Particulate samples, collected on Teflon filters by dichotomous samplers in Denver, Colorado, for 12 months during 1979, were analyzed for mass by beta radiation attenuation and for elemental composition by x-ray fluorescence. The resulting data were analyzed in terms of a chemical element balance method to resolve particulate mass into the following six components: ammonium sulfate, motor vehicle exhaust, shale, limestone, road salt, and refuse incineration. Time series plots of monthly values revealed that the road salt component was important only during winter and that the motor vehicle exhaust component was substantially elevated during fall and winter. Although the magnitude of the motor vehicle component in the fine particle fraction was elevated during the fall-winter season, its percentage contribution to the total observed mass (about 25%) remained reasonably constant throughout the year. The six components plus carbon and nitrate account for almost all of the total particulate mass, although the chemical element balance model underestimated by a factor of 4 the amount of carbon during January. Further mathematical analysis of the data to apportion the carbon more accurately and additional analyses to determine crystalline phases and individual particles are needed and discussed.