Scanning electron miscroscopy interfaced with automated image analysis and x-ray energy spectroscopy (SAX) can be employed for individual particle characterization of aerosol samples in a time efficient manner. Such an individual particle analysis partitioning of the bulk chemical data provides a new perspective on the heterogeneity of ambient aerosols. As particles are individuals, it is possible to increase the source resolution of conventional receptor models which are based on bulk chemical analyses. This paper presents a particle class balance (PCB) which is directly analogous, in mathematical approach, to the Chemical mass balance types of receptor models. Samples of ambient aerosol and potential source materials from Syracuse, NY were characterized by SAX.