The properties of gas-borne aggregates are important in nano-technology and for potential health effects.Gold aggregates from three generators (one commercial and one custom built spark discharge generator and one high-temperature furnace) have been characterized. The aggregate surface areas were determined using five approaches - based on aggregation theory and/or measured aggregate properties. The characterization included mass-mobility relationships, effective densities (assessed by an Aerosol Particles Mass analyzer), primary particle analysis (based on Transmission Electron Microscopy), as well as total mass and number concentration outputs.The relationships between mass and mobility are well described by power-law functions with exponents of 2.18-2.35. For all generators, the primary particles of the aggregates were fused together by a bridge with a diameter typically ~60-70% of the primary particle diameter (5-10 nm). The total mass outputs were 6.1-48.1 mg/m3 and the predicted surface area outputs in the range 0.9×10-3-17×10-3 cm2/cm3.The aggregate effective densities differed considerably between generators. The difference could partly be explained by the differences in primary particle diameter, but not fully. This in turn may be explained either by a varying primary particle size with aggregate size, or by that there are slight differences in the morphology of the aggregates from the generators.