Characterization of Aerosols Containing Zn, Pb, and Cl from an Industrial Region of Mexico City

Recent ice core measurements show lead concentrations increasing since 1970, suggesting new nonautomobile-related sources of Pb are becoming important worldwide(1). Developing a full understanding of the major sources of Pb and other metals is critical to controlling these emissions. During the March, 2006 MILAGRO campaign, single particle measurements in Mexico City revealed the frequent appearance of particles internally mixed with Zn, Pb, Cl, and P. Pb concentrations were as high as 1.14 μg/m3 in PM10 and 0.76 μg/m3 in PM2.5. Real time measurements were used to select time periods of interest to perform offline analysis to obtain detailed aerosol speciation. Many Zn-rich particles had needle-like structures and were found to be composed of ZnO and/or Zn(NO3)2·6H2O. The internally mixed Pb−Zn−Cl particles represented as much as 73% of the fine mode particles (by number) in the morning hours between 2−5 am. The Pb−Zn−Cl particles were primarily in the submicrometer size range and typically mixed with ele...