Articles | Volume 9, issue 17
Atmos. Chem. Phys., 9, 6633–6653, 2009

Special issue: MILAGRO/INTEX-B 2006

Atmos. Chem. Phys., 9, 6633–6653, 2009

  11 Sep 2009

11 Sep 2009

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. Aiken*,2,1, D. Salcedo3, M. J. Cubison2, J. A. Huffman2,1, P. F. DeCarlo4,*,2, I. M. Ulbrich2,1, K. S. Docherty2, D. Sueper5,2, J. R. Kimmel2, D. R. Worsnop5, A. Trimborn5,**, M. Northway5,***, E. A. Stone6, J. J. Schauer6, R. M. Volkamer2,1, 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. Jimenez2,1 A. C. Aiken et al.
  • 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
  • 6Environmental Chemistry and Technology Program, University of Wisconsin-Madison, 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
  • 13University of Nevada Reno and the Desert Research Institute, Reno, NV, USA
  • 14Molina Center for Energy and the Environment and Massachusetts Institute of Technology, USA
  • 15IMP, Eje Central Norte Lazaro Cardenas 152, Mexico City, DF 07730, Mexico
  • *now at: Institute for Atmospheric and Climate Science, Swiss Federal Institute of Technology Zurich (ETH-Zurich), 8092 Zurich, Switzerland
  • **now at: Paul Scherrer Institut, 5232 Villigen-PSI, Switzerland
  • ***now at: Department of Meteorology, University of Reading, Reading, UK

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 at least an order-of-magnitude larger than in the inventory.

Special issue
Final-revised paper