<?xml version="1.0" encoding="utf-8" standalone="no"?>
<!DOCTYPE article SYSTEM "http://www.atmos-chem-phys.net/inc/acp/copernicus.dtd">
<article language="en">
	<journal>
		<journal_title>Atmospheric Chemistry and Physics</journal_title>
		<journal_url>www.atmos-chem-phys.net</journal_url>
		<issn>1680-7316</issn>
		<eissn>1680-7324</eissn>
		<volume_number>7</volume_number>
		<issue_number>2</issue_number>
		<publication_year>2007</publication_year>
	</journal>
	<doi>10.5194/acp-7-329-2007</doi>
	<article_url>http://www.atmos-chem-phys.net/7/329/2007/</article_url>
	<abstract_html>http://www.atmos-chem-phys.net/7/329/2007/acp-7-329-2007.html</abstract_html>
	<fulltext_pdf>http://www.atmos-chem-phys.net/7/329/2007/acp-7-329-2007.pdf</fulltext_pdf>
	<start_page>329</start_page>
	<end_page>353</end_page>
	<publication_date>2007-01-23</publication_date>
	<article_title content_type="html">Distribution, magnitudes, reactivities, ratios and diurnal patterns of volatile organic compounds in the Valley of Mexico during the MCMA 2002 &amp; 2003 field campaigns</article_title>
	<authors>
		<author numeration="1" affiliations="1,9">
			<name>E. Velasco</name>
			<email>evelasco@mce2.org</email>
		</author>
		<author numeration="2" affiliations="1">
			<name>B. Lamb</name>
		</author>
		<author numeration="3" affiliations="1">
			<name>H. Westberg</name>
		</author>
		<author numeration="4" affiliations="1">
			<name>E. Allwine</name>
		</author>
		<author numeration="5" affiliations="2">
			<name>G. Sosa</name>
		</author>
		<author numeration="6" affiliations="2">
			<name>J. L. Arriaga-Colina</name>
		</author>
		<author numeration="7" affiliations="3,10">
			<name>B. T. Jobson</name>
		</author>
		<author numeration="8" affiliations="3">
			<name>M. L. Alexander</name>
		</author>
		<author numeration="9" affiliations="3">
			<name>P. Prazeller</name>
		</author>
		<author numeration="10" affiliations="4">
			<name>W. B. Knighton</name>
		</author>
		<author numeration="11" affiliations="4">
			<name>T. M. Rogers</name>
		</author>
		<author numeration="12" affiliations="5">
			<name>M. Grutter</name>
		</author>
		<author numeration="13" affiliations="6">
			<name>S. C. Herndon</name>
		</author>
		<author numeration="14" affiliations="6">
			<name>C. E. Kolb</name>
		</author>
		<author numeration="15" affiliations="7">
			<name>M. Zavala</name>
		</author>
		<author numeration="16" affiliations="7,9">
			<name>B. de Foy</name>
		</author>
		<author numeration="17" affiliations="8">
			<name>R. Volkamer</name>
		</author>
		<author numeration="18" affiliations="7,9">
			<name>L. T. Molina</name>
		</author>
		<author numeration="19" affiliations="8">
			<name>M. J. Molina</name>
		</author>
	</authors>
	<affiliations>
		<affiliation numeration="1" content_type="html">Laboratory for Atmospheric Research, Department of Civil and Environmental Engineering, Washington State University, Pullman WA, USA</affiliation>
		<affiliation numeration="2" content_type="html">Laboratorio de Química de la Atmósfera, Instituto Mexicano del Petróleo, México D.F., México</affiliation>
		<affiliation numeration="3" content_type="html">Atmospheric Sciences. Battelle Pacific Northwest National Laboratory, Richland WA, USA</affiliation>
		<affiliation numeration="4" content_type="html">Department of Chemistry and Biochemistry, Montana State University, Bozeman MO, USA</affiliation>
		<affiliation numeration="5" content_type="html">Centro de Ciencias de la Atmósfera, Universidad Nacional Autónoma de México, México D.F., México</affiliation>
		<affiliation numeration="6" content_type="html">Center for Atmospheric and Environmental Chemistry, Aerodyne Research Inc., Billerica, MA, USA</affiliation>
		<affiliation numeration="7" content_type="html">Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge MA, USA</affiliation>
		<affiliation numeration="8" content_type="html">Department of Chemistry and Biochemistry, University of California, San Diego, USA</affiliation>
		<affiliation numeration="9" content_type="html">now at: Molina Center for Energy and the Environment (mce2.org), La Jolla CA, USA</affiliation>
		<affiliation numeration="10" content_type="html">now at: Washington State University, Pullman WA, USA</affiliation>
	</affiliations>
	<abstract content_type="html">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 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.</abstract>
	<references>
		<reference numeration="1" content_type="text"> Arriaga, J. L., Escalona, S., Cervantes, A. D., Ordu&amp;ntilde;ez, R. and Lopez, T.: Seguimiento de COV en aire urbano de la ZMCM 1992-1996, in: Contaminación Atmosférica, Vol. 2, edited by: Colin L. G. and Varela J. R., UAM, Mexico, 1997. </reference>
		<reference numeration="2" content_type="text"> Arriaga-Colina, J. L., West, J. J., Sosa, G., Escalona, S. S., Ordu&amp;ntilde;ez, R. M., and Cervantes, A. D. M.: Measurements of VOCs in Mexico City (1992&amp;ndash;2001) and evaluation of VOCs and CO in the emissions inventory, Atmos. Environ., 38, 2523&amp;ndash;2533, 2004. </reference>
		<reference numeration="3" content_type="text"> Atkinson, R.: Gas-phase tropospheric chemistry of organic compounds, J. Phys. Chem. Ref. Data, 2, 11&amp;ndash;216, 1994. </reference>
		<reference numeration="4" content_type="text"> Atkinson, R.: Gas-phase tropospheric chemistry of volatile organic compounds, J. Phys. Chem. Ref. Data, 26, 215&amp;ndash;290, 1997. </reference>
		<reference numeration="5" content_type="text"> Barletta, B., Meinardi, S., Simpson, I. J., Khwaja, H. A., Blake, D. R., and Rowland, F. S.: Mixing ratios of volatile organic compounds (VOCs) in the atmosphere of Karachi, Pakistan, Atmos. Environ., 36, 3429&amp;ndash;3443, 2002. </reference>
		<reference numeration="6" content_type="text"> Blake, D. R. and Sherwood, F.: Urban leakage of liquefied petroleum gases and its impact on Mexico City air quality, Science, 269, 953&amp;ndash;956, 1995. </reference>
		<reference numeration="7" content_type="text"> Borbon, A., Fontaine, H., Veillerot, M., Locoge, N., Galloo, J. C., and Guillermo, R.: An investigation into the traffic-related fraction of isoprene at an urban location, Atmos. Environ. 35, 3749&amp;ndash;3760, 2001. </reference>
		<reference numeration="8" content_type="text"> Bravo, H., Sosa, R., Sanchez, P., Bueno, E., and Gonzalez, L.: Concentration of benzene and toluene of the southwestern area at the Mexico City Metropolitan Zone, Atmos. Environ., 36, 3843&amp;ndash;3849, 2002. </reference>
		<reference numeration="9" content_type="text"> Carter, W. P. L.: Development of ozone reactivity scales for volatile organic compounds, J. Air &amp; Waste Manage. Assoc., 44, 881&amp;ndash;899, 1994. </reference>
		<reference numeration="10" content_type="text"> Carter, W. P. L.: Documentation of the SAPRC-99 Chemical Mechanism for VOC reactivity assessment, final report to California Air Resources Board, contracts 92-329 and 95-308, Calif. Air Res. Board, Sacramento, California, www.cert.ucr.edu/~carter, 2000. </reference>
		<reference numeration="11" content_type="text"> CAM: Inventario de emisiones a la atmósfera, Zona Metropolitana del Valle de México, 1998, Comisión Ambiental Metropolitana, Mexico, 2001. </reference>
		<reference numeration="12" content_type="text"> Conner, T. L., Lonneman, W. A., and Seila, R. L.: Transportation related volatile hydrocarbon source profiles measured in Atlanta, J. Air Waste Manage. Assoc., 45, 383&amp;ndash;394, 1995. </reference>
		<reference numeration="13" content_type="text"> Cruz-Nu&amp;ntilde;ez, X., Hernandez-Solis, J. M., and Ruiz-Suarez, L. G.: Evaluation of vapor recovery systems efficiency and personal exposure in service stations in Mexico City, Sci. Total Environ., 309, 59&amp;ndash;68, 2003. </reference>
		<reference numeration="14" content_type="text"> de Foy, B., Caetano, E., Maga&amp;ntilde;a, V., Zitácuaro, A., Cárdenas, B., Retama, A., Ramos, R., Molina, L. T., and Molina, M. J.: Mexico City basin wind circulation during the MCMA-2003 field campaign, Atmos. Chem. Phys., 5, 2267&amp;ndash;2288, 2005. </reference>
		<reference numeration="15" content_type="text"> de Gouw, J. A., Goldan, P. A., Warneke, C., Kuster, W. C., Roberts, J. M., Marchewka, M., Bertman, S. B., Pszenny, A. A. P., and Keene, W. C.: Validation of proton transfer reaction-mass spectrometry (PTR-MS) measurements of gas-phase organic compounds in the atmosphere during the New England Air Quality Study (NEAQS) in 2002, J. Geophys. Res., 108, 4682&amp;ndash;4199, 2003. </reference>
		<reference numeration="16" content_type="text"> Doran, J. C. and Zhong, S.: Thermally driven gap winds into the Mexico City basin, J. Appl. Meteor., 39, 1330&amp;ndash;1340, 2000. </reference>
		<reference numeration="17" content_type="text"> Evans, J., Levy, J., Hammitt, J., Santos-Burgoa, C., and Castillejos, M.: Health benefits of air pollution control, in: Air Quality in the Mexico Megacity. An integrated assessment, edited by: Molina, L. T. and Molina M. J., Kluwer Academic Publishers, Netherlands, 2002. </reference>
		<reference numeration="18" content_type="text"> Etzkorn, T., Klotz, B., Sorensen, S., Patroescu, I. V., Barnes, I., Becker, K. H., and Platt, U.: Gas-phase absorption cross sections of 24 monocyclic aromatic hydrocarbons in the UV and IR spectral ranges, Atmos. Environ., 33, 525&amp;ndash;540, 1999. </reference>
		<reference numeration="19" content_type="text"> FIMEVIC: Metrobus, sistema de transporte colectivo, www.fimevic.df.gob.mx/metrobus/default.htm, 2006. </reference>
		<reference numeration="20" content_type="text"> Finlayson-Pitts, B. J. and Pitts, J. N.: Chemistry of the upper and lower atmosphere, Academic Press, USA, 2000. </reference>
		<reference numeration="21" content_type="text"> Fraser, M. P., Cass, G. R., and Simoneit, B. R. T.: Gas-phase and particle-phase organic compounds emitted from motor vehicle traffic in a Los Angeles roadway tunnel, Environ. Sci. Technol., 32, 2051&amp;ndash;2060, 1998. </reference>
		<reference numeration="22" content_type="text"> Gakenheimer, R., Molina, L. T., Sussman, J., Zegras, C., Howitt, A., Makler, J., Lacy, R., Slott, R., and Villegas A.: The MCMA transportation system: mobility and pollution, in: Air Quality in the Mexico Megacity. An integrated assessment, edited by: Molina, L. T. and Molina M. J., Kluwer Academic Publishers, Netherlands, 2002. </reference>
		<reference numeration="23" content_type="text"> Garcia, A. R., Volkamer, R., Molina, L. T., Molina M. J., Samuelson, J., Mellqvist, J., Galle, B., Herndon, S. C., and Kolb, C. E.: Separation of emitted and photochemical formaldehyde in Mexico City using a statistical analysis and a new pair of gas-phase tracers, Atmos. Chem. Phys., 6, 4545&amp;ndash;4557, 2006. </reference>
		<reference numeration="24" content_type="text"> Gasca, J., Ortiz, E., Castillo, H., Jaimes, J. L., and Gonzalez, U.: The impact of liquefied petroleum gas usage on air Quality in Mexico City. Atmos. Environ., 38, 3517&amp;ndash;3527, 2004. </reference>
		<reference numeration="25" content_type="text"> GDF: Informe del Estado de la Calidad del Aire y Tendencias 2003 para la Zona Metropolitana del Valle de México, Dirección General de Gestión Ambiental del Aire, Mexico, 2004. </reference>
		<reference numeration="26" content_type="text"> Gomez-Perales, J. E., Colvile, R. N., Nieuwenhuijsen, M. J., Fernández-Bremauntz, A., Gutiérrez-Avedoy, V. J., Páramo-Figueroa, V. H., Blanco-Jiménez, S., Bueno-López, E., Mandujano, F., Bernabé-Cabanillas, R., and Ortiz-Segovia, E.: Commuters&apos; exposure to PM$_2.5$, CO, and benzene in public transport in the metropolitan area of Mexico City, Atmos. Environ., 38, 1219&amp;ndash;1229, 2004. </reference>
		<reference numeration="27" content_type="text"> Grutter, M., Flores, E., Basaldud, R., and Ruiz-Suarez, L. G.: Open-path FTIR spectroscopic studies of trace gases over Mexico City, Atmos. Oceanic Opt., 16, 232&amp;ndash;236, 2003. </reference>
		<reference numeration="28" content_type="text"> Grutter, M. and Flores, E.: Air pollution monitoring with two optical remote sensing techniques in Mexico City, Proceedings of SPIE 5571, Gran Canaria, Spain, 13&amp;ndash;16 September, 2004. </reference>
		<reference numeration="29" content_type="text"> Grutter, M., Flores, E., Andraca-Ayala, G., and Baez, A.: Formaldehyde levels in downtown Mexico City during 2003, Atmos. Environ., 39, 1027&amp;ndash;1034, 2005. </reference>
		<reference numeration="30" content_type="text"> Guenther, A. and Hills, A.: Eddy covariance measurement of isoprene fluxes, J. Geophys. Res., 103, 13 145&amp;ndash;13 152, 1998. </reference>
		<reference numeration="31" content_type="text"> Herndon, S. C., Jayne, J. T., Zahniser, M. S., Worsnop, D. R., Knighton, B., Alwine, E., Lamb, B. K., Zavala, M., Nelson, D. D., McManus, J. B., Shorter, J. H., Canagaratna, M. R., Onasch, T. B., and Kolb, C. E.: Characterization of urban pollutant emission fluxes and ambient concentration distributions using a mobile laboratory with rapid response instrumentation, Faraday Discuss., 130, 327&amp;ndash;339, 2005. </reference>
		<reference numeration="32" content_type="text"> INE: Almanaque de datos y tendencias de la calidad del aire en ciudades mexicanas, INE-SEMARNAT, Mexico, 2000. </reference>
		<reference numeration="33" content_type="text"> IPCS: Chemical Safety Information from Intergovernmental Organizations, www.inchem.org, 2005. </reference>
		<reference numeration="34" content_type="text"> Jeffries, H. E., Sexton, K. G., Arnold, J. R., and Kale T. L.: Validation testing of new mechanisms with outdoor chamber data, Volume 2: analysis of VOC data for the CBA and CAL photochemical mechanisms, final report EPA-600/3-89-010b, Environmental Protection Agency, USA, 1989. </reference>
		<reference numeration="35" content_type="text"> Jobson, B. T., Berkowitz, C. M., Kuster, W. C., Goldan, P. D., Williams, E. J., Fesenfeld, F. C., Apel, E. C., Karl, T., Lonneman, W. A., and Riemer, D.: Hydrocarbon source signatures in Houston, Texas: influence of the photochemical industry, J. Geophys. Res., 109, D24305, doi:10.1029/2004JD004887, 2004. </reference>
		<reference numeration="36" content_type="text"> Kim, K. H.: Comparison of BTX measurements using a differential optical absorption spectroscopy and on-line gas chromatography system, Environ. Eng. Sci., 21(2), 181&amp;ndash;194, 2004. </reference>
		<reference numeration="37" content_type="text"> Kirchstetter, T. W., Singer, B. C., Harley, R. A., Kendall, G. R., and Chan W.: Impact of oxygenated gasoline use on California light duty vehicle emissions, Environ. Sci. Technol., 30, 661&amp;ndash;670, 1996. </reference>
		<reference numeration="38" content_type="text"> Kolb, C. E., Herndon, S. C., Mcmanus, J. B., Shorter, J. H., Zahniser, M. S., Nelson, D. D., Jayne, J., Canagaratna, M. R., and Worsnop, D. R.: Mobile laboratory with rapid response instruments for real-time measurements of urban and regional trace gas and particulate distributions and emission source characteristics, Environ. Sci. Technol., 38, 5694&amp;ndash;5703, 2004. </reference>
		<reference numeration="39" content_type="text"> Lei, W., de Foy, B., Zavala, M., Volkamer, R., and Molina, L. T.: Characterizing ozone production in the Mexico City Metropolitan Area: a case study using a chemical transport model, Atmos. Chem. Phys. Discuss, 6, 7959&amp;ndash;8009, 2006. </reference>
		<reference numeration="40" content_type="text"> Lindinger, W., Hansel, A., and Jordan, A.: On-line monitoring of volatile organic compounds at pptv levels by means of proton-transfer-reaction mass spectroscopy (PTR-MS): Medical applications, food control and environmental research, Int. J. Mass Spectrom. Ion Processes, 173, 191&amp;ndash;241, 1998. </reference>
		<reference numeration="41" content_type="text"> Meneses, F., Romieu, I., Ramirez, M., Colome, S., Kochy, F., Ashley, D., and Hernandez-Avila, M.: A survey of personal exposures to benzene in Mexico city, Archives of Environmental Health, 54, 359&amp;ndash;363, 1999. </reference>
		<reference numeration="42" content_type="text"> Molina, L. T. and Molina, M. J.: Cleaning the air: a comparative study, in: Air Quality in the Mexico Megacity. An integrated assessment, edited by: Molina, L. T. and Molina M. J., Kluwer Academic Publishers, Netherlands, 2002. </reference>
		<reference numeration="43" content_type="text"> Mugica, V., Vega, E., Arriaga, J. L., and Ruiz, M. E.: Determination of motor vehicle profiles for non-methane organic compounds in the Mexico City Metropolitan Area, J. Air &amp; Waste Manage. Assoc., 48, 1060&amp;ndash;1068, 1998. </reference>
		<reference numeration="44" content_type="text"> Mugica, V., Vega, E., Chow, J., Reyes, E., Sanchez, G., Arriaga, J. L., Egami, R., and Watson, J.: Speciated non-methane organic compounds emissions from food cooking in Mexico, Atmos. Environ., 35, 1729&amp;ndash;1734, 2001a. </reference>
		<reference numeration="45" content_type="text"> Mugica, V., Vega, E., Sanchez, G., Reyes, E., Arriaga, J. L., Chow, J., Watson, J., and Arriaga, J. L.: Volatile organic compounds emissions from gasoline and diesel powered vehicle, Atmosfera 14, 29&amp;ndash;37, 2001b. </reference>
		<reference numeration="46" content_type="text"> Mugica, V., Vega, E., Ruiz, H., Sanchez, G., Reyes, E., and Cervantes, A.: Photochemical reactivity and sources of individual VOCs in Mexico City, in: Air pollution X, edited by: Brebbia, C. A. and Martin-Duque, J. F., WIT Press, UK, 2002a. </reference>
		<reference numeration="47" content_type="text"> Mugica, V., Watson, J., Vega, E., Reyes, E., Ruiz, M. E., and Chow, J.: Receptor model source apportionment of nonmethane hydrocarbons in Mexico City, The Scientific World Journal, 2, 844&amp;ndash;860, 2002b. </reference>
		<reference numeration="48" content_type="text"> Mugica, V., Ruiz, M. E., Watson, J., and Chow, J.: Volatile aromatic compounds in Mexico City atmosphere: levels and source apportionment, Atmosfera, 16, 15&amp;ndash;27, 2003. </reference>
		<reference numeration="49" content_type="text"> Ortiz, E., Alemon, E., Romero, D., Arriaga, J. L., Olaya, P., Guzman, F., and Rios, C.: Personal exposure to benzene, toluene and xylene in different microenvironments at the Mexico City metropolitan zone, Sci. Total Environ., 287, 241&amp;ndash;248, 2002. </reference>
		<reference numeration="50" content_type="text"> Parrish, D. D., Trainer, M., Young, V., Goldan, P. D., Kuster, W. C., Jobson, B. T., Fehsenfeld, F. C., Lonneman, W. A., Zika, R. D., Farmer, C. T., Riemer, D. D., and Rodgers, M. O.: Internal consistency tests for evaluation of measurements of anthropogenic hydrocarbons in the troposphere, J. Geophys. Res., 103, 22 339&amp;ndash;22 359, 1998. </reference>
		<reference numeration="51" content_type="text"> Pinhua, X., Wenqing, L., Qiang, F., Ruibin, W., Jianguo, L., and Qingnong, W.: Intercomparison of NO&lt;sub&gt;x&lt;/sub&gt;, SO&lt;sub&gt;2&lt;/sub&gt;, O&lt;sub&gt;3&lt;/sub&gt;, and aromatic hydrocarbons measured by a commercial DOAS system and traditional point monitoring techniques, Adv. Atmos. Sci., 21, 211&amp;ndash;219, 2004. </reference>
		<reference numeration="52" content_type="text"> Raga, G. B., Baumgardner, D., Kok, G., and Rosas, I.: Some aspects of boundary layer evolution in Mexico City, Atmos. Environ., 33, 5013&amp;ndash;5021, 1999. </reference>
		<reference numeration="53" content_type="text"> Raga, G. B., Baumgardner, D., Castro, T., Martinez-Arroyo, A., and Navarro-Gonzalez, R.: Mexico City air quality: a qualitative review of gas and aerosol measurements (1960&amp;ndash;2000), Atmos. Environ., 35, 4041&amp;ndash;4058, 2001. </reference>
		<reference numeration="54" content_type="text"> Reimann, S., Calanca, P., and Hofer, P.: The anthropogenic fraction contribution to isoprene concentrations in a rural atmosphere, Atmos. Environ., 34, 109&amp;ndash;115, 2000. </reference>
		<reference numeration="55" content_type="text"> Rogak, S. N., Pott, U., Dann, T., and Wang D.: Gaseous emissions from vehicles in a traffic tunnel in Vancouver, British Columbia, J. Air Waste Manage. Assoc., 48, 604&amp;ndash;615, 1998. </reference>
		<reference numeration="56" content_type="text"> Rogers, T. M., Grimsrud, E. P., Herndon, S. C., Jayne, J. T., Kolb, C. E., Allwine, E., Westberg, H., Lamb, B. K., Zavala, M., Molina, L. T., Molina, M. J., and Knighton, W. B.: On-road measurements of volatile organic compounds in the Mexico City Metropolitan Area using Proton Transfer Reaction Mass Spectrometry, Int. J. Mass Spectrom., 252, 26&amp;ndash;37, 2006. </reference>
		<reference numeration="57" content_type="text"> Sagebiel, J. C., Zielinska, B., Pierson, W. R., and Gertler, A. W.: Real world emissions and calculated reactivities of organic species from motor vehicles, Atmos. Environ., 30, 2287&amp;ndash;2296, 1996. </reference>
		<reference numeration="58" content_type="text"> Schifter, I., Diaz, L., Duran, J., Guzman, E., Chavez, O., and Lopez-Salina, E.: Remote sensing study of emissions from motor vehicles in the Metropolitan Area of Mexico City, Environ. Sci. Technol., 37, 395&amp;ndash;401, 2003. </reference>
		<reference numeration="59" content_type="text"> Schifter, I., Diaz, L., Lopez-Salinas, E., Rodriguez, R., Avalos, S., and Guerrero, V.: An evaluation of the LPG vehicles program in the metropolitan area of Mexico City, J. Air Waste Manage. Assoc., 50, 301&amp;ndash;309, 2000. </reference>
		<reference numeration="60" content_type="text"> Shiohara, N., Fernández-Bremauntz, A., Blanco-Jiménez, S., and Yanagisawa Y.: The commuters&apos; exposure to volatile chemicals and carcinogenic risk in Mexico City, Atmos. Environ., 39, 3481&amp;ndash;3489, 2005. </reference>
		<reference numeration="61" content_type="text"> Shirley, T. R., Brune, W. H., Ren, X., Mao, J., Lesher, R., Cardenas, R., Volkamer, R., Molina, L. T., Molina, M. J., Lamb, B., Velasco, E., Jobson, T., and Alexander, M.: Atmospheric oxidation in the Mexico City Metropolitan Area (MCMA) during April 2003, Atmos. Chem. Phys., 6, 2753&amp;ndash;2765, 2006. </reference>
		<reference numeration="62" content_type="text"> USEPA: Compendium method TO-14a. Determination of volatile organic compounds (VOCs) in ambient air using specially prepared canisters with subsequent analysis by gas chromatography (EPA/625/R-96/010b). Compendium of methods for the determination of toxic organic compounds in ambient air, 2nd Edition, US EPA, Cincinnati, OH, 1999a. </reference>
		<reference numeration="63" content_type="text"> USEPA: Integrated Risk Information System (IRIS) on 1,3-Butadiene, National Center for Environmental Assessment, Office of Research and Development, Washington, DC. 1999b. </reference>
		<reference numeration="64" content_type="text"> USEPA: SPECIATE, VOC/PM speciation data system, version 1.50, Environmental Protection Agency and Radian Corporation, Research Triangle Park, N.C., 1993. </reference>
		<reference numeration="65" content_type="text"> Vega, E., Mugica, M., Carmona, R., and Valencia, E.: Hydrocarbon source apportionment in Mexico City using the chemical mass balance receptor model, Atmos. Environ., 34, 4121&amp;ndash;4129, 2000. </reference>
		<reference numeration="66" content_type="text"> Velasco, E.: Estimates for biogenic non-methane hydrocarbons and nitric oxide emissions in the Valley of Mexico, Atmos. Environ., 37, 625&amp;ndash;637, 2003. </reference>
		<reference numeration="67" content_type="text"> Velasco, E., Lamb, B., Pressley, S., Allwine, E., Westberg, H., Jobson, T., Alexander, M., Prazeller, P., Molina, L., and Molina, M.: Flux measurements of volatile organic compounds from an urban landscape, Geophys. Res. Lett., 32, L20802, doi:10.1029/2005GL023356, 2005. </reference>
		<reference numeration="68" content_type="text"> Volkamer, R., Etzkorn, T., Geyer, A., and Platt, U.: Correction of oxygen interference with UV spectroscopic (DOAS) measurements of monocyclic aromatic hydrocarbons in the atmosphere, Atmos. Environ., 32, 3731&amp;ndash;3747, 1998. </reference>
		<reference numeration="69" content_type="text"> Volkamer, R., Molina, L. T., Molina, M. J., Shirley, T., and Brune, W. H.: DOAS measurement of glyoxal as an indicator for fast VOC chemistry in urban air, Geophys. Res. Lett., 32, L08806, doi:10.1029/2005GL022616, 2005. </reference>
		<reference numeration="70" content_type="text"> Warneke, C., de Gouw, J. A., Kuster, W. C., Goldan, P. D., and Fall, R.: Validation of atmospheric VOC measurements by proton transfer reaction mass spectroscopy using a gas chromatographic preseparation method, Environ. Sci. Technol., 37, 2494&amp;ndash;2501, 2003. </reference>
		<reference numeration="71" content_type="text"> Watson, J. G., Chow, J. C., and Fujita, E. M.: Review of volatile organic compound source apportionment by chemical mass balance, Atmos. Environ., 35, 1567&amp;ndash;1584, 2001. </reference>
		<reference numeration="72" content_type="text"> West, J., Zavala, M. A., Molina, L. T., Molina, M. J., San Martini, F., McRae, J., Sosa, G., and Arriaga-Colina, J. L.: Modeling ozone photochemistry and evaluation of hydrocarbon emissions in the Mexico City metropolitan area, J. Geophys. Res., 109, 19 312&amp;ndash;19 327, 2004. </reference>
		<reference numeration="73" content_type="text"> Whiteman, C. D., Zhong, S., Bian, X., Fast, J. D., and Doran, J. C.: Boundary layer evolution and regional-scale diurnal circulations over the Mexico Basin and Mexican plateau, J. Geophys. Res., 106(D8), 10 081&amp;ndash;10 102, 2000. </reference>
		<reference numeration="74" content_type="text"> Ye, Y., Galbally, I. E., and Weeks, I. A.: Emission of 1,3-butadiene from petrol-driven motor vehicles, Atmos. Environ. 31, 1157&amp;ndash;1165, 1997. </reference>
		<reference numeration="75" content_type="text"> Zavala, M., Herndon, S. C., Slott, R. S., Dunlea, E. J., Marr, L. C., Shorter, J. H., Zahniser, M., Knighton, W. B., Rogers, T. M., Kolb, C. E., Molina, L. T., and Molina, M. J.: 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, Atmos. Chem. Phys., 6, 5129&amp;ndash;5142, 2006. </reference>
	</references>
</article>

