Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 10 3 2010 10.5194/acpd-10-6567-2010 http://www.atmos-chem-phys-discuss.net/10/6567/2010/ http://www.atmos-chem-phys-discuss.net/10/6567/2010/acpd-10-6567-2010.html http://www.atmos-chem-phys-discuss.net/10/6567/2010/acpd-10-6567-2010.pdf 6567 6639 2010-03-09 Major components of atmospheric organic aerosol in southern California as determined by hourly measurements of source marker compounds B. J. Williams brentw@me.umn.edu A. H. Goldstein N. M. Kreisberg S. V. Hering D. R. Worsnop I. M. Ulbrich K. S. Docherty J. L. Jimenez Dept. of Environmental Science, Policy, and Management, University of California, 147 Mulford Hall, Berkeley, CA, USA Center for Aerosol and Cloud Chemistry, Aerodyne Research Inc., 45 Manning Rd., Billerica, MA, USA Dept. of Mechanical Engineering, University of Minnesota, 271 Mechanical Engineering, 111 Church Street S.E., Minneapolis, MN, USA Dept. of Civil and Environmental Engineering, University of California, 147 Mulford Hall, Berkeley, CA, USA Aerosol Dynamics Inc., 935 Grayson St., Berkeley, CA, USA Department of Physics, University of Kuopio, Kuopio, Finland Finnish Meteorological Institute, Helsinki, Finland Department of Physics, University of Helsinki, Helsinki, Finland Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO, USA Cooperative Institute for Research in the Environmental Sciences, Boulder, CO, USA now at: Alion Science and Technology, EPA Office of Research and Development, EPA Research and Development, Research Triangle Park, NC, USA 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 contribute an average 88% of the total fine OA mass during summer afternoons. 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 which contain SOA are inseparable from covarying primary emissions, and therefore we can not 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. 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