A graphical technique for determining major components in a mixed aerosol. I. Descriptive aspects

A persistent problem in aerosol science is how best to determine the compositions of the major components in mixed samples. This paper presents a graphical technique for extracting the elemental compositions of the crustal, marine, and general pollution components in large suites of samples from single sites. Log-log scatter diagrams are constructed, with the vertical axis being the X/Al ratios of the samples (where X is an element of interest and Al is the crustal reference element) and the horizontal axis being either Na/Al or Se/Al (where Na and Se are marine and pollution reference elements, respectively). If the crustal component is sufficiently enriched in enough samples, a horizontal “compositional tail” of X/Al will appear at the left-hand end of the plots, with an asymptotic value equal to the ratio in the pure crustal aerosol. If the second component is sufficiently enriched in enough samples, its compositional tail will appear as a 45° zone at the right-hand end of the plots. Depending on the choice of component, the asymptotic value of this tail will be the X/Se ratio in the pollution component or the X/Na ratio in the marine component. When the sample set is large enough, compositions of components can frequently be determined to uncertainties of 10% or less. Results for elements in a large suite of aerosol samples from Narragansett, RI, measured by neutron-activation analysis, reveal well-defined compositional tails for most elements and a smooth progression of elements from purely crustal to purely pollution derived. This graphical technique can also be applied to precipitation, provided only that it has been sampled and analyzed in ways that make its data directly analogous to those of aerosol.