Enhancement of contact nucleation by scavenging of charged aerosol particles

The influence of interparticle electrical forces on the particle collection rates of charged water drops are investigated using a particle-droplet trajectory model. For the charge levels expected naturally on supercooled water drops and aerosol active as contact nuclei, the charge-enhanced collection efficiency leads to an increased capture of ice nuclei (IN), causing the freezing probability by contact nucleation to be increased over neutral collisions. The collection efficiency depends on the aerosol charge, but not on the sign or charge carried by water drops. A threefold increase in the collection efficiency is found for aerosols carrying up to 10 elementary charges, collecting submicron aerosol. Modest charges on aerosol particles (APs) arising from natural asymmetries in ion concentration are sufficient to increase collision rates with suitable freezing nuclei. (C) 2002 Elsevier Science B.V. All rights reserved.