Influence of mineral dust mixing-state and reaction probabilities on size-resolved sulfate formation in Northeast Asia

Abstract

Significant differences were found between two particulate sulfate size-distributions measured using a MOUDI impactor at Gosan, Jeju Island, Korea, and simulated via the Lagrangian photochemical model under a condition of aerosol internal mixing between mineral dust and urban pollution particles. It was suspected that these differences might have resulted from: (1) the assumption of aerosol internal mixing and (2) the uses of identical reaction probabilities (gamma) of the gaseous sulfate precursors (SO2 and H2SO4) onto both urban pollution particles and mineral dust in the Lagrangian photochemical model simulations. In this study; therefore, some cases of aerosol external mixing between urban-derived pollution aerosols and mineral dust were investigated, with different magnitudes of gamma for the gas-phase sulfate precursors onto the two different condensing media. The model simulations under the external mixing condition, with different magnitudes of the reaction probabilities (gamma(i,urban) and gamma(i,dust)) onto urban pollution particles and mineral dust, successfully reproduced the size-dependent particulate sulfate formation measured at the Gosan station. Further attempts were made to approximate the magnitudes of gamma(SO2,urban) and gamma(H2SO2,dust) under external mixing state conditions with the fixed gamma(SO2,dust) and gamma(H2SO2,urban) values of 10(-4) and 1.0. The best-estimates of gamma(SO2,urban) and gamma(H2SO2,dust) found in this study were in the orders of 10(-4)-10(-5) and 10(-2)-10(-3), respectively. (C) 2011 Elsevier Ltd. All rights reserved.