Combustion produced soot is a highly variable material. Physically the nanostructure can range from amorphous to graphitic to fullerenic. Chemically nearly any element could be included, though the surface functional groups are predominantly oxygen-based. Electron microscopic and spectroscopic methods have great potential for carbonaceous aerosol characterization. Results will be presented for analysis of HRTEM images of the physical nanostructure and XPS analysis of the chemical composition of soots collected from plant, institutional and residential scale oil-fired boilers, diesel engine, gas-turbine combustor (jet engines) and a wildfire. Physically soots from these emission source classes may be differentiated based on carbon lamella length, mean separation and tortuosity using HRTEM and image analyses algorithms. Chemically these soots may also be distinguished by elemental composition, surface (oxygen) functional groups and carbon bonding by XPS.