Experiments on Aerosol Scavenging by Natural Snow Crystals

Part III. The Effect of Snow Crystal Charge on Collection Efficiency

Abstract

The collection efficiency of charged natural snow crystals (carrying an average charge of 0.4 e. s. u. cm^-2) for aerosol particles of 0.1μm to 6μm in diameter was experimentally examined under conditions where phoretic forces and external electric fields were negligibly small. From a comparison between the collection efficiency of charged snow crystals (the present experiments) and that of uncharged snow crystals (Murakami et al., 1985a), the effects of snow crystal charge on the collection efficiency were estimated.
The enhancement of collection efficiency due to electrostatic charges on snow crystals increased with the decreasing aerosol size, and became maximum at around 0.2μm in diameter. Coulombic force was considered to be the dominant electrostatic force under the conditions of the present experiments.
On the basis of the present experimental results and the previous results obtained by Murakami et al. (1985a, b), the semi-empirical expression for the collection efficiency of plane-type snow crystals was derived.