A laboratory study of the scavenging of sub‐micron aerosol by charged raindrops

Laboratory experiments were conducted in order to measure the collection efficiencies, E, with which small water drops (radii varying from 270 to 600μm) carrying electric charges, Q, of magnitude similar to those carried on natural raindrops (10−14 to 10−11 C) collect spherical aerosol particles of radii ranging from about 0·2 to 1 μm. The values of E were found to increase with Q, were characteristically in the range 1 to 10%, and were independent of the sign of Q. They agree reasonably well with the results of earlier workers and are about two orders of magnitude greater than charge‐free (Q = 0) values. A simple analysis indicates that the observed rates at which atmospheric visibility increases as a consequence of scavenging of particulates by rainfall are consistent with the measured values of E.