Nucleation scavenging of submicrometer aerosol particles

The efficiency of nucleation scavenging of submicrometric aerosol particles with radii between 0.028—0.28 μm was measured at Tsukuba, Japan, during the summer and winter of 1987 by using two thermal gradient diffusion chambers, with and without a water vapor source. The efficiencies were measured as a function of the supersaturations (S). Although the efficiencies in winter tended to be lower than those in summer, mean efficiency by volume was evaluated to be 0.75 at S = 0.25%, 0.81 at S = 0.51% and 0.93 at S = 1.04%. On several occasions, individual aerosol particles were collected with a low-pressure impactor and were examined by the dialysis (extraction) of water-soluble material with water. It was suggested on the basis of these data that the efficiency of nucleation scavenging for submicrometer aerosol particles was closely related to the hygroscopic properties. Further, the reduction in the efficiencies at supersaturations less than 0.5% was mainly due to the presence of particles with small volume fractions of water-soluble material. Structural features of some cloud-inactive particles were also indicated.