ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-8-7353-2008 Using 3DVAR data assimilation system to improve ozone simulations in the Mexico City basin Bei N. 1 2 de Foy B. 1 3 Lei W. 1 2 Zavala M. 1 2 Molina L. T. 1 2 Molina Center for Energy and the Environment, La Jolla, CA, USA Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA Saint Louis University, Saint Louis, MO, USA 11 12 2008 8 24 7353 7366 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/8/7353/2008/acp-8-7353-2008.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/8/7353/2008/acp-8-7353-2008.pdf

This study investigates the improvement of ozone (O<sub>3</sub>) simulations in the Mexico City basin using a three-dimensional variational (3DVAR) data assimilation system in meteorological simulations during the MCMA-2003 field measurement campaign. Meteorological simulations from the NCAR/Penn State mesoscale model (MM5) are used to drive photochemical simulations with the Comprehensive Air Quality Model with extensions (CAMx) during a four-day episode on 13–16 April 2003. The simulated wind circulation, temperature, and humidity fields in the basin with the data assimilation are found to be more consistent with the observations than those from the reference deterministic forecast. This leads to improved simulations of plume position, peak O<sub>3</sub> timing, and peak O<sub>3</sub> concentrations in the photochemical model. The improvement in O<sub>3</sub> simulations is especially strong during the daytime. The results demonstrate the importance of applying data assimilation in meteorological simulations for air quality studies in the Mexico City basin.

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