References

ACP

Atmospheric Chemistry and Physics

ACP

1680-7324

Copernicus GmbH

Göttingen, Germany

10.5194/acp-11-13305-2011

Formation of semivolatile inorganic aerosols in the Mexico City Metropolitan Area during the MILAGRO campaign

Karydis

V. A.

¹ ² Tsimpidi

A. P.

¹ ² Lei

⁴ Molina

L. T.

³ ⁴ Pandis

S. N.

¹ ² ⁵

Institute of Chemical Engineering and High Temperature Chemical Processes, Foundation for Research and Technology Hellas, Patras, Greece

Dept. of Chemical Engineering, University of Patras, Patras, Greece

Dept. of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, USA

Molina Center for Energy and the Environment (MCE2), La Jolla, CA 92037, USA

Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA

22 12 2011

11 24 13305 13323

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/11/13305/2011/acp-11-13305-2011.html

The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/13305/2011/acp-11-13305-2011.pdf

One of the most challenging tasks for chemical transport models (CTMs) is the prediction of the formation and partitioning of the major semi-volatile inorganic aerosol components (nitrate, chloride, ammonium) between the gas and particulate phases. In this work the PMCAMx-2008 CTM, which includes the recently developed aerosol thermodynamic model ISORROPIA-II, is applied in the Mexico City Metropolitan Area in order to simulate the formation of the major inorganic aerosol components. The main sources of SO2 (such as the Miguel Hidalgo Refinery and the Francisco Perez Rios Power Plant) in the Mexico City Metropolitan Area (MCMA) are located in Tula, resulting in high predicted PM1 (particulate matter with diameter less than 1 μm) sulfate concentrations (over 25 μg m-3) in that area. The average predicted PM1 nitrate concentrations are up to 3 μg m−3 (with maxima up to 11 μg m−3) in and around the urban center, mostly produced from local photochemistry. The presence of calcium coming from the Tolteca area (7 μg m−3) as well as the rest of the mineral cations (1 μg m−3 potassium, 1 μg m−3 magnesium, 2 μg m−3 sodium, and 3 μg m−3 calcium) from the Texcoco Lake resulted in the formation of a significant amount of aerosol nitrate in the coarse mode with concentrations up to 3 μg m−3 over these areas. PM1−10 (particulate matter with diameter between 1 and 10 μm) chloride is also high and its concentration exceeds 2 μg m−3 in Texcoco Lake. PM1 ammonium concentrations peak at the center of Mexico City (2 μg m−3) and the Tula vicinity (2.5 μg m−3). The performance of the model for the major inorganic PM components (sulfate, ammonium, nitrate, chloride, sodium, calcium, and magnesium) is encouraging. At the T0 measurement site, located in the Mexico City urban center, the average measured values of PM1 sulfate, nitrate, ammonium, and chloride are 3.5 μg m−3, 3.5 μg m−3, 2.1 μg m−3, and 0.36 μg m−3, respectively. The corresponding predicted values are 3.7 μg m−3, 2.7 μg m−3, 1.7 μg m−3, and 0.25 μg m−3. High sulfate concentrations are associated with the transport of sulfate from the Tula vicinity, while in periods where southerly winds are dominant; the concentrations of sulfate are low. The underprediction of nitrate can be attributed to the underestimation of OH levels by the model during the early morning. Ammonium is sensitive to the predicted sulfate concentrations and the nitrate levels. The performance of the model is also evaluated against measurements taken from a suburban background site (T1) located north of Mexico City. The average predicted PM2.5 (particulate matter with diameter less than 2.5 μm) sulfate, nitrate, ammonium, chloride, sodium, calcium, and magnesium are 3.3, 3.2, 1.4, 0.5, 0.3, 1.2, and 0.15 μg m−3, respectively. The corresponding measured concentrations are 3.7, 2.9, 1.5, 0.3, 0.4, 0.6, and 0.15 μg m−3. The overprediction of calcium indicates a possible overestimation of its emissions and affects the partitioning of nitric acid to the aerosol phase resulting occasionally in an overprediction of nitrate. Additional improvements are possible by improving the performance of the model regarding the oxidant levels, and revising the emissions and the chemical composition of the fugitive dust. The hybrid approach in which the mass transfer to the fine aerosol is simulated using the bulk equilibrium assumption and to the remaining aerosol sections using a dynamic approach, is needed in order to accurately simulate the size distribution of the inorganic aerosols. The bulk equilibrium approach fails to reproduce the observed coarse nitrate and overpredicts the fine nitrate. Sensitivity tests indicate that sulfate concentration in Tula decreases by up to 0.5 μg m−3 after a 50% reduction of SO2 emissions while it can increase by up to 0.3 μg m−3 when NOx emissions are reduced by 50%. Nitrate concentration decreases by up to 1 μg m−3 after the 50% reduction of NOx or NH3 emissions. Ammonium concentration decreases by up to 1 μg m−3, 0.3 μg m−3, and 0.1 μg m−3 after the 50% reduction of NH3, NOx, and SO2 emissions, respectively.

References 1

Adhikary, B., Carmichael, G. R., Kulkarni, S., Wei, C., Tang, Y., D'Allura, A., Mena-Carrasco, M., Streets, D. G., Zhang, Q., Pierce, R. B., Al-Saadi, J. A., Emmons, L. K., Pfister, G. G., Avery, M. A., Barrick, J. D., Blake, D. R., Brune, W. H., Cohen, R. C., Dibb, J. E., Fried, A., Heikes, B. G., Huey, L. G., O'Sullivan, D. W., Sachse, G. W., Shetter, R. E., Singh, H. B., Campos, T. L., Cantrell, C. A., Flocke, F. M., Dunlea, E. J., Jimenez, J. L., Weinheimer, A. J., Crounse, J. D., Wennberg, P. O., Schauer, J. J., Stone, E. A., Jaffe, D. A., and Reidmiller, D. R.: A regional scale modeling analysis of aerosol and trace gas distributions over the eastern Pacific during the INTEX-B field campaign, Atmos. Chem. Phys., 10, 2091–2115, http://dx.doi.org/10.5194/acp-10-2091-2010doi:10.5194/acp-10-2091-2010, 2010.

Aiken, A. C., Salcedo, D., Cubison, M. J., Huffman, J. A., DeCarlo, P. F., Ulbrich, I. M., Docherty, K. S., Sueper, D., Kimmel, J. R., Worsnop, D. R., Trimborn, A., Northway, M., Stone, E. A., Schauer, J. J., Volkamer, R. M., Fortner, E., de Foy, B., Wang, J., Laskin, A., Shutthanandan, V., Zheng, J., Zhang, R., Gaffney, J., Marley, N. A., Paredes-Miranda, G., Arnott, W. P., Molina, L. T., Sosa, G., and Jimenez, J. L.: Mexico City aerosol analysis during MILAGRO using high resolution aerosol mass spectrometry at the urban supersite (T0) � Part 1: Fine particle composition and organic source apportionment, Atmos. Chem. Phys., 9, 6633–6653, http://dx.doi.org/10.5194/acp-9-6633-2009doi:10.5194/acp-9-6633-2009, 2009.

Ansari, A. S. and Pandis, S. N.: Response of inorganic PM to precursor concentrations, Environ. Sci. Technol., 32, 2706–2714, 1998.

Ansari, A. S. and Pandis, S. N.: Prediction of multicomponent inorganic atmospheric aerosol behavior, Atmos. Environ., 33, 745–757, 1999a.

Ansari, A. S. and Pandis, S. N.: An analysis of four models predicting the partitioning of semivolatile inorganic aerosol components, Aerosol Sci. Technol., 31, 129–153, 1999b.

Ansari, A. S. and Pandis, S. N.: The effect of metastable equilibrium states on the partitioning of nitrate between the gas and aerosol phases, Atmos. Environ., 34, 157–168, 2000.

Apel, E. C., Emmons, L. K., Karl, T., Flocke, F., Hills, A. J., Madronich, S., Lee-Taylor, J., Fried, A., Weibring, P., Walega, J., Richter, D., Tie, X., Mauldin, L., Campos, T., Weinheimer, A., Knapp, D., Sive, B., Kleinman, L., Springston, S., Zaveri, R., Ortega, J., Voss, P., Blake, D., Baker, A., Warneke, C., Welsh-Bon, D., de Gouw, J., Zheng, J., Zhang, R., Rudolph, J., Junkermann, W., and Riemer, D. D.: Chemical evolution of volatile organic compounds in the outflow of the Mexico City Metropolitan area, Atmos. Chem. Phys., 10, 2353–2375, http://dx.doi.org/10.5194/acp-10-2353-2010doi:10.5194/acp-10-2353-2010, 2010.

Arellano Jr., A. F., Raeder, K., Anderson, J. L., Hess, P. G., Emmons, L. K., Edwards, D. P., Pfister, G. G., Campos, T. L., and Sachse, G. W.: Evaluating model performance of an ensemble-based chemical data assimilation system during INTEX-B field mission, Atmos. Chem. Phys., 7, 5695–5710, http://dx.doi.org/10.5194/acp-7-5695-2007doi:10.5194/acp-7-5695-2007, 2007.

Aumont, B., Chervier, F., and Laval, S.: Contribution of HONO sources to the NOx/HO$_x$/O−3 chemistry in the polluted boundary layer, Atmos. Environ., 37, 487–498, 2003.

Bassett, M. and Seinfeld, J. H.: Atmospheric equilibrium-model of sulfate and nitrate aerosols, Atmos. Environ., 17, 2237–2252, 1983.

Capaldo, K. P., Pilinis, C., and Pandis, S. N.: A computationally efficient hybrid approach for dynamic gas/aerosol transfer in air quality models, Atmos. Environ., 34, 3617–3627, 2000.

Carter, W. P. L.: Implementation of the SAPRC-99 chemical mechanism into the models-3 framework: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.25.293&rep=rep1&type=pdf, last access: 2 August 2011, 2000.

Chow, J. C. and Egami, R. T.: San Joaquin Valley 1995 integrated monitoring study: Documentation, evaluation, and descriptive data analysis of PM10, PM2.5, and precursor gas measurements. Technical Support Studies No. 4 and No. 8. Final Report prepared for the Technical Support Division, California Air Resources Board, Sacramento, CA by Desert Research Institute, Reno, NV, DRI Document No. 5460.1F1, 1997.

Clegg, S. L., Brimblecombe, P., and Wexler, A. S.: Thermodynamic model of the system H$^+$-NH$_4^+$-Na$^+$-SO$_4^2-$-NB$_3^-$-Cl$^-$-H2O at 298.15 K, J. Phys. Chem. A, 102, 2155–2171, 1998a.

Clegg, S. L., Brimblecombe, P., and Wexler, A. S.: Thermodynamic model of the system H$^+$-NH$_4^+$-SO$_4^2-$-NO$_3^-$-H2O at tropospheric temperatures, J. Phys. Chem. A, 102, 2137–2154, 1998b.

Dassios, K. G. and Pandis, S. N.: The mass accommodation coefficient of ammonium nitrate aerosol, Atmos. Environ., 33, 2993–3003, http://dx.doi.org/10.1016/s1352-2310(99)00079-5doi:10.1016/s1352-2310(99)00079-5, 1999.

DeCarlo, P. F., Kimmel, J. R., Trimborn, A., Northway, M. J., Jayne, J. T., Aiken, A. C., Gonin, M., Fuhrer, K., Horvath, T., Docherty, K. S., Worsnop, D. R., and Jimenez, J. L.: Field-deployable, high-resolution, time-of-flight aerosol mass spectrometer, Anal. Chem., 78, 8281–8289, http://dx.doi.org/10.1021/ac061249ndoi:10.1021/ac061249n, 2006.

DeCarlo, P. F., Dunlea, E. J., Kimmel, J. R., Aiken, A. C., Sueper, D., Crounse, J., Wennberg, P. O., Emmons, L., Shinozuka, Y., Clarke, A., Zhou, J., Tomlinson, J., Collins, D. R., Knapp, D., Weinheimer, A. J., Montzka, D. D., Campos, T., and Jimenez, J. L.: Fast airborne aerosol size and chemistry measurements above Mexico City and Central Mexico during the MILAGRO campaign, Atmos. Chem. Phys., 8, 4027–4048, http://dx.doi.org/10.5194/acp-8-4027-2008doi:10.5194/acp-8-4027-2008, 2008.

Draxler, R. R., Gillette, D. A., Kirkpatrick, J. S., and Heller, J.: Estimating PM$_10$ air concentrations from dust storms in Iraq, Kuwait and Saudi Arabia, Atmos. Environ., 35, 4315–4330, 2001.

Environ: User's guide to the comprehensive air quality model with extensions (CAMx). Version 4.02. Report prepared by ENVIRON International Corporation, Novato, CA. , 2003.

Fahey, K. M. and Pandis, S. N.: Optimizing model performance: variable size resolution in cloud chemistry modeling, Atmos. Environ., 35, 4471–4478, 2001.

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, http://dx.doi.org/10.5194/acp-7-2233-2007doi:10.5194/acp-7-2233-2007, 2007.

Fast, J., Aiken, A. C., Allan, J., Alexander, L., Campos, T., Canagaratna, M. R., Chapman, E., DeCarlo, P. F., de Foy, B., Gaffney, J., de Gouw, J., Doran, J. C., Emmons, L., Hodzic, A., Herndon, S. C., Huey, G., Jayne, J. T., Jimenez, J. L., Kleinman, L., Kuster, W., Marley, N., Russell, L., Ochoa, C., Onasch, T. B., Pekour, M., Song, C., Ulbrich, I. M., Warneke, C., Welsh-Bon, D., Wiedinmyer, C., Worsnop, D. R., Yu, X.-Y., and Zaveri, R.: Evaluating simulated primary anthropogenic and biomass burning organic aerosols during MILAGRO: implications for assessing treatments of secondary organic aerosols, Atmos. Chem. Phys., 9, 6191–6215, http://dx.doi.org/10.5194/acp-9-6191-2009doi:10.5194/acp-9-6191-2009, 2009.

Finlayson-Pitts, B. J. and Pitts, J. N.: Chemistry of the Upper and Lower Atmosphere, Academic Press, San Diego, 2000.

%Fountoukis, C. and Nenes, A.: ISORROPIA II: a computationally efficient %thermodynamic equilibrium model for %K$^+$-Ca$^2+$-Mg$^2+$-NH$_4^+$-Na$^+$-SO$_4^2-$-NO$_3^-$-Cl$^-$-H2O %aerosols, Atmos. Chem. Phys., 7, 4639-4659, 2007. Fountoukis, C. and Nenes, A.: ISORROPIA II: a computationally efficient thermodynamic equilibrium model for K$^+$-Ca$^2+$-Mg$^2+$-NH$_4^+$-Na$^+$-SO$_4^2-$-NO$_3^-$-Cl$^-$-H2O aerosols, Atmos. Chem. Phys., 7, 4639–4659, http://dx.doi.org/10.5194/acp-7-4639-2007doi:10.5194/acp-7-4639-2007, 2007.

Fountoukis, C., Nenes, A., Sullivan, A., Weber, R., Van Reken, T., Fischer, M., Mat�as, E., Moya, M., Farmer, D., and Cohen, R. C.: Thermodynamic characterization of Mexico City aerosol during MILAGRO 2006, Atmos. Chem. Phys., 9, 2141–2156, http://dx.doi.org/10.5194/acp-9-2141-2009doi:10.5194/acp-9-2141-2009, 2009.

Fountoukis, C., Racherla, P. N., Denier van der Gon, H. A. C., Polymeneas, P., Charalampidis, P. E., Pilinis, C., Wiedensohler, A., Dall'Osto, M., O'Dowd, C., and Pandis, S. N.: Evaluation of a three-dimensional chemical transport model (PMCAMx) in the European domain during the EUCAARI May 2008 campaign, Atmos. Chem. Phys., 11, 10331–10347, http://dx.doi.org/10.5194/acp-11-10331-2011doi:10.5194/acp-11-10331-2011, 2011.

Gaydos, T. M., Pinder, R., Koo, B., Fahey, K. M., Yarwood, G., and Pandis, S. N.: Development and application of a three-dimensional aerosol chemical transport model, PMCAMx, Atmos. Environ., 41, 2594–2611, http://dx.doi.org/10.1016/j.atmosenv.2006.11.034doi:10.1016/j.atmosenv.2006.11.034, 2007.

Gaydos, T. M., Koo, B., Pandis, S. N., and Chock, D. P.: Development and application of an efficient moving sectional approach for the solution of the atmospheric aerosol condensation/evaporation equations, Atmos. Environ., 37, 3303–3316, http://dx.doi.org/10.1016/s1352-2310(03)00267-xdoi:10.1016/s1352-2310(03)00267-x, 2003.

Hildemann, L. M., Russell, A. G., and Cass, G. R.: Ammonia and nitric-acid concentrations in equilibrium with atmospheric aerosols – experiment vs.\ theory, Atmos. Environ., 18, 1737-1750, 1984.

Hodzic, A., Jimenez, J. L., Madronich, S., Aiken, A. C., Bessagnet, B., Curci, G., Fast, J., Lamarque, J.-F., Onasch, T. B., Roux, G., Schauer, J. J., Stone, E. A., and Ulbrich, I. M.: Modeling organic aerosols during MILAGRO: importance of biogenic secondary organic aerosols, Atmos. Chem. Phys., 9, 6949–6981, http://dx.doi.org/10.5194/acp-9-6949-2009doi:10.5194/acp-9-6949-2009, 2009.

Hodzic, A., Jimenez, J. L., Madronich, S., Canagaratna, M. R., DeCarlo, P. F., Kleinman, L., and Fast, J.: Modeling organic aerosols in a megacity: potential contribution of semi-volatile and intermediate volatility primary organic compounds to secondary organic aerosol formation, Atmos. Chem. Phys., 10, 5491–5514, http://dx.doi.org/10.5194/acp-10-5491-2010doi:10.5194/acp-10-5491-2010, 2010.

Jacobson, M. Z.: Development and application of a new air pollution modeling system .2. Aerosol module structure and design, Atmos. Environ., 31, 131–144, 1997a.

Jacobson, M. Z., Tabazadeh, A., and Turco, R. P.: Simulating equilibrium within aerosols and nonequilibrium between gases and aerosols, J. Geophys. Res.-Atmos., 101, 9079–9091, 1996.

Jacobson, M. Z.: Numerical techniques to solve condensational and dissolutional growth equations when growth is coupled to reversible reactions, Aerosol Sci. Technol., 27, 491–498, 1997b.

Jacobson, M. Z.: Studying the effects of calcium and magnesium on size-distributed nitrate and ammonium with EQUISOLV II, Atmos. Environ., 33, 3635–3649, 1999.

Karydis, V. A., Tsimpidi, A. P., and Pandis, S. N.: Evaluation of a three-dimensional chemical transport model (PMCAMx) in the eastern United States for all four seasons, J. Geophys. Res.-Atmos., 112, D14211, http://dx.doi.org/10.1029/2006jd007890doi:10.1029/2006jd007890, 2007.

Karydis, V. A., Tsimpidi, A. P., Fountoukis, C., Nenes, A., Zavala, M., Lei, W. F., Molina, L. T., and Pandis, S. N.: Simulating the fine and coarse inorganic particulate matter concentrations in a polluted megacity, Atmos. Environ., 44, 608–620, http://dx.doi.org/10.1016/j.atmosenv.2009.11.023doi:10.1016/j.atmosenv.2009.11.023, 2010.

Kim, Y. P. and Seinfeld, J. H.: Atmospheric gas-aerosol equilibrium .3. Thermodynamics of crustal elements Ca$^2+$, K$^+$, and Mg$^2+$, Aerosol Sci. Technol., 22, 93–110, 1995.

Kim, Y. P., Seinfeld, J. H., and Saxena, P.: Atmospheric gas-aerosol equilibrium 2. Analysis of common approximations and activity-coefficient calculation methods, Aerosol Sci. Technol., 19, 182–198, 1993a.

Kim, Y. P., Seinfeld, J. H., and Saxena, P.: Atmospheric gas aerosol equilibrium .1. Thermodynamic model, Aerosol Sci. Technol., 19, 157–181, 1993b.

Koo, B. Y., Ansari, A. S., and Pandis, S. N.: Integrated approaches to modeling the organic and inorganic atmospheric aerosol components, Atmos. Environ., 37, 4757–4768, http://dx.doi.org/10.1016/j.atmosenv.2003.08.016doi:10.1016/j.atmosenv.2003.08.016, 2003.

Kumar, N., Lurmann, F. W., Pandis, S. N., and Ansari, A. S.: Final Report: analysis of atmospheric chemistry during 1995 integrated monitoring study. Final Report Prepared for the California Air Resources Board, Sacramento, CA by Sonoma Technology Inc., Santa Rosa, CA.STI-997214-1791-DFR, 1998.

Lane, T. E., Donahue, N. M., and Pandis, S. N.: Simulating secondary organic aerosol formation using the volatility basis-set approach in a chemical transport model, Atmos. Environ., 42, 7439–7451, http://dx.doi.org/10.1016/j.atmosenv.2008.06.026doi:10.1016/j.atmosenv.2008.06.026, 2008.

Lawson, D. R.: The southern california air-quality study, J. Air Waste Manage. Assoc., 40, 156–165, 1990.

Li, G., Lei, W., Zavala, M., Volkamer, R., Dusanter, S., Stevens, P., and Molina, L. T.: Impacts of HONO sources on the photochemistry in Mexico City during the MCMA-2006/MILAGO Campaign, Atmos. Chem. Phys., 10, 6551–6567, http://dx.doi.org/10.5194/acp-10-6551-2010doi:10.5194/acp-10-6551-2010, 2010.

Li, G., Zavala, M., Lei, W., Tsimpidi, A. P., Karydis, V. A., Pandis, S. N., Canagaratna, M. R., and Molina, L. T.: Simulations of organic aerosol concentrations in Mexico City using the WRF-CHEM model during the MCMA-2006/MILAGRO campaign, Atmos. Chem. Phys., 11, 3789–3809, http://dx.doi.org/10.5194/acp-11-3789-2011doi:10.5194/acp-11-3789-2011, 2011a.

Li, G., Bei, N., Tie, X., and Molina, L. T.: Aerosol effects on the photochemistry in Mexico City during MCMA-2006/MILAGRO campaign, Atmos. Chem. Phys., 11, 5169–5182, http://dx.doi.org/10.5194/acp-11-5169-2011doi:10.5194/acp-11-5169-2011, 2011b.

Lurmann, F. W., Wexler, A. S., Pandis, S. N., Musarra, S., Kumar, N., and Seinfeld, J. H.: Modelling urban and regional aerosols .2. Application to California's South Coast Air Basin, Atmos. Environ., 31, 2695–2715, 1997.

Meng, Z. Y. and Seinfeld, J. H.: Time scales to achieve atmospheric gas-aerosol equilibrium for volatile species, Atmos. Environ., 30, 2889–2900, http://dx.doi.org/10.1016/1352-2310(95)00493-9doi:10.1016/1352-2310(95)00493-9, 1996.

Meng, Z. Y., Seinfeld, J. H., Saxena, P., and Kim, Y. P.: Atmospheric gas-aerosol equilibrium .4. Thermodynamics of \mboxcarbonates, Aerosol Sci. Technol., 23, 131–154, 1995.

Meng, Z. Y., Dabdub, D., and Seinfeld, J. H.: Size-resolved and chemically resolved model of atmospheric aerosol dynamics, J. Geophys. Res.-Atmos., 103, 3419–3435, 1998.

Michalakes, J., Dudhia, J., Gill, D., Henderson, T., Klemp, J., Skamarock, W., and Wang, W.: The weather research and forecast model: Software architecture and performance, Use of High Performance Computing in Meteorology, edited by: Zwieflhofer, W. and Mozdzynski, G., World Scientific Publ. Co Pte Ltd, Singapore, 156–168, 2005.

Molina, L. T. and Molina, M. J.: Air Quality in the Mexico Megacity: An Integrated Assessment, Kluwer Academic Publishers, Dordrecht, The Netherlands, 2002.

Molina, L. T., Madronich, S., Gaffney, J. S., Apel, E., de Foy, B., Fast, J., Ferrare, R., Herndon, S., Jimenez, J. L., Lamb, B., Osornio-Vargas, A. R., Russell, P., Schauer, J. J., Stevens, P. S., Volkamer, R., and Zavala, M.: An overview of the MILAGRO 2006 Campaign: Mexico City emissions and their transport and transformation, Atmos. Chem. Phys., 10, 8697–8760, http://dx.doi.org/10.5194/acp-10-8697-2010doi:10.5194/acp-10-8697-2010, 2010.

Moya, M., Madronich, S., Retama, A., Weber, R., Baumann, K., Nenes, A., Castillejos, M., and de Leon, C. P.: Identification of chemistry-dependent artifacts on gravimetric PM fine readings at the T1 site during the MILAGRO field campaign, Atmos. Environ., 45, 244–252, http://dx.doi.org/10.1016/j.atmosenv.2010.08.059doi:10.1016/j.atmosenv.2010.08.059, 2011.

Murphy, B. N. and Pandis, S. N.: Simulating the Formation of Semivolatile Primary and Secondary Organic Aerosol in a Regional Chemical Transport Model, Environ. Sci. Technol., 43, 4722–4728, http://dx.doi.org/10.1021/es803168adoi:10.1021/es803168a, 2009.

Nenes, A., Pandis, S. N., and Pilinis, C.: ISORROPIA: A new thermodynamic equilibrium model for multiphase multicomponent inorganic aerosols, Aquat. Geochem., 4, 123–152, 1998.

Nenes, A., Pandis, S. N., and Pilinis, C.: Continued development and testing of a new thermodynamic aerosol module for urban and regional air quality models, Atmos. Environ., 33, 1553–1560, 1999.

Nguyen, M. T., Jamka, A. J., Cazar, R. A., and Tao, F. M.: Structure and stability of the nitric acid ammonia complex in the gas phase and in water, J. Chem. Phys., 106, 8710–8717, http://dx.doi.org/10.1063/1.473925doi:10.1063/1.473925, 1997.

Orsini, D. A., Ma, Y. L., Sullivan, A., Sierau, B., Baumann, K., and Weber, R. J.: Refinements to the particle-into-liquid sampler (PILS) for ground and airborne measurements of water soluble aerosol composition, Atmos. Environ., 37, 1243–1259, http://dx.doi.org/10.1016/S1352-2310(02)01015-4doi:10.1016/S1352-2310(02)01015-4, 2003.

Pandis, S. N., Wexler, A. S., and Seinfeld, J. H.: Secondary organic aerosol formation and transport 2. Predicting the ambient secondary organic aerosol-size distribution, Atmos. Environ. A-Gen., 27, 2403–2416, 1993.

Pilinis, C. and Seinfeld, J. H.: Continued development of a general equilibrium-model for inorganic multicomponent atmospheric aerosols, Atmos. Environ., 21, 2453–2466, 1987.

Pilinis, C. and Seinfeld, J. H.: Development and evaluation of an eulerian photochemical gas aerosol model, Atmos. Environ., 22, 1985–2001, 1988.

Pilinis, C., Capaldo, K. P., Nenes, A., and Pandis, S. N.: MADM – A new multicomponent aerosol dynamics model, Aerosol Sci. Technol., 32, 482–502, http://dx.doi.org/10.1080/027868200303597doi:10.1080/027868200303597, 2000.

Racherla, P. N. and Adams, P. J.: Sensitivity of global tropospheric ozone and fine particulate matter concentrations to climate change, J. Geophys. Res.-Atmos., 111, D24103, http://dx.doi.org/10.1029/2005jd006939doi:10.1029/2005jd006939, 2006.

Russell, A. G., McCue, K. F., and Cass, G. R.: Mathematical-modeling of the formation of nitrogen-containing air-pollutants 1. Evaluation of an eulerian photochemical model, Environ. Sci. Technol., 22, 263–270, 1988.

Saxena, P., Hudischewskyj, A. B., Seigneur, C., and Seinfeld, J. H.: A comparative-study of equilibrium approaches to the chemical characterization of secondary aerosols, Atmos. Environ., 20, 1471–1483, 1986.

Seinfeld, J. H. and Pandis, S. N.: Atmospheric Chemistry and Physics: From Air Pollution to Climate Change, 2nd edn., John Wiley & Sons, Inc., Hoboken, New Jersey, USA, 2006.

Shinozuka, Y., Clarke, A. D., DeCarlo, P. F., Jimenez, J. L., Dunlea, E. J., Roberts, G. C., Tomlinson, J. M., Collins, D. R., Howell, S. G., Kapustin, V. N., McNaughton, C. S., and Zhou, J.: Aerosol optical properties relevant to regional remote sensing of CCN activity and links to their organic mass fraction: airborne observations over Central Mexico and the US West Coast during MILAGRO/INTEX-B, Atmos. Chem. Phys., 9, 6727–6742, http://dx.doi.org/10.5194/acp-9-6727-2009doi:10.5194/acp-9-6727-2009, 2009.

Shrivastava, M., Fast, J., Easter, R., Gustafson, W. I., Zaveri, R. A., Jimenez, J. L., Saide, P., and Hodzic, A.: Modeling organic aerosols in a megacity: comparison of simple and complex representations of the volatility basis set approach, Atmos. Chem. Phys., 11, 6639–6662, http://dx.doi.org/10.5194/acp-11-6639-2011doi:10.5194/acp-11-6639-2011, 2011.

Shrivastava, M. K., Lane, T. E., Donahue, N. M., Pandis, S. N., and Robinson, A. L.: Effects of gas particle partitioning and aging of primary emissions on urban and regional organic aerosol concentrations, J. Geophys. Res.-Atmos., 113, D18301, http://dx.doi.org/10.1029/2007jd009735doi:10.1029/2007jd009735, 2008.

Singh, H. B., Brune, W. H., Crawford, J. H., Flocke, F., and Jacob, D. J.: Chemistry and transport of pollution over the Gulf of Mexico and the Pacific: spring 2006 INTEX-B campaign overview and first results, Atmos. Chem. Phys., 9, 2301–2318, http://dx.doi.org/10.5194/acp-9-2301-2009doi:10.5194/acp-9-2301-2009, 2009.

Song, J., Lei, W., Bei, N., Zavala, M., de Foy, B., Volkamer, R., Cardenas, B., Zheng, J., Zhang, R., and Molina, L. T.: Ozone response to emission changes: a modeling study during the MCMA-2006/MILAGRO Campaign, Atmos. Chem. Phys., 10, 3827–3846, http://dx.doi.org/10.5194/acp-10-3827-2010doi:10.5194/acp-10-3827-2010, 2010.

Stokes, R. H. and Robinson, R. A.: Interactions in aqueous nonelectrolyte solutions. I. Solute-solvent equilibria, J. Phys. Chem., 70, 2126–2131, http://dx.doi.org/10.1021/j100879a010doi:10.1021/j100879a010, 1966.

Tanner, R. L.: An ambient experimental-study of phase-equilibrium in the atmospheric system-aerosol H$^+$, NH$_4^+$,~SO$_4^2-$, NO$_3^-$, NH3(g), HNO3(g), Atmos. Environ., 16, 2935–2942, 1982.

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, http://dx.doi.org/10.5194/acp-9-4621-2009doi:10.5194/acp-9-4621-2009, 2009.

Tsimpidi, A. P., Karydis, V. A., and Pandis, S. N.: Response of inorganic fine particulate matter to emission changes of sulfur dioxide and ammonia: The eastern United States as a case study, J. Air Waste Manage. Assoc., 57, 1489–1498, http://dx.doi.org/10.3155/1047-3289.57.12.1489doi:10.3155/1047-3289.57.12.1489, 2007.

Tsimpidi, A. P., Karydis, V. A., Zavala, M., Lei, W., Molina, L., Ulbrich, I. M., Jimenez, J. L., and Pandis, S. N.: Evaluation of the volatility basis-set approach for the simulation of organic aerosol formation in the Mexico City metropolitan area, Atmos. Chem. Phys., 10, 525–546, http://dx.doi.org/10.5194/acp-10-525-2010doi:10.5194/acp-10-525-2010, 2010.

Tsimpidi, A. P., Karydis, V. A., Zavala, M., Lei, W., Bei, N., Molina, L., and Pandis, S. N.: Sources and production of organic aerosol in Mexico City: insights from the combination of a chemical transport model (PMCAMx-2008) and measurements during MILAGRO, Atmos. Chem. Phys., 11, 5153–5168, http://dx.doi.org/10.5194/acp-11-5153-2011doi:10.5194/acp-11-5153-2011, 2011.

Vega, E., Mugica, V., Reyes, E., Sanchez, G., Chow, J. C., and Watson, J. G.: Chemical composition of fugitive dust emitters in Mexico City, Atmos. Environ., 35, 4033–4039, 2001.

Voss, P. B., Zaveri, R. A., Flocke, F. M., Mao, H., Hartley, T. P., DeAmicis, P., Deonandan, I., Contreras-Jimenez, G., Martinez-Antonio, O., Estrada, M. F., 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., 10, 7137–7159, http://dx.doi.org/10.5194/acp-10-7137-2010doi:10.5194/acp-10-7137-2010, 2010.

Watson, J. G., Chow, J. C., Lurmann, F. W., and Musarra, S. P.: Ammonium-nitrate, nitric-acid, and ammonia equilibrium in wintertime Phoenix, Arizona, J. Air Waste Manage. Assoc., 44, 405–412, 1994.

Wexler, A. S., and Seinfeld, J. H.: 2nd-generation inorganic aerosol model, Atmos. Environ. A-Gen., 25, 2731–2748, 1991.

Ying, Z. M., Tie, X. X., Madronich, S., Li, G. H., and Massie, S.: Simulation of regional dust and its effect on photochemistry in the Mexico City area during MILAGRO experiment, Atmos. Environ., 45, 2549–2558, http://dx.doi.org/10.1016/j.atmosenv.2011.02.018doi:10.1016/j.atmosenv.2011.02.018, 2011.

Zaveri, R. A., Easter, R. C., Fast, J. D., and Peters, L. K.: Model for Simulating Aerosol Interactions and Chemistry (MOSAIC), J. Geophys. Res.-Atmos., 113, D13204, http://dx.doi.org/10.1029/2007jd008782doi:10.1029/2007jd008782, 2008.

Zhang, K. M. and Wexler, A. S.: Modeling urban and regional aerosols – Development of the UCD Aerosol Module and implementation in CMAQ model, Atmos. Environ., 42, 3166–3178, http://dx.doi.org/10.1016/j.atmosenv.2007.12.052doi:10.1016/j.atmosenv.2007.12.052, 2008.

Zhang, Y., Seigneur, C., Seinfeld, J. H., Jacobson, M., Clegg, S. L., and Binkowski, F. S.: A comparative review of inorganic aerosol thermodynamic equilibrium modules: similarities, differences, and their likely causes, Atmos. Environ., 34, 117–137, 2000.

Zhang, J., Chameides, W. L., Weber, R., Cass, G., Orsini, D., Edgerton, E., Jongejan, P., and Slanina, J.: An evaluation of the thermodynamic equilibrium assumption for fine particulate composition: Nitrate and ammonium during the 1999 Atlanta Supersite Experiment, J. Geophys. Res.-Atmos., 108, 8414, http://dx.doi.org/10.1029/2001jd001592doi:10.1029/2001jd001592, 2002.

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, http://dx.doi.org/10.5194/acp-9-3777-2009doi:10.5194/acp-9-3777-2009, 2009.

%Zheng, J., Zhang, R., Fortner, E. C., Volkamer, R. M., Molina, L., Aiken, A. %C., Jimenez, J. L., Gaeggeler, K., Dommen, J., Dusanter, S., Stevens, P. S., %and Tie, X.: Measurements of HNO3 and N2O$_5$ using ion %drift-chemical ionization mass spectrometry during the MILAGRO/MCMA-2006 %campaign, Atmos. Chem. Phys., 8, 6823-6838, 2008. Zheng, J., Zhang, R., Fortner, E. C., Volkamer, R. M., Molina, L., Aiken, A. C., Jimenez, J. L., Gaeggeler, K., Dommen, J., Dusanter, S., Stevens, P. S., and Tie, X.: Measurements of HNO3 and N2O$_5$ using ion drift-chemical ionization mass spectrometry during the MILAGRO/MCMA-2006 campaign, Atmos. Chem. Phys., 8, 6823–6838, http://dx.doi.org/10.5194/acp-8-6823-2008doi:10.5194/acp-8-6823-2008, 2008.