Authors of the abstract come from :: University or Research Institution Submit your abstract below (400 words): Attention to indoor air quality has strongly increased over the last 30 years. VOCs are the most numerous gaseous pollutants, present in indoor air within the concentration range 1-1000 ppb. Among them, aromatics are major compounds. The photocatalytic oxidation (PCO) of VOCs is one of the most promising techniques to achieve indoor air purification. Although many studies on PCO of VOCs were published, few extensive investigations on the influence of PCO process parameters have been made yet. The aim of the present work is to assess the impact of photocatalytic media geometry on the contact time during the PCO of toluene, chosen as a typical aromatic pollutant. The residence time on the photocatalyst as a function of global flowrate was estimated by performing CFD simulations. Experiments were conducted under conditions close to real indoor atmospheres. The PCO of toluene was performed in a dynamic loop reactor with control of key process parameters: UV-light intensity, air flow rate and residence time. The initial concentration of toluene was fixed at 800 ppb. The relative humidity was set at 50% (i.e. 13 000 ppm) to be close to real indoor air conditions. The photocatalytic media was supplied by Ahlström Paper Group. Two geometries were used for the media configuration, a plane geometry and a folded one. CFD simulations were performed with ANSYS-CFX® computational fluid software. The calculations used the finite volume method on which the software is based. PCO was proved to be more efficient in the folded configuration. Three main reasons account for this efficiency increase: (i) the surface and thus the catalyst mass are higher, (ii) the residence time is longer and (iii) the quantum yield is better optimized. Simulation results showed a good homogeneity of the fluid distribution at the media surface. The superficial velocities are low, i.e. around 0.2 m/s. It is evidenced that local decrease of gases velocity through the media surface is induced by its geometry. This decrease is proportional to a local contact time increase. Consequently, this phenomenon can lead to an additional noticeable improvement of global PCO process efficiency. This work provides understanding elements to explain why some media geometry has a positive influence on the global efficiency of the PCO process. Type of presentation :: Poster Highlight 1: PCO was proved to be more efficient in the folded configuration. Highlight 2: The local decrease of gases velocity through the media surface is induced by its geometry Highlight 3: Simulation results showed good homogeneity of the fluid distribution at the media surface