Scavenging of Aerosol Particles by a Falling Water Drop

Abstract

This experimental study of the collection efficiency of freely fallingwater drops for AgCl aerosol particles in nitrogen extends earlier work(Kerker and Hampl, 1974) to submillimeter drop radii. In this case it wasnot necessary, as in the earlier work, to extrapolate to conditionscorresponding to terminal velocity. The results are used to calculatewashout coefficients for some hypothetical rainfalls, and they indicatethat a significant fraction of the submicron aerosol may be removed bywashout. In addition, the effect of charging the drops (for drop radii A =0.62 and 1.82 mm) was measured. Five-fold increases in collectionefficiency were obtained for surface charge densities in the range 2 to 9× 10Ý10 C cmÝ2 which would indicate that there may be substantiveincreases in scavenging due to charge effects such as encountered inthunderstorms.