A theoretical study of the effect of electric charges on the efficiency with which aerosol particles are collected by ice crystal plates

Abstract

Two theoretical models are presented which allow computing the efficiency with which electrically charged aerosol particles of radius 0.001 ≤ r ≤ 10 μm are collected by electrically charged plate-like ice crystals of radius 50 ≤ a c ≤ 640 μm in air of various relative humidities and of 700 mb and −10°C. Particle capture due to thermophoresis, diffusiophoresis, Brownian diffusion, inertial impaction, and electrostatic forces is considered. It is shown that Brownian diffusion dominates the capture process by ice crystals if r ≤ 0.01 μm, while inertial impaction controls the capture process if r > 0.1 μm. For aerosol particles of 0.01 ≤ r ≤ 0.1 μm, the collection efficiency is controlled by phoretic forces. Electrical forces significantly affect the collection of aerosol particles in the size range of 0.01 ≤ r ≤ 5 μm. Trajectory analysis demonstrates that electrically charged and uncharged aerosol particles are preferentially captured at the rim of plate-like ice crystals. Electrically neutral ice crystals of N Re < 50 capture particles only on the underside of the ice crystal. Ice crystals which are electrically charged collect aerosol particles by rear capture if N Re ≤ 0.5.