Atmospheric Chemistry and Physics Discussions
www.atmos-chem-phys-discuss.net
1680-7367
1680-7375
6
4
2006
10.5194/acpd-6-7959-2006
http://www.atmos-chem-phys-discuss.net/6/7959/2006/
http://www.atmos-chem-phys-discuss.net/6/7959/2006/acpd-6-7959-2006.html
http://www.atmos-chem-phys-discuss.net/6/7959/2006/acpd-6-7959-2006.pdf
7959
8009
2006-08-17
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
Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, MA, USA
Molina Center for Energy and the Environment, CA, USA
now at: Department of Chemistry and Biochemistry, University of California, San Diego, CA, USA
An episodic simulation is conducted to characterize ozone (O<sub>3</sub>)
photochemical production and investigate its sensitivity to emission changes
of ozone precursors in the Mexico City Metropolitan Area (MCMA) using the
Comprehensive Air Quality Model with extensions (CAMx). High O<sub>x</sub>
(O<sub>3</sub>+NO<sub>2</sub>) photochemical production rates of 10–80 ppb/h are
predicted due to the high reactivity of volatile organic compounds (VOCs) in
which alkanes, alkenes, and aromatics exert comparable contributions. The
predicted ozone production efficiency is between 4–10 O<sub>3</sub> molecules per
NO<sub>x</sub> molecule oxidized, and increases with VOC-to-NO<sub>2</sub> reactivity
ratio. Process apportionment analyses indicate significant outflow of
pollutants such as O<sub>3</sub> 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<sub>3</sub> production suggest that O<sub>3</sub> formation in the MCMA urban
region with less chemical aging (NO<sub>z</sub>/NO<sub>y</sub><0.3) is VOC-limited.
Both the simulated behavior of O<sub>3</sub> production and its sensitivities to
precursors suggest that midday O<sub>3</sub> formation during this episode is VOC
sensitive in the urban region on the basis of the current emissions
inventory. More episodic studies are needed to construct a comprehensive and
representative picture of the O<sub>3</sub> production characteristics and its
response to emission controls.