Soot is a highly variable material. Physically the nanostructure can range from amorphous to graphitic to fullerenic. Chemically nearly any element may be included, while the surface functional groups are predominantly oxygen-based. Presented here are HRTEM image analysis results of the physical nanostructure and XPS analysis of the surface chemical composition of soot collected from plant and industrial scale oil-fired boilers, a diesel engine, jet engine and a wildfire. Physically soots from these emission source classes may be differentiated on the basis of carbon lamella length, mean separation and tortuosity. Chemically these soots may also be distinguished by elemental composition and surface functional groups. Together, this suite of parameters can be used to differentiate natural from anthropogenic soots. (C) 2009 Elsevier Ltd. All rights reserved.