Isotope labeling eyed for tracing smoke particles

In an effort to track emissions from coal-fired power plants to their sources, researchers at the National Bureau of Standards and the University of Maryland are developing a technique that shows promise as a simple and definitive way of tracing smoke particles. The researchers say the method, which uses stable isotopes of rare-earth elements to tag emission particles (fly ash), may be the first one suitable for tracing fine particles over long distances. It would complement techniques based on tracer gases, which detect only gaseous components of stack emissions, not particles