Formation of Sulfate in a Cloud-Free Environment

Abstract

A model of sulfate aerosol growth, containing homogeneous gas kinetics, particle growth by coagulationand heteromolecular diffusion, and solar radiation effects has been developed to examine the microphysicalmechanisms associated with clear-air transformation of sulfur dioxide to sulfates in the lower atmosphere.Results indicate that the maximum oxidation rate of sulfur dioxide is approximately 1% h and that thesulfate particles produced by clear-air oxidation processes evolve to give a spectrum with an active modeat 0.03 m radius. The oxidation of sulfur dioxide undergoes a diurnal variation in response to the diurnalsolar cycle. The transformation rate of sulfur dioxide increases as atmospheric opacity decreases and thenumber density of sulfate particles increases with increasing atmospheric humidity.