Atmospheric gas-phase reactions of dimethylsulphoxide and dimethylsulphone with OH and NO3 radicals, Cl atoms and ozone

Abstract Kinetics and products of the gas-phase oxidation of dimethylsulphoxide (DMSO) and dimethylsulphone (DMSO 2 ), two sulphur compounds produced in the gas-phase oxidation of dimethylsulphide, have been investigated. The reactions of DMSO and DMSO 2 with some of the most important oxidising species in the atmosphere were investigated, which include reactions with OH and NO 3 radicals, Cl atoms and ozone (O 3 ). The experiments were carried out at room temperature and at (740±5) Torr in a 480 l reaction chamber. FT-IR spectrometry was used as the analytical technique. Using a relative rate reaction technique or a pseudo-first-order reaction rate 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)×10 −11 , k NO 3 =(5.0±3.8)×10 −13 , k Cl =(7.4±1.0)×10 −11 and k O 3 −19 . For the reactions of DMSO 2 : k OH −13 , k NO 3 −15 , k Cl =(2.4±0.8)×10 −14 and k O 3 −19 (all values are given with 2 σ overall uncertainties). SO 2 , MSPN (methylsulphonyl peroxynitrate) and DMSO 2 were identified as the main gas-phase sulphur-containing products of the oxidation of DMSO by Cl atoms, similar to what has previously been observed for the reaction with OH radicals. From the reaction between DMSO and the NO 3 radical, DMSO 2 was the only gas-phase sulphur-containing product observed. All of the reactions of DMSO 2 were very slow and no sulphur-containing products were observed in the gas phase. The results obtained here indicate that in the atmosphere DMSO could be oxidised both by the gas-phase reaction with the OH radical leading to SO 2 and DMSO 2 , and by transfer to the liquid phase, where the oxidation products are unknown. DMSO 2 on the other hand will mainly be transferred to the liquid phase before undergoing further degradation.