1Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 01239-4307, USA
2Chalmers Tekniska Hoegskola, Goeteborg, Sweden
3Center for Atmospheric and Environmental Chemistry, Aerodyne Research, Inc. Billerica, MA 01821-3976, USA
*now at: CCA-UNAM: Centro de Ciencias de la Atmósfera, Universidad Nacional Autónoma de México, México D.F., 04510, Mexico
**now at: UCSD: Department of Chem and Biochem, La Jolla, CA 92093-0356, USA
Abstract. Photochemical pollution control strategies require an understanding of photochemical oxidation precursors, making it important to distinguish between primary and secondary sources of HCHO. Estimates for the relative strengths of primary and secondary sources of formaldehyde (HCHO) were obtained using a statistical regression analysis with time series data of carbon monoxide (CO) and glyoxal (CHOCHO) measured in the Mexico City Metropolitan Area (MCMA) during the spring of 2003. Differences between Easter week and more typical weeks are evaluated. The use of CO-CHOCHO as HCHO tracers is more suitable for differentiating primary and secondary sources than CO-O3. The application of the CO-O3 tracer pair to mobile laboratory data suggests a potential in-city source of background HCHO. A significant amount of HCHO observed in the MCMA is associated with primary emissions.