The catalytic oxidation of sulfite by transition metal ions (TMI) is a significant pathway for aqueous sulfate formation. Sulfoxy radicals i.e., SO3–, SO4– and SO5– radicals, are the major intermediates in this catalytic reaction and can also react with organics to produce organosulfur compounds, which are important tracers of secondary organic aerosol (SOA) formation. However, the mechanism for organosulfur compounds formation via this pathway is still not well understood. Here, we investigate the formation of organosulfur compounds from the aqueous reaction of isoprene oxidation products, in this case, methacrolein (MACR) and methyl vinyl ketone (MVK), with bisulfite (HSO3–) and how this process is influenced by the presence of different TMI, i.e., Cu2+, Fe3+ and Mn2+. No organosulfur compounds are formed in the presence of Cu2+ except the MVK/MACR-S(IV) adducts, however, Fe3+ and Mn2+ have distinctly different impacts on the organosulfur compounds formation mechanism. Both C2–C4 organosulfur compounds and their oligomers are formed in the presence of Fe3+, whereas only C2–C4 organosulfur compounds are observed in the presence of Mn2+. Fe3+ dominates the formation of organosulfur compounds when both Fe3+ and Mn2+ are present, as indicated by the occurrence of the pronounced peak at m/z 291 (C12H19SO6) even at a low ratio of Fe3+ to Mn2+ (1:25). Furthermore, the formation of organosulfur compounds indicates a reduction of sulfite converted to inorganic sulfate, this inhibition effect of MVK/MACR on the catalytic oxidation of sulfite by TMI is also discussed.

Effects of transition metal ions on the formation of aqueous organosulfur compounds from methacrolein and methyl vinyl ketone

2019 Fall National Meeting

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