The enhanced performance of the ozone-enhanced photocatalysis process (O-3-PCO) on toluene destruction was evaluated and its mechanism was investigated.The toluene removal efficiency (TRE) and stability of O-3-PCO was compared with that of conventional PCO. The gaseous intermediates of toluene oxidation in various processes were analyzed by GC-MS. The formation pathways of main oxidants and their role in toluene destruction were studied. Results indicated that the IRE of O-3-PCO was 8 times higher than that of PCO because more oxidants were generated besides hydroxyl radicals (OH center dot). The generation rate and amount of OH center dot was remarkably increased in the O-3-PCO process which contained more pathways (such as UV/O-3 and O-3/TiO2) to produce OH center dot besides UV/TiO2. The GC-MS results showed that the types and amounts of byproducts were dramatically reduced due to the formation of more oxidants and complete oxidation, leading to remarkable enhancement of the photocatalyst's durability in the O-3-PCO process. Its mechanism was greatly different from the conventional PCO. Both OH center dot and active oxygen (O center dot) played a key role in the O-3-PCO process. Based on the intermediates and the main oxidants, possible pathways of toluene degradation were proposed. (C) 2010 Elsevier B.V. All rights reserved.