Abstract
Ozonolysis of isoprene, the most abundant alkene, produces three distinct Criegee intermediates (CIs): CH2OO, methyl vinyl ketone oxide (MVKO) and methacrolein oxide (MACRO). The oxidation of SO2 by CIs is a potential source of H2SO4, an important precursor of aerosols. Here we investigated the UV-visible spectroscopy and reaction kinetics of thermalized MACRO. An extremely fast reaction of anti-MACRO with SO2 has been found, kSO2 = (1.5 ± 0.4) × 10−10 cm3 s−1 (±1σ, σ is the standard deviation of the data) at 298 K (150 − 500 Torr), which is ca. 4 times the value for syn-MVKO. However, the reaction of anti-MACRO with water vapor has been observed to be quite slow with an effective rate coefficient of (9 ± 5) × 10−17 cm3 s−1 (±1σ) at 298 K (300 to 500 Torr), which is smaller than current literature values by 1 or 2 orders of magnitude. Our results indicate that anti-MACRO has an atmospheric lifetime (best estimate ca. 18 ms at 298 K and RH = 70%) much longer than previously thought (ca. 0.3 or 3 ms), resulting in a much higher steady-state concentration. Owing to larger reaction rate coefficient, the impact of anti-MACRO on the oxidation of atmospheric SO2 would be substantial, even more than that of syn-MVKO.
Highlights
Ozonolysis of isoprene, the most abundant alkene, produces three distinct Criegee intermediates (CIs): CH2OO, methyl vinyl ketone oxide (MVKO) and methacrolein oxide (MACRO)
CH2OO and anti-CH3CHOO, which have a H-atom at the syn position, the main decay pathway is their reactions with water vapor (H2O monomer and dimer)[18,19,20,21,22,23]
The presence of IO and I2 is similar to previous investigations of CH2OO47–49, CH3CHOO23,50, (CH3)2COO51, and MVKO35,36
Summary
Ozonolysis of isoprene, the most abundant alkene, produces three distinct Criegee intermediates (CIs): CH2OO, methyl vinyl ketone oxide (MVKO) and methacrolein oxide (MACRO). Owing to larger reaction rate coefficient, the impact of anti-MACRO on the oxidation of atmospheric SO2 would be substantial, even more than that of syn-MVKO. For. CH2OO and anti-CH3CHOO, which have a H-atom at the syn position, the main decay pathway is their reactions with water vapor (H2O monomer and dimer)[18,19,20,21,22,23]. CH2OO and anti-CH3CHOO, which have a H-atom at the syn position, the main decay pathway is their reactions with water vapor (H2O monomer and dimer)[18,19,20,21,22,23] These reactions are extremely fast, resulting in very low steady-state concentrations of such CIs, which are too low to oxidize atmospheric SO2 at any substantial level[17]. Different from alkyl-substituted CIs, MVKO and MACRO have a C=C double bond, which forms extended conjugation with the carbonyl oxide functional group (resonance stabilized)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
