Formation of Organosulfur Compounds through Transition Metal Ion-Catalyzed Aqueous Phase Reactions

Organosulfur compounds, particularly organosulfates, are considered as important tracers of secondary organic aerosol formation. However, the mechanistic pathways for the formation of these compounds in the atmosphere are still not well understood. In this study, we show for the first time that C-2-C-4 organosulfur compounds, as well as their oligomers, can form in the aqueous phase from reactions of unsaturated carbonyl compounds, i.e., methacrolein (MACR) and methyl vinyl ketone (MVK), with the bisulfite anion (HSO3-) in the presence of Fe3+. The mechanism for product formation in the presence of Fe(3+ )involves sulfite and sulfate ion radicals. As shown here, the formation of specific organosulfur compounds depends on the concentrations of MVK and MACR and the solution pH. Our findings provide new insights into pathways for forming organosulfur compounds in the atmosphere and the role that transition metal ions, such as Fe3+, play in catalyzing these reactions.