Characterizing ozone production and response under different meteorological conditions in Mexico City
Photochemistry in polluted atmospheres, particu- larly the formation of ozone (O3), depends not only on pollu- tant emissions, but also on meteorological conditions. In this study a 3-D chemical transport model CAMx was employed to investigate the O3 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 O3 forma- tion characteristics and sensitivity to emissions change were found to be weakly dependent on the meteorological condi- tions. The evolution of O3 formation and its sensitivity to NOx and VOC levels were also examined along the photo- chemical plume transport pathway. The midday O3 produc- tion was found to undergo a rapid increase in a narrow range of chemical aging, while downwind plumes were character- ized with low and constant O3 production, and plumes along their transport pathway were characterized by a combina- tion of the two. The O3 formation was more VOC sensitive near the source area, but as the plume became chemically aged, O3 formation became progressively VOC insensitive and more NOx sensitive.