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 u sing total NOx concentrations varying from 0 to similar to 1800 ppbv (30-60 0 ppbv NO2 and 140-1760 ppbv NO). Clear trends in the formation yields of t he products SO2, COS, MSA, MTF (methyl thiolformate), MSPN (methanesulphony l 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 co ncentration, whereas the yields of DMSO and SO2 decrease. The following app roximate changes in the yield, not corrected for possible loss processes, h ave been measured for variation of NOx between 0 and similar to 1800 ppbv: DMSO decreases from 20 to 3%S; DMSO2 increases from 3 to 15%S, SO2 decrease s from 70 to 30%S and MSA increases from 4 to 17%S, Under the experiments c onditions NOx levels of several tens of ppbv are required before a percepti ble change is observed in the MSA yield. If applicable to the atmosphere su ch a situation is only likely to be observed near coastal areas affected by pollution. MSPN (CH3SO2O2NO2) is observed as an oxidation product in the p resence of NO2 even at low levels (e.g. 60 ppbv). Its possible role as a NO x reservoir in the troposphere is considered. (C) 1998 Elsevier Science Ltd . All rights reserved.