Direct kinetic measurements and theoretical predictions of an isoprene-derived Criegee intermediate

Rebecca L Caravan, Michael Vansco, Kendrew Au, M Anwar H Khan, Yu-Lin Li, Frank A. F. Winiberg, Kristen Zuraski, Yen-Hsiu Lin, Wen Chao, Nisalak Trongsiriwat, Patrick Walsh, David Osborn, Carl Percival, Jim Jr-Min Lin, Dudley E Shallcross, Leonid Sheps, Stephen J. Klippenstein, Craig Taatjes, Marsha I Lester*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

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Abstract

Isoprene has the highest emission into Earth’s atmosphere of any nonmethane hydrocarbon. Atmospheric processing of alkenes, including isoprene, via ozonolysis leads to the formation of zwitterionic reactive intermediates, known as Criegee intermediates (CIs). Direct studies have revealed that reactions involving simple CIs can significantly impact the tropospheric oxidizing capacity, enhance particulate formation, and degrade local air quality. Methyl vinyl ketone oxide (MVK-oxide) is a four-carbon, asymmetric, resonance-stabilized CI, produced with 21 to 23% yield from isoprene ozonolysis, yet its reactivity has not been directly studied. We present direct kinetic measurements of MVK-oxide reactions with key atmospheric species using absorption spectroscopy. Direct UV-Vis absorption spectra from two independent flow cell experiments overlap with the molecular beam UV-Vis-depletion spectra reported recently [M. F. Vansco, B. Marchetti, M. I. Lester, J. Chem. Phys. 149, 44309 (2018)] but suggest different conformer distributions under jet-cooled and thermal conditions. Comparison of the experimental lifetime herein with theory indicates only the syn-conformers are observed; anti-conformers are calculated to be removed much more rapidly via unimolecular decay. We observe experimentally and predict theoretically fast reaction of syn-MVK-oxide with SO2 and formic acid, similar to smaller alkyl-substituted CIs, and by contrast, slow removal in the presence of water. We determine products through complementary multiplexed photoionization mass spectrometry, observing SO3 and identifying organic hydroperoxide formation from reaction with SO2 and formic acid, respectively. The tropospheric implications of these reactions are evaluated using a global chemistry and transport model.
Original languageEnglish
Pages (from-to)9733-9740
Number of pages8
JournalProceedings of the National Academy of Sciences of the United States of America
Volume117
Issue number18
DOIs
Publication statusPublished - 5 May 2020

Keywords

  • atmospheric chemistry
  • Criegee intermediates
  • chemical kinetics
  • ab initio calculations
  • spectroscopy

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