ABSTRACTThe use of corn oil as an alternative aerosol base in instruments for testing respirators and filters has been recommended by NIOSH as a safe substitute to Di-ethylhexyl phthal-ate (DOP) which is thought to be a potential biological co-carcinogen. Experimental measurements of the thermophysical properties related to aerosol size distribution and filter penetration have been conducted using photometry, inertial impactors, and laser spectrometry. Aerosols were generated using a pneumatic generator that combined the concepts of the Laskin nozzle and Wright nebulizer systems under various conditions of pressure, temperature and relative humidity and were evaluated for particle size distribution and filter penetration. Experiments demonstrated that heating corn oil from 20^°C to 40^°C has a minimal effect on size distribution and mass whereas DOP showed a greater sensitivity to temperature with respect to the same properties. These evaluations also demonstrated that corn oil produced a stable, smaller, and more consistent aerodynamic size distribution than DOP at the comparative experimental conditions. Comparable filter penetration characteristics obtained by experimental observations strongly show that corn oil aerosols are justified as an alternative aerosol for DOP. Enhanced performance coupled with safety considerations suggest that corn oil is an acceptable substitute for DOP especially in those applications of testing human subjects such as quantitative fit testing.