Photodegradation of (CH3CH2)2S and CH3CH2SCH3 initiated by OH radicals at atmospheric pressure. Product yields and mechanism in NOx free air

Abstract

The product distribution of the gas-phase reactions of OH radicals with diethyl sulfide (CH3CH2)2S and ethyl methyl sulfide, CH3CH2SCH3, determined in the absence of NOx, is presented. The experiments were performed in a 1080 L quartz-glass photoreactor and a 405 L borosilicate glass photoreactor in synthetic air at (298 2) K using long path “in situ” FTIR spectroscopy for the analysis of the reactants and products. SO2 and CH3CHO were identified as major primary products for both title reactions together with HCHO as a co-product in the photodegradation of CH3CH2SCH3. Formation of CO and HCOOH was observed, however, the concentrationetime behavior of these products show that they are secondary in origin and are produced from the further oxidation of major primary products. Traces of OCS were observed; its concentrationetime behavior suggests that it is a minor primary product. The yields of the products obtained for the reaction of OH radicals with (CH3CH2)2S were the following: (50 3)% and (91 3)% for SO2 and CH3CHO, respectively. While, for the reaction of OH radicals with CH3CH2SCH3 yields of (51 2)%, (57 3)% and (46 4)% were obtained for SO2, CH3CHO and HCHO, respectively. The present results are compared with previous results for the well studied reaction of dimethyl sulfide, CH3SCH3, with OH radicals and simple atmospheric degradation mechanisms are postulated to explain the formation of the observed products.