Atmos. Chem. Phys. Discuss., 8, 20283-20309, 2008
© Author(s) 2008. 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.
Assessing the regional impacts of Mexico City emissions on air quality and chemistry
M. Mena-Carrasco1,2, G. R. Carmichael3, J. E. Campbell4, D. Zimmerman5, Y. Tang3, B. Adhikary3, A. D'allura6, L. T. Molina2,7, M. Zavala2,7, A. García8, F. Flocke9, T. Campos9, A. J. Weinheimer9, R. Shetter9, E. Apel9, D. D. Montzka9, D. J. Knapp9, and W. Zheng9
1Universidad Andrés Bello, Department of Environmental Engineering, Santiago, Chile
2Massachusetts Institute of Technology, Department of Earth, Atmospheric and Planetary Sciences, Cambridge, MA, USA
3The University of Iowa, Center for Global and Regional Environmental Research, Iowa City, IA, USA
4University of California at Merced, School of Engineering, Merced, CA, USA
5The University of Iowa, Department of Statistical and Actuarial Science, Iowa City, IA, USA
6Arianet Environmental Modeling, Milan, Italy
7Molina Center for Energy and the Environment, La Jolla, CA, USA
8Universidad Nacional Autónoma de México, Delegación Coyoacán, México
9National Center for Atmospheric Research, Boulder, CO, USA

Abstract. The impact of Mexico City (MCMA) emissions is examined by studying its effects on air quality, photochemistry, and on ozone production regimes by combining model products and aircraft observations from the MILAGRO experiment. The influence of MCMA emissions to enhancements in surface level NOx, CO, and O3 concentrations are confined to distances <200 km. However, the extent of the influence is significantly larger at higher altitudes. Broader MCMA impacts (some 900 km Northeast of the city) are shown for specific outflow conditions in which enhanced ozone, NOy, and MTBE mixing ratios over the Gulf of Mexico are linked to MCMA by source tagged tracers and sensitivity runs. This study shows that the "footprint" of MCMA on average is fairly local, with exception to reactive nitrogen, which can be transported long range in the form of PAN, acting as a reservoir and source of NOx with important regional ozone formation implications. The simulated effect of MCMA emissions of anthropogenic aerosol on photochemistry showed a maximum regional decrease of 40% in J[NO2→NO+O], and resulting in the reduction of ozone production by 5–10%. Observed ozone production efficiencies and photolysis rates are evaluated as a function of distance from MCMA, and by modeled influence from MCMA. These tend to be much lower closer to MCMA, and with higher MCMA influence. This research shows that MCMA emissions have a discernible effect on regional air quality and photochemistry, both contributing large amounts of ozone and its precursors, but with caveat that aerosol concentrations hinder formation of ozone to its potential due to its reduction in photolysis rates.

Citation: Mena-Carrasco, M., Carmichael, G. R., Campbell, J. E., Zimmerman, D., Tang, Y., Adhikary, B., D'allura, A., Molina, L. T., Zavala, M., García, A., Flocke, F., Campos, T., Weinheimer, A. J., Shetter, R., Apel, E., Montzka, D. D., Knapp, D. J., and Zheng, W.: Assessing the regional impacts of Mexico City emissions on air quality and chemistry, Atmos. Chem. Phys. Discuss., 8, 20283-20309, doi:10.5194/acpd-8-20283-2008, 2008.
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