Experiments on Aerosol Scavenging by Nattiral Snow Crystals

Part II: Attachment Rate of 0.1μm Dia. Particles to Stationary Snow Crystals

Abstract

The attachment rate of 0.1μm dia. particles to stationary uncharged snow crystals was experimentally obtained using an aerosol chamber. The experiment was performed under conditions where the external electric field and phoretic forces were negligibly small. The measured attachment rates were considerably greater than the values calculated from the stationary Brownian diffusion theory. This discrepancy might result from the increase of the measured attachment rate due to additional factors (image force, turbulent diffusion, etc.) in the experiment. The attachment rate of stationary snow crystals was extrapolated to the collection efficiency of falling snow crystals using the ventilation coefficient. The comparison between the measured and extrapolated collection efficiencies showed that the convective Brownian diffusion was the main scavenging mechanism although the additional factors (image force and turbulent diffusion) might enhance the collection efficiency.