Exploring the chemical fate of the sulfate radical anion by reaction with sulfur dioxide in the gas phase

Abstract

The gas phase reaction between SO4-(H2O)n and SO2, n = 0-2, is investigated using ab initio calculations and kinetic modelling. Structures of reactants, transition states and products are reported. Our calculations predict that the SO2SO4-(H2O)n cluster ion, which is formed upon SO2 and SO4-(H2O)n collision, can isomerize to SO3SO3-(H2O)n. The overall reaction is SO2 oxidation by the SO4-(H2O)n anionic cluster. The results show that SO4-(H2O)n is a good SO2 oxidant, especially at low relative humidity, with a reaction rate constant up to 1.5 × 10-10 cm3 molecule-1s-1. At high relative humidity, instead, the re-evaporation of SO2 from the SO2SO4-(H2O)n cluster ion is favoured.