Atmos. Chem. Phys. Discuss., 9, 8377-8427, 2009
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Mexico City aerosol analysis during MILAGRO using high resolution aerosol mass spectrometry at the urban supersite (T0) – Part 1: Fine particle composition and organic source apportionment
A. C. Aiken1,2,*, D. Salcedo3, M. J. Cubison2, J. A. Huffman1,2, P. F. DeCarlo2,4,**, I. M. Ulbrich1,2, K. S. Docherty2, D. Sueper2,5, J. R. Kimmel2, D. R. Worsnop5, A. Trimborn5, M. Northway5, E. A. Stone6, J. J. Schauer6, R. Volkamer1,2, E. Fortner5,7,8, B. de Foy9, J. Wang10, A. Laskin11, V. Shutthanandan11, J. Zheng8, R. Zhang8, J. Gaffney12, N. A. Marley12, G. Paredes-Miranda13, W. P. Arnott13, L. T. Molina14, G. Sosa15, and J. L. Jimenez1,2
1Department of Chemistry, University of Colorado at Boulder, 215 UCB, Boulder, CO 80309, USA
2Cooperative Institute for Research in the Environmental Sciences (CIRES), University of Colorado at Boulder, 216 UCB, Boulder, CO 80309, USA
3Centro de Investigaciones Quimicas, Universidad Autónoma del Estado de Morelos, Cuernavaca Morelos, Mexico
4Department of Atmospheric and Oceanic Sciences, University of Colorado at Boulder, UCB 311, Boulder, CO 80309, USA
5Aerodyne Research Inc., 45 Manning Rd., Billerica, MA, 01821, USA
6University of Wisconsin, 660 North Park St., Madison, WI 53706, USA
7Montana State University, Bozeman, MT 59717, USA
8Texas A&M, 3150 TAMU, College Station, TX 77843, USA
9Saint Louis University, St. Louis, MO 63108, USA
10Brookhaven National Laboratory, P.O. Box 5000, Upton, NY 11973, USA
11Pacific Northwest National Laboratory, Richland, WA, USA
12University of Arkansas, 2801 S. University Avenue, Little Rock, AR 72204, USA
13Univ. of Nevada Reno and the Desert Research Institute, Reno, NV, USA
14Molina Center for Energy and the Environment and Massachusetts Inst. of Technology, USA
15IMP, Eje Central Norte Lazaro Cardenas 152, Mexico City, D.F. 07730, Mexico
*now at: ETH-Zurich, 8092 Zurich, Switzerland
**now at: Paul Scherrer Institut, 5232 Villigen-PSI, Switzerland

Abstract. Submicron aerosol was analyzed during the MILAGRO field campaign in March 2006 at the T0 urban supersite in Mexico City with a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and complementary instrumentation. Mass concentrations, diurnal cycles, and size distributions of inorganic and organic species are similar to results from the CENICA supersite in April 2003 with organic aerosol (OA) comprising about half of the fine PM mass. Positive Matrix Factorization (PMF) analysis of the high resolution OA spectra identified three major components: chemically-reduced urban primary emissions (hydrocarbon-like OA, HOA), oxygenated OA (OOA, mostly secondary OA or SOA), and biomass burning OA (BBOA) that correlates with levoglucosan and acetonitrile. BBOA includes several very large plumes from regional fires and likely also some refuse burning. A fourth OA component is a small local nitrogen-containing reduced OA component (LOA) which accounts for 9% of the OA mass but one third of the organic nitrogen, likely as amines. OOA accounts for almost half of the OA on average, consistent with previous observations. OA apportionment results from PMF-AMS are compared to the PM2.5 chemical mass balance of organic molecular markers (CMB-OMM, from GC/MS analysis of filters). Results from both methods are overall consistent. Both assign the major components of OA to primary urban, biomass burning/woodsmoke, and secondary sources at similar magnitudes. The 2006 Mexico City emissions inventory underestimates the urban primary PM2.5 emissions by a factor of ~4, and it is ~16 times lower than afternoon concentrations when secondary species are included. Additionally, the forest fire contribution is underestimated by at least an order-of-magnitude in the inventory.

Citation: Aiken, A. C., Salcedo, D., Cubison, M. J., Huffman, J. A., DeCarlo, P. F., Ulbrich, I. M., Docherty, K. S., Sueper, D., Kimmel, J. R., Worsnop, D. R., Trimborn, A., Northway, M., Stone, E. A., Schauer, J. J., Volkamer, R., Fortner, E., de Foy, B., Wang, J., Laskin, A., Shutthanandan, V., Zheng, J., Zhang, R., Gaffney, J., Marley, N. A., Paredes-Miranda, G., Arnott, W. P., Molina, L. T., Sosa, G., and Jimenez, J. L.: Mexico City aerosol analysis during MILAGRO using high resolution aerosol mass spectrometry at the urban supersite (T0) – Part 1: Fine particle composition and organic source apportionment, Atmos. Chem. Phys. Discuss., 9, 8377-8427, doi:10.5194/acpd-9-8377-2009, 2009.
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