Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 117, Issue 18, Pages 9733-9740Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1916711117
Keywords
atmospheric chemistry; Criegee intermediates; chemical kinetics; ab initio calculations; spectroscopy
Categories
Funding
- Division of Chemical Sciences, Geosciences and Biosciences, Office of Basic Energy Sciences (BES), US Department of Energy (USDOE)
- USDOE's National Nuclear Security Administration [DE-NA0003525]
- USDOE, Office of Science, BES, Division of Chemical Sciences, Geosciences, and Biosciences [DE-AC02-06CH11357]
- Office of Science, BES/USDOE at Lawrence Berkeley National Laboratory [DE-AC02-05CH11231]
- USDOE-BES [DE-FG02-87ER13792]
- NSF [CHE-1902509]
- Academia Sinica
- Ministry of Science and Technology, Taiwan [MOST 106-2113-M001-026-MY3]
- Natural Environment Research Council (NERC) [NE/K004905/1]
- Bristol ChemLabS
- Primary Science Teaching Trust
- U.S. Department of Energy (DOE) [DE-FG02-87ER13792] Funding Source: U.S. Department of Energy (DOE)
- NERC [NE/J009008/1, NE/I014381/1, NE/K004905/1] Funding Source: UKRI
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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 lifet-ime 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.
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