Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 6 3 2006 10.5194/acpd-6-4689-2006 http://www.atmos-chem-phys-discuss.net/6/4689/2006/ http://www.atmos-chem-phys-discuss.net/6/4689/2006/acpd-6-4689-2006.html http://www.atmos-chem-phys-discuss.net/6/4689/2006/acpd-6-4689-2006.pdf 4689 4725 2006-06-12 Characterization of on-road vehicle emissions in the Mexico City Metropolitan Area using a mobile laboratory in chase and fleet average measurement modes during the MCMA-2003 field campaign M. Zavala S. C. Herndon R. S. Slott E. J. Dunlea L. C. Marr J. H. Shorter M. Zahniser W. B. Knighton T. M. Rogers C. E. Kolb L. T. Molina M. J. Molina Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA Center for Atmospheric and Environmental Chemistry, Aerodyne Research Inc., Billerica, Massachusetts, USA Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana, USA now at: Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA now at: Department of Civil and Environmental Engineering, Virginia Tech. Blacksburg, Virginia, USA A mobile laboratory was used to measure on-road vehicle emission ratios during the MCMA-2003 field campaign held during the spring of 2003 in the Mexico City Metropolitan Area (MCMA). The measured emission ratios represent a sample of emissions of in-use vehicles under real world driving conditions for the MCMA. From the relative amounts of NO_x and selected VOC's sampled, the results indicate that the technique is capable of differentiating among vehicle categories and fuel type in real world driving conditions. Emission ratios for NO_x, NO_y, NH₃, H₂CO, CH₃CHO, and other selected volatile organic compounds (VOCs) are presented for chase sampled vehicles and fleet averaged emissions. Results indicate that colectivos, particularly CNG-powered colectivos, are potentially significant contributors of NO_x and aldehydes in the MCMA. Similarly, ratios of selected VOCs and NO_y showed a strong dependence on traffic mode. These results are compared with the vehicle emissions inventory for the MCMA, other vehicle emissions measurements in the MCMA, and measurements of on-road emissions in US cities. Our estimates for motor vehicle emissions of benzene, toluene, formaldehyde, and acetaldehyde in the MCMA indicate these species are present in concentrations higher than previously reported. The high motor vehicle aldehyde emissions may have an impact on the photochemistry of urban areas.