The report describes a research effort to determine the feasibility and capability of electron microprobe analysis as a method for obtaining detailed compositional and structural information about pollutant aerosol particles in the atmosphere. Extensive data is presented from known test aerosols, automobile engine exhaust, and atmospheric samples. It was determined that the sampling method is presently the limiting factor in the detection and analysis of small particles, and, by preparing samples to minimize X-ray background, particles as small as 0.1 micron can be successfully analyzed. The theoretical limitations of the microprobe for both wavelength-dispersive and energy-dispersive spectrometers are discussed, and recommendations are made about analysis systems for small particles. (Author)