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What a difference the lead makes.

What a difference the lead makes

One sure way to foment a border dispute is to complain that your neighbor is sending noxious air pollutants in your direction. One such case is the emission of nitrogen and sulfur oxides, the precursors of acid rain. Countries argue about how much of the pollution comes from neighbors and how much is generated locally. Over the last few years, scientists have been exploring the value of measuring ratios of selected trace elements to identify the origin of wind-carried particles (SN: 1/21/84, p.39). The idea is that because different regions use different fuels, have different industries and require different levels and types of pollution controls, particles in the air are likely to have different chemical signatures. Now two Canadian researchers suggest the use of lead isotope ratios to differentiate between U.S. and Canadian emissions.

In the Sept. 10 NATURE, L.A. Barrie and W.T. Sturges of the Atmospheric Environment Service in Downsview, Ontario, say that lead emitted into the air by industrial processes or gasoline consumption carries with it the distinctive isotope ratio of the ore from which the lead was derived. That ratio varies from ore body to ore body. Because most lead emitted in the United States comes from geological sources that differ from Canada's, the variations in isotope ratios can be used to apportion blame.

"We have discovered,' say the researchers, "that . . . the [lead isotope ratio] is sufficiently constant between sites in each country over periods of several months to allow characteristic isotope ratios to be defined for each.'

Barrie and Sturges applied the technique to samples collected from March to May 1986 at a site in central Ontario. They found that about 69 percent of lead pollution came from Canadian factories and cars; 24 percent was from the United States. The remainder seemed to come from copper smelters in northern Ontario. A similar approach applied by the same researchers on a hemispheric scale is providing insight into the source of atmospheric lead in the Arctic.
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Title Annotation:isotopes tags to distinguish lead emission from the US and Canada
Publication:Science News
Date:Sep 26, 1987
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