1Dept. of Environmental Science, Policy, & Management, University of California, 147 Mulford Hall, Berkeley, CA, USA
2Center for Aerosol and Cloud Chemistry, Aerodyne Research Inc., 45 Manning Rd., Billerica, MA, USA
3Dept. of Mechanical Engineering, University of Minnesota, 271 Mechanical Engineering, 111 Church Street S.E., Minneapolis, MN, USA
4Dept. of Energy, Environmental, and Chemical Engineering, Washington University in St. Louis, 3026 Brauer Hall, St. Louis, MO, USA
5Dept. of Civil and Environmental Engineering, University of California, 147 Mulford Hall, Berkeley, CA, USA
6Aerosol Dynamics Inc., 935 Grayson St., Berkeley, CA, USA
7Dept. of Physics, University of Kuopio, Kuopio, Finland
8Finnish Meteorological Institute, Helsinki, Finland
9Dept. of Physics, University of Helsinki, Helsinki, Finland
10Dept. of Chemistry and Biochemistry, University of Colorado, Boulder, CO, USA
11Cooperative Institute for Research in the Environmental Sciences, Boulder, CO, USA
*now at: Alion Science and Technology, EPA Office of Research and Development, Research Triangle Park, NC, USA
Received: 26 Feb 2010 – Discussion started: 09 Mar 2010
Abstract. We report the first hourly in-situ measurements of speciated organic aerosol (OA) composition in an urban environment. Field measurements were made in southern California at the University of California–Riverside during the 2005 Study of Organic Aerosol at Riverside (SOAR), which included two separate measurement periods: a summer study (15 July–15 August) and a fall study (31 October–28 November). Hourly measurements of over 300 semivolatile and nonvolatile organic compounds were made using the thermal desorption aerosol gas chromatograph (TAG). Positive matrix factorization (PMF) was performed on a subset of these compounds to identify major components contributing to submicron (i.e., PM1) OA at the site, as measured by an aerosol mass spectrometer (AMS). PMF analysis was performed on an 11-day focus period in each season, representing average seasonal conditions during the summer and a period of urban influence during the fall. As a result of this analysis, we identify multiple types of primary and secondary OA (POA and SOA). Secondary sources contribute substantially to fine OA mass at Riverside, which commonly receives regional air masses that pass through metropolitan Los Angeles during the summer. Four individual summertime SOA components are defined, and when combined, they are estimated to contribute an average 88% of the total fine OA mass during summer afternoons according to PMF results. These sources appear to be mostly from the oxidation of anthropogenic precursor gases, with one SOA component having contributions from oxygenated biogenics. During the fall, three out of four aerosol components that contain SOA are inseparable from covarying primary emissions, and therefore we cannot estimate the fraction of total OA that is secondary in nature during the fall study. Identified primary OA components are attributed to vehicle emissions, food cooking, primary biogenics, and biomass burning aerosol. While a distinction between local and regional vehicle emissions is made, a combination of these two factors accounted for approximately 11% of observed submicron OA during both sampling periods. Food cooking operations contributed ~10% of submicron OA mass during the summer, but was not separable from SOA during the fall due to high covariance of sources. Biomass burning aerosol contributed a larger fraction of fine OA mass during the fall (~11%) than compared to summer (~7%). Primary biogenic aerosol was also identified during the summer, contributing ~1% of the OA, but not during the fall. While the contribution of both local and regional primary vehicle OA accounts for only ~11% of total OA during both seasons, gas-phase vehicle emissions likely create a substantial fraction of the observed SOA as a result of atmospheric processing.
Revised: 15 Nov 2010 – Accepted: 17 Nov 2010 – Published: 07 Dec 2010
Williams, B. J., Goldstein, A. H., Kreisberg, N. M., Hering, S. V., Worsnop, D. R., Ulbrich, I. M., Docherty, K. S., and Jimenez, J. L.: Major components of atmospheric organic aerosol in southern California as determined by hourly measurements of source marker compounds, Atmos. Chem. Phys., 10, 11577-11603, doi:10.5194/acp-10-11577-2010, 2010.