HR: 0800h
AN: A11A-0027    [Abstracts]
TI: UV-B Measurements in Mexico City: Comparison with Modeled UVB and Black Carbon
AU: * Marley, N A
EM: marley@anl.gov
AF: Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439 United States
AU: Gaffney, J S
EM: gaffney@anl.gov
AF: Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439 United States
AU: Frederick, J E
EM: frederic@uchicago.edu
AF: Center for Environmental Science, The University of Chicago, Chicago, IL 60627 United States
AB: Ultraviolet-B radiation (UV-B) represents a chemically important region of the sun's spectrum. At the earth's surface, UV-B can initiate a number of important photochemical reactions (e.g., ozone photolysis) that lead to the formation of OH radicals. Where levels of nitrogen oxides are high and reactive hydrocarbons are found, as in Mexico City and other megacities, UV-B can initiate photochemical smog formation. We used a broadband instrument to obtain UV-B measurements in Mexico City during the Mexico City Metropolitan Area 2003/Mexico City Megacity 2003 field study. We then used a simple radiation model for the Mexico City latitude, altitude, and time of year to construct UV-B contours for comparison with our results. Early morning discrepancies involve reductions in UV-B that are consistent with the presence of significant levels of BC in the Mexico City environment. During most afternoons, UV-B reductions were dominated by clouds. The results are discussed in terms of the potential impacts of BC on UV-B and downwind photochemical processes. The authors wish to thank the researchers at Centro Nacional de Investigaci˘n en Calidad Ambiental (CENICA), Mexico City. This work was supported by the U.S. Department of Energy, Atmospheric Science Program (Marley and Gaffney), and the U.S. Environmental Protection Agency (Frederick). We also wish to acknowledge Drs. Mario and Luisa Molina for their help in organizing and directing the Mexico City Metropolitan Area 2003 field study, during which these data were collected.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0345 Pollution--urban and regional (0305)
DE: 0365 Troposphere--composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting