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Numerical modeling of transport of gas- and aerosol-phase persistent organic pollutants in the Northern hemisphere
.i. Aerosol Sci. Vol. 30, Suppl. 1, pp. S235-S236, 1999 1999 Published by Elsevier Science Ltd. All tights reserved • Printed in Great Britain 0021-8502/99/$ - see front matter
Pergamon
NUMERICAL MODELING OF TRANSPORT OF GAS- AND AEROSOL-PHASE PERSISTENT ORGANIC POLLUTANTS IN THE NORTHERN HEMISPHERE A.E. Aloyan, V.O. Arutyunyan Institute for Numerical Mathematics, RAS Gubkin str., 8, Moscow, 117951, GSP-1, Russia KEYWORDS numerical modeling, pollutant transport, persistent organic pollutant, aerosol particles, dry and wet deposition, degradation, emission NUMERICAL MODEL A numerical model for the transport of persistent organic pollutants in the Northern hemisphere was developed accounting for a series of physical mechanisms of their evolution in the environment. Persistent Organic Pollutants (POP) being anthropogenic and having harmful impacts on the environment and human health are known to accumulate and transport in the atmosphere for long time periods and distances (Smith, 1991; UN-ECE, 1994). The POP in the environment are available both in the gaseous (as vapor) and aerosol states being subject to dry and wet deposition as well as degradation. They also pass through different types of transformations in soil and water media. The variability of POP in the aerosol phase is considered by resolving the kinetic equation of coagulation (the Smoluchowski equation) in each point of the three-dimensional domain. This allows us to keep track of the aerosol particle size spectrum. In so doing, the initial size of aerosol particles is assumed to be approximately 0.1 Ixm. The numerical model consists of the following modules (Aloyan and Shapovalova, 1993; Aloyan et aL, 1995; 1997; Marchuk and Aloyan, 1995; Aloyan and Arutyunyan, 1997): equation of POP transport in the atmosphere; degradation of POP in the atmosphere and soil; exchange between soil and atmosphere; dry and wet deposition of POP in the atmosphere; equation of coagulation for POP aerosol particles in the atmosphere. The dry deposition is described by using the equation for resistance of pollutant with the surface as a sum of the following three terms: aerodynamic resistance, quasi-laminar boundary layer resistance, and surface resistance. The flux of POP in the soil and water is simulated based on the method described in Jacobs and Van Pool (1996), Van .]aar,weM et. al (1997). The total flux of POP in the soil depends on the solute velocity and effective gas-liquid diffusion coefficient. It is supposed that in the air-sea interface POP is in equilibrium and obeys Henry's law. The removal of POP from the atmosphere by precipitation is characterized by the scavenging ratio. The gaseous molecules entering into a drop dissolved so quickly that this process can be considered instantaneous having regard to the spatial and temporal scales of the general problem under consideration. Since the Henry constant is inversely proportional to the scavenging ratio, the POP concentrations can be partitioned to gas- and liquid-phase equilibrium components. As in Jacobs and Van Pul (1996) the transformations of POP in the atmosphere are described by specifying an effective degradation coefficient in the respective kinetic equation. In soil POPs exists mainly in three states: water (dissolved), gaseous, and adsorbed - the crystal state is not considered here. Therefore the concentration of POP can be represented as ~r = Ps~,~ + ~ L + ( O - S ) ~ where Ps is is the volume density of soil; ~g is the volume humidity of soil; ® is soil porousity; concentrations q~s, ([:)L, and q~g relate to the soil solution mass, skeleton, and free vapor space, respectively.
S235
$236
Abstracts of the 1999 EuropeanAerosol Conference
The adsorption of POP in soil depends on soil features and particularly its organic content. So, the transport in soil is calculated having regard to the soil porousity and organic content. To determine the turbulence and flow field characteristics in water area, combined set of equations for the atmospheric and ocean boundary layers is resolved using the turbulence energy balance and dissipation rate equations. NUMERICAL CALCULATION RESULTS In carrying out numerical experiments on the transport and transformation of persistent organic pollutants in the Northern hemisphere, lindane (the T-isomer of hexachlorocyclohexane - HCH) was taken as an example. Using the above-mentioned model, some features of the transport and transformations of lindane emitted from European sources for January to Dcember, 1992, were determined. The spatial and temporal variability oflindane concentrations in the atmosphere, soil, and water area was investigated for each month. Also the percentile distribution of lindane in various media as well as its degradation fraction in the atmosphere and soil were estimated. The results of numerical calculations show that, in the period from February to June, lindane can transport horizontally rather far beyond the European region and, due to convective processes and turbulent mixing, to the upper troposphere in the vertical direction. At times, the lindane concentrations in the troposphere even turn to be higher than those in the boundary layer which is caused by wet deposition The transport of lindane in the atmosphere is shown to essentially depend on atmospheric circulation characteristics conditioned by non-uniform distribution of continents and water areas. The spatial and temporal variability of lindane concentrations is of clearly defined seasonal dynamics with the particular importance of its dry and wet deposition. Due to large spatial and temporal inhomogeneity, a considerable part of lindane concentrations is accumulated in water areas. In this respect the consideration of interactions between boundary layers of the atmosphere and ocean along with oceanic flows for distinct seasons allows us to describe the transport in water area more accurately. The results of numerical calculations also demonstrated that as a result of coagulation processes aerosol particles with diameter up to 1~tm can be formed.
ACKNOWLEDGEMENTS This work was supported by the ISTC project No. 1078. REFERENCES Aloyan A.E., T.S.Shapovalova Interaction of the atmospheric and ocean boundary, layers and pollution transport. MeteoroLGidroL, 1993, No.5, pp.60-70. (In Russian) Aloyan A.E., Arutyunyan V.O. Numerical modeling of lindane transport in the Nothern Hemisphere. MSCEast Pep., 1997, 37p. Aloyan A.E., Aru.tyunyan V.O., Lushnikov A.A., Zagainov V.A. Transport of coagulating aerosol in the atmosphere, d. Aeros. Sci., 1997, Vol. 28, No. 1, pp. 67-85. Aloyan A.E., Aru.tyunyan V.O., Marchuk G.I. Dynamicsof Mesoscale Boundary Atmospheric Layer and Impurity Spreading with the Photochemical Transformation allowed for. Russ.d. Num.Anal. Math.Model., 1995, Vol. 10, No. 2., pp. 93-114. Jacobs C.M. and Van Pul W.A.J. Long-range atmospheric transport of persistent organic pollutants, I: Description of surface-atmosphere exchange modules and implementation in EUROS. RIVM, Report 722401013, 1996. Marchuk G.I. and A.E. Aloyan Global transport of pollutant in the atmosphere. Izv. AN: Fizika Atm. Okeana, 1995 (31), No. 5, 597-606. (in Russian). Smith A.G. Chlorinated Hydrocarbon Insecticides. In: Handbook of Pesticide Toxicology, Vol. 3, Classes of Pesticides. W.J. Hayes Jr. and E.R. Laws, Jr. eds. Academic Press, Inc., 1991, NY. Van Jaarsveld J.A., Van Pul W.A.J., De Leeuw F.A.A.M Modelling the long-range transport and deposition of persistent organic pollutants in the European region. Atmospheric Environment, 1997, V. 31, No. 7, 1011-1024. UN-ECE. State of knowledge report of UN ECE Task force on Persistent Organic Pollutants for the Convention on Long-Range Transboundary Air Pollution, 1994.
Pergamon
NUMERICAL MODELING OF TRANSPORT OF GAS- AND AEROSOL-PHASE PERSISTENT ORGANIC POLLUTANTS IN THE NORTHERN HEMISPHERE A.E. Aloyan, V.O. Arutyunyan Institute for Numerical Mathematics, RAS Gubkin str., 8, Moscow, 117951, GSP-1, Russia KEYWORDS numerical modeling, pollutant transport, persistent organic pollutant, aerosol particles, dry and wet deposition, degradation, emission NUMERICAL MODEL A numerical model for the transport of persistent organic pollutants in the Northern hemisphere was developed accounting for a series of physical mechanisms of their evolution in the environment. Persistent Organic Pollutants (POP) being anthropogenic and having harmful impacts on the environment and human health are known to accumulate and transport in the atmosphere for long time periods and distances (Smith, 1991; UN-ECE, 1994). The POP in the environment are available both in the gaseous (as vapor) and aerosol states being subject to dry and wet deposition as well as degradation. They also pass through different types of transformations in soil and water media. The variability of POP in the aerosol phase is considered by resolving the kinetic equation of coagulation (the Smoluchowski equation) in each point of the three-dimensional domain. This allows us to keep track of the aerosol particle size spectrum. In so doing, the initial size of aerosol particles is assumed to be approximately 0.1 Ixm. The numerical model consists of the following modules (Aloyan and Shapovalova, 1993; Aloyan et aL, 1995; 1997; Marchuk and Aloyan, 1995; Aloyan and Arutyunyan, 1997): equation of POP transport in the atmosphere; degradation of POP in the atmosphere and soil; exchange between soil and atmosphere; dry and wet deposition of POP in the atmosphere; equation of coagulation for POP aerosol particles in the atmosphere. The dry deposition is described by using the equation for resistance of pollutant with the surface as a sum of the following three terms: aerodynamic resistance, quasi-laminar boundary layer resistance, and surface resistance. The flux of POP in the soil and water is simulated based on the method described in Jacobs and Van Pool (1996), Van .]aar,weM et. al (1997). The total flux of POP in the soil depends on the solute velocity and effective gas-liquid diffusion coefficient. It is supposed that in the air-sea interface POP is in equilibrium and obeys Henry's law. The removal of POP from the atmosphere by precipitation is characterized by the scavenging ratio. The gaseous molecules entering into a drop dissolved so quickly that this process can be considered instantaneous having regard to the spatial and temporal scales of the general problem under consideration. Since the Henry constant is inversely proportional to the scavenging ratio, the POP concentrations can be partitioned to gas- and liquid-phase equilibrium components. As in Jacobs and Van Pul (1996) the transformations of POP in the atmosphere are described by specifying an effective degradation coefficient in the respective kinetic equation. In soil POPs exists mainly in three states: water (dissolved), gaseous, and adsorbed - the crystal state is not considered here. Therefore the concentration of POP can be represented as ~r = Ps~,~ + ~ L + ( O - S ) ~ where Ps is is the volume density of soil; ~g is the volume humidity of soil; ® is soil porousity; concentrations q~s, ([:)L, and q~g relate to the soil solution mass, skeleton, and free vapor space, respectively.
S235
$236
Abstracts of the 1999 EuropeanAerosol Conference
The adsorption of POP in soil depends on soil features and particularly its organic content. So, the transport in soil is calculated having regard to the soil porousity and organic content. To determine the turbulence and flow field characteristics in water area, combined set of equations for the atmospheric and ocean boundary layers is resolved using the turbulence energy balance and dissipation rate equations. NUMERICAL CALCULATION RESULTS In carrying out numerical experiments on the transport and transformation of persistent organic pollutants in the Northern hemisphere, lindane (the T-isomer of hexachlorocyclohexane - HCH) was taken as an example. Using the above-mentioned model, some features of the transport and transformations of lindane emitted from European sources for January to Dcember, 1992, were determined. The spatial and temporal variability oflindane concentrations in the atmosphere, soil, and water area was investigated for each month. Also the percentile distribution of lindane in various media as well as its degradation fraction in the atmosphere and soil were estimated. The results of numerical calculations show that, in the period from February to June, lindane can transport horizontally rather far beyond the European region and, due to convective processes and turbulent mixing, to the upper troposphere in the vertical direction. At times, the lindane concentrations in the troposphere even turn to be higher than those in the boundary layer which is caused by wet deposition The transport of lindane in the atmosphere is shown to essentially depend on atmospheric circulation characteristics conditioned by non-uniform distribution of continents and water areas. The spatial and temporal variability of lindane concentrations is of clearly defined seasonal dynamics with the particular importance of its dry and wet deposition. Due to large spatial and temporal inhomogeneity, a considerable part of lindane concentrations is accumulated in water areas. In this respect the consideration of interactions between boundary layers of the atmosphere and ocean along with oceanic flows for distinct seasons allows us to describe the transport in water area more accurately. The results of numerical calculations also demonstrated that as a result of coagulation processes aerosol particles with diameter up to 1~tm can be formed.
ACKNOWLEDGEMENTS This work was supported by the ISTC project No. 1078. REFERENCES Aloyan A.E., T.S.Shapovalova Interaction of the atmospheric and ocean boundary, layers and pollution transport. MeteoroLGidroL, 1993, No.5, pp.60-70. (In Russian) Aloyan A.E., Arutyunyan V.O. Numerical modeling of lindane transport in the Nothern Hemisphere. MSCEast Pep., 1997, 37p. Aloyan A.E., Aru.tyunyan V.O., Lushnikov A.A., Zagainov V.A. Transport of coagulating aerosol in the atmosphere, d. Aeros. Sci., 1997, Vol. 28, No. 1, pp. 67-85. Aloyan A.E., Aru.tyunyan V.O., Marchuk G.I. Dynamicsof Mesoscale Boundary Atmospheric Layer and Impurity Spreading with the Photochemical Transformation allowed for. Russ.d. Num.Anal. Math.Model., 1995, Vol. 10, No. 2., pp. 93-114. Jacobs C.M. and Van Pul W.A.J. Long-range atmospheric transport of persistent organic pollutants, I: Description of surface-atmosphere exchange modules and implementation in EUROS. RIVM, Report 722401013, 1996. Marchuk G.I. and A.E. Aloyan Global transport of pollutant in the atmosphere. Izv. AN: Fizika Atm. Okeana, 1995 (31), No. 5, 597-606. (in Russian). Smith A.G. Chlorinated Hydrocarbon Insecticides. In: Handbook of Pesticide Toxicology, Vol. 3, Classes of Pesticides. W.J. Hayes Jr. and E.R. Laws, Jr. eds. Academic Press, Inc., 1991, NY. Van Jaarsveld J.A., Van Pul W.A.J., De Leeuw F.A.A.M Modelling the long-range transport and deposition of persistent organic pollutants in the European region. Atmospheric Environment, 1997, V. 31, No. 7, 1011-1024. UN-ECE. State of knowledge report of UN ECE Task force on Persistent Organic Pollutants for the Convention on Long-Range Transboundary Air Pollution, 1994.