Atmos. Chem. Phys. Discuss., 12, 11899-11939, 2012
© Author(s) 2012. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
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. VanReken3, I. M. Ulbrich4, E. Velasco7, and B. K. Lamb3
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 99164, USA
4Department of Chemistry & Biochemistry, University of Colorado, Boulder, CO 80309, USA
5Molina Center for Energy and the Environment (MCE2), USA
6Centre for Ecology and Hydrology, Edinburgh, UK
7Center for Environmental Sensing and Modeling, Singapore-MIT Alliance for Research and Technology, Singapore
*formerly at: Washington State University, Pullman, WA 99163, 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 0.09 μg m−2 s−1, OOA fluxes were −0.002 μg m−2 s−1, and BBOA fluxes were −0.03 μg m−2 s−1. The average diurnal flux results showed that the 2006 gridded emissions inventory of Mexico City underestimates mid-day and evening rush hour emissions of submicron aerosols for the monitored neighborhood, but averaged daily, the emission inventory and flux measurements for this location were in close agreement.

Citation: Zalakeviciute, R., Alexander, M. L., Allwine, E., Jimenez, J. L., Jobson, B. T., Molina, L. T., Nemitz, E., Pressley, S. N., VanReken, T., Ulbrich, I. M., Velasco, E., and Lamb, B. K.: Chemically-resolved aerosol eddy covariance flux measurements in urban Mexico City during MILAGRO 2006, Atmos. Chem. Phys. Discuss., 12, 11899-11939, doi:10.5194/acpd-12-11899-2012, 2012.
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