The morphology, microstructure, surface area, porosity, and chemical composition of soot particles emitted from a gas-turbine combustor have been studied. Combustor soot particles appear to be chemically and structurally unstable and present microporosity and a strongly disordered graphitic structure. Discrepancies between the properties of combustor-generated soots arise from their postformation conditions, quenching environments, and sampling conditions. During long accumulation time, soot collected on the combustor walls experiences graphitization and oxidation. Upon long processing by hot exhaust gases, soot particles collected far from the combustor exit exhibit significant transformations (1) from paracrystalline to nodular amorphous microstructure and (2) from spherical particles to fused agglomerates following the increase in microporosity and oxygen content. Combustor-generated soot properties are compared to those of kerosene flame soot, which is produced in the laboratory and is proposed to be a surrogate of combustor soot for atmospheric studies. It is shown that the chemical composition, porosity, and extent of graphitization of combustor-generated and kerosene flame soots influence their electrical and hygroscopic properties. The characteristics of kerosene soot appear to be close to those of combustor soot but exhibit a number of specific feature variations such as graphitized nanostructure and ultramicroporosity, which influence its water adsorbability.