Organosulfur Compounds Formed from Heterogeneous Reaction between SO₂ and Particulate-Bound Unsaturated Fatty Acids in Ambient Air

Laboratory studies have demonstrated that uptake of SO₂ on oleic acid (OLA) could directly produce organosulfates (OS); yet, it is unknown whether this pathway is significant in secondary organosulfur production in ambient air. Here, we collected filter-based samples of ambient fine particles (PM_2.5) in the Pearl River Delta region in southern China and determined organosulfur compounds with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The results are in agreement with the occurrence of organosulfurs formed from the reactive uptake of SO₂ by OLA and a wider range of C₁₄-C₂₄ unsaturated fatty acids in ambient air as reported by laboratory studies, as well as additional species that are likely oxidation products of the primary products previously identified. OS formed from the heterogeneous reaction between SO₂ and unsaturated fatty acids accounted for 7%-13% sulfur of the CHOS species and 5%-7% sulfur of all the CHOS and CHONS species. They contributed about 0.3‰-0.9‰ of the total organic mass of the fine particle samples collected.