American Association for Aerosol Research - Abstract Submission

AAAR 36th Annual Conference
October 16 - October 20, 2017
Raleigh Convention Center
Raleigh, North Carolina, USA

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Secondary Organic Aerosol Formation from Ambient Air in an Oxidation Flow Reactor at GoAmazon2014/5

BRETT PALM, Suzane de Sá, Douglas Day, Pedro Campuzano-Jost, Weiwei Hu, Roger Seco, Steve Sjostedt, Alex Guenther, Saewung Kim, Joel Brito, Florian Wurm, Paulo Artaxo, Lindsay Yee, Rebecca Wernis, Gabriel Isaacman-VanWertz, Allen H. Goldstein, Ryan Thalman, Jian Wang, Yingjun Liu, Stephen Springston, Rodrigo A. F. Souza, Lizabeth Alexander, Scot Martin, Jose-Luis Jimenez, et al., CIRES, University of Colorado

     Abstract Number: 234
     Working Group: Aerosol Chemistry

Abstract
Secondary organic aerosol (SOA) formation from the oxidation of ambient air was studied using an oxidation flow reactor (OFR) during both the wet and dry seasons at the GoAmazon2014/5 field campaign. Ambient air was oxidized using variable concentrations of either OH or O3, over ranges from hours to days (O3) or to weeks (OH) of equivalent atmospheric aging. The measured SOA formation from ambient air was compared to the amount predicted from the concentrations of measured ambient SOA precursors and their SOA yields. While measured precursor concentrations were generally sufficient to explain the amount of SOA formed from O3, they could only explain 10–50% of the SOA formed from OH. Previous OFR studies have shown that typically unmeasured semivolatile and intermediate volatility gases (S/IVOCs) are present in ambient air and can explain such additional SOA formation. To investigate the sources of SOA-forming gases (including unmeasured S/IVOCs) during this campaign, multilinear regression analysis was performed between measured SOA formation and gas-phase tracers representing different precursor sources. The observed potential for SOA formation was attributed roughly 50% (69%), 46% (13%), and 3% (18%) to biogenic, anthropogenic, and biomass burning emissions during the wet (dry) season. The comparisons and contrasts between the results in the wet and dry seasons will be discussed, and the strength of these conclusions will be evaluated in context of all available information. SOA yields of individual VOCs under OFR conditions were measured by standard addition into ambient air, and the yields were consistent with published environmental chamber-derived SOA yields. Also, the CCN activity of the OH-aged aerosol was measured while sampling under two types of conditions: where the measurements were dominated by new SOA formation in the OFR (~1–3 equivalent atmospheric days OH aging), or dominated by heterogeneous oxidation of pre-existing OA (~several equivalent weeks OH aging).