The Deposition Of The Atmospheric Pollutants
the deposition of the atmospheric pollutants
on the underlying surface
V.I. Lepyoshkin, A.G. Tarnopolsky
Ukrainian Scientific Centre of the Ecology of Sea, Odessa, Ukraine
At an estimation of possible sources of pollution of sea water areas waste water and river drain, as a rule, is taken into account only. However, as is underlined in [1], deposition of some pollutants from an atmosphere on a water surface is comparable to their receipt with waste water and river drain.
A method of account deposition of pollutants from an atmosphere on northern half of Black Sea [2] is developed on the basis of models of distribution of impurity of an anthropogenous origin [3] and structure of an atmospheric boundary layer (ABL) [4].
The regional numerical model of carry is applied for an estimation deposition of pollutants on water area of the seas and dispersion of impurity in ABL [3]. With the purpose of definition of a field of concentration of an impurity the combination of the Lagrange’s and Eiler’s approaches is used. In the present research the model is realized for stationary, continuously working source under stationary meteorological conditions. The trajectory of a cloud of polluting substance is calculated with the help of the Lagrange’s method as a sequence of horizontal coordinates of its centre. The speed of carry of a cloud is determined by averaging speed of a wind within the limits of a layer of distribution of an impurity on a vertical. The weight multipliers in procedure of averaging are proportional to concentration of an impurity at each height.
Entrance parameters of model are:
- phase, element and dispersion structure of emission;
- total weight of emission;
- effective height of a source;
- three-dimensional fields of a wind, temperature and parameters of the turbulence.
The characteristics of a source are the given sizes, and the parameters of atmospheric carry and turbulent of an exchange paid off on model of a
geophysical boundary layer, which special case is ABL [ 4 ]. In [4] the three-dimensional non-stationary model ABL, including the evolutionary and diagnostic equations of hydrothermodynamics is developed, and their short circuit is carried out with the help of the equations for kinetic of energy turbulent of whirlwinds, speed them dissipation, ratio Kolmogorov and Smagorinsky.
The developed algorithm of an estimation deposition of pollutants from an atmosphere on northern part of the Black Sea was realized for account of concentration of technical carbon (soot).
Total weight of emissions of soot for various synoptic of the situations is submitted in the table 1.
Table 1. Total weight of emissions of soot (t)
Synoptical
Region
situation
Odessa
Nikolaev
Cherson
Zaporozje
Donetsk
Crimea
Cyclonic
49,8
37,6
8,5
66,1
171,0
21,7
Anticyclonic
149,4
112,8
25,5
198,3
513,0
65,1
Distribution of a deposit of soot along a meridian and the parallels in northern part of the Black Sea are submitted in the tables 2 and 3. As it is visible from the table 2, for cyclone of a situation density of a deposit decreases in process of removal from coastal feature and on leeward border of coastal zone in 8 times less, than on windward.
Table 2. Distribution of density of the deposit of soot (g/m3) along the meridian 31o (east) above northern part of the Black Sea
Synoptical
Degrees, north
situation
46,0
45,5
45,0
44,5
44,0
43,5
43,0
Cyclonic
120
40
30
25
20
20
15
Anticyclonic
160
60
20
25
130
100
70
For anticyclonic of the situation distribution of the deposit along a meridian more complex. Two maxima in this case are observed: one - near to coastal feature, another - in the high sea.
The distribution of density of a deposit along a parallel (table 3) is characterized by the greater variability, is especial for cyclone of the situation. The area weak deposition of pollutants from an atmosphere on a sea surface alternates with areas of the intensive deposition. On distance 1 degree of the longitudes the size of a deposit can change in 10 times. For cyclone of the situation the sharp change of a deposit between 34-35o and 35-36o (east) is marked. For anticyclonic of the situation the sharp reduction of a deposit between 34o that 35o (east) is marked. On water area to the south 44o (north) and to the east 35o deposition of the pollutants very weak. The given distributions of density of a deposit are caused by an arrangement of sources, circulating conditions and intensity turbulence of an exchange in considered situations.
Table 3. Distribution of density of a deposit of soot (g/km2) along the parallel 44o (north) above northern part of the Black Sea
Degrees, east
29
30
31
32
33
34
Synoptical
Cyclonic
2
20
7
2
10
situation
Anticyclonic
70
150
130
190
170
40
Degrees, east
35
36
37
38
39
40
Synoptical
Cyclonic
100
10
3
8
40
50
situation
Anticyclonic
The comparison of size of density of a deposit to total weight of emissions from all sources has shown, that in northern part of the Black Sea deposit approximately 2-2,5 % of total weight of emissions influencing pollution sea environment. This estimation for soot makes 4 %. The received results are close to estimations given in [5].
The results of the carried out research confirm a conclusion that deposition of the pollutants from an atmosphere on a water surface brings in the essential contribution to pollution of northern part of the Black Sea. This source of pollution should be taken into account with a river drain and waste water, that will be coordinated to conclusions [1].
One of the important parameters in process of deposition of the pollutants from atmosphere is the speed dry deposition of an impurity - .
By comparison of calculations on a hydrodynamic model of an atmospheric boundary layer (ABL) and on experimental data the contribution of the principal physical mechanisms to process of deposition of an admixture on a sea surface is determined.
The total carrying of any admixture from atmosphere to a marine surface is represented as sum turbulent and gravitation flux:. According [6] a flux is accepted to proportional a volume concentration of an admixture at some altitude z above an underlying surface with a coefficient of proportionality .
. (1)
For calculation of dry deposition velocity , conditioned only by turbulent mixing, we take into account, then
(2)
or
, (3)
were - coefficient of vertical turbulent change at the altitude . As the marine surface completely absorbs an admixture, so =0 and
. (4)
By the hydrodynamic model ABL [4] values for different velocities of a wind and conditions of stratification are obtained. In the table 4 the values at the altitude = 12 m for neutral stratification and data about , counted on the formula (4) are reduced.
Table 4. Coefficients of vertical turbulent exchange and dry deposition velocity , conditioned by turbulent mixing, for different wind velocities
Parameter
Wind velocity, m/s
2,5
5,0
7,5
10,0
12,5
, m2/s
0,07
0,09
0,13
0,17
0,24
, mm/s
3
4
5
7
10
For an estimation of velocity of gravitation deposition it is necessary to know a spectrum distribution of the depositing particles. On experimental data in a boundary layer above sea the particles with radius 1-20 µm dominate. The calculations on Stokes formula have shown, that for radiuses = 1-2µm = 0,1-0,5 mm/s, for = 10-20 µm = 13-52mm/s. The comparison of magnitudes and demonstrates, that at >, and at > 15 µm >>. Thus, at carrying aerosols of a small size the deposition on water surface is formed at the expense of turbulent mixing, and at carrying of a large particles the defining factor of the deposition of pollutants is the gravitation precipitation.
Besides the estimate on experimental data obtained in the Black Sea on research vessels of Ukrainian Scientific Centre of the Ecology of Sea in the 1992-1994 years is executed. On data of measurement the magnitudes of concentration of an admixture in an atmosphere air at the altitude 12 m above sea level (q) and flux of pollutants from atmosphere on unit area for an unit of time (P) were determined. Most representatives have appeared sample of data for ions of sulphate (94 definitions), which one was used for an estimate by formula (1). This formula describes combined effect of turbulent and gravitation deposition.
The dispertion of values illustrates table 5, from which one follows, that velocity of dry deposition is less 45 mm/s in 84 % of cases, and greatest number of cases is with £ 5 mm/s.
Table 5. Distribution (%) of velocity of the dry deposition mm/s
Velocity of the dry deposition , mm/s
5
6-15
16-25
26-35
36-45
46-55
56-65
66-75
76-85
>85
27,7
17,0
16,0
11,7
11,7
3,2
4,2
2,1
3,2
3,2
The experimental dependence from a wind velocity has appeared like linear (See figure).
Fig. Dependence of deposition velocity from wind velocity on experimental data
The experimental data about are agreed satisfactorily with theoretical estimations , as with magnification of a wind velocity the maximum in a spectrum of the sizes of transferred particles is sheared in the side of the large sizes and the role of gravitation deposition increases.
References
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