1Molina Center for Energy and the Environment, CA, USA
2Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Inst. of Technology, MA, USA
3Department of Earth and Atmospheric Sciences, Saint Louis Univ., MO, USA
4Department of Chemistry and Biochemistry, Univ. of Colorado at Boulder, CO, USA
5Department of Chemistry and Biochemistry, Univ. 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 contributing significantly to the ambient HCHO concentration, but also enhancing 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%. 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 morning, culminates at mid-morning and is sustained until early afternoon.