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Reassessing the atmospheric oxidation mechanism of toluene

Ji, Yuemeng and Zhao, Jun and Terazono, Hajime and Misawa, Kentaro and Levitt, Nicholas P. and Li, Yixin and Lin, Yun and Peng, Jianfei and Wang, Yuan and Duan, Lian and Pan, Bowen and Zhang, Fang and Feng, Xidan and An, Taicheng and Marrero-Ortiz, Wilmarie and Secrest, Jeremiah and Zhang, Annie L. and Shibuya, Kazuhiko and Molina, Mario J. and Zhang, Renyi (2017) Reassessing the atmospheric oxidation mechanism of toluene. Proceedings of the National Academy of Sciences of the United States of America, 114 (31). pp. 8169-8174. ISSN 0027-8424. PMCID PMC5547634. http://resolver.caltech.edu/CaltechAUTHORS:20170718-101050720

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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.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1073/pnas.1705463114DOIArticle
http://www.pnas.org/content/114/31/8169PublisherArticle
http://www.pnas.org/lookup/suppl/doi:10.1073/pnas.1705463114/-/DCSupplementalPublisherSupporting Information
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5547634/PubMed CentralArticle
ORCID:
AuthorORCID
Molina, Mario J.0000-0003-2339-3225
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.
Funders:
Funding AgencyGrant Number
National Natural Science Foundation of China41675122
National Natural Science Foundation of China41373102
National Natural Science Foundation of China21577177
National Natural Science Foundation of China41425015
Guangzhou City201707010188
Robert A. Welch FoundationA-1417
Ministry of Science and Technology of China2013CB955800
Texas A&M UniversityUNSPECIFIED
NASA Earth and Space Science FellowshipUNSPECIFIED
Subject Keywords:aromatics; oxidation; ozone; secondary organic aerosol; air pollution
PubMed Central ID:PMC5547634
Record Number:CaltechAUTHORS:20170718-101050720
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20170718-101050720
Official Citation:Yuemeng Ji, Jun Zhao, Hajime Terazono, Kentaro Misawa, Nicholas P. Levitt, Yixin Li, Yun Lin, Jianfei Peng, Yuan Wang, Lian Duan, Bowen Pan, Fang Zhang, Xidan Feng, Taicheng An, Wilmarie Marrero-Ortiz, Jeremiah Secrest, Annie L. Zhang, Kazuhiko Shibuya, Mario J. Molina, and Renyi Zhang Reassessing the atmospheric oxidation mechanism of toluene PNAS 2017 114 (31) 8169-8174; published ahead of print July 17, 2017, doi:10.1073/pnas.1705463114
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:79149
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:18 Jul 2017 18:07
Last Modified:14 Aug 2017 01:01

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