4). The Volmer theory of heterogeneous nucleation on
Heterogeneous nucleation of water vapor on monodisperse subplane insoluble surfaces was confirmed by Twomey (5) but micrometer particles is investigated in a flow cloud chamber. The disagreeing results have also been reported (6). According size dependence of critical supersaturation in the range of 15 to to the Fletcher version of the Volmer theory, at a given 120 nm is experimentally determined. Three types of aerosol, SiC, temperature, the nucleation rate of not perfectly wetted and SiO 2 , and naphthalene, are tested. The results show that all three insoluble particles depends only on the contact angle and aerosols induce heterogeneous nucleation much better than that the particle radius. Yet the dependence of the contact angle predicted based on bulk physical properties and, for SiC and SiO 2 , on embryo and particle radii is not known. Differences beeven better than perfectly wetted particles. The experimental crititween microscopic and macroscopic contact angles have cal supersaturation is smaller than that predicted by the Fletcher version of the Volmer theory of heterogeneous nucleation even been observed (7-9). Measurements of heterogeneous nuwith the line tension and surface diffusion taken into account and cleation of water vapor on submicrometer AgI and wax partihas a size dependence in qualitative agreement with that theoreticles (10) and on DOP particles (11) show that these particles cally predicted but to a lesser degree. The discrepancy cannot be behave like pure water droplets. The physical processes infully accounted for by the effects of line tension and surface diffuvolved in nucleation of not perfectly wettable and insoluble sion and the existing theory concerning the curvature dependent small particles are not fully understood. physical properties. We conclude that the macroscopic theory of Recently, Porstendorfer et al. (12) have investigated the heterogeneous nucleation leads to significant underestimation of heterogeneous nucleation of supersaturated vapor on ulthe nucleation rate and prediction of higher critical supersaturatrafine Ag and NaCl aerosols and observed significant depention than that experimentally measured.