Atmospheric gas-phase reactions of dimethylsulphoxide and dimethylsulphonewith ON and NO3 radicals, Cl atoms and ozone

Kinetics and products of the gas-phase oxidation of dimethylsulphoxide (DMS O) and dimethylsulphone (DMSO2), two sulphur compounds produced in the gas- phase oxidation of dimethylsulphide, have been investigated. The reactions of DMSO and DMSO2 with some of the most important oxidising species in the atmosphere were investigated, which include reactions with OH and NO3 radic als, Cl atoms and ozone (O-3) The experiments were carried out at room temp erature and at (740 +/- 5) Torr in a 4801 reaction chamber. FT-LR spectrome try was used as the analytical technique. Using a relative rate reaction technique or a pseudo-first-order reaction r ate technique, the following rate constants (expressed in cm(3) molecule(-1 ) s(-1)) have been determined: For the reactions of DMSO: k(OH) = (5.9 +/- 1.5)x 10(-11) k(NO3) = (5-0 +/- 3.8) x 10(-13), k(Cl) = (7.4 +/- 1.0) x 10( -11) and k(O3) < 1 x 10(-19). For the reactions of DMSO2: k(OH) < 3 x 10(-1 3), k(NO3) < 2 X 10(-15) k(Cl) = (2.4 +/- 0.8)x 10(-14) and k(O3) < 1 x 10( -19) (all values are given with 2 sigma overall uncertainties). SO2, MSPN ( methylsulphonyl peroxynitrate) and DMSO2 were identified as the main gas-ph ase sulphur-containing products of the oxidation of DMSO by Cl atoms, simil ar to what has previously been observed for the reaction with OH radicals. From the reaction between DMSO and the NO3 radical, DMSO2 was the only gas- phase sulphur-containing product observed. All of the reactions of DMSO2 we re very slow and no sulphur-containing products were observed in the gas ph ase. The results obtained here indicate that in the atmosphere DMSO could be oxi dised both by the gas-phase reaction with the OH radical leading to SOt and DMSO2, and by transfer to the liquid phase, where the oxidation products a re unknown. DMSO2 on the other hand will mainly be transferred to the liqui d phase before undergoing further degradation. (C) 2000 Elsevier Science Lt d. All rights reserved.