A Theoretical Determination of the Efficiency with which Aerosol Particles are Collected by Simple Ice Crystal Plates

Abstract

Two theoretical models are presented which allow computing the efficiency with which aerosol particles of radius 0.001 ≤ r ≤ 10 μm are collected by simple ice crystal plates of radius 50 ≤ a_c ≤ 640 μm, in air of various relative humidity, temperature and pressure. Particle capture due to Brownian diffusion, thermophoresis, diffusiophoresis and inertial impaction is considered. It is shown that, analogous to water drops, ice crystal plates exhibit a minimum collection efficiency within a specific size interval of aerosol particles. This minimum is strongly affected by the relative humidity of the ambient air. The collection efficiency of particles with r > 1 μm is controlled by the flow field around the ice crystal, while the collection efficiency of particles with r < 0.01 μm is controlled by convective Brownian diffusion. Trajectory analysis predicts that aerosol particles are preferentially captured by the ice crystal rim. Our theoretical results are found to agree satisfactorily with laboratory studies presently available.