Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 10 2 2010 10.5194/acpd-10-3547-2010 http://www.atmos-chem-phys-discuss.net/10/3547/2010/ http://www.atmos-chem-phys-discuss.net/10/3547/2010/acpd-10-3547-2010.html http://www.atmos-chem-phys-discuss.net/10/3547/2010/acpd-10-3547-2010.pdf 3547 3604 2010-02-09 Investigation of the correlation between odd oxygen and secondary organic aerosol in Mexico City and Houston E. C. Wood ezrawood@aerodyne.com M. R. Canagaratna S. C. Herndon J. H. Kroll T. B. Onasch C. E. Kolb D. R. Worsnop W. B. Knighton R. Seila M. Zavala L. T. Molina P. F. DeCarlo J. L. Jimenez A. J. Weinheimer D. J. Knapp B. T. Jobson J. Stutz W. C. Kuster E. J. Williams Aerodyne Research, Inc., Billerica, Massachusetts, USA Department of Chemistry, Montana State University, Bozeman, Montana, USA United States Environmental Protection Agency, Research Triangle Park, North Carolina, USA Molina Center for Energy and the Environment, La Jolla, California, USA Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, Colorado, USA Cooperative Institute for Research in the Environmental Sciences (CIRES), University of Colorado, Boulder, Colorado, USA Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado, USA National Center for Atmospheric Research, Boulder, Colorado, USA Department of Civil and Environmental Engineering, Washington State University, Pullman, Washington, USA Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, California, USA NOAA 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 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 ([O_x]≡[O₃]+[NO₂]) and the oxygenated component of organic aerosol (OOA), which is interpreted as a surrogate for SOA. OOA and O_x 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 &mu;g m^&minus;3 ppm^&minus;1 (STP) in Houston during time periods affected by large petrochemical plant emissions to as high as 160 &mu;g m^&minus;3 ppm^&minus;1 in Mexico City, where typical values were near 120 &mu;g m^&minus;3 ppm^&minus;1. On several days in Mexico City, the [OOA]/[O_x] ratio decreased by a factor of ~2 between 08:00 and 13:00 LT. 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 O_x production rate using ambient VOC measurements and traditional laboratory SOA yields are lower than the observed [OOA]/[O_x] 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 <i>P</i>(SOA)/<i>P</i>(O_x) can serve as a useful test of photochemical models using improved formulation mechanisms for SOA. 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