ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-9-7325-2009 Eddy covariance flux measurements of pollutant gases in urban Mexico City Velasco E. 1 3 5 Pressley S. 2 Grivicke R. 2 Allwine E. 2 Coons T. 2 Foster W. 2 Jobson B. T. 2 Westberg H. 2 Ramos R. 4 6 Hernández F. 4 Molina L. T. 1 3 Lamb B. 2 Molina Center for Energy and the Environment (MCE2), La Jolla, CA, USA Laboratory for Atmospheric Research, Dept. of Civil and Environmental Engineering, Washington State University, Pullman, WA, USA Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA Secretaría del Medio Ambiente del Gobierno del Distrito Federal, México D.F., México now at: Dept. of Geography, Faculty of Arts and Social Sciences, National University of Singapore, Singapore now at: William J. Clinton Foundation, Clinton Climate Initiative, México D.F., México 02 10 2009 9 19 7325 7342 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/9/7325/2009/acp-9-7325-2009.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/9/7325/2009/acp-9-7325-2009.pdf

Eddy covariance (EC) flux measurements of the atmosphere/surface exchange of gases over an urban area are a direct way to improve and evaluate emissions inventories, and, in turn, to better understand urban atmospheric chemistry and the role that cities play in regional and global chemical cycles. As part of the MCMA-2003 study, we demonstrated the feasibility of using eddy covariance techniques to measure fluxes of selected volatile organic compounds (VOCs) and CO<sub>2</sub> from a residential district of Mexico City (Velasco et al., 2005a, b). During the MILAGRO/MCMA-2006 field campaign, a second flux measurement study was conducted in a different district of Mexico City to corroborate the 2003 flux measurements, to expand the number of species measured, and to obtain additional data for evaluation of the local emissions inventory. Fluxes of CO<sub>2</sub> and olefins were measured by the conventional EC technique using an open path CO<sub>2</sub> sensor and a Fast Isoprene Sensor calibrated with a propylene standard. In addition, fluxes of toluene, benzene, methanol and C<sub>2</sub>-benzenes were measured using a virtual disjunct EC method with a Proton Transfer Reaction Mass Spectrometer. The flux measurements were analyzed in terms of diurnal patterns and vehicular activity and were compared with the most recent gridded local emissions inventory. In both studies, the results showed that the urban surface of Mexico City is a net source of CO<sub>2</sub> and VOCs with significant contributions from vehicular traffic. Evaporative emissions from commercial and other anthropogenic activities were significant sources of toluene and methanol. The results show that the emissions inventory is in reasonable agreement with measured olefin and CO<sub>2</sub> fluxes, while C<sub>2</sub>-benzenes and toluene emissions from evaporative sources are overestimated in the inventory. It appears that methanol emissions from mobile sources occur, but are not reported in the mobile emissions inventory.

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