We consider the mathematical model of a multicomponent pollutant transport, taking into account photochemical transformation and aerosol formation in the troposphere of the Northern Hemisphere and kinetic processes of nucleation, condensation, and coagulation. The size distribution of aerosol particles is resolved for 25 discrete intervals starting from 10" 5 m, with Separation between intervals doubled. In the model we consider the oxidation processes of gaseous sulphur dioxide by a series of photochemical reactions with the formation of sulphuric acid vapour. At certain levels this leads to supersaturation of H2SO4-H2O with the subsequent precipitation of the water solution of sulphuric acid on the surfaces of condensation nuclei. The drops can increase in size or evaporate depending on the area and physical environment. If they evaporate, their interiors are released äs solid nuclei. We consider the main principles of the construction of mathematical models and the algorithms of their numerical Implementation. We give the results of numerical experiments on modelüng the transformation of sulphuric acid vapour and the formation of condensation trails in the troposphere of the Northern Hemisphere.The formation and removal of aerosol particles are described by many processes, for example, nucleation, condensation, coagulation, chemical transformation in gas and liquid phases, hydrothermodynamic processes äs well äs interphase exchanges, dry and wet deposition. The chemical composition of particles substantially changes depending on their size, which is of fundamental importance for physics of aerosols and chemistry of atmosphere. Of major importance in atmospheric dispersive Systems are sulphate aerosols. The sulphate particles in the atmosphere can directly or indirectly affect a climate System. These particles form in different parts of the atmosphere, viz. in the free troposphere, in the marine boundary layer, in Arctic regions and so on. The numerical experiments show that new sulphate particles can also nucleate in the stratosphere and in the urban polluted air [10,20,29,38,40]. Most of these examples show that these particles form due to homogeneous nucleation, for example, water and sulphuric acid nucleation and so on. The sizes of aerosol particles are known to increase in coagulation processes and gas-particle transformations. The spectrum of particle sizes changes by these two mechanisms. The rate of gas-particle transformations may depend on the rate of vapour molecule diffusion to the surface of a particle and the rate of the reaction that involves an adsorbed vapour molecule and the substance of the particle surface. In this case it is very important to find out the mechanisms of gas-particle transformations, which result in the formation of condensation-capable substances such äs sulphuric acid, ammonia sulphate, ammonia nitrate and so on.An instantaneous equilibrium is assumed to exist in the gas-aerosol System in most three-dimensional models of aerosol dynamics. However, äs shown in [25,39], unde...
A coupled model of hydrothermodynamics of the mesoscale boundary atmospheric layer and an equation of the polydisperse aerosol have been developed having regard to condensation kinetics. To solve the coupled problem a three-dimensional non-hydrostatic numerical model of atmosphere hydrothermodynamics is used taking into account orographic and thermal inhomogeneities. A system of kinetic equations is solved using the values of meteorological and turbulent atmosphere characteristics obtained from the dynamic model. The model involved allows us to simulate the processes of the fluctuational new particle creation and the further growth of particles in the supersaturated vapour which results in the appearance and development of the disperse phase. The model described makes it possible to reproduce the volume condensation processes hi various situations 'ή the laws of changing the thermodynamic variables are known.The results of numerical experiments and then-analysis as applied to the sulphuric acid aerosol formation in the atmosphere are given. We have also estimated the condensation rate depending on the presence of the natural nuclei of condensation in the atmosphere.The man's economic activity results in polluting the atmosphere with large amounts of chemical substances in gaseous and aerosol state. In the atmosphere these substances undergo a variety of physical and chemical modifications via the mechanisms of photochemical transformation, particle coagulation, and supersaturated vapour condensation. All the mechanisms are in mutual relations, each of them being a part of a general complex ecological problem. Amongst the man-made pollutants the most dangerous are the sulphur and nitrogen oxides, the metallic dust, etc. For example, acid rains having a severe impact on the biosphere are favoured by the sulphur oxide pollutions transferring to the aerosol phase. In addition, the pollutions bring into existence several toxic effects observed in smog.The increase of the aerosol particle sizes is known to occur in the coagulation processes and the gas-particle transformations. These two mechanisms are responsible for the change of the particle size spectrum. The rate of the gas-particle transformations can be determined from the rate of the vapour molecule diffusion to the particle surface and the rate of the reaction of the adsorbed vapour molecule and the substance of the particle surface. In these processes it is important to reveal the mechanisms of the gas-particle transformations leading to the formation of condensable substances such as sulphuric acid, ammonium sulphate, ammonium nitrate, etc.The atmospheric pollutants as a rule are polydisperse in character, therefore for the mathematical modelling of their dynamics the following two mechanisms should be taken into account: the transfer and turbulent diffusion of the pollutant, and the variation of the disperse composition and concentration of aerosol due to kinetic processes of condensation, coagulation, precipitation, etc. As these processes take place in th...
A non-hydrostatic spatial numerical model of hydrothermodynamics of the boundary atmospheric layer is developed on the basis of the splitting method. The problem is treated in the Cartesian coordinate system. In this case the design mesh becomes nonuniform depending on the configuration of the relief. In the paper, the difficulties associated with the relief are overcome by using some ideas of fictitious domain method. The results of numerical experiments on studying the development of atmospheric circulation under the combined action of orographic and thermal inhomogeneities of an underlying surface are given.In many problems of physics of atmosphere the assumption of atmospheric motions being quasi-static is quite reasonable. However, for some atmospheric processes where the horizontal and vertical sizes are comparable, one can show that quasi-static approximation does not suffice. For example, this is the case for the following types of atmospheric motions: leeward and gravitational wave motions in highlands, convective processes, meteorological processes induced by anthropogenic heat sources, etc.To describe these processes one should make use of non-hydrostatic models. During the last decade great progress was made in the numerical modelling of local atmospheric motions above the flat underlying surface. In these models, taking account of vertical accelerations does not lead to considerable modification of the computational algorithm. This especially refers to the schemes where a splitting algorithm is employed. Numerical algorithms used to solve nonlinear hydrothermodynamic equations are complicated by the presence of mountains and orographic inhomogeneities. One of the difficulties is, for example, the assigment of boundary conditions at the lower boundary of the domain of integration. This is accounted for by the fact that in this case a normal to the surface does not coincide with the vertical axis z. Looking at the situation from the standpoint of constructive implementation, non-hydrostatic models that allow for orography may be divided into two groups.The models of the first group use the Cartesian coordinate system, special methods of describing the interaction of air mass with the actual surface relief being employed to allow for the conditions at the lower boundary.The numerical models of the second group use a transformation of the coordinate system which results in the boundaries of the domain of integration becoming coincident with the coordinate surfaces in new coordinates.The non-hydrostatic numerical models of the first group were constructed in [8,14]. In [14] a two-dimensional problem with a fairly simple geometry (a linear mountain ridge with the slopes inclined at 45°) is considered. In this case the mesh domain is introduced so that all its bottom boundary points are the design points for a rectangular domain. The extension of this model to the three-dimensional case of an Brought to you by | University of Arizona Authenticated Download Date | 7/13/15 6:37 AM
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