An experimental nuclear aerosol test facility has been built at the Bhabha Atomic Research Centre for validating the aerosol behavior computer codes used in nuclear reactor safety assessment. Its essential components are the 10-m3 stainless steel test vessel, plasma torch aerosol generator, and aerosol instrumentation to study the aerosol characteristics. Studies have been conducted with metal/metal oxide aerosols in dry environments under varying turbulence conditions and the results have been compared with the predictions of NAUA (Mod 5) code. The code predictions were found to differ from the experimental observations. To explain the differences under calm conditions, a gravity-induced spatial stratification model was formulated and solved. It was found that NAUA prediction agrees fairly well with the depletion of total airborne mass given by this model. In the presence of turbulence, the code overestimated the airborne concentrations. This is attributed to the noninclusion of particle removal by inertial impaction. Accordingly, the deposition velocity formula used in the code was modified based on the Crump-Seinfeld approach. With this modification, the results of airborne mass depletion agreed quite well with the measured data. On the whole, the study provides validated modifications in the NAUA (Mod 5) code to include turbulence effects and a formulation of gravity-induced stratification of aerosols under calm conditions.