Stable lead isotope ratios in arctic aerosols: evidence for the origin of arctic air pollution

Abstract

The isotopic composition of aerosol lead in the polar region potentially contains information on the origin of Arctic pollution which will complement that from meteorological and trace elemental composition studies. Weekly samples of atmospheric aerosols were collected at three locations in the Canadian Arctic from mid-1983 to mid-1984. They were analyzed for elemental composition and stable lead isotope ratios (Pb $\text{206}\text{207}$). High crustal enrichment factors confirmed that the majority of samples contained lead of anthropogenic origin. Pb $\text{206}\text{207}$ ratios were very uniform over time and between sites, suggesting a common origin of lead pollution in the Canadian Arctic. The mean isotope ratios at the Alert and Mould Bay stations were 1.160±0.010 and 1.161±0.006, respectively (samples from a third site at Igloolik were evidently contaminated by local sources). A small number of samples from Spitsbergen, taken during flow predominantly out of the northern U.S.S.R., were found to have a similar mean Pb $\text{206}\text{207}$ ratio of 1.154 ±0.006. From published lead isotope analyses of Soviet lead-bearing ores, we would expect a mean isotope ratio in industrial and vehicular emissions in the U.S.S.R. of around 1.158. Contributions to Arctic lead pollution from the U.S. and western Canadian sources can probably be ruled out, as they have significantly higher Pb $\text{206}\text{207}$ ratios. Similarly, emissions from northern Canadian and Kola Peninsula smelters can be disregarded, as they appear to have low isotope ratios. Eastern Canadian automotive lead aerosol contained only marginally lower Pb $\text{206}\text{207}$ratios than in the Arctic, but meteorological studies argue against this region being a major source area for Arctic pollution. Scant European data suggest that European Pb emissions generally have lower isotope ratios than the Arctic samples. However, more data in Eurasia are needed before apportionments of Arctic Pb between sources within the region can be made.