Isoprene photo-oxidation products quantify the effect of pollution on hydroxyl radicals over Amazonia

Author(s):Show less -

Liu, Yingjun ^{[1, 2]} ; Seco, Roger ^[3] ; Kim, Saewung ^[3] ; Guenther, Alex B. ^[3] ; Goldstein, Allen H. ^[1] ; Keutsch, Frank N. ^{[2, 4]} ; Springston, Stephen R. ^[5] ; Watson, Thomas B. ^[5] ; Artaxo, Paulo ^[6] ; Souza, Rodrigo A. F. ^[7] ; McKinney, Karena A. ^{[2, 8]} ; Martin, Scot T. ^{[2, 9]}

Affiliation

^[1] Univ Calif Berkeley, Dept Environm Sci Policy & Management, Berkeley, CA 94720 - USA

^[2] Harvard Univ, Sch Engn & Appl Sci, Cambridge, MA 02138 - USA

^[3] Univ Calif Irvine, Dept Earth Syst Sci, Irvine, CA 92697 - USA

^[4] Harvard Univ, Dept Chem & Chem Biol, Cambridge, MA 02138 - USA

^[5] Brookhaven Natl Lab, Dept Environm & Climate Sci, Upton, NY 11973 - USA

^[6] Univ Sao Paulo, Dept Appl Phys, BR-05508 Sao Paulo - Brazil

^[7] Amazonas State Univ, Dept Appl Phys, BR-69050 Manaus, Amazonas - Brazil

^[8] Colby Coll, Dept Chem, Waterville, ME 04901 - USA

^[9] Harvard Univ, Dept Earth & Planetary Sci, Cambridge, MA 02138 - USA

• Document type: Journal article
• Source: SCIENCE ADVANCES; v. 4, n. 4 APR 2018.
• Web of Science Citations: 5

Abstract

Nitrogen oxides (NOx) emitted from human activities are believed to regulate the atmospheric oxidation capacity of the troposphere. However, observational evidence is limited for the low-to-median NOx concentrations prevalent outside of polluted regions. Directly measuring oxidation capacity, represented primarily by hydroxyl radicals (OH), is challenging, and the span in NOx concentrations at a single observation site is often not wide. Concentrations of isoprene and its photo-oxidation products were used to infer the equivalent noontime OH concentrations. The fetch at an observation site in central Amazonia experienced varied contributions from background regional air, urban pollution, and biomass burning. The afternoon concentrations of reactive nitrogen oxides (NOy), indicative of NOx exposure during the preceding few hours, spanned from 0.3 to 3.5 parts per billion. Accompanying the increase of NOy concentration, the inferred equivalent noontime OH concentrations increased by at least 250% from 0.6 x 10(6) to 1.6 x 10(6) cm(-3). The conclusion is that, compared to background conditions of low NOx concentrations over the Amazon forest, pollution increased NOx concentrations and amplified OH concentrations, indicating the susceptibility of the atmospheric oxidation capacity over the forest to anthropogenic influence and reinforcing the important role of NOx in sustaining OH concentrations. (AU)

• FAPESP's process: 17/17047-0 - Aerosol and clouds life cycles in Amazonia: biogenic emissions, biomass burning and impacts on ecosystem
• Grantee: Paulo Eduardo Artaxo Netto
• Support Opportunities: Research Program on Global Climate Change - Thematic Grants