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Title: The reaction of hydroxyl and methylperoxy radicals is not a major source of atmospheric methanol

Abstract

Methanol is a benchmark for understanding tropospheric oxidation, but is underpredicted by up to 100% in atmospheric models. Recent work has suggested this discrepancy can be reconciled by the rapid reaction of hydroxyl and methylperoxy radicals with a methanol branching fraction of 30%. However, for fractions below 15%, methanol underprediction is exacerbated. Theoretical investigations of this reaction are challenging because of intersystem crossing between singlet and triplet surfaces – ~45% of reaction products are obtained via intersystem crossing of a pre-product complex – which demands experimental determinations of product branching. Here we report direct measurements of methanol from this reaction. A branching fraction below 15% is established, consequently highlighting a large gap in the understanding of global methanol sources. These results support the recent high-level theoretical work and substantially reduce its uncertainties.

Authors:
ORCiD logo [1]; ORCiD logo [2];  [1];  [1];  [1]; ORCiD logo [1];  [1];  [1];  [1];  [1]; ORCiD logo [1]; ORCiD logo [3];  [3];  [4];  [4];  [4];  [4];  [5];  [2]; ORCiD logo [1]
  1. Sandia National Lab. (SNL-CA), Livermore, CA (United States)
  2. Bristol Univ. (United Kingdom)
  3. Université Lille, CNRS, UMR (France)
  4. Université Lille (France)
  5. California Inst. of Technology (CalTech), La Canada Flintridge, CA (United States). Jet Propulsion Lab.
Publication Date:
Research Org.:
Sandia National Lab. (SNL-CA), Livermore, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division; USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1483975
Report Number(s):
SAND-2018-11575J
Journal ID: ISSN 2041-1723; 669351
Grant/Contract Number:  
AC04-94AL85000; NA0003525; AC02-05CH11231
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nature Communications
Additional Journal Information:
Journal Volume: 9; Journal Issue: 1; Journal ID: ISSN 2041-1723
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Caravan, Rebecca L., Khan, M. Anwar H., Zádor, Judit, Sheps, Leonid, Antonov, Ivan O., Rotavera, Brandon, Ramasesha, Krupa, Au, Kendrew, Chen, Ming-Wei, Rösch, Daniel, Osborn, David L., Fittschen, Christa, Schoemaecker, Coralie, Duncianu, Marius, Grira, Asma, Dusanter, Sebastien, Tomas, Alexandre, Percival, Carl J., Shallcross, Dudley E., and Taatjes, Craig A. The reaction of hydroxyl and methylperoxy radicals is not a major source of atmospheric methanol. United States: N. p., 2018. Web. doi:10.1038/s41467-018-06716-x.
Caravan, Rebecca L., Khan, M. Anwar H., Zádor, Judit, Sheps, Leonid, Antonov, Ivan O., Rotavera, Brandon, Ramasesha, Krupa, Au, Kendrew, Chen, Ming-Wei, Rösch, Daniel, Osborn, David L., Fittschen, Christa, Schoemaecker, Coralie, Duncianu, Marius, Grira, Asma, Dusanter, Sebastien, Tomas, Alexandre, Percival, Carl J., Shallcross, Dudley E., & Taatjes, Craig A. The reaction of hydroxyl and methylperoxy radicals is not a major source of atmospheric methanol. United States. doi:10.1038/s41467-018-06716-x.
Caravan, Rebecca L., Khan, M. Anwar H., Zádor, Judit, Sheps, Leonid, Antonov, Ivan O., Rotavera, Brandon, Ramasesha, Krupa, Au, Kendrew, Chen, Ming-Wei, Rösch, Daniel, Osborn, David L., Fittschen, Christa, Schoemaecker, Coralie, Duncianu, Marius, Grira, Asma, Dusanter, Sebastien, Tomas, Alexandre, Percival, Carl J., Shallcross, Dudley E., and Taatjes, Craig A. Fri . "The reaction of hydroxyl and methylperoxy radicals is not a major source of atmospheric methanol". United States. doi:10.1038/s41467-018-06716-x. https://www.osti.gov/servlets/purl/1483975.
@article{osti_1483975,
title = {The reaction of hydroxyl and methylperoxy radicals is not a major source of atmospheric methanol},
author = {Caravan, Rebecca L. and Khan, M. Anwar H. and Zádor, Judit and Sheps, Leonid and Antonov, Ivan O. and Rotavera, Brandon and Ramasesha, Krupa and Au, Kendrew and Chen, Ming-Wei and Rösch, Daniel and Osborn, David L. and Fittschen, Christa and Schoemaecker, Coralie and Duncianu, Marius and Grira, Asma and Dusanter, Sebastien and Tomas, Alexandre and Percival, Carl J. and Shallcross, Dudley E. and Taatjes, Craig A.},
abstractNote = {Methanol is a benchmark for understanding tropospheric oxidation, but is underpredicted by up to 100% in atmospheric models. Recent work has suggested this discrepancy can be reconciled by the rapid reaction of hydroxyl and methylperoxy radicals with a methanol branching fraction of 30%. However, for fractions below 15%, methanol underprediction is exacerbated. Theoretical investigations of this reaction are challenging because of intersystem crossing between singlet and triplet surfaces – ~45% of reaction products are obtained via intersystem crossing of a pre-product complex – which demands experimental determinations of product branching. Here we report direct measurements of methanol from this reaction. A branching fraction below 15% is established, consequently highlighting a large gap in the understanding of global methanol sources. These results support the recent high-level theoretical work and substantially reduce its uncertainties.},
doi = {10.1038/s41467-018-06716-x},
journal = {Nature Communications},
issn = {2041-1723},
number = 1,
volume = 9,
place = {United States},
year = {2018},
month = {10}
}

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Figures / Tables:

Figure 1 Figure 1: Formaldehyde and methanol time profiles from the methylperoxy self- and hydroxyl reactions. Comparison of the contributions from 13CH3OO selfreaction and reaction of 13CH3OO with OH in producing methanol in the photolysis experiments at P= 30 Torr. a CH3OO self-reaction (photolysis of 13CH3I in the presence of O2) comparedmore » to a kinetic model employing literature rate coefficients and directly measured reactant concentrations, wall loss and two fits to the photolytic depletion. b Measurements at the same conditions as (a) except with the addition of H2O2. The contribution from 13CH3OO self-reaction is represented by the signal from another product at m/z= 64, 13CH3OO13CH3 (formed only by the self-reaction), scaled using directly measured branching fractions of the self-reaction. The additional, rapidly formed 13CH3OH arises from the reactions of 13CH3OO with OH and 13CH3O with HO2. The temporal resolution of the methanol and CH3OOCH3 signals is here reduced by a factor of five to more clearly show the amplitudes« less

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Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.