“Sizing‿Heterogeneous Chemistry in the Conversion of Gaseous Dimethyl Sulfide to Atmospheric Particles

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• 作者：Shinichi Enami ; Yosuke Sakamoto ; Keiichiro Hara ; Kazuo Osada ; Michael R. Hoffmann ; Agustín J. Colussi
• 刊名：Environmental Science & Technology
• 出版年：2016
• 出版时间：February 16, 2016
• 年：2016
• 卷：50
• 期：4
• 页码：1834-1843
• 全文大小：654K
• ISSN：1520-5851

文摘

The oxidation of biogenic dimethyl sulfide (DMS) emissions is a global source of cloud condensation nuclei. The amounts of the nucleating H₂SO₄(g) species produced in such process, however, remain uncertain. Hydrophobic DMS is mostly oxidized in the gas phase into H₂SO₄(g) + DMSO(g) (dimethyl sulfoxide), whereas water-soluble DMSO is oxidized into H₂SO₄(g) in the gas phase and into SO₄^2– + MeSO₃^– (methanesulfonate) on water surfaces. R = MeSO₃^–/(non-sea-salt SO₄^2–) ratios would therefore gauge both the strength of DMS sources and the extent of DMSO heterogeneous oxidation if R_het = MeSO₃^–/SO₄^2– for DMSO(aq) + ·OH(g) were known. Here, we report that R_het = 2.7, a value obtained from online electrospray mass spectra of DMSO(aq) + ·OH(g) reaction products that quantifies the MeSO₃^– produced in DMSO heterogeneous oxidation on aqueous aerosols for the first time. On this basis, the inverse R dependence on particle radius in size-segregated aerosol collected over Syowa station and Southern oceans is shown to be consistent with the competition between DMSO gas-phase oxidation and its mass accommodation followed by oxidation on aqueous droplets. Geographical R variations are thus associated with variable contributions of the heterogeneous pathway to DMSO atmospheric oxidation, which increase with the specific surface area of local aerosols.