On the Effect of Electric Charges on the Scavenging of Aerosol Particles by Clouds and Small Raindrops

Abstract

A theoretical model is described which determines the efficiency E with which aerosol particles of radius r are collected by water drops of radius a due to the combined action of Brownian diffusion, thermo- and diffusiophoresis and electric forces, in the absence of inertial impaction effects. The results of this model are combined with the results of our earlier model which determines the collection efficiency of drops for particles due to the combined action of inertial impaction, thermo- and diffusiophoresis and electric forces, in the absence of effects due to Brownian diffusion. Both models combined quantitatively determine the variation of E vs r for 0.001≤r≤10 ?m, and 42≤a≤310 ?m, for relative humidities up to and including 100%, and for electric charges on drops and aerosol particles ranging in magnitude up to that found under thunder-storm conditions. In particular, a combination of both models allows a quantitative description of the particle size range where the collection efficiency of drops is minimum.