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A wide array of volatile organic compound (VOC) measurements was conductedin the Valley of Mexico during the MCMA-2002 and 2003 field campaigns. Studysites included locations in the urban core, in a heavily industrial area andat boundary sites in rural landscapes. In addition, a novelmobile-laboratory-based conditional sampling method was used to collectsamples dominated by fresh on-road vehicle exhaust to identify those VOCswhose ambient concentrations were primarily due to vehicle emissions. Fourdistinct analytical techniques were used: whole air canister samples withGas Chromatography/Flame Ionization Detection (GC-FID), on-line chemicalionization 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 AbsorptionSpectrometers (DOAS). The simultaneous use of these techniques provided awide range of individual VOC measurements with different spatial andtemporal scales. The VOC data were analyzed to understand concentration andspatial distributions, diurnal patterns, origin and reactivity in theatmosphere of Mexico City. The VOC burden (in ppbC) was dominated by alkanes(60%), followed by aromatics (15%) and olefins (5%). The remaining20% was a mix of alkynes, halogenated hydrocarbons, oxygenated species(esters, ethers, etc.) and other unidentified VOCs. However, in terms ofozone production, olefins were the most relevant hydrocarbons. Elevatedlevels of toxic hydrocarbons, such as 1,3-butadiene, benzene, toluene andxylenes, were also observed. Results from these various analyticaltechniques showed that vehicle exhaust is the main source of VOCs in MexicoCity and that diurnal patterns depend on vehicular traffic in addition tometeorological processes. Finally, examination of the VOC data in terms oflumped modeling VOC classes and its comparison to the VOC lumped emissionsreported in other photochemical air quality modeling studies suggests thatsome alkanes are underestimated in the emissions inventory, while someolefins and aromatics are overestimated

atmospheric chemistry and physics

Distribution, magnitudes, reactivities, ratios and diurnal patterns of volatile organic compounds in the Valley of Mexico during the MCMA 2002 &amp;amp; 2003 field campaigns