Development and evaluation of an expression for polydisperse particle scavenging coefficient for the below-cloud scavenging as a function of rain intensity using the moment method

An analytical expression for wet scavenging coefficient for below-cloud scavenging that is function of collision efficiency, raindrop terminal velocity, raindrop size distribution, and particle size distribution is obtained and tested. The parameters of raindrop size distribution are related with rain intensity since rain intensity can be easily measured. Then, the moment method is applied to the expression for scavenging coefficient to derive an analytical expression. Two widely used raindrop size distribution, Marshall-Palmer and lognormal distributions are considered and lognormal particle size distribution is assumed. The derived scavenging coefficient expression is applied to three model environments, urban, rural, and desert to demonstrate its applicability.