ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-8-19605-2008 Impact of primary formaldehyde on air pollution in the Mexico City Metropolitan Area Lei W. 1 2 Zavala M. 1 2 de Foy B. 1 3 Volkamer R. 2 4 Molina M. J. 2 5 Molina L. T. 1 2 Molina Center for Energy and the Environment, CA, USA Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Inst. of Technology, MA, USA Department of Earth and Atmospheric Sciences, Saint Louis Univ., MO, USA Department of Chemistry and Biochemistry, Univ. of Colorado at Boulder, CO, USA Department of Chemistry and Biochemistry, Univ. of California, San Diego, La Jolla, CA, USA 18 11 2008 8 6 19605 19635 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys-discuss.net/8/19605/2008/acpd-8-19605-2008.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/8/19605/2008/acpd-8-19605-2008.pdf

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 RO<sub>x</sub> radical budget, and on ozone (O<sub>3</sub>) formation in the MCMA. Important radical sources, including HCHO, HONO, and O<sub>3</sub>-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 contributing significantly to the ambient HCHO concentration, but also enhancing the radical budget and O<sub>3</sub> 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 O<sub>3</sub> concentration by up to 8%. While primary HCHO contributes predominantly to the ambient HCHO concentration between nighttime and morning rush hours, significant influence on the radical budget and O<sub>3</sub> production starts early morning, culminates at mid-morning and is sustained until early afternoon.

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