Influence of the Turbulence Effect on the Rainfall Scavenging Coefficient

Abstract

Rainfall removal of aerosol particles is an important atmospheric aerosol self-scavenging process. Studying the scavenging mechanism of rainfall on aerosol particles and developing a suitable theoretical model are of great significance for preventing and controlling aerosol pollution and improving the accuracy of air quality forecasting. In this paper, the influence of the turbulence effect on aerosol capture by raindrops is investigated using numerical simulation, and the contribution of the turbulence effect to the capture of aerosol particles by raindrops, E_t, is given via the introduction of dimensionless parameters. The scavenging coefficients of the accumulated model particles calculated by simultaneously considering seven mechanisms, namely, Brownian diffusion, interception, inertial impaction, thermophoretic action, diffusiophoretic action, electrostatic action, and the turbulence effect, were found to be 2–10 times higher than those calculated using the currently commonly used Slinn formula (which considers only Brownian diffusion, interception, and inertial impaction). A rainfall scavenging of polydisperse aerosol prediction model was established by taking the actual rainfall events in Guangzhou City, China, as an example and considering seven mechanisms simultaneously, and the characteristics of small particulate matter (PM_2.5) changes over time simulated using the model matched well with the actual measurements.