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Volume 11, issue 23 | Copyright

Special issue: Megacities: air quality and climate impacts from local to...

Atmos. Chem. Phys., 11, 12387-12420, 2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 12 Dec 2011

Research article | 12 Dec 2011

The 2005 Study of Organic Aerosols at Riverside (SOAR-1): instrumental intercomparisons and fine particle composition

K. S. Docherty1,2,*, A. C. Aiken1,2,**, J. A. Huffman1,2,***, I. M. Ulbrich1,2, P. F. DeCarlo1,3,****, D. Sueper1,2,4, D. R. Worsnop4, D. C. Snyder5,*****, R. E. Peltier6,******, R. J. Weber6, B. D. Grover7, D. J. Eatough7, B. J. Williams8,*******, A. H. Goldstein8, P. J. Ziemann9, and J. L. Jimenez1,2 K. S. Docherty et al.
  • 1Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA
  • 2Dept. of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado, USA
  • 3Dept. of Oceanic and Atmospheric Science, University of Colorado, Boulder, Colorado, USA
  • 4Aerodyne Research, Inc., Billerica, Massachusetts, USA
  • 5Environmental Chemistry and Technology Program, University of Wisconsin, Madison, Wisconsin, USA
  • 6School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
  • 7Dept. of Chemistry and Biochemistry, Brigham Young University, Provo, Utah, USA
  • 8Dept. of Environmental Science, Policy, and Management, University of California, Berkeley, California, USA
  • 9Air Pollution Research Center and Depts. of Environmental Science and Chemistry, University of California, Riverside, California, USA
  • *currently at: Alion Science and Technology, US EPA Office of Research and Development, Research Triangle Park, North Carolina, USA
  • **currently at: Los Alamos National Laboratory, Los Alamos, New Mexico, USA
  • ***currently at: Max Planck Institute for Chemistry, Mainz, Germany
  • ****currently at: AAAS Science and Technology Policy Fellow hosted by the US EPA, Washington, DC, USA
  • *****currently at: Department of Chemistry, University of Wisconsin, Stevens Point, Wisconsin, USA
  • ******currently at: School of Public Health, University of Massachusetts, Amherst, Massachusetts, USA
  • *******currently at: Department of Energy, Environmental, & Chemical Engineering, Washington University, St. Louis, Missouri, USA

Abstract. Multiple state-of-the-art instruments sampled ambient aerosol in Riverside, California during the 2005 Study of Organic Aerosols at Riverside (SOAR) to investigate the chemical composition and potential sources of fine particles (PMf) in the inland region of Southern California. In this paper, we briefly summarize the spatial, meteorological and gas-phase conditions during SOAR-1 (15 July–15 August), provide detailed intercomparisons of high-resolution aerosol mass spectrometer (HR-AMS) measurements against complementary measurements, and report the average composition of PMf including the composition of the organic fraction measured by the HR-AMS. Daily meteorology and gas-phase species concentrations were highly consistent, displaying clear diurnal cycles and weekday/weekend contrast. HR-AMS measurements of non-refractory submicron (NR-PM1) mass are consistent and highly correlated with those from a filter dynamics measurement system tapered-element oscillating microbalance (TEOM), while the correlation between HR-AMS and heated TEOM measurements is lower due to loss of high volatility species including ammonium nitrate from the heated TEOM. Speciated HR-AMS measurements are also consistent with complementary measurements as well as with measurements from a collocated compact AMS while HR-AMS OC is similar to standard semi-continuous Sunset measurements within the combined uncertainties of both instruments. A correction intended to account for the loss of semi-volatile OC from the Sunset, however, yields measurements ~30% higher than either HR-AMS or standard Sunset measurements. On average, organic aerosol (OA) was the single largest component of PMf. OA composition was investigated using both elemental analysis and positive matrix factorization (PMF) of HR-AMS OA spectra. Oxygen is the main heteroatom during SOAR-1, with O/C exhibiting a diurnal minimum of 0.28 during the morning rush hour and maximum of 0.42 during the afternoon. O/C is broadly anti-correlated with H/C, while N/C and S/C (excluding organonitrate (ON) and organosulfate (OS) functionalities) are far lower than O/C at about 0.015 and ~0.001, respectively. When ON and OS estimates are included O/C, N/C, and S/C increase by factors of 1.21, 2, and 30, respectively, while H/C changes are insignificant. The increase in these ratios implies that ON accounts for ~1/2 of the organic nitrogen while OS dominate organic sulfur at this location. Accounting for the estimated ON and OS also improves the agreement between anions and cations measured by HR-AMS by ~8%, while amines have only a very small impact (1%) on this balance. Finally, a number of primary and secondary OA components were resolved by PMF. Among these a hydrocarbon-like OA and two minor, local OA components, one of which was associated with amines, were attributed to primary emissions and contributed a minor fraction (~20%) of OA mass. The remaining OA mass was attributed to a number of secondary oxidized OA (OOA) components including the previously-identified low-volatility and semi-volatile OOA components. In addition, we also report for the first time the presence of two additional OOA components.

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