The development of photocatalysis processes offers a significant number of perspectives especially in gaseous phase depollution. It is proved that the photo-oxidizing proper-ties of photocatalyst (TiO2) activated by UV plays an important role in the degradation of volatile organic compounds (VOC). Heterogeneous photocatalysis is based on the absorption of UV radiations by TiO2. This phenomenon leads to the degradation and the oxidation of the compounds, according to a mechanism that associates the pollutant's adsorption on the photocatalyst and radical degradation reactions. The main objective of the study is the understanding of the TiO2-photocatalysis phenomenon including gaseous and adsorbed phase mechanisms. Results obtained with three different apparatus are compared; gaseous phases are analysed and mechanisms at the gaseous phase/photocatalyst interface are identified. This study leads to improve understanding of various mechanisms during pollutant photodegradation: adsorption of pollutants on TiO2 first takes place, then desorption and/or photodegradation, and finally, desorption of degradation products on TiO2. The association of analytical methods and different processes makes the determination of all parameters that affect the photocatalytic process possible. Mastering these parameters is fundamental for the design and construction of industrial size reactors that aim to purify the atmosphere. (c) 2007 Elsevier B.V. All rights reserved.