Pb Isotopic Composition of Airborne Particulate Material from France and the Southern United Kingdom:  Implications for Pb Pollution Sources in Urban Areas

Pb isotopic studies of airborne particulate matter, incinerator ash, and gasoline have been carried out to determine sources of Pb pollution in urban areas from France and the southern United Kingdom. 206Pb/207Pb ratios in gasoline range from 1.061 to 1.094 (average values are 1.084 for France and 1.067 for the U.K.) while for industrially-derived Pb, 206Pb/207Pb ratios vary from 1.143 to 1.155. Natural Pb is more radiogenic and literature values for pre-industrial sedi ments give 206Pb/207Pb ratios of 1.19−1.20 in France and 1.17−1.19 in the U.K. The measured Pb isotopic signature of airborne particulate matter reflects the relative importance of each of these sources, and samples taken from urban areas close to traffic in France and the U.K. show 206Pb/207Pb ratios that vary widely from 1.085 to 1.158. While alkyl-lead additives in gasoline are typically still the dominant source of Pb in urban particulate matter, the relative importance of gasoline-derived Pb has decreased, and as a result other sources (industrial and natural) can be identified using isotopic studies. This is a consequence of recent EU environmental legislation that significantly limits concentrations of Pb in gasoline and the increased market penetration of unleaded gasoline. In addition, at a given location, the Pb isotopic composition of particulate matter can vary considerably due to temporal variations in sources (i.e., variations in traffic density) and with wind direction.