Heterogeneous Nucleation of Water Vapor on Particles of SiO2, Al2O3, TiO2, and Carbon Black

Abstract

Heterogenous nucleation of water vapor on submicrometer particles is investigated in a flow cloud chamber (FCC). As aerosol passes through the FCC, supersaturated water vapor condenses onto the particles which grow to larger sizes and settle out with appreciable velocities. Particles that traverse a distance less than the FCC length are removed. The removal efficiency is experimentally measured as a function of supersaturation and is also theoretically evaluated using the Fletcher version of the Volmer theory of heterogeneous nucleation. Four types of aerosol are tested. The results show that the four aerosols behave as if they have the ability to induce heterogeneous nucleation better than that of perfectly wetted particles, and lead to a conclusion that the macroscopic theory of heterogeneous nucleation leads to a significant underestimation of the nucleation rate and a prediction of critical supersaturation higher by up to 30% than that experimentally measured.