Characterizing ozone production in the Mexico City Metropolitan Area: a case study using a chemical transport model

W. Lei, B. de Foy, M. Zavala, R. Volkamer, L. T. Molina
2006 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
more » ... 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.
doi:10.5194/acpd-6-7959-2006 fatcat:nofq7znhdbes3kp3opz65sp6fy