Target transformation factor analysis (TTFA) has been applied to an analysis of a subset of the aerosol-composition data acquired during the Regional Air Pollution Study (RAPS) for St. Louis, MO. The purpose of the study was to evaluate the capability of TTFA to resolve sources of airborne particulate matter in a set of ambient-aerosol samples. Only the samples from July and August 1976, both fine and coarse fractions, were examined in this study. Because of the large number of different sources in the St. Louis area, superior results were obtained from the examination of the variation in aerosol composition with time at a single location rather than the spatial variation of over multiple sites during a shorter time period.