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

[摘要] An episodic simulation is conducted to characterize midday (12:00–17:00 CDT) ozone(O₃) photochemical production and to investigate its sensitivity toemission changes of ozone precursors in the Mexico City Metropolitan Area(MCMA) during an "O₃-South" meteorological episode using theComprehensive Air Quality Model with extensions (CAMx). High O_x(O₃+NO₂) photochemical production rates of 10–80 ppb/h arepredicted due to the high reactivity of volatile organic compounds (VOCs) inwhich alkanes, alkenes, and aromatics exert comparable contributions. Thepredicted ozone production efficiency is between 4–10 O₃ molecules perNO_x molecule oxidized, and increases with VOC-to-NO₂ reactivityratio. Process apportionment analyses indicate significant outflow ofpollutants such as O₃ and peroxyacetyl nitrate (PAN) from the urbanarea to the surrounding regional environment. PAN is not in chemical-thermalequilibrium during the photochemically active periods. Sensitivity studiesof O₃ production suggest that O₃ formation in the MCMA urbanregion with less chemical aging (NO_z/NO_y<0.3) is VOC-limited.Both the simulated behavior of O₃ production and its sensitivities toprecursors suggest that midday O₃ formation during this episode isVOC-sensitive in the urban region on the basis of the current emissionsinventory estimates, and current NO_x levels depress the O₃production.

[学科分类] 大气科学