1: Hean measured sulphate concentrations in preci- pitation

E,

mean calculated S02-concentrations

q

defined by eq. (2), and total amount of pre- cipitation at some LRTAP sites for the years 1973 and 1974. The sulphate concentrations have been corrected for sea spray where this is con- sidered necessary.

The station A 1 in Austria was discontinued in August 1973, and was succeeded by another station in the same region (A 2).

z: 0 z:

-

⁰

_J f--

-

c:i::

-

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⁰

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=

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>- ^(/)

=

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~ c:i:: 0

0::: _J 0 (_'.J

LJ...J 0::: z :z:

>- ^{(_'.J LJ...J} c:i::

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0::: ::c ^_J ::.<:

f-- c:i:: :;;::: Y- 0 = ^{f-- 0:::}

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-

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::::,

= -

c:i:: c:i:: u LJ...J >- ~ c:i:: LJ...J

~

^LJ...J

C) f-- (_'.J z ^{_J z:: f-- _J 3: 0 f-- f--} u ^(/) ::::, LJ...J LJ...J ^_J z:: z:

-

c:i:: ^{0::: (/)} LJ...J f-- c:i:: LJ...J ::c 0::: 0 LJ...J 3: 3:

- -

z::

c:i:: co 0 LL LL 3:

-

^{f-- z (/) (/) ::::,}

Cf) c::

0

·,-!

.µ

-,-!

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Q) .µ 0

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H '"C QJ .µ Q) 'O

c:: :>

;j Q) 'O 0 -,-! Q)

UH.µ QJ ro

Q) ..0 Ei

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_µ Q) .µ H Cfl

~ ro QJ 0

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u ^{·ri _µ} ro .µ QJ C:: H

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0 .µ

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;j ro

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Cf)

c:: 0

-,-!

.µ

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Cf)

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Q) .µ

'"C L() c::

r-- ^;j

0 E

H ro

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c:: 0 Q)

0 _µ .µ

-,-! .µ

Cf) ("') ·ri

Cf) r-- Ei

-,-! Q)

Ei ^N

QJ H QJ

'"C (") .c _µ QJ H

.µ H

ro re o Ei O ~

·ri ·ri .µ H 010

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N

Q) H ..0 ro

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'/i '

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(

2

1

C).s- .... , "· ·.

r , ·-·,

\ '.

I . ,

Figure 1: Total precipitation P(m) for the period 13.12.73 to 1.4.75, obtained by adding all the daily precipitation fields. The values over the sea result from the method of objective analysis employed, with a "distance of in- fluence" for precipitation data of 300 km over the sea, and 100 km over land.

c(mgl-1)

8

6

4

2-

0

20

10 30

Figure 2: Mean observed sulphate concentrations

c

in precipitation plotted against mean computed S02-concentrations q at some LRTAP sampling sites using 1973-data.

Both means are weighted, using daily precipitation measurements (see text) Values of cand q for 1973 and 1974 are given in Table 1.

•

,--.·-:

^{.. ~~}

't\ \ \

I\' ~

\..\ \ \ \,./;~

,, '( j :

~I, ,J (

\ \

, b~9

>-) i , l. ,_)

.--J-.

~-\ ~~.

',-

. ' 6

~ _{2 __ -J}

Figure 3: Estimated sulphate wet deposition pattern for the period 13.12.73 to 1.4.75. Unit: g S02 m-2. The

minimum in the North Sea arises from the lack of precipitation data over the sea, see Figure land text.

,' \ I

' ' ,

, '-.-,

✓ ,· \

,. .. ^-~ ... /

Figure 4: Measured sulphate wet deposition at LRTAP sampling sites, same period as Figure 3.

Unit: g s02m-²•

---+--+---~---,L"':;·., so~ 2_j _+---+---+--+---+-s--+-s~5 4o 2,0 1,0+~-~sh~o -.o t'i 0 I

·t;

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0 o 1·, I I ; '· 10

I

^{20 ·} 5o 40 Joo so ⁵⁰ i ^{30 1} 5 ¹ i :r· 4o L::,_

·,. 20 20' :io i

20

1150 ^{1500 3oof}

200~~9_:-_0';~1

so

,o '1, i ^2~0 I ^{50 20} I 10 '40 200· 300 200 2o0 10 1o0 150 [joe 4o ~,oi s~ ,o, 20 I ²⁰ 20 20 3o I ^{30 ,o 4o .so ,4oo}

+---+-~-+----+-+---#-',._...,,____,~~--,---+---,,_._...,._._2_o-+·-2.-0-+!-1-, .... l-2-o~[ :io-_~: 2.a' 20 20 40 100 200 ¹⁵⁰

8 I ^{zo , 2J)} 2.0 100 20 I 60 ' 50 50 100 200 :0

ISO I IO IO j 25D 80 ! 40 70 ~00 50 40 20 50 /0 , 20 10 I 70 50 40 150 so' 50 40 2U 50

--

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/--+--~-+---+-~----+--- --- ~ •.-. " I ' J \.

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( '< - ·, .

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~o~_::5,,1_~210•:~253•'-,6o,41~;Yti1,

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: 403 t, -10 2.B ,- t ^,4 120 j 10

- --- ~- ---'-'-'-'''---,=-"',_-::,,~-=.+::.;;::::;.,,,...""""-·:,,._,'--""~-',--

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:2. 9 /7 51 10 50 10"20

-- _I___ . 3o ,

r~ ;-;;- ^lo~-;z.T ·-~~----~~o

^{I 5'}

100 '90 ,7,-.. 86, 35' 113 , 148 i ¹⁴⁵² 2a1i'21o_;z20, 5o ' 30 So Joo ·99

. -~·

---

--- '

10; ,o Bo' 5 . 10 IO 5o ¹⁰ 5' 5 2 2 2

Figure 5: S0₂-emissions used in this work. The data are believed to be within ±20%

of the actual figures, but may be more uncertain for the eastern european countries. Natural sources have not been taken into account.

Unit: 10³ tonnes S0₂yr-¹•

\

\

\

. -- , I

Figure 6: Estimated S0₂ dry deposition pattern for the period 13.12.73 to 1.4.75.

Unit: g

so

2m-^2•

) :·-.

\ >

·- .i

\

Figure 7: Total sulphur deposition pattern, obtained by adding the wet deposition of Figure 3 and the dry deposition of Figure 6. Dry deposition of particulate sulphate is neglected.

Unit: g

so

2m-²•

Il \') \ 1 }d Zl l¹ J~

l\ •

:, .,, . " . "

'

E,·

^{·" •I}

·•'\

^{.:, ., ., .} "

I .;'J} -J!l,I n -i •H .JJ

Figure 8 Difference between of sulphur for each period. Unit: 10³

total grid tonnes

deposition and element during

S02.

emission the