X-ray fluorescence (XRF) has become an effective technique for determining the elemental content of aerosol samples. For quantitative analysis, the aerosol particles must be collected as uniform deposits on the surface of Teflon membrane filters. An energy dispersive XRF spectrometer having a pulsed x-ray source that excites Ti, Mo, and Sm secondary targets has sufficiently low minimum detectable limits to enable 20-25 different elements to be detected and analyzed in atmospheric aerosol samples. For quantitative analysis using an energy dispersive spectrometer, the x-ray spectra are analyzed using a least squares procedure to eliminate interferences. Thin film standards are used to calibrate the spectrometer. Applications include the XRF analysis of 34,000 samples from the Regional Air Pollution Study in St. Louis.