Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 9 1 2009 10.5194/acpd-9-3265-2009 http://www.atmos-chem-phys-discuss.net/9/3265/2009/ http://www.atmos-chem-phys-discuss.net/9/3265/2009/acpd-9-3265-2009.html http://www.atmos-chem-phys-discuss.net/9/3265/2009/acpd-9-3265-2009.pdf 3265 3306 2009-01-30 Evolution of anthropogenic pollution at the top of the regional mixed layer in the central Mexico plateau D. Baumgardner darrel@servidor.unam.mx M. Grutter J. Allan C. Ochoa B. Rappenglueck L. M. Russell P. Arnott Centro de Ciencias de la Atmósfera, Universidad Nacional Autónoma de México, Mexico City, Mexico School of Earth, Atmospheric & Environmental Science, University of Manchester, Manchester, UK Earth and Atmospheric Sciences Dept., University of Houston, Houston, TX, USA Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA Dept. of Physics, University of Nevada, Reno, NV, USA The concentrations of gases and properties of aerosol particles have been measured at the mountain site of Altzomoni approximately equidistant from Mexico City, Puebla and Cuernavaca, at an altitude of 4010 m. At this location there is a diurnal transition from local to regional mixed layer air whose properties depend on prevailing winds and larger scale circulation. Three days during March 2006 have been evaluated during which time the synoptic scale air flow was from the east, southeast and southwest. In general the properties of gases and particles were similar when the regional mixed layer (RML) was below the research site, regardless of the direction of flow. When the RML reached the site, the highest concentrations of CO, O3 and aerosol particles were from the east, decreasing as the flow shifted to the southeast then to the southwest. The maximum concentration of condensation nuclei (CN) was greater than 25×10−3 when winds were from the east. The highest mass concentrations of organic matter (OM), sulfate (SO4−), and Nitrate (NO3+ were 80, 4 and 8 μg m−3, at standard temperature and pressure in air from the east. The mass concentration of OM in the RML was greater than 70% of the total mass, regardless of the air mass origin. This compares to less than the 60% that has been reported for Mexico City. At night, the mass fraction of sulfate went up by a factor of ten from the daytime value when air arrived from the east. 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