Trace Elements as Tracers

In a number of studies, the elemental composition of aerosol particles has been related to their source. Schroeder and co-workers (1987) review the sources, sinks, analysis, deposition, chemical forms, and global cycles of various trace elements. Because the relative amounts of trace elements vary for coal compared to oil-fueled power plants, for example, it has been suggested that certain elements or ratios of elements may serve as tracers for various sources (e.g., see Gordon, 1988 and Rahn and Lowenthal, 1984). Thus V and Ni are indicative of oil combustion, and elevated concentrations of elements such as As and Se are usually 

TABLE 9.15 Mean Concentrations of Ammonium, Nitrate, and Sulfate by Size in Particles in Southern California in 1987  

The relative concentrations of rare earth elements in fine particles have also been suggested as being indicative of emissions from oil-fired power plants and from refineries. For example, the ratio of lanthanum to samarium is much higher in emissions from these sources than found in particles formed from the earth s crust (Olmez and Gordon, 1985). Thus the La Sm ratio was measured to be about 20 for refinery emissions and 28 for emissions from an oil-fired power plant compared to 5 from a coal-fired power plant and 9 from the earth s crust (Olmez and Gordon, 1985 Kitto et al., 1992). 

Rare earth isotopes have also been suggested as being useful for tracer studies. That is, they can be intentionally added to a source, such as flue gas or the fuel used in combustion, and their unique isotopic signature used to follow the plume as it disperses downwind. This approach, using the isotopes of Nd, for example, is discussed in more detail by Ondov and co-workers (Ondov and Kelly, 1991 Wight et al., 1991 Ondov et al., 1992 Lin et al., 1992). 

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