Importance of rain scavenging in below-cloud altitudinal redistribution of soluble gaseous pollutants in the atmosphere

Boris Krasovitov (1), Tov Elperin (1), Andrew Fominykh (1), Alexander Vikhansky (2)

(1) Ben-Gurion University of the Negev, Israel (2) Queen Mary, University of London, UK

     Abstract Number: 518
     Last modified: May 13, 2010

Abstract
Wet deposition, including below-cloud precipitation scavenging by rains, is one of the most important removal mechanisms that control the distribution, concentration and life-time of many gaseous species in the atmosphere. In the present investigation we developed a model for predicting precipitation scavenging of soluble gaseous pollutants from the atmosphere by the rain. The developed model is valid for arbitrary gradients of soluble gaseous pollutants in a gaseous phase and is suitable for predicting scavenging of moderately soluble gases, e.g., sulfur dioxide (SO2), carbon dioxide (CO2) and ammonia (NH3) from the atmosphere. Using the equation of mass balance for soluble gaseous species in gaseous and liquid phases we derived a nonstationary convective-diffusion equation for evaluating the amount of precipitation required for scavenging of various soluble gaseous pollutants from the atmosphere and determined transient altitude distribution of these gases in the atmosphere during rain fall. Numerical solution of the derived equation with the appropriate initial and boundary conditions showed that soluble gas in the atmosphere is washed down by precipitation and is smeared by diffusion. Using the suggested model we analyzed the temporal evolution of the vertical profiles of ammonia and sulfur dioxide in the atmosphere caused by their washout. We calculated also scavenging coefficient. It was showed that the magnitude of scavenging coefficient varies with time and altitude and depends on the vertical distribution of soluble gaseous pollutants in the atmosphere and on the rain intensity. The predictions of the developed model were compared with the available experimental data.

References

Elperin T., A. Fominykh and B. Krasovitov, Journal of the Atmospheric Sciences, 66, 2349–2358 (2009).
Elperin T., A. Fominykh and B. Krasovitov and A. Vikhansky, ASME 14th International Heat Transfer Conference, August 8–13, 2010 Washington, US.