5 - Scavenging and Transportation of Aerosol Particles by Ice Crystals in Clouds

Abstract

This chapter discusses the impact of ice crystals on aerosol particles in clouds, focusing on aerosol collection by ice particles. The chapter compares the calculated collection efficiencies of cloud droplets, ice plates, and ice columns, and draws several conclusions from the experimental data. The three collectors are about equally efficient in collecting very small aerosol particles. Ice plates are most efficient in removing aerosol particles in the size range between 0.01 and 1.0 μm. For aerosol particles of radius greater than 1 μm, both droplets and columnar ice crystals are fairly efficient in removing them. Because snow crystals have complicated shapes, it is impossible to describe both the size and the shape simultaneously by a single parameter. Therefore, in experimental results, the chapter presents collection efficiencies as a function of crystal size only. The data points show a fair amount of scatter, which may be due to many factors, such as non-uniformity of ice crystals and exposure to environmental air. The effect of aerosol charge on the collection efficiency is also investigated in the chapter. Because of the many experimental difficulties and non-ideal conditions, an exact comparison is not possible. Thus, the only parameter that can be used as the basis of comparison is the crystal length.