ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-2353-2010 Chemical evolution of volatile organic compounds in the outflow of the Mexico City Metropolitan area Apel E. C. 1 Emmons L. K. 1 Karl T. 1 Flocke F. 1 Hills A. J. 1 Madronich S. 1 Lee-Taylor J. 1 Fried A. 1 Weibring P. 1 Walega J. 1 Richter D. 1 Tie X. 1 Mauldin L. 1 Campos T. 1 Weinheimer A. 1 Knapp D. 1 Sive B. 2 Kleinman L. 3 Springston S. 3 Zaveri R. 4 Ortega J. 4 12 Voss P. 5 Blake D. 6 Baker A. 6 Warneke C. 7 Welsh-Bon D. 7 de Gouw J. 7 Zheng J. 8 Zhang R. 8 Rudolph J. 9 Junkermann W. 10 Riemer D. D. 11 National Center for Atmospheric Research, Boulder, CO, USA University of New Hampshire, Durham, NH, USA Brookhaven National Laboratory, Upton, NY, USA Pacific Northwest National Laboratory, Richland, WA, USA Smith College and the University of Massachusetts, Amherst, MA, USA University of California, Irvine, CA, USA National Oceanic and Atmospheric Administration, Boulder, CO, USA Department of Atmospheric Sciences, Texas A&M, College Station, TX, USA York University, Toronto, Ontario, Canada Institute for Meteorology and Climate Research, IMK-IFU, Research Center Karlsruhe, Garmisch-Partenkirchen, Germany University of Miami, Rosenstiel School of Marine and Atmospheric Sciences, Miami, FL, USA currently at: the National Center for Atmospheric Research, Boulder, CO, USA 08 03 2010 10 5 2353 2375 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/10/2353/2010/acp-10-2353-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/2353/2010/acp-10-2353-2010.pdf

The volatile organic compound (VOC) distribution in the Mexico City Metropolitan Area (MCMA) and its evolution as it is uplifted and transported out of the MCMA basin was studied during the 2006 MILAGRO/MIRAGE-Mex field campaign. The results show that in the morning hours in the city center, the VOC distribution is dominated by non-methane hydrocarbons (NMHCs) but with a substantial contribution from oxygenated volatile organic compounds (OVOCs), predominantly from primary emissions. Alkanes account for a large part of the NMHC distribution in terms of mixing ratios. In terms of reactivity, NMHCs also dominate overall, especially in the morning hours. However, in the afternoon, as the boundary layer lifts and air is mixed and aged within the basin, the distribution changes as secondary products are formed. The WRF-Chem (Weather Research and Forecasting with Chemistry) model and MOZART (Model for Ozone and Related chemical Tracers) were able to approximate the observed MCMA daytime patterns and absolute values of the VOC OH reactivity. The MOZART model is also in agreement with observations showing that NMHCs dominate the reactivity distribution except in the afternoon hours. The WRF-Chem and MOZART models showed higher reactivity than the experimental data during the nighttime cycle, perhaps indicating problems with the modeled nighttime boundary layer height. <br><br> A northeast transport event was studied in which air originating in the MCMA was intercepted aloft with the Department of Energy (DOE) G1 on 18 March and downwind with the National Center for Atmospheric Research (NCAR) C130 one day later on 19 March. A number of identical species measured aboard each aircraft gave insight into the chemical evolution of the plume as it aged and was transported as far as 1000 km downwind; ozone was shown to be photochemically produced in the plume. The WRF-Chem and MOZART models were used to examine the spatial extent and temporal evolution of the plume and to help interpret the observed OH reactivity. The model results generally showed good agreement with experimental results for the total VOC OH reactivity downwind and gave insight into the distributions of VOC chemical classes. A box model with detailed gas phase chemistry (NCAR Master Mechanism), initialized with concentrations observed at one of the ground sites in the MCMA, was used to examine the expected evolution of specific VOCs over a 1–2 day period. The models clearly supported the experimental evidence for NMHC oxidation leading to the formation of OVOCs downwind, which then become the primary fuel for ozone production far away from the MCMA.

 References Altuzar, V., Tomás, S. A., Zelaya-Angel, O., Sánchez-Sinencio, F., and Arriaga, J. L.: Atmospheric ethene concentrations in Mexico City: Indications of strong diurnal and seasonal dependences, Atmos. Env., 39, 5219–5225, 2005. Apel, E. C., Calvert, J. G., and Fehsenfeld, F. C.: The Non-Methane Hydrocarbon Intercomparison Experiment (NOMHICE): Tasks 1 and 2, J. Geophys. Res., 99(D8), 16651–16664, 1994. Apel, E. C., Calvert, J. G., Gilpin, T., Parrish, D. D., and Fehsenfeld, F. C.: The Non-Methane Hydrocarbon Intercomparison Experiment (NOMHICE): Task 3, J. Geophys. Res., 104, 26069–26086, 1999. Apel, E. C., Hills, A. J., Lueb, R., Zindel, S., Eisele, S., and Riemer, D. D.: A Fast-GC/MS system to measure C<sub>2</sub> to C<sub>4</sub> carbonyls, and methanol aboard aircraft, J. Geophys. Res., 108, 8794, doi:10.1029/2002JD003199, 2003. Atkinson, R. and Arey, J.: Chem. Rev., 103, 1–246, 2003. Atkinson, R.: Gas phase tropospheric chemistry of organic compounds: a review, Atmos. Environ., 24A, 1–41, 1990. Atkinson, R., Kinetics and mechanisms of the gas phase reactions of the hydroxyl radical with organic compounds, J. Phys. Chem. Ref. Data, Monograph 1, 1, 4605–4638, 1989. Baez, A. P., Belmont, R., and Padilla, H.: Measurements of formaldehyde and acetaldehyde in the atmosphere of Mexico City, Environ. Poll., 89, 163–167, 1995. Baez, A. P., Padilla, H., Torres, M. C., and Belmont, R.: Ambient levels of carbonyls in Mexico City, Atmosfera, 13, 121-131, 2000. Baker, A. K., Beyersdorf, A. J., Doezema, L. A., Katzenstein, A., Meinardi, S., Simpson, I. J., Blake, D. R., and Rowland, F. S.: Measurements of nonmethane hydrocarbons in 28 United States cities, Atmos. Environ., 42, 170–182, 2008. Baker, A., et al.: VOC Measurements in the MCMA basin during MIRAGE –MEX, Atmos. Chem, Phys., to be submitted, 2010. Blake, D. and Rowland, F. S.: Urban leakage of liquefied Petroleum Gas and Its Impact on Mexico City Air Quality, Science, 269, 953-956, 1995. Chang, J. S., Binkowski, F. S., Seaman, N. L., McHenry, J. N., Samson, P. J., Stockwell, W. R., Walcek, C. J., Madronich, S., Middleton, P. B., Pleim, J. E., and Lansford, H. H.: The regional acid deposition model and engineering model, State-of-Science/Technology, Report 4, National Acid Precipitation Assessment Program, Washington DC, USA, 1989. Colman, J. J., Swanson, A. L., Meinardi, S., Sive, B. C., Blake, D. R., and Rowland, F. S.: Description of the analysis of a wide range of volatile organic compounds in whole air samples collected during PEM-Tropics A and B, Anal. Chem., 73, 3723–3731, 2001. Crounse, J. D., DeCarlo, P. F., Blake, D. R., Emmons, L. K., Campos, T. L., Apel, E. C., Clarke, A. D., Weinheimer, A. J., McCabe, D. C., Yokelson, R. J., Jimenez, J. L., and Wennberg, P. O.: Biomass burning and urban air pollution over the Central Mexican Plateau, Atmos. Chem. Phys., 9, 4929–4944, 2009. de Foy, B., Varrela, J. R., Molina, L., and Molina, M.: Rapid ventilation of the Mexico City basin and regional fate of the urban plume, Atmos. Chem. Phys., 6, 2321–2335, 2006. de Gouw, J. A., Goldan, P. D., Warneke, C., Kuster, W. C., Roberts, J. M., Marchewka, M., Bertman, S. B., Pszenny, A. A., 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), J. Geophys. Res., 108, doi:10.1029/2003JD003863, 2003, 2002. de Gouw, J., Warneke, C., Karl, T., Eerdekens, G., Van der Veen, C., and Fall, R.: Sensitivity and specificity of atmospheric trace gas detection by proton-transfer-reaction mass spectrometry, Int. J. Mass Spect., 223–224, 365–382, 2003. de Gouw, J. A., Middlebrook, A. M., Warneke, C., et al.: Budget of organic carbon in a polluted atmosphere: Results from the New England Air Quality Study in 2002, J. Geophys. Res., 110, D16305, doi:10.1029/2004JD005623, 2005. de Gouw, J. and Warneke, C.: Measurements of volatile organic compounds in the earth's atmosphere using proton-transfer-reaction mass spectrometry, Mass Spectrom. Rev., 26, 223–257, 2007. de Gouw, J. A., Welsh-Bon, D., Warneke, C., Kuster, W. C., Alexander, L., Baker, A. K., Beyersdorf, A. J., Blake, D. R., Canagaratna, M., Celada, A. T., Huey, L. G., Junkermann, W., Onasch, T. B., Salcido, A., Sjostedt, S. J., Sullivan, A. P., Tanner, D. J., Vargas, O., Weber, R. J., Worsnop, D. R., Yu, X. Y., and Zaveri, R.: Emission and chemistry of organic carbon in the gas and aerosol phase at a sub-urban site near Mexico City in March 2006 during the MILAGRO study, Atmos. Chem. Phys., 9, 3425–3442, 2009. Doskey, P. V., Porter J. A., and Scheff, P. A.: Source fingerprints for volatile non-methane hydrocarbons, J. Air Waste Manag. Assoc. 42, 1437–1445, 1992. Emmons,~L K., Walters,~S., Hess,~P G., Lamarque,~J.-F., Pfister,~G G., Fillmore,~D., Granier,~C., Guenther,~A., Kinnison,~D., Laepple,~T., Orlando,~J., Tie,~X., Tyndall,~G., Wiedinmyer,~C., Baughcum,~S L., and Kloster,~S.: Description and evaluation of the Model for Ozone and Related chemical Tracers, version 4 (MOZART-4), Geosci. Model Dev., 3, 43–67, 2010a Emmons, L. K., Apel, E. C., Lamarque, J.-F., et al.: Impact of Mexico City emissions on regional air quality from MOZART-4 simulations, Atmos. Chem. Phys. Discuss., 10, 3457–3498, 2010b. Fast, J. D., de Foy, B., Acevedo Rosas, F., Caetano, E., Carmichael, G., Emmons, L., McKenna, D., Mena, M., Skamarock, W., Tie, X., Coulter, R. L., Barnard, J. C., Wiedinmyer, C., and Madronich, S.: A meteorological overview of the MILAGRO field campaigns, Atmos. Chem. Phys., 7, 2233–2257, 2007. Fast, J. D.: Evaluating simulated primary anthropogenic and biomass burning organic aerosols during MILAGRO: implications for assessing treatments of secondary organic aerosols, Atmospheric Chemistry and Physics Discussions, 9, 4805–4871, 2009. Fortner,~E C., Zheng,~J., Zhang,~R., Berk~Knighton,~W., Volkamer,~R M., Sheehy,~P., Molina,~L., and André,~M.: Measurements of Volatile Organic Compounds Using Proton Transfer Reaction – Mass Spectrometry during the MILAGRO 2006 Campaign, Atmos. Chem. Phys., 9, 467–481, 2009. Fried, A. Weibring, P., Walega, J., et al.: Detailed Comparisons of Airborne Tunable Diode Laser Absorption Spectroscopy Measurements of Formaldehyde with Box Model Calculations during the 2006 INTEX-B Campaign over Mexico, the Gulf of Mexico and the Remote Pacific Ocean, in preparation, Atmos. Chem, Phys., 2010. Galbally, I. E. and Kirstine, W.: The production of methanol by flowering plants and the global cycle of methanol, J. Atmos. Chem., 43, 195–229, 2002. 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, 4545–4557, 2006. Gelencsér, A., Siszler, K., and Hlavay, J.: Toluene-benzene concentration ratio as a tool for characterizing the distance from vehicular emission sources, Environ. Sci. Technol., $31$, 2869–2872, 1997. Granier, C. et al.: Present and future surface emissions of atmospheric compounds, European Commission report EVK 2199900011, http://www.aero.jussieu.fr/projet/ACCENT/POET.php, 2004. Grell, G. A., Peckham, S. E., Schmitz, R., McKeen, S. A., Wilczak, J., and B. Eder, Fully coupled "online" chemistry within the WRF model, Atmos. Environ. 39, 6957–6975, 2005. Grutter, M., Flores, E., Andraca-Ayala, G., and Baez, A.: Formaldehyde levels in downtown Mexico City during 2003, Atmos. Environ., 39, 1027–1034, 2005. Hak,~C., Pundt,~I., Trick,~S., Kern,~C., Platt,~U., Dommen,~J., Ordóñez,~C., Prévôt,~A S H., Junkermann,~W., Astorga-Lloréns,~C., Larsen,~B R., Mellqvist,~J., Strandberg,~A., Yu,~Y., Galle,~B., Kleffmann,~J., Lörzer,~J C., Braathen,~G O., and Volkamer,~R.: Intercomparison of four different in-situ techniques for ambient formaldehyde measurements in urban air, Atmos. Chem. Phys., 5, 2881–2900, 2005. Heikes, B. G., Chang, W., Pilson, M. E. Q., Swift, E., Singh, H. B., Guenther, A., Jacob, D. J., Field, B. D., Fall, R., Riemer, D., and Brand, L.: Atmospheric Methanol Budget and Ocean Implications, Global Biogeochem. Cy., 16(80), 1–13, 2002. Jacob, D. J., Crawford, J. H., Kleb, M. M., Connors, V. S., Bendura, R. J., Raper, J. L., Sachse, G. W., Gille, J. C., Emmons, L., and Heald, C. L.: The Transport and Chemical Evolution over the Pacific (TRACE-P) aircraft mission: design, execution, and first results, J. Geophys. Res., 108, 9000, doi:10.1029/2002JD003276, 2003. Junkermann W. and Burger, J. M.: A new portable instrument for continuous measurement of formaldehyde in ambient air, J. Atmos. Ocean. Technol., 23, 38–45, 2006. Karl, T.,~Apel, E.,~Hodzic, A.,~Riemer, D D.,~Blake, D R., and~Wiedinmyer, C.: Emissions of volatile organic compounds inferred from airborne flux measurements over a megacity, Atmos. Chem. Phys.,~9,~271–285, 2009 Lei, W., Zavala, M., de Foy, B., Volkamer, R., and Molina, L. T.: Characterizing ozone production and response under different meteorological conditions in Mexico City Atmos. Chem. Phys., 8, 7571–7581, 2008. 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., 7, 1347–1366, 2007. Lei, W., Zavala, M., de Foy, B., Volkamer, R., Molina, M. J., and Molina, L. T.:Impact of primary formaldehyde on air pollution in the Mexico City Metropolitan Area, Atmos. Chem. Phys., 9, 2607–2618, 2009. Lin, X., Trainer, M., and Liu, S. C.: On the nonlinearity of the tropospheric ozone production, J. Geophys. Res., 93(D12), 15879–15888, doi:10.1029/88JD03750, 1988. Lindinger, W., Hansel, A., and Jordan, A.: Proton transfer reaction-mass spectrometry (PTR-MS): on-line monitoring of volatile organic compounds at pptv levels, Chem. Soc. Rev., 27, 347–354, 1998. Madronich, S. and Flocke, S.: The role of solar radiation in atmospheric chemistry, in Handbook of Environmental Chemistry, edited by: Boule, P., Springer-Verlag, Heidelberg, Germany, 1–26, 1999. Madronich, S.: Chemical evolution of gaseous air pollutants down-wind of tropical megacities: Mexico City case study, Atmos. Environ., 40, 6012–6018, 2006. McKeen, S., Liu, S., Hsie, E.-Y., Lin, X., Bradshaw, J., Smyth, S., Gregory, G., and Blake, D.: Hydrocarbon ratios during PEM West A: a model perspective, J. Geophys. Res., 101D, 15, 2087–2109, 1996. Mena-Carrasco, M., Carmichael, G. R., Campbell, J. E., Zimmerman, D., Tang, Y., Adhikary, B., D'allura, A., Molina, L. T., Zavala, M., García, A., Flocke, F., Campos, T., Weinheimer, A. J., Shetter, R., Apel, E., Montzka, D. D., Knapp, D. J., and Zheng, W.: Assessing the regional impacts of Mexico City emissions on air quality and chemistry, Atmos. Chem. Phys., 9, 3731–3743, 2009. Millet,~D B., Jacob,~D J., Custer,~T G., de~Gouw,~J A., Goldstein,~A H., Karl,~T., Singh,~H B., Sive,~B C., Talbot,~R W., Warneke,~C., and Williams,~J.: New constraints on terrestrial and oceanic sources of atmospheric methanol, Atmos. Chem. Phys., 8, 6887–6905, 2008. Molina, L. and Molina, M. (Eds.): Air Quality in the Mexico MegaCity: An Integrated Assessment, Kluwer Academic Publishers, Dordrecht, The Netherlands, 384 pp., 2002. Molina, L., E., de Foy, B., Fast, J., et al.: An Overview of the MILAGRO 2006 Campaign: Mexico City Emissions and their Transport and Transformation, submitted, Atmos. Chem Phys. Discuss., submitted, 2010. Molina, L. T., Madronich, S., Gaffney, J. S., and Singh, H. B.: Overview of MILAGRO/INTEX-B Campaign, IGAC Newsletter, 38, 2–15, 2008. Ortega, J., Karl, T., Kleinman, L., et al.: Intercomparison of in-flight VOC concentrations using proton transfer mass spectrometry (PTR-MS) during the MILAGRO Campaign (March 2006): Battelle G-1 vs. NCAR C-130 coordinated flights, First MILAGRO Science Meeting, 2006. Parrish, D. D., Trainer, M., Holloway, J. S., Yee, J. E., Warshawsky, M. S., Fehsenfeld, F. C., Forbes, G. L., and Moody, J. L.: Relationships between ozone and carbon monoxide at surface sites in the North Atlantic region, J. Geophys. Res., 103, 20, 13357–13376, 1998. Parrish, D. D., Dunlea, E., Atlas, E., Schauffler, S., Donnelly, S., Stroud, V., Goldstein, A., Millet, D., McKay, M., Jaffe, D., Price, H., Hess, P., Flocke, F., and Roberts, J.: Changes in the photochemical environment of the temperate North Pacific troposphere in response to increased Asian emissions, J. Geophys. Res. 109, D23S18, doi:10.1029/2004JD004978, 2004. Seila, R. L., Lonneman, W. A., and Meeks, S. A.: Determination of C<sub>2</sub> to C$_12$ ambient air hydrocarbons in 39 U.S. cities, from 1984 through 1986, project summary, US Environ. Prot. Agency, Washington DC, USA, 418 pp., 1989. Singh, H. B., Kanakidou, M., Crutzen, P. J., and Jacob, D. J.: High concentrations and photochemical fate of oxygenated hydrocarbons in the global troposphere, Nature, 378, 50–54, 1995. Stroud, C. A., Morneau, G., Makar, P. A., Moran, M. D., Gong, W., Pabla, B., Zhang, J., Bouchet, V. S., Fox, D., Venkatesh, S., Wang, D., and Dann, T.: OH-reactivity of volatile organic compounds at urban and rural sites across Canada: Evaluation of air quality model predictions using speciated VOC measurements, Atmos. Env., 42, 7746–7756, 2008. Roberts, J., Fehsenfeld, F., Liu, S., Bollinger, M., Hahn, C., Albritton, D., and Sievers, R.: Measurements of aromatic hydrocarbon ratios and NO<sub>x</sub> concentrations in the rural troposphere: observation of air mass photochemical aging and NO<sub>x</sub> removal, Atmos. Environ., 18, 2421–2432, 1984. Rogers, T. M., Grimsrud, E. R., 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, 26–37, 2006. Sommariva, R., Osthoff, H. D., Brown, S. S., Bates, T. S., Baynard, T., Coffman, D., de Gouw, J. A., Goldan, P. D., Kuster, W. C., Lerner, B. M., Stark, H., Warneke, C., Williams, E. J., Fehsenfeld, F. C., Ravishankara, A. R., and Trainer, M.: Radicals in the marine boundary layer during NEAQS 2004: a model study of day-time and night-time sources and sinks, Atmos. Chem. Phys., 9, 3075–3093, 2009. Tie, X., Madronich, S., Walters, S., Rasch, P., and Collins, W.: Effect of Clouds on photolysis and oxidants in the troposphere, J. Geophys. Res., 108, 4642, doi:10.1029/2003JD003659, 2003. Tie, X. X., Madronich, S., Li, G. H., Ying, Z. M., Zhang, R. Y., Garcia, A. R., Lee-Taylor, J., and Liu, Y. B.: Characterizations of chemical oxidants in Mexico City: A regional chemical dynamical model (WRF-Chem) study, Atmos. Environ., 41, 1989–2008, 2007. Tie X., Madronich, S., Li, G., Ying, Z., Weinheimer, A., Apel, E., and Campos, T.: Simulation of Mexico City Plumes during the MIRAGE-Mex Field Campaign using the WRF-Chem model, Atmos. Chem. Phys., 9, 4621–4638, 2009. Vega, E., Mugica, V., Carmona, R., and Valencia, E.: Hydrocarbon source apportionment in Mexico City using the chemical mass balance receptor model, Atmos. Environ., 34, 4121–4129, 2000. 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. Velasco, E., B. Lamb, H. Westberg, E. Allwine, G. Sosa, J. L. Arriaga-Colina, B. T. Jobson, M. L. 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, and M. J. Molina Distribution, magnitudes, reactivities, ratios and diurnal patterns of volatile organic compounds in the Valley of Mexico during the MCMA 2002 & 2003 field campaigns, Atmos. Chem. Phys., 7, 329–353, 2007. 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. Volkamer, R., San Martini, F., Salcedo, D., Molina, L. T., Jimenez, J. L., and Molina, M. J.: A Missing Sink for Gas-Phase Glyoxal in Mexico City: Formation of Secondary Organic Aerosol, Geophys. Res. Lett., 34, L19807, doi:10.1029/2007GL030752, 2007. Voss, P. B., Zaveri, R. A., Flocke, F. M., Mao, H., Hartley, T. P., DeAmicis, P., Deonandan, I., Contreras-Jiménez, G., Martínez-Antonio, O., Figueroa Estrada, M., Greenberg, D., Campos, T. L., Weinheimer, A. J., Knapp, D. J., Montzka, D. D., Crounse, J. D., Wennberg, P. O., Apel, E., Madronich, S., and de Foy, B.: Long-range pollution transport during the MILAGRO-2006 campaign: a case study of a major Mexico City outflow event using free-floating altitude-controlled balloons, Atmos. Chem. Phys. Discuss., 10, 3347–3399, 2010. Voss, P., Hartley, T. P., DeAmicis, P., et al.: Reconstruction of trajectories, mixing, and dispersion of a Mexico City pollution outflow event using in-situ observations from free-floating altitude-controlled balloons, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract A41F-07, 2007. Warneke, C., McKeen, S. A., de Gouw, J. A., et al.: Determination of urban volatile organic compound emission ratios and comparison with an emissions database, J. Geophys. Res., 112, D10S47, doi:10.1029/2006JD007930, 2007. Warneke, C., de Gouw, J. A., Lovejoy, E. R., Murphy, P. C., Kuster, W. C., and Fall, R.: Development of Proton-Transfer Ion Trap-Mass Spectrometry: on-line detection and identification of volatile organic compounds in air, J. Amer.. Soc. M. Spectrom. 16, 1316–1324, 2005a. Wert, B. P., Trainer, M., Fried, A., et al.: Signatures of terminal alkene oxidation in airborne formaldehyde measurements during TexAQS 2000, J. Geophys. Res., 108, 4104, doi:10.1029/2002JD002502, 2003. Wesely, M. L.: Parameterization of surface resistance to gaseous dry deposition in regional-scale numerical models, Atmos. Environ. 23, 1293–1304, 1989. West, J. J., Zavala, M. A., Molina, L. T., Molina, M. J., Martini, F. S., McRae, G. J., Iglesias, G. S., and Colina, J. L.: Modeling ozone photochemistry and evaluation of hydrocarbon emissions in the Mexico City metropolitan area, J. Geophys. Res., 109, D19312, doi:10.1029/2004JD004614, 2004. Wiedinmyer, C., Quayle, B., Geron, C., Belote, A., McKenzie, D., Zhang, X., O'Neill, S., and Wynne, K.: Estimating emissions from fires in North America for air quality modeling, Atmos. Environ., 40, 3419–3432, 2006. Wood, E. C., Herndon, S. C., Onasch, T. B., Kroll, J. H., Canagaratna, M. R., Kolb, C. E., Worsnop, D. R., Neuman, J. A., Seila, R., Zavala, M., and Knighton, W. B.: A case study of ozone production, nitrogen oxides, and the radical budget in Mexico City, Atmos. Chem. Phys., 9, 2499–2516, 2009. Yokelson, R. B., Urbanski, S. P., Atlas, E. L., Toohey, D. W., Alvarado, E. C., Crounse, J. D., Wennberg, P. O., Fisher, M. E., Wold, C. E., Campos, T. L. Adachi, K., Buseck, P. R., and Hao, W. M., Emissions from forest fires near Mexico City, Atmos. Chem. Phys., 7, 5569–5584, 2007. 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, 5129–5142, 2006. Zhang, Q., Streets, D. G., Carmichael, G. R., He, K. B., Huo, H., Kannari, A., Klimont, Z., Park, I. S., Reddy, S., Fu, J. S., Chen, D., Duan, L., Lei, Y., Wang, L. T., and Yao, Z. L.: Asian emissions in 2006 for the NASA INTEX-B mission, Atmos. Chem. Phys., 9, 5131–5153, 2009a. Zhang, Y., Dubey, M. K., Olsen, S. C., Zheng, J., and Zhang, R.: Comparisons of WRF/Chem simulations in Mexico City with ground-based RAMA measurements during the 2006-MILAGRO, Atmos. Chem. Phys., 9, 3777–3798, 2009. Zhao, J. and Zhang, R. Y.: Proton transfer reaction rate constants between hydronium ion (H<sub>3</sub>O$^(+)$) and volatile organic compounds, Atmos. Environ., 38, 2177–2185, 2004.