Significant Conversion of Organic Sulfur from Hydroxymethanesulfonate to Inorganic Sulfate and Peroxydisulfate Ions upon Heterogeneous OH Oxidation

Abstract

Hydroxymethanesulfonate (CH2(OH)SO3–, HMS) has been found to be an important organosulfur compound in atmospheric aerosols. However, its atmospheric fate is largely uncertain. In this work, we investigated the heterogeneous OH oxidation of HMS using an oxidation flow reactor. In particular, we examined the rate and chemistry of the sulfur conversion from its organic form to its inorganic counterparts upon oxidation by quantifying HMS and inorganic sulfur species (i.e., sulfate (SO42–) and peroxydisulfate (S2O82–) ions) by using ion chromatography. Kinetic data show that OH oxidation of HMS can proceed efficiently with an effective OH uptake coefficient, γeff of 0.35 ± 0.03. Upon oxidation, the formation of SO42– and S2O82– can explain the aerosol sulfur conversion. An aerosol sulfur mass closure was also obtained by quantifying the amount of HMS, SO42–, and S2O82– before and after oxidation. Kinetic model simulations show that reaction kinetics and product formation can be well explained by a series of aerosol-phase chain reactions initiated by the sulfite radical anion (SO3•–) under our experimental conditions. Overall, our results highlight a significant conversion of organic sulfur from HMS to inorganic sulfur species, including S2O82– upon heterogeneous OH oxidation.