CaltechAUTHORS
Published August 1, 2017 | Version Supplemental Material + Published
Journal Article Open

Reassessing the atmospheric oxidation mechanism of toluene

Creators

  • 1. ROR icon Guangdong University of Technology
  • 2. ROR icon Texas A&M University
  • 3. ROR icon Sun Yat-sen University
  • 4. ROR icon California Institute of Technology
  • 5. ROR icon East China University of Science and Technology
  • 6. ROR icon Beijing Normal University
  • 7. ROR icon Zhongkai University of Agriculture and Engineering
  • 8. ROR icon The University of Texas at Austin
  • 9. ROR icon University of California, San Diego

Abstract

Photochemical oxidation of aromatic hydrocarbons leads to tropospheric ozone and secondary organic aerosol (SOA) formation, with profound implications for air quality, human health, and climate. Toluene is the most abundant aromatic compound under urban environments, but its detailed chemical oxidation mechanism remains uncertain. From combined laboratory experiments and quantum chemical calculations, we show a toluene oxidation mechanism that is different from the one adopted in current atmospheric models. Our experimental work indicates a larger-than-expected branching ratio for cresols, but a negligible formation of ring-opening products (e.g., methylglyoxal). Quantum chemical calculations also demonstrate that cresols are much more stable than their corresponding peroxy radicals, and, for the most favorable OH (ortho) addition, the pathway of H extraction by O_2 to form the cresol proceeds with a smaller barrier than O_2 addition to form the peroxy radical. Our results reveal that phenolic (rather than peroxy radical) formation represents the dominant pathway for toluene oxidation, highlighting the necessity to reassess its role in ozone and SOA formation in the atmosphere.

Additional Information

© 2017 National Academy of Sciences. Freely available online through the PNAS open access option. Contributed by Mario J. Molina, June 8, 2017 (sent for review April 3, 2017; reviewed by Sasha Madronich and Fangqun Yu). Published online before print July 17, 2017. This work was supported by National Natural Science Foundation of China (Grants 41675122, 41373102, 21577177, and 41425015), Science and Technology Program of Guangzhou City (Grant 201707010188), the Robert A. Welch Foundation (Grant A-1417), the Ministry of Science and Technology of China (Grant 2013CB955800), and a collaborative research program between Texas A&M University and the National Natural Science Foundation of China. B.P. was supported by a NASA Earth and Space Science Fellowship Program, and W.M.-O. was supported by the National Science Foundation Graduate Research Fellowship Program. Additional support for this research was provided by the Texas A&M University Supercomputing Facilities. The authors acknowledge the use of the Laboratory for Molecular Simulations at Texas A&M. Author contributions: Y.J. and R.Z. designed research; Y.J., J.Z., H.T., K.M., N.P.L., Y. Li, Y. Lin, J.P., Y.W., L.D., B.P., F.Z., X.F., T.A., W.M.-O., J.S., A.L.Z., K.S., and R.Z. performed research; M.J.M. and R.Z. contributed new reagents/analytic tools; Y.J., M.J.M., and R.Z. analyzed data; and Y.J., J.Z., and R.Z. wrote the paper. Reviewers: S.M., National Center for Atmospheric Research; and F.Y., State University of New York at Albany. The authors declare no conflict of interest. This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1705463114/-/DCSupplemental.

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Published - PNAS-2017-Ji-8169-74.pdf

Supplemental Material - pnas.1705463114.sapp.pdf

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Additional details

Identifiers

PMCID
PMC5547634
Eprint ID
79149
DOI
10.1073/pnas.1705463114
Resolver ID
CaltechAUTHORS:20170718-101050720

Funding

National Natural Science Foundation of China
41675122
National Natural Science Foundation of China
41373102
National Natural Science Foundation of China
21577177
National Natural Science Foundation of China
41425015
Guangzhou City
201707010188
Robert A. Welch Foundation
A-1417
Ministry of Science and Technology of China
2013CB955800
Texas A&M University
NASA Earth and Space Science Fellowship

Dates

Created
2017-07-18
Created from EPrint's datestamp field
Updated
2022-03-23
Created from EPrint's last_modified field