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Volume 12, issue 16 | Copyright

Special issue: Megacities: air quality and climate impacts from local to...

Special issue: MILAGRO/INTEX-B 2006

Atmos. Chem. Phys., 12, 7809-7823, 2012
https://doi.org/10.5194/acp-12-7809-2012
© Author(s) 2012. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 31 Aug 2012

Research article | 31 Aug 2012

Chemically-resolved aerosol eddy covariance flux measurements in urban Mexico City during MILAGRO 2006

R. Zalakeviciute1,*, M. L. Alexander2, E. Allwine3, J. L. Jimenez4, B. T. Jobson3, L. T. Molina5, E. Nemitz6, S.N. Pressley3, T. M. VanReken3, I. M. Ulbrich4, E. Velasco7, and B. K. Lamb3 R. Zalakeviciute et al.
  • 1Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, USA
  • 2Pacific Northwest National Laboratory, Richland, WA, USA
  • 3Laboratory for Atmospheric Research, Washington State University, Pullman, WA, USA
  • 4Department of Chemistry & Biochemistry, University of Colorado, Boulder, CO, USA
  • 5Molina Center for Energy and the Environment (MCE2), USA
  • 6Centre for Ecology and Hydrology, Edinburgh, UK
  • 7Center for Environmental Sensing and Modeling, Singapore
  • *formerly at: Laboratory for Atmospheric Research, Washington State University, Pullman, WA, USA

Abstract. As part of the MILAGRO 2006 field campaign, the exchange of atmospheric aerosols with the urban landscape was measured from a tall tower erected in a heavily populated neighborhood of Mexico City. Urban submicron aerosol fluxes were measured using an eddy covariance method with a quadrupole aerosol mass spectrometer during a two week period in March, 2006. Nitrate and ammonium aerosol concentrations were elevated at this location near the city center compared to measurements at other urban sites. Significant downward fluxes of nitrate aerosol, averaging −0.2 μg m−2 s−1, were measured during daytime. The urban surface was not a significant source of sulfate aerosols. The measurements also showed that primary organic aerosol fluxes, approximated by hydrocarbon-like organic aerosols (HOA), displayed diurnal patterns similar to CO2 fluxes and anthropogenic urban activities. Overall, 47% of submicron organic aerosol emissions were HOA, 35% were oxygenated (OOA) and 18% were associated with biomass burning (BBOA). Organic aerosol fluxes were bi-directional, but on average HOA fluxes were 0.1 μg m−2 s−1, OOA fluxes were −0.03 μg m−2 s−1, and BBOA fluxes were −0.03 μg m−2 s−1. After accounting for size differences (PM1 vs PM2.5) and using an estimate of the black carbon component, comparison of the flux measurements with the 2006 gridded emissions inventory of Mexico City, showed that the daily-averaged total PM emission rates were essentially identical for the emission inventory and the flux measurements. However, the emission inventory included dust and metal particulate contributions, which were not included in the flux measurements. As a result, it appears that the inventory underestimates overall PM emissions for this location.

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