Vertical distribution of ozone and VOCs in the low boundary layer of Mexico CityReport as inadecuate

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1 Molina Center for the Energy and the Environment MCE2 2 Department of Earth 3 Centro Nacional de Investigación y Capacitación Ambiental del Instituto Nacional de Ecología CENICA-INE 4 Japanese International Cooperation Agency JICA 5 Atmospheric Environmental Science Laboratory

Abstract : The evolution of ozone and 13 volatile organic compounds VOCs in the boundary layer of Mexico City was investigated during 2000?2004 to improve our understanding of the complex interactions between those trace gases and meteorological variables, and their influence on the air quality of a polluted megacity. A tethered balloon, fitted with electrochemical and meteorological sondes, was used to obtain detailed vertical profiles of ozone and meteorological parameters up to 1000 m above ground during part of the diurnal cycle 02:00?18:00 h. VOCs samples were collected up to 200 m by pumping air to canisters with a Teflon tube attached to the tether line. Overall, features of these profiles were found to be consistent with a simple picture of nighttime trapping of ozone in an upper residual layer and of VOCs in a shallow unstable layer above the ground. After sunrise an ozone balance is determined by photochemical production, entrainment from the upper residual layer and destruction by titration with NO, delaying the ground-level ozone rise by 2 h. The subsequent evolution of the conductive boundary layer and vertical distribution of pollutants are discussed in terms of the energy balance, the presence of turbulence and the atmospheric stability.

Author: E. Velasco - C. Márquez - E. Bueno - R. M. Bernabé - A. Sánchez - O. Fentanes - H. Wöhrnschimmel - B. Cárdenas - A. Kamilla



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