Numerical study of the oxidation process of dimethylsulfide in the marine atmosphere |
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| Authors: | Seizi Koga Hiroshi Tanaka |
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| Institution: | (1) Water Research Institute, Nagoya University, Chikusa-ku, 464-01 Nagoya, Japan |
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| Abstract: | A box model, involving simple heterogeneous reaction processes associated with the production of non-sea-salt sulfate (nss-SO
4
2–
) particles, is used to investigate the oxidation processes of dimethylsulfide (DMS or CH3SCH3) in the marine atmosphere. The model is applied to chemical reactions in the atmospheric surface mixing layer, at intervals of 15 degrees latitude between 60° N and 60° S. Given that the addition reaction of the hydroxyl radical (OH) to the sulfur atom in the DMS molecule is faster at lower temperature than at higher temperature and that it is the predominant pathway for the production of methanesulfonic acid (MSA or CH3SO3H), the results can well explain both the increasing tendency of the molar ratio of MSA to nss-SO
4
2–
toward higher latitudes and the uniform distribution with latitude of sulfur dioxide (SO2). The predicted production rate of MSA increases with increasing latitude due to the elevated rate constant of the addition reaction at lower temperature. Since latitudinal distributions of OH concentration and DMS reaction rate with OH are opposite, a uniform production rate of SO2 is realized over the globe. The primary sink of DMS in unpolluted air is caused by the reaction with OH. Reaction of DMS with the nitrate radical (NO3) also reduces DMS concentration but it is less important compared with that of OH. Concentrations of SO2, MSA, and nss-SO
4
2–
are almost independent of NO
x
concentration and radiation field. If dimethylsulfoxide (DMSO or CH3S(O)CH3) is produced by the addition reaction and further converted to sulfuric acid (H2SO4) in an aqueous solution of cloud droplets, the oxidation process of DMSO might be important for the production of aerosol particles containing nss-SO
4
2–
at high latitudes. |
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| Keywords: | Marine atmosphere dimethylsulfide sulfur dioxide dimethylsulfoxide dimethylsulfone methanesulfonic acid non-sea-salt sulfate addition reaction heterogeneous reaction |
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