AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Probing Complex Hydrocarbon Mixtures in Atmospheric Organic Aerosols: Insights into Sources and Mechanisms
ARTHUR CHAN, Gabriel Isaacman, David Worton, Chris Ruehl, Katherine Schilling, John Seinfeld, Kevin Wilson, Allen H. Goldstein, University of California, Berkeley
Abstract Number: 474 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Detailed speciation of organic compounds in ambient aerosol is often challenging owing to their complexity. In particular, a significant fraction of the hydrocarbons present in organic aerosol are not resolved by conventional gas chromatography (GC) techniques and show up in the so-called unresolved complex mixture (UCM). In this work, we combine the separation capabilities of comprehensive GCxGC with vacuum ultraviolet photoionization mass spectrometry (GCxGC/VUV-HRTOFMS) to analyze the composition of hydrocarbon mixtures in ambient aerosols. Using this technique, we are able to not only distinguish among compound classes (aliphatic, aromatic, oxygenated), but also resolve hydrocarbons in the UCM by their carbon number, branching and degree of unsaturation. Here we present analysis of aerosol filters collected from two different urban sites (Calnex LA and Bakersfield, 2010) and a rural site downwind of an urban area (BEARPEX 2009), and during a large biomass burning event (Station Fire 2009). The ratio of observed branched to straight-chain alkanes in the UCM was significantly higher in Bakersfield, CA than in Pasadena, CA (8.7-14.5 and 0.3-1.1, respectively) and can be explained by the difference in oxidation timescales between these two sites. The source of the UCM is shown to be related to motor vehicles based on isomer patterns. Since the UCM is a significant contributor to reduced organic aerosol (classified as HOA in aerosol mass spectrometry), these observations highlight the differences in the degree of processing of motor vehicle related emissions in these two sites. Also, semivolatile compounds observed during Station Fire contain many rings and double bonds owing to their terpenoid backbones. This results in good GCxGC separation from the alkanes found in the UCM and provides a unique signature of biomass burning aerosol in a 2-dimensional chromatogram.