Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 5 3 2005 10.5194/acpd-5-4183-2005 http://www.atmos-chem-phys-discuss.net/5/4183/2005/ http://www.atmos-chem-phys-discuss.net/5/4183/2005/acpd-5-4183-2005.html http://www.atmos-chem-phys-discuss.net/5/4183/2005/acpd-5-4183-2005.pdf 4183 4221 2005-06-28 Characterization of ambient aerosols in Mexico City during the MCMA-2003 campaign with Aerosol Mass Spectrometry – Part II: overview of the results at the CENICA supersite and comparison to previous studies D. Salcedo K. Dzepina T. B. Onasch M. R. Canagaratna J. T. Jayne D. R. Worsnop J S. Gaffney N. A. Marley K. S. Johnson B. Zuberi L. T. Molina M. J. Molina V. Shutthanandan Y. Xie J. L. Jimenez Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos, Cuernavaca, Mexico Cooperative Institute for Research in the Environmental Sciences (CIRES), University of Colorado at Boulder, Boulder, CO, USA Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, CO, USA Center for Aerosol and Cloud Chemistry, Aerodyne Research Inc., Billerica, MA, USA Argonne National Laboratory, Argonne, IL, USA Department of Earth, Atmospheric and Planetary Sciences and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA William R. Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, USA now at: GEO2 Technologies, Woburn, MA, USA An Aerodyne Aerosol Mass Spectrometer (AMS) was deployed at the CENICA Supersite during the Mexico City Metropolitan Area field study from 31 March–4 May 2003. The AMS provides real time information on mass concentration and composition of the non-refractory species in particulate matter less than 1 µm (NR-PM₁) with high time and size-resolution. Measurements of Black Carbon (BC) using an aethalometer, and estimated soil concentrations from Proton-Induced X-Ray Emission (PIXE) analysis of impactor substrates are also presented and combined with the AMS in order to include refractory material and estimate the total PM_2.5 mass concentration at CENICA during this campaign. In Mexico City, the organic fraction of the estimated PM_2.5 at CENICA represents 54.6% of the mass, with the rest consisting of inorganic compounds (mainly ammonium nitrate and sulfate/ammonium salts), BC, and soil. Inorganic compounds represent 27.5% of PM_2.5; BC mass concentration is about 11%; while soil represents about 6.9%. The NR species and BC have diurnal cycles that can be qualitatively interpreted as the interplay of direct emissions, photochemical production in the atmosphere followed by condensation and gas-to-particle partitioning, boundary layer dynamics, and/or advection. Bi- and trimodal size distributions are observed for the AMS species, with a small combustion (likely traffic) organic particle mode and an accumulation mode that contains mainly organic and secondary inorganic compounds. The AMS and BC mass concentrations, size distributions, and diurnal cycles are found to be qualitatively similar to those from most previous field measurements in Mexico City.