Tracking anthropogenic influence on isoprene chemistry over Amazonia

Monday, 15 December 2014: 2:40 PM
Yingjun Liu1, Karena A McKinney1, Thomas B Watson2, Stephen R. Springston2, Roger Seco3, Jeong-Hoo Park4, Saewung Kim3, John E Shilling5, Alex B Guenther5, Matthew Ryan Dorris6, Mitchell Thayer6, Frank N Keutsch6, Lindsay Yee7, Gabriel A Isaacman7, Allen H Goldstein7, Florian Wurm8, Joel Ferreira De Brito8, Paulo Artaxo8, Maria A. F. Silva Dias8, Karla Longo9, Rodrigo Augusto Ferreira de Souza10, Antonio O Manzi11 and Scot T Martin1, (1)Harvard University, Cambridge, MA, United States, (2)Brookhaven National Laboratory, Upton, NY, United States, (3)University of California Irvine, Irvine, CA, United States, (4)National Center for Atmospheric Research, Boulder, CO, United States, (5)Pacific Northwest National Laboratory, Richland, WA, United States, (6)University of Wisconsin Madison, Madison, WI, United States, (7)University of California Berkeley, Berkeley, CA, United States, (8)USP University of Sao Paulo, São Paulo, Brazil, (9)INPE National Institute for Space Research, Sao Jose dos Campos, Brazil, (10)Organization Not Listed, Washington, DC, United States, (11)National Institute for Amazon Research (INPA), Manaus, AM, Brazil
Primarily emitted by vegetation, isoprene is the dominant nonmethane hydrocarbon in the atmosphere. Photooxidation of isoprene has a large influence on the oxidation capacity of the atmosphere and the production of secondary organic aerosol (SOA). As a part of the GoAmazon2014 Experiment, isoprene and some of its oxidation products were measured using a proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS) at a research site 60 km west of the city of Manaus, Brazil. The fetch of the research site oscillated between the extremes of a pristine atmosphere and the interactions of heavy pollution from Manaus with the natural environment, which allowed for an assessment of the modifications of natural isoprene chemistry by anthropogenic pollution over Amazonia. Photooxidation of isoprene leads to chemically different oxidation products depending on the fate of isoprene peroxy radicals (ISOPOO), but different oxidation products can produce the same ions in PTR-MS analysis due to similarity in their chemical structures. A cold trap was deployed in front of the PTR-TOF-MS for separation and differential classification of some of these isoprene oxidation products. For example, isoprene-derived hydroperoxides (C5H10O3) and methyl vinyl ketone/methacrolein (C4H6O), which are the major oxidation products of the HO2 and NO pathways of ISOPOO reaction, respectively, and both detected as C4H7O+ ion by PTR-MS, were separately measured. Using the measurements of these and other oxidation products of isoprene by PTR-TOF-MS and other complementary measurements, the isoprene chemistry (particularly the fate of ISOPOO) under pristine and polluted scenarios are compared and the implication for SOA formation is discussed.