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

Abstract

Abstract.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. Four 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 Correspondence to: E. Velasco (evelasco@mce2.org) 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 in addition to meteorological processes. 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 alkanes are underestimated in the emissions inventory, while some olefins and aromatics are overestimated.

Direct detection of acetylene in air by continuous wave cavity ring-down spectroscopy

“…Somewhat lower mean values of 0.87 and 0.52 ppbv were recorded in a smaller city [9] and a rural area [8] in France, respectively. Much higher mean levels of tens of ppbv were observed in highly populated areas [1][2][3]7] and cities with a large number of vehicles running on biofuels [36]. Similar to our observations, the studies conducted in urban areas report wide ranges of detected acetylene levels and occasional high peak values, indicating strong fluctuations.…”

“…While volatile organic compounds (VOCs) and nitrogen oxides (NOx) are the most important chemical precursors of tropospheric ozone (O 3 ) [7], acetylene (a light VOC) is one of the most photochemically unreactive hydrocarbon species with almost negligible contribution to ozone formation [3,7]. As with other hydrocarbons, it is mainly removed from the atmosphere by a reaction with the hydroxyl radical (OH).…”

“…Acetylene (C 2 H 2 ) is one of the most common hydrocarbons in the troposphere [1][2][3] originating almost exclusively from anthropogenic sources [4]. It is a regular product of combustion processes, mainly present in vehicle exhausts (fossil fuels and biofuels) but also caused by biomass burning [5].…”

“…The compound can thus be employed as a marker for anthropogenic emissions and to trace polluted air masses. Furthermore, it is common to use VOC/acetylene ratios in atmospheric investigations to identify VOC sources other than combustion [2,3]. Such ratios are also helpful in evaluating the impact of vehicle exhausts on the seasonal variation of the total VOC concentration [8,9].…”

Measurements of volatile organic compounds at a suburban ground site (T1) in Mexico City during the MILAGRO 2006 campaign: measurement comparison, emission ratios, and source attribution

“…Hydrocarbon measurements in 1993Hydrocarbon measurements in , 2002Hydrocarbon measurements in , and 2003 showed highly elevated levels of many anthropogenic VOCs within the city (Blake and Rowland, 1995;Rogers et al, 2006;Velasco et al, 2007). The MILAGRO campaign (Megacity Initiative: Local and Global Research Observations) in March 2006 was designed to address the impact of these emissions on a variety of scales from local to global, and builds on results from smaller multi-investigator campaigns such as IMADA-AVER andMCMA-2003 (Edgerton et al, 1999;Molina et al, , 2010.…”