Articles | Volume 10, issue 18
Atmos. Chem. Phys., 10, 8947–8968, 2010

Special issue: MILAGRO/INTEX-B 2006

Atmos. Chem. Phys., 10, 8947–8968, 2010

  27 Sep 2010

27 Sep 2010

Investigation of the correlation between odd oxygen and secondary organic aerosol in Mexico City and Houston

E. C. Wood1, M. R. Canagaratna1, S. C. Herndon1, T. B. Onasch1, C. E. Kolb1, D. R. Worsnop1, J. H. Kroll1,*, W. B. Knighton2, R. Seila3, M. Zavala4, L. T. Molina4, P. F. DeCarlo5,6,**, J. L. Jimenez5,6,7, A. J. Weinheimer8, D. J. Knapp8, B. T. Jobson9, J. Stutz10, W. C. Kuster11, and E. J. Williams11 E. C. Wood et al.
  • 1Aerodyne Research, Inc., Billerica, Massachusetts, USA
  • 2Department of Chemistry, Montana State University, Bozeman, Montana, USA
  • 3United States Environmental Protection Agency, Research Triangle Park, North Carolina, USA
  • 4Molina Center for Energy and the Environment, La Jolla, California, USA
  • 5Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, Colorado, USA
  • 6Cooperative Institute for Research in the Environmental Sciences (CIRES), University of Colorado, Boulder, Colorado, USA
  • 7Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado, USA
  • 8National Center for Atmospheric Research, Boulder Colorado, USA
  • 9Department of Civil and Environmental Engineering, Washington State University, Pullman, Washington, USA
  • 10Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, California, USA
  • 11NOAA Earth System Research Laboratory, Boulder, Colorado, USA
  • *now at: Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
  • **now at: Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Switzerland

Abstract. Many recent models underpredict secondary organic aerosol (SOA) particulate matter (PM) concentrations in polluted regions, indicating serious deficiencies in the models' chemical mechanisms and/or missing SOA precursors. Since tropospheric photochemical ozone production is much better understood, we investigate the correlation of odd-oxygen ([Ox]≡[O3]+[NO2]) and the oxygenated component of organic aerosol (OOA), which is interpreted as a surrogate for SOA. OOA and Ox measured in Mexico City in 2006 and Houston in 2000 were well correlated in air masses where both species were formed on similar timescales (less than 8 h) and not well correlated when their formation timescales or location differed greatly. When correlated, the ratio of these two species ranged from 30 μg m−3/ppm (STP) in Houston during time periods affected by large petrochemical plant emissions to as high as 160 μg m−3/ppm in Mexico City, where typical values were near 120 μg m−3/ppm. On several days in Mexico City, the [OOA]/[Ox] ratio decreased by a factor of ~2 between 08:00 and 13:00 local time. This decrease is only partially attributable to evaporation of the least oxidized and most volatile components of OOA; differences in the diurnal emission trends and timescales for photochemical processing of SOA precursors compared to ozone precursors also likely contribute to the observed decrease. The extent of OOA oxidation increased with photochemical aging. Calculations of the ratio of the SOA formation rate to the Ox production rate using ambient VOC measurements and traditional laboratory SOA yields are lower than the observed [OOA]/[Ox] ratios by factors of 5 to 15, consistent with several other models' underestimates of SOA. Calculations of this ratio using emission factors for organic compounds from gasoline and diesel exhaust do not reproduce the observed ratio. Although not succesful in reproducing the atmospheric observations presented, modeling P(SOA)/P(Ox) can serve as a useful test of photochemical models using improved formulation mechanisms for SOA.

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