Japan Geoscience Union Meeting 2016

Presentation information


Symbol A (Atmospheric and Hydrospheric Sciences) » A-AS Atmospheric Sciences, Meteorology & Atmospheric Environment

[A-AS12] Atmospheric Chemistry

Wed. May 25, 2016 3:30 PM - 5:00 PM 303 (3F)

Convener:*Hitoshi Irie(Center for Environmental Remote Sensing, Chiba University), Toshinobu Machida(National Institute for Environmental Studies), Hiroshi Tanimoto(National Institute for Environmental Studies), Yoko Iwamoto(Faculty of Science Division I, Tokyo University of Science), Chair:Motoki Sasakawa(National Institute for Environmental Studies), Motoki Sasakawa(NIES National Institute of Environmental Studies), Hitoshi MATSUI(Graduate School of Environmental Studies, Nagoya University)

4:45 PM - 5:00 PM

[AAS12-12] Experimental study on the heterogeneous reaction of gaseous OH radical with aqueous DMSO: Determination of the CH3SO3-/ SO42- production ratio

*Shinichi Enami1 (1.The Hakubi Center, Kyoto university)

Keywords:Aerosol, Photochemical aging, Climate change, heterogeneous reaction, marine chemistry

The oxidation of dimethyl sulfide (DMS) emitted from ocean (~ 45 Tg S per year) is a global source of cloud condensation nuclei. Hydrophobic DMS is mostly oxidized in the gas-phase into H2SO4(g) + DMSO(g) (dimethyl sulfoxide), whereas water-soluble DMSO is oxidized into SO42- + CH3SO3- (methane sulfonate) on water surfaces. R = CH3SO3-/SO42- ratios therefore indicate the extent of DMSO heterogeneous oxidation if Rhet = CH3SO3-/SO42- for DMSO(aq) + ·OH(g) were determined. Here, products and intermediates of the oxidation of aqueous DMSO initiated by gas-phase hydroxyl radicals, OH(g), at the air-water interface were directly detected by mass spectrometry in a novel setup under various experimental conditions. Exposure of millimolar DMSO aqueous microjets to ~ 10 ns OH(g) pulses from the 266 nm laser flash photolysis of O3(g)/O2(g)/H2O(g)/N2(g) mixtures yielded an array of interfacial intermediates/products, including CH3SO3- and HSO4-, that were unambiguously and simultaneously identified in situ by mass spectrometry. We determined Rhet = 2.7 from the heterogeneous OH-oxidation of DMSO on aqueous aerosols for the first time. The nearly quantitative production of H2SO4(g) (that leads to SO42-) in the oxidation of DMSO in the gas-phase versus the Rhet ~ 2.7 value determined at the air-water interface means that R = CH3SO3-/nss-SO42- variations in the aerosol, particularly in remote locations, should arise from the competition between the gas-phase versus the heterogeneous DMSO oxidation pathways. The present study reveals that interfacial OH-oxidation processes play a more significant role in the generation and growth of atmospheric aerosol over ocean than previously envisioned.