Atmospheric oxidation in the Mexico City Metropolitan Area (MCMA) during April 2003 T. R. Shirley1, W. H. Brune1, X. Ren1, J. Mao1, R. Lesher1, B. Cardenas2, R. Volkamer3, L. T. Molina3, M. J. Molina3, B. Lamb4, E. Velasco4, T. Jobson5, and M. Alexander5 1Pennsylvania State University, University Park, PA, USA 2Autonomous Metropolitan University, Mexico City, Mexico 3Massachusetts Institute of Technology, Cambridge, MA, USA 4Washington State University, Pullman, WA, USA 5Pacific Northwest National Laboratory, Richland, WA, USA
Abstract. The Mexico City Metropolitan Area (MCMA) study in April 2003 had
measurements of many atmospheric constituents, including OH and HO2. It
provided the first opportunity to examine atmospheric oxidation in a
megacity in a developing country that has more pollution than typical U.S. and
European cities. At midday, OH typically reached 0.35 pptv (~7×106 cm−3), comparable to amounts observed in U.S. cities, but
HO2 reached 40 pptv, more than observed in most U.S. cities. The OH
reactivity was also measured, even during the highly polluted morning rush
hour. MCMA's OH reactivity was 25 s−1 during most of the day and 120 s−1
at morning rush hour, which was several times greater than has been
measured in any U.S. city. Median measured and modeled OH and HO2
agreed to within combined uncertainties, although for OH, the model exceeded
the measurement by more than 30% during midday. OH production and loss,
which were calculated from measurements, were in balance to within
uncertainties, although production exceeded loss during morning rush hour.
This imbalance has been observed in other cities. The HO2/OH ratio from
measurements and steady-state analyses have essentially the same dependence
on NO, except when NO was near 100 ppbv. This agreement is unlike other
urban studies, in which HO2/OH ratio decreased much less than expected
as NO increased. As a result of the active photochemistry in MCMA 2003, the
median calculated ozone production from measured HO2 reached 50 ppb h−1,
a much higher rate than observed in U.S. cities.
Citation: Shirley, T. R., Brune, W. H., Ren, X., Mao, J., Lesher, R., Cardenas, B., Volkamer, R., Molina, L. T., Molina, M. J., Lamb, B., Velasco, E., Jobson, T., and Alexander, M.: Atmospheric oxidation in the Mexico City Metropolitan Area (MCMA) during April 2003, Atmos. Chem. Phys., 6, 2753-2765, doi:10.5194/acp-6-2753-2006, 2006.