Atmos. Chem. Phys. Discuss., 6, 5999-6040, 2006
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Implementation of a Markov Chain Monte Carlo Method to inorganic aerosol modeling of observations from the MCMA-2003 Campaign. Part II: Model application to the CENICA, Pedregal and Santa Ana sites
F. M. San Martini1,*, E. J. Dunlea2, R. Volkamer1,***, T. B. Onasch3, J. T. Jayne3, M. R. Canagaratna3, D. R. Worsnop3, C. E. Kolb3, J. H. Shorter3, S. C. Herndon3, M. S. Zahniser3, D. Salcedo4, K. Dzepina2,6, J. L. Jimenez2,6, J. M. Ortega1,**, K. S. Johnson1, G. J. McRae5, L. T. Molina1,7, and M. J. Molina1,***
1Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
2Cooperative Institute for Research in the Environmental Sciences (CIRES), University of Colorado at Boulder, Boulder, CO, USA
3Aerodyne Research Inc., Billerica, MA, USA
4Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos, Cuernevaca, Morelos, México
5Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
6Department of Chemistry and Biochemistry, University of Colorado-Boulder, Boulder, CO, USA
7Molina Center on Energy and the Environment, La Jolla, CA, USA
*now at: the Board on Chemical Sciences and Technology, National Academies, Washington D.C., USA
**now at: Sandia National Laboratory, Livermore, CA, USA
***now at: University of California San Diego, La Jolla, CA, USA

Abstract. A Markov Chain Monte Carlo model for integrating the observations of inorganic species with a thermodynamic equilibrium model was presented in Part I of this series. Using observations taken at three ground sites, i.e. a residential, industrial and rural site, during the MCMA-2003 campaign in Mexico City, the model is used to analyze the inorganic aerosol and ammonia data and predict gas phase concentrations of nitric and hydrochloric acid. In general the model is able to accurately predict the observed inorganic aerosol concentrations at all three sites. The agreement between the predicted and observed gas phase ammonia concentration is excellent. The NOz concentration calculated from the NOy, NO and NO2 observations is of limited use in constraining the gas phase nitric acid concentration given the large uncertainties in this measure of nitric acid and additional reactive nitrogen species. Focusing on the acidic period of 9–11 April identified by Salcedo et al. (2006), the model accurately predicts the aerosol phase observations during this period with the exception of the nitrate predictions after 10:00 a.m. (CDT) on 9 April, where the model underpredicts the observations by, on average, 20%. For periods when the aerosol chloride observations are consistently above the detection limit, the model is able to both accurately predict the aerosol chloride predictions and provide well-constrained HCl (g) concentrations. When the aerosols are aqueous, the most likely concentrations of HCl (g) are in the sub-ppbv range. The most likely predicted concentration of HCl (g) was found to reach concentrations of order 10 ppbv if the aerosols are dry. Finally, the atmospheric relevance of HCl (g) is discussed in terms of its indicator properties for the possible influence of chlorine-mediated photochemistry in Mexico City.

Citation: San Martini, F. M., Dunlea, E. J., Volkamer, R., Onasch, T. B., Jayne, J. T., Canagaratna, M. R., Worsnop, D. R., Kolb, C. E., Shorter, J. H., Herndon, S. C., Zahniser, M. S., Salcedo, D., Dzepina, K., Jimenez, J. L., Ortega, J. M., Johnson, K. S., McRae, G. J., Molina, L. T., and Molina, M. J.: Implementation of a Markov Chain Monte Carlo Method to inorganic aerosol modeling of observations from the MCMA-2003 Campaign. Part II: Model application to the CENICA, Pedregal and Santa Ana sites, Atmos. Chem. Phys. Discuss., 6, 5999-6040, doi:10.5194/acpd-6-5999-2006, 2006.
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