HR: 11:38h
AN: A22C-06    [Abstracts]
TI: Hydroxyl and Hydroperoxy Radical Chemistry during the MCMA-2006 Field Campaign: Measurement and Model Comparison
AU: * Dusanter, S
EM: sdusante@indiana.edu
AF: Center for Research in Environmental Science, School of Public and Environmental Affairs, and Department of Chemistry, Indiana University, Bloomington, IN 47405,
AU: Vimal, D
AF: Center for Research in Environmental Science, School of Public and Environmental Affairs, and Department of Chemistry, Indiana University, Bloomington, IN 47405,
AU: Stevens, P S
AF: Center for Research in Environmental Science, School of Public and Environmental Affairs, and Department of Chemistry, Indiana University, Bloomington, IN 47405,
AU: Volkamer, R
AF: Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309,
AU: Molina, L T
AF: Molina Center for Energy and the Environment, 3262 Holiday Ct., La Jolla, CA 92037,
AU: Molina, L T
AF: Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139,
AB: The Mexico City Metropolitan Area (MCMA) field campaign, held in March 2006, was a unique opportunity to collect data in one of the most polluted megacities in the world. Such environments exhibit a complex oxidation chemistry involving a strong coupling between odd hydrogen radicals (HO_X=OH+HO₂) and nitrogen oxides species (NO_X=NO+NO₂). High levels of volatile organic compounds (VOCs) and NO_X control the HO_X budget and lead to elevated tropospheric ozone formation. The HO_X-NO_X coupling can be investigated by comparing measured and model-predicted HOx concentrations. Atmospheric HO_X concentrations were measured by the Indiana University laser-induced fluorescence instrument and data were collected at the Instituto Mexicano del Petroleo between 14 and 31 March. Measured hydroxyl radical (OH) concentrations are comparable to that measured in less polluted urban environments and suggest that the OH concentrations are highly buffered under high NO_X conditions. In contrast, hydroperoxy radical (HO₂) concentrations are more sensitive to the NO_X levels and are highly variable between different urban sites. Enhanced levels of OH and HO₂ radicals were observed on several days between 9h30-11h00 AM and suggest an additional HO_X source for the morning hours and/or a fast HO_X cycling under the high NO_X conditions of the MCMA. A preliminary investigation of the HO_X chemistry occurring in the MCMA urban atmosphere was performed using a photochemical box model based on the Regional Atmospheric Chemistry Mechanism (RACM). Model comparisons will be presented and the agreement between measured and predicted HO_X concentrations will be discussed.
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0365 Troposphere: composition and chemistry
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting