Title: Isoprene photochemistry over the Amazon rainforest

Abstract

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 (HO₂) 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 HO2 to that with NO of approximately unity. Also, a value of unity is significantly smaller than simulated at present by global chemical transport models for this important, nominally low-NO, forested region ofmore » 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). In conclusion, 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.« less

Authors:

Liu, Yingjun ^[1]; Brito, Joel ^[2]; Dorris, Matthew R. ^[3]; Rivera-Rios, Jean C. ^[4]; Seco, Roger ^[5]; Bates, Kelvin H. ^[6]; Artaxo, Paulo ^[2]; Duvoisin, Jr., Sergio ^[7]; Keutsch, Frank N. ^[8]; Kim, Saewung ^[5]; Goldstein, Allen H. ^[9]; Guenther, Alex B. ^[10]; Manzi, Antonio O. ^[11]; Souza, Rodrigo A. F. ^[12]; Springston, Stephen R. ^[13]; Watson, Thomas B. ^[13]; McKinney, Karena A. ^[1]; Martin, Scot T.  ^[14]

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+ Show Author Affiliations

1. John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138,
2. Department of Applied Physics, University of São Paulo, São Paulo 05508, Brazil,
3. Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706,
4. Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706,, Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138,
5. Department of Earth System Science, University of California, Irvine, CA 92697,
6. Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125,
7. Department of Chemistry, Universidade do Estado do Amazonas, Manaus, AM 69050, Brazil,
8. John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138,, Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706,, Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138,
9. Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA 94720,
10. Department of Earth System Science, University of California, Irvine, CA 92697,, Pacific Northwest National Laboratory, Richland, WA 99354,
11. Instituto Nacional de Pesquisas da Amazonia, Manaus, AM 69067, Brazil,
12. Department of Meteorology, Universidade do Estado do Amazonas, Manaus, AM 69050, Brazil,
13. Department of Environmental and Climate Sciences, Brookhaven National Laboratory, Upton, NY 11973,
14. John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138,, Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138

Publication Date:

Mon May 16 00:00:00 EDT 2016

Research Org.:

Brookhaven National Laboratory (BNL), Upton, NY (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER)

OSTI Identifier:

1253389

Alternate Identifier(s):

OSTI ID: 1336083

Report Number(s):

BNL-112478-2016-JA
Journal ID: ISSN 0027-8424

Grant/Contract Number:  

0; SC00112704

Resource Type:

Published Article

Journal Name:

Proceedings of the National Academy of Sciences of the United States of America

Additional Journal Information:

Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Volume: 113 Journal Issue: 22; Journal ID: ISSN 0027-8424

Publisher:

Proceedings of the National Academy of Sciences

Country of Publication:

United States

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES; isoprene photochemistry; Amazon; organic hydroperoxides