Aerosol samples were collected in Mexico City during April of 2003 and March of 2006 and analyzed for 210Pb and daughters 210Bi and 210Po. The samples were collected using a 1 micron cutoff using a high volume impactor system. Samples were analyzed using methods previously developed by the authors for rapid separation of 210Bi and 210Po from the parent 210Pb. Gamma counting was used to determine 210Pb levels on the samples that were taken twice daily (day and night - 12 hour). The results will be discussed and compared to measurements in other sites. The data indicate that there are significant amounts of background aerosols that have fairly long lifetimes compared to the fresh aerosols produced in Mexico City. The results are consistant with the long range transport of black carbonaceous and other organic aerosols that are not hygroscopic and are in the 0.1 to 0.6 micron size range.

This work was supported as part of the Megacity Aerosol Experiment - Mexico City and was supported by the Department of Energy's Atmospheric Science Program.