A project was conducted to design, fabricate, and test a particulate emission monitor utilizing a beta radiation attenuation and filter sampler technique. The instrument was to have a minimum sensitivity of 125 plus or minus 25 micrograms per cubic meter and be capable of operation in either a manual or automatic mode of operation. Carbon-14 was selected as the optimum isotope and a filter 'cassette' was used to collect the particles. The effect of moisture absorption by various types of filter media were investigated and reported. A series of tests were performed on automobiles using leaded, low-leaded and non-leaded fuels. The results of these tests are reported as well as recommendations for future effort. (Author)