Open AccessModeling the methanesulfonate to non‐sea‐salt sulfate molar ratio and dimethylsulfide oxidation in the atmosphere
Author(s) -
Koga Seizi,
Tanaka Hiroshi
Publication year - 1999
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/1999jd900069
Subject(s) - atmosphere (unit) , sulfate , sea salt , chemistry , atmospheric chemistry , radical , decomposition , hydrogen atom abstraction , yield (engineering) , ozone , meteorology , materials science , organic chemistry , aerosol , physics , metallurgy
A photochemical box model is used to examine the latitudinal and seasonal variations of the methanesulfonate (MSA, CH 3 SO 3 − ) to non‐sea‐salt sulfate (nss‐SO 4 2− ) molar ratio in NO x ‐poor environments of the remote marine atmosphere. Reasonable agreement between observed and modeled results was obtained. The unimolecular decomposition rates of both CH 3 SO 2 and CH 3 SO 3 are assumed to strongly depend on air temperature. These radicals are thought to be produced through the hydrogen abstraction reaction and the addition reaction of dimethylsulfide (DMS, CH 3 SCH 3 ) with both OH and NO 3 . In this model, the production of MSA is assumed to occur through the OH addition reaction of DMS along with the hydrogen abstraction reaction. If the MSA production through the OH addition reaction is neglected, the predicted MSA to nss‐SO 4 2− molar ratios are not in agreement with the latitudinal and seasonal variations observed in the atmosphere. Assuming a MSA production yield of 10% through the OH addition reaction in addition to the further oxidation of CH 3 SO 3 without breaking the C‐S bond, the model calculations can reproduce MSA/nss‐SO 4 2− molar ratios similar to the observed latitudinal and seasonal variations. Since the reaction of DMS with OH is the most important sink of DMS in the summer the addition and abstraction reactions appear to control the MSA production during this season. At middle and high latitudes during the winter, DMS is mainly oxidized by reaction with NO 3 . Therefore MSA in the winter may primarily be produced from the further oxidation of CH 3 SO 3 . It appears that competition between the decomposition and the further oxidation of CH 3 SO 3 is a determining factor of the winter MSA/nss‐SO 4 2− molar ratio.