FT-IR product study of the OH-initiated oxidation of DMS in the presence of NOx

The influence of NOx (NO+NO2) concentrations on the product distribution of the OH-initiated oxidation of DMS has been studied at room temperature using total NOx concentrations varying from 0 to 1800 ppbv (30–600 ppbv NO2 and 140–1760 ppbv NO). Clear trends in the formation yields of the products SO2, COS, MSA, MTF (methyl thiolformate), MSPN (methanesulphonyl peroxynitrate), DMSO and DMSO2 have been observed with variation in NOx. The presence of low levels of NO reduces the yields of both MTF and COS to zero. The formation yields of MSA and DMSO2 increase with increasing NOx concentration, whereas the yields of DMSO and SO2 decrease. The following approximate changes in the yield, not corrected for possible loss processes, have been measured for variation of NOx between 0 and 1800 ppbv: DMSO decreases from 20 to 3%S; DMSO2 increases from 3 to 15%S, SO2 decreases from 70 to 30%S and MSA increases from 4 to 17%S. Under the experiments conditions NOx levels of several tens of ppbv are required before a perceptible change is observed in the MSA yield. If applicable to the atmosphere such a situation is only likely to be observed near coastal areas affected by pollution. MSPN (CH3SO2O2NO2) is observed as an oxidation product in the presence of NO2 even at low levels (e.g. 60 ppbv). Its possible role as a NOx reservoir in the troposphere is considered.