Detailed studies have been conducted to characterise the output of a Palas GFG 1000 spark discharge aerosol generator utilising graphite electrodes' Adjusting argon shielding and primary dilution airflow influenced particle size distribution through its effect on coagulation rates. An increased spark frequency enhanced the total particle number production, the modal diameter and the aerosol mass concentration. Transmission electron microscopy revealed relatively simple structures for particles with mobility diameters of 30 and 60 nm and turbostratic (partially graphitic) structures were also imaged. Particles with mobility diameters of approximately 100 nm possessed more complex structures, appearing to result from both nucleation/condensation and coagulation processes. Application of fractal geometry indicated fractal structures superficially comparable to those generated by high-temperature combustion sources. These differ markedly from fractal clusters derived from combustion of hydrocarbon fuels, due to the presence of a large nucleated/condensed component. Furthermore, upon reducing the argon shielding flow rate, more compact structures were generated. Although marked differences indeed exist between the spark discharge-generated graphitic aerosols and carbonaceous particles produced by hydrocarbon combustion, their comparable mobility diameters and surface features may lend them to be utilised as model combustion aerosols. Coupled into a refined human challenge delivery system, the generator and delivery system may be employed in studies to investigate the human health impacts from model combustion aerosol. (C) 2003 Elsevier Ltd. All rights reserved.