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We suggest a model of rain scavenging of soluble gaseous pollutants in the atmosphere. It is shown that below-cloud gas scavenging is determined by non-stationary convective diffusion equation with the effective Peclet number. The obtained equation was analyzed numerically in the case of log-normal droplet size distribution. Calculations of scavenging coefficient and the rates of precipitation scavenging are performed for wet removal of ammonia (NH 3 ) and sulfur dioxide (SO 2 ) from the atmosphere. It is shown that scavenging coefficient is non-stationary and height-dependent. It is found also that the scavenging coefficient strongly depends on initial concentration distribution of soluble gaseous pollutants in the atmosphere. It is shown that in the case of linear distribution of the initial concentration of gaseous pollutants whereby the initial concentration of gaseous pollutants decreases with altitude, the scavenging coefficient increases with height in the beginning of rainfall. At the later stage of the rain scavenging coefficient decreases with height in the upper below-cloud layers of the atmosphere.

In this study the mutual influence of heat and mass transfer during gas absorption and evaporation or condensation on the surface of a stagnant droplet in the presence of inert admixtures containing noncondensable soluble gas is investigated numerically. The performed analysis is pertinent to slow droplet evaporation or condensation. The system of transient conjugate nonlinear energy and mass conservation equations was solved using anelastic approximation. Using the material balance at the droplet surface the authors obtained equations for Stefan velocity and the rate of change of the droplet radius taking into account the effect of soluble gas absorption at the gas-liquid interface. The authors also derived boundary conditions at gas-liquid interface taking into account the effect of nonisothermal gas absorption. It is demonstrated that the average concentration of the dissolved species in a droplet strongly depends on the relative humidity (RH) for highly soluble and for slightly soluble gaseous atmospheric pollutants. Therewith the difference between the average concentration of the dissolved species in water droplets attains tens of percent for different values of RH.

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