Second-Order Kinetic Rate Coefficients for the Aqueous-Phase Sulfate Radical (SO₄^•–) Oxidation of Some Atmospherically Relevant Organic Compounds

Abstract

The sulfate anion radical (SO₄^•-) is a reactive oxidant formed in the autoxidation chain of sulfur dioxide, among other sources. Recently, new formation pathways toward SO₄^•- and other reactive sulfur species have been reported. This work investigated the second-order rate coefficients for the aqueous SO₄^•- oxidation of the following important organic aerosol compounds (<i>k</i>_SO4): 2-methyltetrol, 2-methyl-1,2,3-trihydroxy-4-sulfate, 2-methyl-1,2-dihydroxy-3-sulfate, 1,2-dihydroxyisoprene, 2-methyl-2,3-dihydroxy-1,4-dinitrate, 2-methyl-1,2,4-trihydroxy-3-nitrate, 2-methylglyceric acid, 2-methylglycerate, lactic acid, lactate, pyruvic acid, pyruvate. The rate coefficients of the unknowns were determined against that of a reference in pure water in a temperature range of 298-322 K. The decays of each reagent were measured with nuclear magnetic resonance (NMR) and high-performance liquid chromatography-high-resolution mass spectrometry (HPLC-HRMS). Incorporating additional SO₄^•- reactions into models may aid in the understanding of organosulfate formation, radical propagation, and aerosol mass sinks.