Characterizing ozone production in the Mexico City Metropolitan Area: a case study using a chemical transport model
Atmospheric Chemistry and Physics Discussions
An episodic simulation is conducted to characterize midday (12:00-17:00 CDT) ozone (O 3 ) photochemical production and to investigate its sensitivity to emission changes of ozone precursors in the Mexico City Metropolitan Area (MCMA) during an "O 3 -South" meteorological episode using the Comprehensive Air Quality Model with extensions (CAMx). High O x (O 3 +NO 2 ) photochemical production rates of 10-80 ppb/h are predicted due to the high reactivity of volatile organic compounds (VOCs) in
... unds (VOCs) in which alkanes, alkenes, and aromatics exert comparable contributions. The predicted ozone production efficiency is between 4-10 O 3 molecules per NO x molecule oxidized, and increases with VOC-to-NO 2 reactivity ratio. Process apportionment analyses indicate significant outflow of pollutants such as O 3 and peroxyacetyl nitrate (PAN) from the urban area to the surrounding regional environment. PAN is not in chemical-thermal equilibrium during the photochemically active periods. Sensitivity studies of O 3 production suggest that O 3 formation in the MCMA urban region with less chemical aging (NO z /NO y <0.3) is VOC-limited. Both the simulated behavior of O 3 production and its sensitivities to precursors suggest that midday O 3 formation during this episode is VOC-sensitive in the urban region on the basis of the current emissions inventory estimates, and current NO x levels depress the O 3 production.