An x-ray powder diffraction system has been developed for the automated measurement and analysis of particulate aerosol samples. The system is optimized to process samples with particle loadings of about 100 micrograms/sq cm which are acquired with dichotomous air samplers. A position sensitive pressurized gas proportional chamber is used as the x-ray detector. This detector acquires information simultaneously over an angular range of up to seven degrees and increases the data acquisition rate by over 20 times compared to a conventional system. The use of a position sensitive detector also reduces spectral artifacts due to preferred particle orientations since each spectral point is measured at many goniometer settings. The on-line data analysis procedure begins with a background subtraction of the radiation scattered from the sample substrate. A spectral analysis routine then automatically finds peaks and fits them with an analytic function to determine their position and intensity. A search-match procedure is then used to determine the major chemical species present on each sample. Results from this powder diffraction analysis are then combined with an x-ray fluroescence measurement of the chemical concentrations to give quantitative analysis of the major chemical compounds present on these environmental samples.