Measurements of in-situ SOA Formation and Chemistry Using an Oxidation Flow Reactor at GoAmazon2014 and Other Campaigns

Tuesday, 16 December 2014
Brett B Palm1,2, Pedro Campuzano Jost1,2, Douglas A Day2,3, Weiwei Hu1,2, Amber M Ortega1,2, Suzane S. de Sá4, Roger Seco5, Jeong-Hoo Park6, Alex B Guenther7, Saewung Kim8, Joel Ferreira De Brito9, Florian Wurm9, Paulo Artaxo9, Ryan M Thalman10, Jian Wang11, Lina Hacker12, Astrid Kiendler-Scharr12, Lindsay Yee13, Gabriel A Isaacman13, Allen H Goldstein13, Rodrigo Augusto Ferreira de Souza14, Antonio O Manzi15, Oscar Vega16, Julio Tota17, Matt K Newburn18, M. Lizabeth Alexander7, Scot T Martin4, William H Brune19 and Jose L Jimenez1,2, (1)University of Colorado at Boulder, Boulder, CO, United States, (2)Cooperative Institute for Research in Environmental Sciences, Boulder, CO, United States, (3)University of Colorado at Boulder, Dept. of Chemistry and Biochemistry, Boulder, CO, United States, (4)Harvard University, Cambridge, MA, United States, (5)University of California Irvine, Department of Earth System Science, Irvine, CA, United States, (6)National Center for Atmospheric Research, Boulder, CO, United States, (7)Pacific Northwest National Laboratory, Richland, WA, United States, (8)University of California Irvine, Irvine, CA, United States, (9)USP University of Sao Paulo, São Paulo, Brazil, (10)Brookhaven National Laboratory, Upton, NY, United States, (11)Brookhaven Natl Lab, Upton, NY, United States, (12)Forschungszentrum Jülich, Institute for Energy and Climate Research: Troposphere (IEK-8), Jülich, Germany, (13)University of California Berkeley, Berkeley, CA, United States, (14)Universidade do Estado do Amazonas, Manaus, AM, Brazil, (15)Instituto Nacional de Pesquisas da Amazônia, Manaus, Brazil, (16)IPEN Nuclear Energy Research Institute, Sao Paulo, Brazil, (17)Federal University of Western Para, Santarem, Brazil, (18)Pacific Northwest National Laboratory, Environmental Molecular Sciences Laboratory, Richland, WA, United States, (19)Pennsylvania State University Main Campus, University Park, PA, United States
During several recent field campaigns including GoAmazon2014, ambient gases and particles were exposed to controlled concentrations of OH, O3 or NO3 in-situ using a Potential Aerosol Mass oxidation flow reactor. Oxidant exposure in the reactor ranged from an hour to several weeks of equivalent atmospheric residence time, allowing the study of SOA formation and chemistry over long time scales. Oxidized air from the reactor was sampled directly (e.g., HR-AMS, ACSM, PTR-TOFMS, SMPS, CCN), and these results were compared with collocated biogenic and anthropogenic tracers (e.g., SV-TAG sesquiterpenes and PTR-TOFMS aromatics, isoprene, and monoterpenes). In all studies, OH oxidation of ambient air in the reactor led to substantial SOA mass production (often several µg/m3 of SOA) during times of high precursor gas concentrations. While SOA production correlated with measured gas-phase precursors, the total mass formed in the reactor was generally several times larger than could be explained by the aerosol yields of measured VOC’s. This suggests that a majority of gases that formed SOA in the reactor were not the primary VOCs considered as traditional SOA precursors. Additionally, most of the SOA mass increase occurred in the first day of equiv. atmospheric aging, suggesting that ambient SOA is predominantly formed close to emission sources of precursors with gas-phase reaction lifetimes of <1 day. At a remote Colorado pine forest site (during BEACHON-RoMBAS), the mainly biogenic aerosol formed in the reactor from <1 equivalent day of oxidation had an atomic O:C of 0.54, similar to the existing ambient aerosol O:C of 0.61. As OH exposures increased (up to 10-20 equivalent days), the OA became highly oxidized (O:C>1) and partially revolatilized, demonstrating the competing effects of functionalization/condensation at low exposures vs. fragmentation/evaporation reactions for high exposures. SOA formation from O3 and NOoxidation correlated with biogenic gas-phase precursors, but led to smaller (<0.5 µg/m3) SOA production, consistent with the ability for OH to achieve more generations of oxidation than O3 or NO3. Measurements taken in a variety of biogenic ecosystems with a wide range of anthropogenic influence were compared, allowing investigation of the effects of anthropogenic pollution on SOA formation.