Graphical techniques for interpreting the composition of individual aerosol particles

A graphical technique that uses X−Y and ternary plots is presented for interpreting elemental data for individual aerosol particles. By revealing the multiple functional relationships between the elements, it offers more insight into the groups of particles and the transitions between them than traditional techniques such as factor analysis and cluster analysis alone are able to. For a sample of dust storm aerosol from Beijing in March 2002, X–Y plots revealed areas, lines, and “dots” that represented clays, smooth transitions to asymptotes of pure single-component minerals, and pure minor minerals or special particles, respectively. Ternary plots further revealed ratios of elements and potential minerals. Careful use of cluster analysis revealed subgroups of particles that were not separated by clear borders. The dust storm had three major components, clay/quartz (Al2O3, SiO2, etc.), basic calcium (CaO, CaCO3), and salts (sulfate, phosphate, chloride). Some sulfates, including CaSO4 and (NH4)xH2−xSO4, were mixed with the quartz and clay. A five-step sequence that combines graphics, basic statistics, cluster analysis, and SEM photography seems to extract the maximum information from suites of single particles.