ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-9-6191-2009 Evaluating simulated primary anthropogenic and biomass burning organic aerosols during MILAGRO: implications for assessing treatments of secondary organic aerosols Fast J. 1 Aiken A. C. 2 Allan J. 3 Alexander L. 1 Campos T. 4 Canagaratna M. R. 5 Chapman E. 1 DeCarlo P. F. 6 de Foy B. 7 Gaffney J. 8 de Gouw J. 9 Doran J. C. 1 Emmons L. 4 Hodzic A. 4 Herndon S. C. 5 Huey G. 10 Jayne J. T. 5 Jimenez J. L. 2 Kleinman L. 11 Kuster W. 9 Marley N. 8 Russell L. 12 Ochoa C. 13 Onasch T. B. 5 Pekour M. 1 Song C. 1 Ulbrich I. M. 2 Warneke C. 9 Welsh-Bon D. 9 Wiedinmyer C. 4 Worsnop D. R. 5 Yu X.-Y. 1 Zaveri R. 1 Pacific Northwest National Laboratory, Richland, Washington, USA University of Colorado, Boulder, Colorado, USA University of Manchester, Manchester, UK National Center for Atmospheric Research, Boulder, Colorado, USA Aerodyne Research Inc., Billerica, Massachusetts, USA Paul Scherrer Institut, Switzerland Saint Louis University, Saint Louis, Missouri, USA University of Arkansas – Little Rock, Little Rock, Arkansas, USA NOAA Earth System Research Laboratory & Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA Georgia Institute of Technology, Atlanta, Georgia, USA Brookhaven National Laboratory, Upton, New York, USA University of California, San Diego, San Diego, California Universidad Nacional Autónoma de México, Mexico City, Mexico 31 08 2009 9 16 6191 6215 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/9/6191/2009/acp-9-6191-2009.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/9/6191/2009/acp-9-6191-2009.pdf

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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