In our previous studies, three variations of a kinetic model for the transient gas-solid photocatalytic oxidation of aromatic contaminants on titanium dioxide (TiO2) were developed and compared with experimental data. Two of the models, based upon a single type of catalyst site, were not capable of replicating transient experimental data from the photocatalytic oxidation of benzene, toluene, or in-xylene in air at a single feed concentration (50 mg/m(3)). The remaining kinetic model, the Two-Site model, presumed the presence of a more hydrophilic type of site and was capable of replicating the time-varying behavior seen with all three aromatic contaminants considered. In the present study, this Two-Site kinetic model is extended to separately consider the photocatalytic oxidation of gas-phase toluene at various feed concentrations (20-100 mg/m(3)) and the regeneration of used catalysts via flowing, humidified air and UV illumination. Our Two-Site model provides reasonable fits for experimental data collected during the photocatalytic oxidation of toluene at several concentration levels with no significant changes to the prior model. It is also capable of representing catalyst regeneration, although some significant differences between the model predictions and experimental results are noted. (C) 2003 Elsevier B.V. All rights reserved.