Cluster and principal component analysis procedures were used to examine compositions and time-dependent concentrations of aerosol particles collected over a 7-day period near Phoenix, Arizona. The elemental compositions of 13,026 individual particles have been determined by energy dispersive X ray spectrometry using a scanning electron microscope. Cluster analysis of the individual-particle data revealed 15 chemically distinct particle types. Principal component analysis of the time-dependent concentrations of these types indicated five unique concentration versus time patterns. Based on the chemical compositions and size characteristics, as well as on wind patterns during collection, distinct sources for the majority of the particle types can be ascribed. The three major sources are crustal material, copper smelters, and marine air. Two minor types, Ti-rich and Pb-Rich, appear to be of local origin. This combination of the time-dependent chemistry and size and wind data leads to improved source attribution.