Products of the reaction of OH radicals with dimethyl sulphide in the absence of NOx: Experiment and simulation

The reaction of OH radicals with dimethyl sulphide (CH3SCH3, DMS) has been studied in the atmospheric pressure flow tube IfT-LFT at 293 ± 0.5 K in the absence of NOx, [NOx] ≤ 1010 molecule cm−3. OH radicals were generated either via the photolysis of H2O2 under dry conditions or using the photolysis of O3 at a relative humidity of 50%. PTR-MS and FT-IR spectroscopy served as analytical techniques for product analysis. Observed products were SO2, HCHO, methyl thioformate (MTF), dimethyl sulfoxide (DMSO) and likely dimethyl sulfone (DMSO2). The formation of SO2, HCHO and MTF was clearly inhibited under conditions of a favoured reaction of CH3SCH2O2 radicals with HO2. Experiments in the presence of up to 2 × 1012 molecule cm−3 of O3 showed a small increase of the formation yields of SO2 and HCHO with increasing O3 levels. Modelling runs have been performed using the DMS module from the Master Chemical Mechanism, MCMv3.2, with a few modifications. Generally, the simulation slightly under-predicted the measured yields of HCHO. The SO2 yields observed were roughly in agreement with the modelling results. A qualitative description of the experimentally detected MTF production was achieved by neglecting the MTF formation path via CH3SCH2O2 + HO2 as given originally by MCM. The simulation results described well the amount of consumed O3 by DMS intermediates as well as the impact of O3 on products yields.