A Reevaluation of the Role of Thermophoresis as a Mechanism of In- and Below-Cloud Scavenging

Abstract

Abstract A comparison is made of the roles played by thermophoresis, Brownian diffusion and diffusiophoresis in the precipitation scavenging of aerosol particles. It is shown, for a certain range of particles sizes, that thermophoresis dominates provided that the latent heat associated with the phase transition of water is transferred through the air, to or from the precipitation element by conduction. A plot of the resulting washout coefficient shows that thermophoresis enhances the below-cloud rain scavenging of aerosol particles whose radii are between 0.01 and 1.0μ. The solution is presented for the appropriate convective diffusion equation which describes thermophoretic effects on the in-cloud scavenging problem.