Lead 206/207 isotope ratios in the atmosphere of North America as tracers of US and Canadian emissions

Abstract

Lead emitted into the environment (primarily by gasoline combustion and industrial processes) retains the isotopic composition of the ore from which it was derived. Therefore, there is the potential to distinguish sources of lead pollution in the atmosphere by examining the lead isotope ratios^1–4. Such a tracer of atmospheric lead would be valuable in air pollution transport studies, as the relatively long residence time of lead aerosols (∼5–10 days), can result in its dispersal over thousands of kilometres. In practice, the situation is complicated by the wide, and frequently changing, variety of ore types used in gasoline additives and in smelting activities^5,6. This approach has generally only been successful in identifying local sources of pollution^7–9, except where gasoline lead compositions have been deliberately altered¹⁰. We have discovered that the lead isotopic composition of atmospheric particu-late matter in the eastern United States is distinctly different from that in eastern Canada, and that the composition is sufficiently constant between sites in each country over periods of several months to allow characteristic isotope ratios to be defined for each. This offers a new approach to examining transboundary pollution between the United States and Canada.