HETEROGENEOUS NUCLEATION OF WATER-VAPOR ON SUBMICROMETER PARTICLES OFSIC, SIO2, AND NAPHTHALENE

Heterogeneous nucleation of water vapor on monodisperse submicrometer particles is investigated in a how cloud chamber. The size dependence of critical supersaturation in the range of 15 to 120 nm is experiment ally determined. Three types of aerosol, SiC, SiO2, and naphthalene, a re tested. The results show that all three aerosols induce heterogeneo us nucleation much better than that predicted based on bulk physical p roperties and, for SiC and SiO2, even better than perfectly wetted par ticles. The experimental critical supersaturation is smaller than that predicted by the Fletcher version of the Volmer theory of heterogeneo us nucleation even with the line tension and surface diffusion taken i nto account and has a size dependence in qualitative agreement with th at theoretically predicted but to a lesser degree. The discrepancy can not be fully accounted for by the effects of line tension and surface diffusion and the existing theory concerning the curvature dependent p hysical properties. We conclude that the macroscopic theory of heterog eneous nucleation leads to significant underestimation of the nucleati on rate and prediction of higher critical supersaturation than that ex perimentally measured. (C) 1998 Academic Press.