Element from coal-fired plants, enriched

Enrichment factors for stack emissions relative to the earth s crust are shown in Figure 3 for 56 elements. Averages are based on all available data from the 21 studies. An EFcrust of about 1 indicates that an element is at about the same relative concentration in coal-fired plant emissions as in soil. An EFcrust of less than 1 indicates that an element is depleted relative to soil, while a value greater than one indicates an enrichment of the element in coal-fired plant emissions. Elements such as Na, K, Si, Ca, Rb and Mn are depleted relative to the crust because of depletion in the input coals. Most lithophiles, e.g., Sc, Ti, Fe, and rare earths, have EFs of about 1. 

The use of EF values allows us to set limits on possible sources of elements. In Figure 1, EF values for six cities are compared with the ranges for particles from nine coal-fired power plants. For llthophlle elements such as SI, Tl, Th, K, Mg, Fe and many others not shown, E values are close to unity as expected, as these elements have mainly crustal sources, l.e., entrained soil and the aluminosilicate portion of emissions from coal combustion (see Table I). Many other elements are strongly enriched In some or all cities, and, to account for them, we must find sources whose particles have large values for those elements. Some are fairly obvious from the above discussions Pb from motor vehicles, Na from sea salt In coastal cities, and V and, possibly, N1 from oil In cities where residual oil Is used In large amounts (Boston, Portland, Washington). 

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