Abstract
Abstract. Criegee intermediates (CIs) are formed in the ozonolysis of unsaturated hydrocarbons and play a role in atmospheric chemistry as a non-photolytic OH source or a strong oxidant. Using a relative rate method in an ozonolysis experiment, Newland et al. (2015) reported high reactivity of isoprene-derived Criegee intermediates towards dimethyl sulfide (DMS) relative to that towards SO2 with the ratio of the rate coefficients kDMS+CI/kSO2+CI = 3.5 ± 1.8. Here we reinvestigated the kinetics of DMS reactions with two major Criegee intermediates formed in isoprene ozonolysis, CH2OO, and methyl vinyl ketone oxide (MVKO). The individual CI was prepared following the reported photolytic method with suitable (diiodo) precursors in the presence of O2. The concentration of CH2OO or MVKO was monitored directly in real time through their intense UV–visible absorption. Our results indicate the reactions of DMS with CH2OO and MVKO are both very slow; the upper limits of the rate coefficients are 4 orders of magnitude smaller than the rate coefficient reported by Newland et al. (2015) These results suggest that the ozonolysis experiment could be complicated such that interpretation should be careful and these CIs would not oxidize atmospheric DMS at any substantial level.
Highlights
Our results indicate the reactions of dimethyl sulfide (DMS) with CH2OO and methyl vinyl ketone oxide (MVKO) are both very slow; the upper limits of the rate coefficients are 4 orders of magnitude smaller than the rate coefficient reported by Newland et al (2015) These results suggest that the ozonolysis experiment could be complicated such that interpretation should be careful and these Criegee intermediates (CIs) would not oxidize atmospheric DMS at any substantial level
At t = 0, CH2OO is generated within 10−5 s by photolysis of CH2I2 at 308 nm (Reaction R1) and the fast reaction of CH2I with O2 (Reaction R2) (kO2 = 1.4 × 10−12 cm3 s−1 (Eskola et al, 2006); [O2] = 3.3 × 1017 cm−3)
We present the first direct kinetic study of the reactions of DMS with CH2OO and MVKO, which are the major CIs formed in the ozonolysis of isoprene
Summary
As a non-photolytic OH source or a strong oxidant, Criegee intermediates (CIs) influence the chemical processes in the troposphere (Nguyen et al, 2016; Novelli et al, 2014; Johnson and Marston, 2008; Atkinson and Aschmann, 1993; Gutbrod et al, 1997; Zhang et al, 2002) and, have an impact on the formation of secondary aerosols and other pollutants (Percival et al, 2013; Wang et al, 2016; Meidan et al, 2019). A detailed understanding of CI chemistry under atmospheric conditions is, necessary to be able to accurately predict and describe the evolution of Earth’s atmosphere Due to their high reactivity and, short lifetimes, laboratory studies of the reactions of CIs have been challenging until the work by Welz et al, who reported a novel method to efficiently generate CIs other than through ozonolysis of alkenes (Welz et al, 2012). They utilized Reactions (R1) and (R2) to prepare CH2OO and directly measured the rate coefficients of CH2OO reactions with SO2 and NO2 by following the time-resolved decay of CH2OO. The reaction mechanism may be rather complicated and even the ratios of the rate coefficients need to be treated with care
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