This research program was to provide source emission data for urban particulate models. The objectives were twofold: to determine emission factors for primary sulfate and carbon from a variety of commercial and industrial heating units burning fuel oil, and to evaluate and compare the performance of the miniature acid condensation system (MACS) and the acid condensation system (ACS) methods for determining free sulfuric acid. A total of five boilers were monitored in this study. Two of the units tested were utility boilers. The remaining three units were small process steam or heating boilers ranging in size from 23,500 to 50,000 lb/hr. The results of this study provide evidence that the MACS system, although subject to certain critical sampling parameters, can serve as a primary sulfate characterization method for combustion source measurements. Analytical data on carbon and elemental composition are presented.