The report describes how to access and use the Particulate Data Reduction (PADRE) System, an interactive computer program that facilitates entry, reduction, and analysis of cascade impactor data for particle size distributions. It also summarizes its logic and capabilities. The program narrative describes all calculations and algorithms and all messages produced by the system. PADRE was developed to ensure the quality of data included in the Fine Particle Emissions Information Systems (FPEIS), a component of the Environmental Assessment Data Systems (EADS). Users control the logical flow through the system in response to prompts from the program. PADRE can be used to store, review, edit, and analyze data and, through a variety of data checks, to identify invalid or suspect data. Impactor stage cut points are calculated, and cumulative and differential mass concentrations are determined and interpolated to standard diameters.