Kinetics of dimethyl sulfide (DMS) reactions with isoprene-derived Criegee intermediates studied with direct UV absorption

摘要

Criegee intermediates (CIs) are formed in the ozonolysisof unsaturated hydrocarbons and play a role in atmospheric chemistry as anon-photolytic OH source or a strong oxidant. Using a relative rate methodin an ozonolysis experiment, Newland et al. (2015) reported high reactivity of isoprene-derived Criegeeintermediates towards dimethyl sulfide (DMS) relative to that towardsSO2 with the ratio of the rate coefficients kDMS+CI/kSO2+CI = 3.5 ± 1.8. Here we reinvestigated the kinetics of DMS reactionswith two major Criegee intermediates formed in isoprene ozonolysis,CH2OO, and methyl vinyl ketone oxide (MVKO). The individual CI wasprepared following the reported photolytic method with suitable (diiodo)precursors in the presence of O2. The concentration of CH2OO orMVKO was monitored directly in real time through their intense UV–visibleabsorption. Our results indicate the reactions of DMS with CH2OO andMVKO are both very slow; the upper limits of the rate coefficients are 4orders of magnitude smaller than the rate coefficient reported by Newland et al. (2015) Theseresults suggest that the ozonolysis experiment could be complicated suchthat interpretation should be careful and these CIs would not oxidizeatmospheric DMS at any substantial level.