AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
SOA Formation from OFR Oxidation of Rural and Urban Ambient Air Suggests Widespread Importance of S/IVOC Precursors
BRETT PALM, Amber Ortega, Weiwei Hu, Douglas Day, Pedro Campuzano-Jost, William Brune, Lisa Kaser, Thomas Karl, Hansel Armin, James Hunter, Eben Cross, Jesse Kroll, Martin Graus, Carsten Warneke, Jessica Gilman, Joost de Gouw, Suzane de Sá, Lizabeth Alexander, Scot Martin, Roger Seco, Jeong-Hoo Park, Alex Guenther, Saewung Kim, Jose-Luis Jimenez, et al., CIRES, University of Colorado
Abstract Number: 422 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Oxidation flow reactors (OFRs) are popular tools for studying secondary organic aerosol (SOA) formation from OH, O3, or NO3 radical oxidation in both laboratory and field experiments. With a several-minute residence time and a portable design with no inlet, OFRs are particularly suited for oxidizing ambient air to investigate in situ SOA formation from real ambient precursors. In recent years, OFRs have been used to produce SOA from a wide variety of environments, including a rural pine forest, a regionally polluted deciduous/coniferous forest, the Amazon rain forest, air influenced by biomass burning, and urban outflow. With a focus on OH oxidation experiments, we present a comparison of the SOA production from these contrasting sources. In all settings, the amount of SOA formed was typically larger at night than during the day. In forests, the amount of potential SOA formation after oxidation of ambient air correlated with biogenic precursors (e.g., monoterpenes). In urban air, potential SOA formation correlated instead with reactive anthropogenic tracers (e.g., trimethylbenzene). Despite these correlations, the SOA predicted to be formed by the oxidation of speciated ambient VOC concentrations could only explain approximately 10-50% of the total SOA formed from the oxidation of ambient air, regardless of location. Evidence suggests that lower-volatility gases (semivolatile and intermediate-volatility organic compounds; S/IVOCs) are present in ambient air and are a likely source of the SOA formation that can’t be explained by VOCs. These measurements show that S/IVOCs likely play an important intermediary role in ambient SOA formation in all of the sampled locations, from rural forests to urban air. Characteristics of the SOA formed from different air masses, e.g., H:C and O:C ratios of newly formed SOA as well as PMF factor analysis, will also be discussed.