Pb isotopic signatures of the atmosphere of the São Paulo city, Brazil

Abstract
Lead isotopic compositions of the atmosphere of the São Paulo city, Brazil, were determined from particulate matter (PM ₁₀) collected on teflon filters, and rainwater samples at the São Paulo University for the period between Auguste 1999 and September/2000. The PM ₁₀ ²⁰⁷Pb/ ²⁰⁶Pb ratios range from 0.786 to 0.875, and ²⁰⁸Pb/ ²⁰⁶Pb from 1.934 to 2.119, defining an array on the Pb diagram. Lead concentrations range from 3.02 to 254.52 ng/m ³. Rainwater samples displayed the same isotopic ratios measured on PM ₁₀ collected the same day, thus indicating that aerosols are scavenged by rain. Analyses of possible pollutants sources such as gasoline and ethanol, soot from vehicle exhaust pipes, and particulate material from industrial emissions, collected on fiberglass filters, mostly yielded isotopic compositions falling into an interval defined by 84% of the PM ₁₀ samples ( ²⁰⁷Pb/ ²⁰⁶Pb = 0.840-0.870). However, 15% of the PM ₁₀ samples are more radiogenic, indicating a significant, unidentified radiogenic source ( ²⁰⁷Pb/ ²⁰⁶Pb < 0.780), evident mainly in samples collected during weekends and from November/1999 to April/2000. We suggest that most of the anthropogenic Pb found in the São Paulo atmosphere comes from industrial emissions, since the amount of Pb present in vehicular fuels is negligible.