AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Organic Aerosol Composition, Sources, and Modeling for Los Angeles during the 2010 CalNex Campaign
Patrick Hayes, JOSE-LUIS JIMENEZ, Michael Cubison, Amber Ortega, James Allan, Jessica Gilman, William C. Kuster, Joost de Gouw, Gabriel Isaacman, David Worton, Nathan Kreisberg, Susanne Hering, Allen H. Goldstein, Rebecca Washenfelder, Jonathan Taylor, Rainer Volkamer, Eleanor Waxman, Ryan Thalman, Rodney Weber, Xiaolu Zhang, et al., University of Colorado
Abstract Number: 660 Working Group: Urban Aerosols
Abstract Data from an HR-ToF-AMS and complementary instrumentation are used to characterize organic aerosol (OA) during the CalNex-Los Angeles campaign. Positive matrix factorization (PMF) identifies hydrocarbon-like OA (HOA), cooking-influenced OA (CIOA), semi-volatile oxygenated OA (SV-OOA), low-volatility oxygenated OA (LV-OOA), and local OA (LOA), which contains prominent amine fragments. The correlations of the PMF components with tracers and photochemical age indicate that, similar to previous work, HOA is a surrogate for primary organic aerosol from combustion sources, and the OOA components are dominated by secondary organic aerosols (SOA). The HOA and BC concentrations exhibit weekly cycles with substantially lower concentrations on Sundays versus weekdays that are quantitatively consistent with the reductions in diesel emissions during weekends, while OOA does not appear to vary, consistent with recent results indicating the dominance of gasoline emissions on SOA formation. The OOA to odd-oxygen (O3 + NO2) ratios for Pasadena are similar to those observed in Riverside and Mexico City, which suggests that the relative SOA vs. odd-oxygen formation efficiencies are similar at the different sites. In addition, the dilution-corrected OA enhancements for the Pasadena ground site increase with photochemical age and are similar to or slightly higher than analogous data from Mexico City and northeastern United States. The OA elemental composition evolves in a Van Krevelen diagram (H:C vs. O:C) with a slope of -0.6, which confirms that the aging of ambient OOA follows a slope considerably shallower than -1, and near -0.5. A box model of SOA formation along in-basin trajectories is implemented following Washenfelder et al. (JGR 2011), and constrained with VOC and oxidant measurements. SOA formation is an order of magnitude larger than can be explained with aromatic precursors, as observed in many other urban areas. Results for other sets of precursors such as S/IVOCs will also be presented.