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Title: Isoprene photochemistry over the Amazon rainforest

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:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [2] ;  [7] ;  [8] ;  [5] ;  [9] ;  [10] ;  [11] ;  [12] ;  [13] ;  [13] ;  [1] ;  [14]
  1. Harvard Univ., Cambridge, MA (United States). John A. Paulson School of Engineering and Applied Sciences
  2. Univ. of Sao Paulo (Brazil). Department of Applied Physics
  3. University of Wisconsin-Madison, Madison, WI (United States). Department of Chemistry
  4. University of Wisconsin-Madison, Madison, WI (United States). Department of Chemistry ; Harvard Univ., Cambridge, MA (United States). Department of Chemistry and Chemical Biology
  5. Univ. of California, Irvine, CA (United States). Department of Earth System Science
  6. California Inst. of Technology (CalTech), Pasadena, CA (United States). Division of Chemistry and Chemical Engineering
  7. Universidade do Estado do Amazonas, Manaus (Brazil). Department of Chemistry
  8. Harvard Univ., Cambridge, MA (United States). John A. Paulson School of Engineering and Applied Sciences; University of Wisconsin-Madison, Madison, WI (United States). Department of Chemistry; Harvard Univ., Cambridge, MA (United States). Department of Chemistry and Chemical Biology
  9. Univ. of California, Berkeley, CA (United States). Department of Environmental Science, Policy, and Management
  10. Univ. of California, Irvine, CA (United States). epartment of Earth System Science; Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  11. Instituto Nacional de Pesquisas da Amazonia, Manaus (Brazil)
  12. Universidade do Estado do Amazonas, Manaus (Brazil). Department of Meteorology
  13. Brookhaven National Lab. (BNL), Upton, NY (United States). Biological, Environmental & Climate Sciences Dept.
  14. Harvard Univ., Cambridge, MA (United States). John A. Paulson School of Engineering and Applied Sciences ; Harvard Univ., Cambridge, MA (United States). Department of Earth and Planetary Sciences
Publication Date:
Report Number(s):
BNL-112478-2016-JA
Journal ID: ISSN 0027-8424; R&D Project: 2016-BNL-EE630EECA-Budg; KP1701000
Grant/Contract Number:
SC00112704; 0
Type:
Published Article
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 113; Journal Issue: 22; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; isoprene photochemistry; Amazon; organic hydroperoxides
OSTI Identifier:
1253389
Alternate Identifier(s):
OSTI ID: 1336083