Impact of primary formaldehyde on air pollution in the Mexico City Metropolitan Area W. Lei1,2, M. Zavala1,2, B. de Foy1,3, R. Volkamer2,4, M. J. Molina2,5, and L. T. Molina1,2 1Molina Center for Energy and the Environment, CA, USA 2Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, MA, USA 3Department of Earth and Atmospheric Sciences, Saint Louis University, MO, USA 4Department of Chemistry and Biochemistry, University of Colorado at Boulder, CO, USA 5Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA, USA
Abstract. Formaldehyde (HCHO) is a radical source that plays an important role in
urban atmospheric chemistry and ozone formation. The Mexico City
Metropolitan Area (MCMA) is characterized by high anthropogenic emissions of
HCHO (primary HCHO), which together with photochemical production of HCHO
from hydrocarbon oxidation (secondary HCHO), lead to high ambient HCHO
levels. The CAMx chemical transport model was employed to evaluate the
impact of primary HCHO on its ambient concentration, on the ROx radical
budget, and on ozone (O3) formation in the MCMA. Important radical
sources, including HCHO, HONO, and O3-olefin reactions, were
constrained by measurements from routine observations of the local ambient
air monitoring network and the MCMA-2003 field campaign. Primary HCHO was
found not only to contribute significantly to the ambient HCHO
concentration, but also to enhance the radical budget and O3 production
in the urban atmosphere of the MCMA. Overall in the urban area, total
daytime radical production is enhanced by up to 10% and peak O3
concentration by up to 8%; moreover primary HCHO tends to make O3
both production rates and ambient concentration peak half an hour earlier.
While primary HCHO contributes predominantly to the ambient HCHO
concentration between nighttime and morning rush hours, significant
influence on the radical budget and O3 production starts early in the
morning, peaks at mid-morning and is sustained until early afternoon.
Citation: Lei, W., Zavala, M., de Foy, B., Volkamer, R., Molina, M. J., and Molina, L. T.: Impact of primary formaldehyde on air pollution in the Mexico City Metropolitan Area, Atmos. Chem. Phys., 9, 2607-2618, doi:10.5194/acp-9-2607-2009, 2009.