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Isoprene photochemistry over the Amazon rainforest

Liu, Yingjun and Brito, Joel and Dorris, Matthew R. and Rivera-Rios, Jean C. and Seco, Roger and Bates, Kelvin H. and Artaxo, Paulo and Duvoisin, Sergio, Jr. and Keutsch, Frank N. and Kim, Saewung and Goldstein, Allen H. and Guenther, Alex B. and Manzi, Antonio O. and Souza, Rodrigo A. F. and Springston, Stephen R. and Watson, Thomas B. and McKinney, Karena A. and Martin, Scot T. (2016) Isoprene photochemistry over the Amazon rainforest. Proceedings of the National Academy of Sciences of the United States of America, 113 (22). pp. 6125-6130. ISSN 0027-8424. PMCID PMC4896701.

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Isoprene photooxidation is a major driver of atmospheric chemistry over forested regions. Isoprene reacts with hydroxyl radicals (OH) and molecular oxygen to produce isoprene peroxy radicals (ISOPOO). These radicals can react with hydroperoxyl radicals (HO_2) to dominantly produce hydroxyhydroperoxides (ISOPOOH). They can also react with nitric oxide (NO) to largely produce methyl vinyl ketone (MVK) and methacrolein (MACR). Unimolecular isomerization and bimolecular reactions with organic peroxy radicals are also possible. There is uncertainty about the relative importance of each of these pathways in the atmosphere and possible changes because of anthropogenic pollution. Herein, measurements of ISOPOOH and MVK + MACR concentrations are reported over the central region of the Amazon basin during the wet season. The research site, downwind of an urban region, intercepted both background and polluted air masses during the GoAmazon2014/5 Experiment. Under background conditions, the confidence interval for the ratio of the ISOPOOH concentration to that of MVK + MACR spanned 0.4–0.6. This result implies a ratio of the reaction rate of ISOPOO with HO_2 to that with NO of approximately unity. A value of unity is significantly smaller than simulated at present by global chemical transport models for this important, nominally low-NO, forested region of Earth. Under polluted conditions, when the concentrations of reactive nitrogen compounds were high (>1 ppb), ISOPOOH concentrations dropped below the instrumental detection limit (<60 ppt). This abrupt shift in isoprene photooxidation, sparked by human activities, speaks to ongoing and possible future changes in the photochemistry active over the Amazon rainforest.

Item Type:Article
Related URLs:
URLURL TypeDescription Information CentralArticle
Bates, Kelvin H.0000-0001-7544-9580
Goldstein, Allen H.0000-0003-4014-4896
Guenther, Alex B.0000-0001-6283-8288
McKinney, Karena A.0000-0003-1129-1678
Additional Information:© 2016 National Academy of Sciences. Edited by Mark H. Thiemens, University of California, San Diego, La Jolla, CA, and approved April 13, 2016 (received for review December 23, 2015). Published online before print May 16, 2016. We thank John Crounse and Paul Wennberg for supporting GEOS-Chem simulations. We thank Ronald Cohen and Yi Li for helpful discussions. Institutional support was provided by the Central Office of the Large Scale Biosphere Atmosphere Experiment in Amazonia (LBA), the National Institute of Amazonian Research (INPA), and Amazonas State University (UEA). We acknowledge the Atmospheric Radiation Measurement (ARM) Climate Research Facility, a user facility of the United States Department of Energy, Office of Science, sponsored by the Office of Biological and Environmental Research, and support from the Atmospheric System Research (ASR) program of that office. Funding was obtained from the United States Department of Energy (DOE), the Amazonas State Research Foundation (FAPEAM), the São Paulo Research Foundation (FAPESP), the Brazilian Scientific Mobility Program (CsF/CAPES), and the United States National Science Foundation (NSF). The research was conducted under Scientific License 001030/2012-4 of the Brazilian National Council for Scientific and Technological Development (CNPq). Author contributions: Y.L., P.A., F.N.K., A.H.G., A.B.G., A.O.M., R.A.F.S., K.A.M., and S.T.M. designed the research; Y.L., J.B., M.R.D., J.C.R., R.S., K.H.B., S.D., S.K., S.R.S., and T.B.W. performed the research; Y.L., K.A.M., and S.T.M. analyzed the data; and Y.L., K.A.M., and S.T.M. wrote the paper. The authors declare no conflict of interest. This article is a PNAS Direct Submission. This article contains supporting information online at
Funding AgencyGrant Number
Department of Energy (DOE)UNSPECIFIED
Fundação de Amparo à Pesquisa do Estado do Amazonas (FAPEAM)UNSPECIFIED
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)UNSPECIFIED
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)UNSPECIFIED
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)001030/2012-4
Subject Keywords:isoprene photochemistry; Amazon; organic hydroperoxides
Issue or Number:22
PubMed Central ID:PMC4896701
Record Number:CaltechAUTHORS:20160517-073919714
Persistent URL:
Official Citation:Yingjun Liu, Joel Brito, Matthew R. Dorris, Jean C. Rivera-Rios, Roger Seco, Kelvin H. Bates, Paulo Artaxo, Sergio Duvoisin Jr., Frank N. Keutsch, Saewung Kim, Allen H. Goldstein, Alex B. Guenther, Antonio O. Manzi, Rodrigo A. F. Souza, Stephen R. Springston, Thomas B. Watson, Karena A. McKinney, and Scot T. Martin Isoprene photochemistry over the Amazon rainforest PNAS 2016 113 (22) 6125-6130; published ahead of print May 16, 2016, doi:10.1073/pnas.1524136113
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:67147
Deposited By: Tony Diaz
Deposited On:17 May 2016 14:57
Last Modified:09 Mar 2020 13:19

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