Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 6 4 2006 10.5194/acpd-6-7563-2006 http://www.atmos-chem-phys-discuss.net/6/7563/2006/ http://www.atmos-chem-phys-discuss.net/6/7563/2006/acpd-6-7563-2006.html http://www.atmos-chem-phys-discuss.net/6/7563/2006/acpd-6-7563-2006.pdf 7563 7621 2006-08-08 Distribution, magnitudes, reactivities, ratios and diurnal patterns of volatile organic compounds in the Valley of Mexico during the MCMA 2002 and 2003 field campaigns E. Velasco B. Lamb H. Westberg E. Allwine G. Sosa J. L. Arriaga-Colina B. T. Jobson M. Alexander P. Prazeller W. B. Knighton T. M. Rogers M. Grutter S. C. Herndon C. E. Kolb M. Zavala B. de Foy R. Volkamer L. T. Molina M. J. Molina Laboratory for Atmospheric Research, Department of Civil and Environmental Engineering, Washington State University, Pullman WA, USA Laboratorio de QuÍmica de la Atmósfera, Instituto Mexicano del Petróleo, México D.F., México Atmospheric Sciences. Battelle Pacific Northwest National Laboratory, Richland WA, USA Department of Chemistry and Biochemistry, Montana State University, Bozeman MO, USA Centro de Ciencias de la Atmósfera, Universidad Nacional Autónoma de México, México D.F., México Center for Atmospheric and Environmental Chemistry, Aerodyne Research Inc., Billerica, MA, USA Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge MA, USA Department of Chemistry and Biochemistry, University of California, San Diego, USA now at: Molina Center for Energy and the Environment (mce2.org), La Jolla CA, USA now at: Washington State University, Pullman WA, USA A wide array of volatile organic compound (VOC) measurements was conducted in the Valley of Mexico during the MCMA-2002 and 2003 field campaigns. Study sites included locations in the urban core, in a heavily industrial area and at boundary sites in rural landscapes. In addition, a novel mobile-laboratory-based conditional sampling method was used to collect samples dominated by fresh on-road vehicle exhaust to identify those VOCs whose ambient concentrations were primarily due to vehicle emissions. Five distinct analytical techniques were used: whole air canister samples with Gas Chromatography/Flame Ionization Detection (GC-FID), on-line chemical ionization using a Proton Transfer Reaction Mass Spectrometer (PTR-MS), continuous real-time detection of olefins using a Fast Olefin Sensor (FOS), and long path measurements using UV Differential Optical Absorption Spectrometers (DOAS). The simultaneous use of these techniques provided a wide range of individual VOC measurements with different spatial and temporal scales. The VOC data were analyzed to understand concentration and spatial distributions, diurnal patterns, origin and reactivity in the atmosphere of Mexico City. The VOC burden (in ppbC) was dominated by alkanes (60%), followed by aromatics (15%) and olefins (5%). The remaining 20% was a mix of alkynes, halogenated hydrocarbons, oxygenated species (esters, ethers, etc.) and other unidentified VOCs. However, in terms of ozone production, olefins were the most relevant hydrocarbons. Elevated levels of toxic hydrocarbons, such as 1,3-butadiene, benzene, toluene and xylenes were also observed. Results from these various analytical techniques showed that vehicle exhaust is the main source of VOCs in Mexico City and that diurnal patterns depend on vehicular traffic. Finally, examination of the VOC data in terms of lumped modeling VOC classes and its comparison to the VOC lumped emissions reported in other photochemical air quality modeling studies suggests that some, but not all, VOC classes are underestimated in the emissions inventory by factors of 1.1 to 3.