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

Abstract

The reaction of OH radicals with dimethyl sulphide (CH 3 SCH 3 , DMS) has been studied in the atmospheric pressure flow tube IfT -LFT at 293 ± 0.5 K in the absence of NO x , [NO x ] ≤ 10 10 molecule cm −3 . OH radicals were generated either via the photolysis of H 2 O 2 under dry conditions or using the photolysis of O 3 at a relative humidity of 50%. PTR-MS and FT-IR spectroscopy served as analytical techniques for product analysis. Observed products were SO 2 , HCHO, methyl thioformate (MTF), dimethyl sulfoxide (DMSO) and likely dimethyl sulfone (DMSO 2 ). The formation of SO 2 , HCHO and MTF was clearly inhibited under conditions of a favoured reaction of CH 3 SCH 2 O 2 radicals with HO 2 . Experiments in the presence of up to 2 × 10 12 molecule cm −3 of O 3 showed a small increase of the formation yields of SO 2 and HCHO with increasing O 3 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 SO 2 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 CH 3 SCH 2 O 2 + HO 2 as given originally by MCM. The simulation results described well the amount of consumed O 3 by DMS intermediates as well as the impact of O 3 on products yields. ► Product formation from the reaction OH + DMS was measured in the absence of NO x . ► Influence of O 3 on product distribution is investigated. ► Modelling based on MCMv3.2 has been performed.