Ternary nucleation of H_{2}SO_{4}, NH_{3} and H_{2}O in the atmosphere

Abstract

Classical theoly of binary homogeneous nucleation is extended to the ternary system HISO~-NH;-H~OF. or NH; mixing ratios exceeding about 1 ppt, the presence of NH enhances the binary H?S04-H20 nucleation rate by several orders of magnitude. The Gibbs free energies of formation of the critical H2S04-NH;-H20 cluster, as calculated by two independent approaches, are in substantial agreement. The finding that the H,SO,-NH,-H,O ternary nucleation rate is independent of relative humidity over a large range of H2S04 concentrations has wide atmospheric consequences. The limiting component for ternary H2SOr-NHI-H?O nucleation is, as in the binaly H2S04-H70 case, H2SOa; however, the H2S04 concentration needed to achieve significant nucleation rates is several orders of magnitude below that required in the binary case.