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Published October 15, 2008 | public
Journal Article

Apportionment of primary and secondary organic aerosols in Southern California during the 2005 Study of Organic Aerosols in Riverside (SOAR-1)


Ambient sampling was conducted in Riverside, California during the 2005 Study of Organic Aerosols in Riverside to characterize the composition and sources of organic aerosol using a variety of state-of-the-art instrumentation and source apportionment techniques. The secondary organic aerosol (SOA) mass is estimated by elemental carbon and carbon monoxide tracer methods, water soluble organic carbon content, chemical mass balance of organic molecular markers, and positive matrix factorization of high-resolution aerosol mass spectrometer data. Estimates obtained from each of these methods indicate that the organic fraction in ambient aerosol is overwhelmingly secondary in nature during a period of several weeks with moderate ozone concentrations and that SOA is the single largest component of PM1 aerosol in Riverside. Average SOA/OA contributions of 70−90% were observed during midday periods, whereas minimum SOA contributions of ~45% were observed during peak morning traffic periods. These results are contrary to previous estimates of SOA throughout the Los Angeles Basin which reported that, other than during severe photochemical smog episodes, SOA was lower than primary OA. Possible reasons for these differences are discussed.

Additional Information

© 2008 American Chemical Society. Received March 21, 2008. Revised manuscript received July 30, 2008. Accepted July 31, 2008. We acknowledge funding provided by U.S. Environmental Protection Agency (EPA) STAR grants RD832161010 and R831080, National Science Foundation (NSF) grant ATM- 0449815, and NSF/UCAR grant S05-39607. P.F.D. and I.M.U. were supported by EPA Fellowship FP-9165081 and NASA Fellowship NNG05GQ50H, respectively. We also thank Megan McKay and Allen Goldstein for the use of their CO measurements in the CO-tracer calculations, and the rest of the Jimenez group and Aerodyne Research for support in the field and helpful discussions. We would also like to thank Paul Ziemann and the Air Pollution Research Center for hosting the SOAR-1 study. The United States Environmental Protection Agency through its Office of Research and development collaborated in the research described here. It has been subjected to Agency review and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.

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