This study describes photo-conversion in a novel Photo-CREC-Air reactor. Experiments were developed using three model pollutants and two commercial TiO2 photo-catalysts: Degussa P25 and Hombikat UV-100. Apparent quantum efficiencies were evaluated on the basis of the following: (a) 90% of pollutant converted in CO2, (b) initial photo-conversion rates. It was observed that in a significant number of runs the apparent quantum efficiencies were in excess to 100% and this strongly suggests a radical chain reaction mechanism for the photo-conversion process. (C) 2003 Elsevier Science Ltd. All rights reserved.