Photochemistry in polluted atmospheres, particularly the formation of ozone (O<sub>3</sub>), depends not only on pollutant emissions, but also on meteorological conditions. In this study a 3-D chemical transport model CAMx was employed to investigate the O<sub>3</sub> formation and its response to emissions reduction under three distinctively different meteorological conditions in the Mexico City Metropolitan Area during the MCMA-2003 field measurement campaign. The O<sub>3</sub> formation characteristics and sensitivity to emissions change were found to be weakly dependent on the meteorological conditions. The evolution of O<sub>3</sub> formation and its sensitivity to NO<sub>x</sub> and VOC levels were also examined along the photochemical plume transport pathway. The midday O<sub>3</sub> production was found to undergo a rapid increase in a narrow range of chemical aging, while downwind plumes were characterized with low and constant O<sub>3</sub> production, and plumes along their transport pathway were characterized by a combination of the two. The O<sub>3</sub> formation was more VOC sensitive near the source area, but as the plume became chemically aged, O<sub>3</sub> formation became progressively VOC insensitive and more NO<sub>x</sub> sensitive.