Beginning in May 1975 and continuing through April 1977, a total of 35,000 individual ambient aerosol samples were collected at ten selected sampling sites in St. Louis, as part of the Regional Air Pollution Study (RAPS). The samples consisted of membrane filters on which the coarse and fine particulate fractions were collected separately using automatic dichotomous air samplers. The samples were returned to Lawrence Berkeley Laboratory (LBL) for analysis following collection at the field sites. Mass concentrations were determined by a beta-particle attenuation method. This required measurement of tare weights for each individual filter before being sent to the field sites and subsequent measurement on their return. Elemental analysis of the particulate samples was performed for 27 elements using energy dispersive X-ray fluorescence analysis. Optimal sensitivities were obtained using pulsed excitation, and automated data handling was employed to facilitate the 35,000 data sets. This report discusses in detail the procedures used in the aerosol sampling and analysis, and in data processing and validation.