Articles | Volume 9, issue 16
Atmos. Chem. Phys., 9, 6191–6215, 2009

Special issue: MILAGRO/INTEX-B 2006

Atmos. Chem. Phys., 9, 6191–6215, 2009

  31 Aug 2009

31 Aug 2009

Evaluating simulated primary anthropogenic and biomass burning organic aerosols during MILAGRO: implications for assessing treatments of secondary organic aerosols

J. Fast1, A. C. Aiken2, J. Allan3, L. Alexander1, T. Campos4, M. R. Canagaratna5, E. Chapman1, P. F. DeCarlo6, B. de Foy7, J. Gaffney8, J. de Gouw9, J. C. Doran1, L. Emmons4, A. Hodzic4, S. C. Herndon5, G. Huey10, J. T. Jayne5, J. L. Jimenez2, L. Kleinman11, W. Kuster9, N. Marley8, L. Russell12, C. Ochoa13, T. B. Onasch5, M. Pekour1, C. Song1, I. M. Ulbrich2, C. Warneke9, D. Welsh-Bon9, C. Wiedinmyer4, D. R. Worsnop5, X.-Y. Yu1, and R. Zaveri1 J. Fast et al.
  • 1Pacific Northwest National Laboratory, Richland, Washington, USA
  • 2University of Colorado, Boulder, Colorado, USA
  • 3University of Manchester, Manchester, UK
  • 4National Center for Atmospheric Research, Boulder, Colorado, USA
  • 5Aerodyne Research Inc., Billerica, Massachusetts, USA
  • 6Paul Scherrer Institut, Switzerland
  • 7Saint Louis University, Saint Louis, Missouri, USA
  • 8University of Arkansas – Little Rock, Little Rock, Arkansas, USA
  • 9NOAA Earth System Research Laboratory & Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA
  • 10Georgia Institute of Technology, Atlanta, Georgia, USA
  • 11Brookhaven National Laboratory, Upton, New York, USA
  • 12University of California, San Diego, San Diego, California
  • 13Universidad Nacional Autónoma de México, Mexico City, Mexico

Abstract. Simulated primary organic aerosols (POA), as well as other particulates and trace gases, in the vicinity of Mexico City are evaluated using measurements collected during the 2006 Megacity Initiative: Local and Global Research Observations (MILAGRO) field campaigns. Since the emission inventories, transport, and turbulent mixing will directly affect predictions of total organic matter and consequently total particulate matter, our objective is to assess the uncertainties in predicted POA before testing and evaluating the performance of secondary organic aerosol (SOA) treatments. Carbon monoxide (CO) is well simulated on most days both over the city and downwind, indicating that transport and mixing processes were usually consistent with the meteorological conditions observed during MILAGRO. Predicted and observed elemental carbon (EC) in the city was similar, but larger errors occurred at remote locations since the overall CO/EC emission ratios in the national emission inventory were lower than in the metropolitan emission inventory. Components of organic aerosols derived from Positive Matrix Factorization of data from several Aerodyne Aerosol Mass Spectrometer instruments deployed both at ground sites and on research aircraft are used to evaluate the model. Modeled POA was consistently lower than the measured organic matter at the ground sites, which is consistent with the expectation that SOA should be a large fraction of the total organic matter mass. A much better agreement was found when modeled POA was compared with the sum of "primary anthropogenic" and "biomass burning" components derived from Positive Matrix Factorization (PMF) on most days, especially at the surface sites, suggesting that the overall magnitude of primary organic particulates released was reasonable. However, simulated POA from anthropogenic sources was often lower than "primary anthropogenic" components derived from PMF, consistent with two recent reports that these emissions are underestimated. The modeled POA was greater than the total observed organic matter when the aircraft flew directly downwind of large fires, suggesting that biomass burning emission estimates from some large fires may be too high.

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Final-revised paper