The gas-phase photocatalytic destruction of 17 VOCs over illuminated titanium dioxide was investigated using a plug flow reactor with the following experimental conditions: 200 ml min(-1) flow rate, 23% relative humidity, 21% oxygen and an organic compound concentration range of 400-600 ppmv. At steady state, high conversion yields were obtained for trichloroethylene (99.9%), isooctane (98.9%), acetone (98.5%), methanol (97.9%), methyl ethyl ketone (97.1%), t-butyl methyl ether (96.1%), dimethoxymethane (93.9%), methylene chloride (90.4%), methyl isopropyl ketone (88.5%), isopropanol (79.7%), chloroform (69.5%) and tetrachloroethylene (66.6%). However, the photodegradation of isopropylbenzene (30.3%), methyl chloroform (20.5%) and pyridine (15.8%) was not so efficient. Carbon tetrachloride photoreduction was investigated in the presence of methanol as an electron donor. It was observed that the presence of methanol results in higher degradation rates. No reaction byproducts were detected for all VOCs tested under the experimental set-up and conditions described. Also, long-term conversion was obtained for all tested compounds. Catalyst deactivation was detected with toluene only, but the activity was restored by illuminating the catalyst in the presence of hydrogen peroxide. The capacity of the process to destroy different classes of volatile organic compounds present in the atmosphere was demonstrated. (C) 1997 Elsevier Science B.V.14416715568