Scavenging of Aerosol Particles by a Falling Water Drop

Abstract

This experimental study of the collection efficiency of freely falling water drops for AgCl aerosol particles in nitrogen extends earlier work (Kerker and Hampl, 1974) to submillimeter drop radii. In this case it was not necessary, as in the earlier work, to extrapolate to conditions corresponding to terminal velocity. The results are used to calculate washout coefficients for some hypothetical rainfalls, and they indicate that a significant fraction of the submicron aerosol may be removed by washout. In addition, the effect of charging the drops (for drop radii A = 0.62 and 1.82 mm) was measured. Five-fold increases in collection efficiency were obtained for surface charge densities in the range 2 to 9 × 10⁻¹⁰ C cm⁻² which would indicate that there may be substantive increases in scavenging due to charge effects such as encountered in thunderstorms.