Estimation of the most penetrating particle size during snow scavenging process

Among various concepts and theories on an aerosol wet deposition or scavenging process, the prediction of the most penetrating particle size (i.e., scavenging gap) is important. It is because the scavenging gap or minimum-collection efficiency diameter in scavenging process is a critical size where aerosols are not effectively removed by rain or snow hydrometeors. Thus, it is the size where the penetration of particles through rain or snow is maximized, whereas the collection efficiency is minimized. In general, the minimum-collection efficiency diameter can be numerically calculated by differentiation of the collection efficiency. Although there have been many previous studies on the rain scavenging of aerosol particles (e.g., Bae et al., 2010), studies on the snow scavenging, especially for minimum-collection efficiency, are few. Characteristics of snowfall are determined by many factors, such as the size and speed of the falling snow hydrometeors, and variability in these factors under various weather conditions. In this study, an analytic solution of the minimum-collection efficiency and the corresponding minimum-collection efficiency diameter due to snow precipitation were determined. Snow size distributions were assumed using polydisperse gamma distributions and various falling velocities shown in previous studies were compared. Results showed that, during snow precipitation, both the minimum-scavenging coefficient diameter and the minimum-scavenging coefficient increased as the snow intensity increased. The obtained analytic solution showed a good agreement with the numerical solution, especially for the minimum-scavenging coefficient.