Homogeneous nucleation in supersaturated vapor containing foreign seed aerosol

Abstract

The formation of aerosol particles by homogeneous nucleation in a supersaturated vapor containing seed aerosol has been studied experimentally and theoretically. In the laboratory, a room-temperature gas optionally containing zinc chloride particles is continuously mixed with a high-temperature gas saturated with dibutyl phthalate (DBP) vapor in a previously discussed device for the study of aerosol nucleation known as a particle size magnifier (PSM). A highly supersaturated vapor is rapidly formed in the mixing zone of the PSM, and gas-to-particle conversion ensues. The vapor may be converted to the aerosol phase by condensation onto the preexisting particles or by homogeneous nucleation to form new particles which then serve as condensation sites themselves. The split between these alternate pathways for gas-to-particle conversion may be deduced from measurements of the resulting aerosol concentrations for different initial supersaturations, seed aerosol concentrations, and seed aerosol sizes. The measured final aerosol concentrations are compared with those predicted by a dynamic model that combines expressions for classical nucleation theory and for steady-state particle growth, and agreement is found to within experimental uncertainties. Suppression of homogeneous nucleation by seed aerosol is not predicted to be strong unless seed aerosol number concentrations are larger than the number concentrations which would result from homogeneous nucleation alone.