Atmospheric Gas-Phase Formation of Methanesulfonic Acid

Spectroscopic Characterization and Photochemistry of the Atmospherically Relevant Methanesulfenic Acid

“…The atmospheric chemistry of volatile organic sulfur compounds (VOSCs) plays an important role in the global biogeochemical sulfur cycles . Among the various atmospherically relevant VOSCs, dimethyl sulfide (DMS, CH 3 SCH 3 ) is one of the most important reduced-sulfur species that is mainly emitted into the atmosphere by marine bacteria through the enzymatic degradation of phytoplanktonic dimethylsulfoniopropionate (DMSP). , These emissions contribute to the global atmospheric sulfate aerosol between 19 to 42%, whose formation mainly involves the initial oxidation of DMS by its reaction with the principal oxidant hydroxyl radicals (·OH) in the atmosphere. − As the major sulfur-containing oxidation products from DMS, sulfuric acid (H 2 SO 4 ) and methanesulfonic acid (CH 3 SO 3 H) are important precursors to the formation of sulfate-containing aerosol particles and cloud condensation nuclei (CCN) that strongly influence the air quality, climate, and human health. , Therefore, the mechanism for the OH-initiated oxidation of DMS is of vital importance in understanding its atmospheric fate. , According to the recent model, the atmospheric oxidation of DMS by ·OH in an addition pathway proceeds by first formation of an addition reaction intermediate CH 3 S­(·OH)­CH 3 (Scheme ), which can be further oxidized by O 2 to form dimethyl sulfoxide (CH 3 S­(O)­CH 3 , DMSO). Alternatively, this intermediate can dissociate through homolytic C–S bond cleavage by releasing methyl radical (·CH 3 ) and methanesulfenic acid (CH 3 SOH, MSEA).…”

“…In the gas phase, CH 3 SOH was supposed to be very reactive due to oxidation by ozone (O 3 ) in producing sulfur-bearing radicals CH 3 SO· and CH 3 SO 2 ·, which are important intermediates in the atmospheric oxidation of DMS and DMDS . On the other hand, the ·OH-oxidation of CH 3 SOH yields methanesulfinic acid (MSIA, CH 3 S­(O)­OH), a key precursor to CH 3 SO 2 · in the ·OH + DMS reaction.…”

“…Considering the involvement of CH 3 SOH as an intermediate in the atmospheric oxidation reactions of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS), − the photoreaction between CH 3 SOH and O 2 was also studied in an Ar-matrix (Figure ). The IR spectrum for the matrix-isolated pyrolysis products of the CH 3 S­(O)­CH 2 CH 3 /O 2 /Ar (1:50:1000) mixture reveals the presence of CH 3 S­(O)­OO· (1406.2, 1295.4, 1190.8, 1081.3, 942.0, and 686.4 cm –1 ) as the O 2 -oxidation product of CH 3 SO· ( 5 ), whereas, no oxidation of CH 3 SOH was observed under the pyrolysis conditions.…”