Photocatalytic coatings intended for building materials were formulated using TiO2 nanoparticles incorporated in a polymer-matrix-based coating. Their air purification performance levels were assessed on a VOC (volatile organic compound) mixture representative of atmospheric pollution (benzene, toluene, ethylbenzene and xylenes, or BTEX). Experiments were performed using a flow type reactor adapted from the ISO 22197-3 standard under UV-A illumination (6 W m(-2)) at different ranges of inlet concentration (260-2600 ppbV of BTEX), relative humidity (RH: 0-90%) and flow rate (0.1-1.5 L min(-1)). Analysis was conducted by using an automated thermal desorption technique coupled to a GC-FID instrument. At low initial concentrations of pollutants, increasing humidity had a negative impact on the degradation of BTEX. In this case, the reaction was limited by the competition between pollutant and water at the absorptive sites. At higher initial concentrations of pollutant, the conversion of the pollutants increased with the increase in air humidity to an optimum value beyond which the conversion of pollutants decreased. The reaction may have been limited by a lack of hydroxyl radical at the low humidity level while, at higher humidity, competition at the absorptive sites limited pollutant removal. (C) 2013 Elsevier Ltd. All rights reserved.