Air quality improvement is a major concern in developed countries. In the past decade, especially in Eu- rope, legislative measures have been taken to reduce air pollution. The present article promotes photoca- talysis as an air quality improvement technique towards NO pollution. Indoor air depollution by painted plasterboards treated with photocatalytic coating was investigated. First, at laboratory scale, using a bed flow reactor, depollution efficiency of the photocatalytic system was evaluated. Experimental conditions were adapted as much as possible to match indoor environment. Thus, pollution levels remained at ppb scale, temperature and relative humidity (RH) were kept constant (20 °C and 50% RH) and typical indoor lighting systems (fluorescent tubes, Light-Emitting Diode (LED) and halogen bulbs) were used for photoactivation. UV-A fluorescent tube was also used to optimise photocatalytic activity. Second, experiments were conducted at real scale, in a 10-m3 experimental chamber developed at our laboratory. Interior walls were covered with the photocatalytic system and the chamber was used as a reactor. Employing a specific experimental procedure, aiming at keeping pollution level constant in the chamber, photocatalytic depollution was evaluated. The same lighting systems were used for photoactivation. NO2 abatement efficiency was evaluated through the photocatalytic oxidation potential and rate. Results show that NO2 can be significantly removed by this technique. However, the light used for photoactivation is at utmost importance. Furthermore, the results show that at laboratory scale, photocatalytic depollution efficiency of NO2 could be underestimated.
depollution, experimental chamber, indoor air quality, in situ, photocatalysis, TiO , NO2, UV-A light, visible light
 Maggos, T., Bartzis, J. G., Liakou, M. & Gobin, C., Photocatalytic degradation of NOxgases using TiO2-containing paint: A real scale study. Journal of Hazardous Materials, 146(3), pp. 668–673, 2007.
 Maggos, T., Plassais, A., Bartzis, J. G., Vasilakos, C., Moussiopoulos, N. & Bonafous, L., Photocatalytic degradation of NOx in a pilot street canyon configuration using TiO2-mortar panels. Environmental Monitoring and Assessment, 136(1–3), pp. 35–44, 2008.
 Chen, J. & sun Poon, C., Photocatalytic construction and building materials: From fundamentals to applications. Building and Environment, 44(9), pp. 1899–1906, 2009.
 Ohama, Y. & Van Gemert, D., Applications of Titanium Dioxide Photocatalysis to Construction Materials. Dordrecht: Springer Netherlands, 2011.
 Horgnies, M., Dubois-Brugger, I. & Gartner, E. M., NOx de-pollution by hardened concrete and the influence of activated charcoal additions. Cement and Concrete Research, 42(10), pp. 1348–1355, 2012.
 Martinez, T., Bertron, A., Ringot, E. & Escadeillas, G., Degradation of NO using photocatalytic coatings applied to different substrates. Building and Environment, 46(9), pp. 1808–1816, 2011.
 Ângelo, J., Andrade, L., Madeira, L. M. & Mendes, A., An overview of photocatalysis phenomena applied to NOx abatement. Journal of Environmental Management, 129(x), pp. 522–539, 2013.
 Boyjoo, Y., Sun, H., Liu, J., Pareek, V. K. & Wang, S., A review on photocatalysis for air treatment: From catalyst development to reactor design. Chemical Engineering Journal, 310, pp. 537–559, 2017.
 Ballari, M. M., Yu, Q. L. & Brouwers, H. J. H., Experimental study of the NO and NO2 degradation by photocatalytically active concrete. Catalysis Today, 161(1), pp. 175–180, 2011.
 Ballari,M. M. & Brouwers, H. J. H., Full scale demonstration of air-purifying pavement. Journal of Hazardous Materials, 254–255(1), pp. 406–414, 2013.
 Folli, A., et al., Field study of air purifying paving elements containing TiO2. Atmospheric Environment, 107(2), pp. 44–51, 2015.
 Guerrini, G. L., Photocatalytic performances in a city tunnel in Rome: NOx monitoring results. Construction and Building Materials, 27(1), pp. 165–175, 2012.
 Kleffmann, J., Discussion on ‘field study of air purification paving elements containing TiO2’ by Folli et al. (2015). Atmospheric Environment, 129, pp. 95–97, 2016.
 Gallus, M., et al., Photocatalytic de-pollution in the Leopold II tunnel in Brussels: NOxabatement results. Building and Environment, 84(2), pp. 125–133, 2015.
 ISO 22197-1, Fine ceramics (advanced ceramics, advanced technical ceramics) - Test method for air-purification performance of semiconducting photocatalytic materials - Part 1: Removal of nitric oxide. AFNOR, 2016.
 Ifang, S., Gallus, M., Liedtke, S., Kurtenbach, R., Wiesen, P. & Kleffmann, J. Standardization methods for testing photo-catalytic air remediation materials: Problems and solution. Atmospheric Environment, 91, pp. 154–161, 2014.
 Gallus, M., et al., Photocatalytic abatement results from a model street canyon. Environmental Science and Pollution Research, 22(22), pp. 18185–18196, 2015.
 Hot, J., Martinez, T., Wayser, B., Ringot, E. & Bertron, A., Photocatalytic degradation of NO/NO2 gas injected into a 10-m3 experimental chamber. Environmental Science and Pollution Research, 24(14), pp. 12562–12570, 2017.
 Topalov, J., Hot, J., Ringot, E. & Bertron, A., In situ NO abatement by photocatalysis—study under continuous NO injection in a 10-m3 experimental chamber. Air Quality Atmospheric Health, 12(2), pp. 229–240, 2019.
 Hot, J., Topalov, J., Ringot, E., & Bertron, A., Investigation on parameters affecting the effectiveness of photocatalytic functional coatings to degrade NO : TiO2 amount on surface , illumination and substrate roughness. International Journal of Photoenergy, 2017, pp. 1–14, 2017.
 NF EN ISO 9972, Thermal performance of buildings - Determination of air permeability of buildings - Fan pressurization method, 2016.
 Gaya, U. I. & Abdullah, A. H., Heterogeneous photocatalytic degradation of organic contaminants over titanium dioxide: A review of fundamentals, progress and problems. Journal of Photochemistry and Photobiology C: Photochemistry Reviews, 9(1), pp. 1–12, Mar. 2008.
 Mamaghani, A. H., Haghighat, F. & Lee, C. S., Photocatalytic oxidation technology for indoor environment air purification: The state-of-the-art. Applied Catalysis B: Environmental, 203, pp. 247–269, 2017.
 Rajeshwar, K., Fundamentals of Semiconductors Electrochemistry and Photoelectrochemistry. Encyclopedia Electrochemistry, pp. 1–51, 2007.
 Sivachandiran, L., Thevenet, F., Gravejat, P. & Rousseau, A., Investigation of NO and NO2 adsorption mechanisms on TiO2 at room temperature. Applied Catalysis B: Environmental, 142–143(2), pp. 196–204, 2013.
 Horgnies, M., Dubois-Brugger, I. & Stora, E., An innovative de-polluting concrete doped with activated carbon to enhance air quality. in 10th International Concrete Sustainability Conference (NRMCA), At Miami (USA), 2015(July), pp. 0–13.
 Hu, Y., Song, X., Jiang, S. & Wei, C., Enhanced photocatalytic activity of Pt-doped TiO2 for NOx oxidation both under UV and visible light irradiation: A synergistic effect of lattice Pt4+and surface PtO. Chemical Engineering Journal., 274(x), pp. 102–112, 2015.
 Zhou, L., Tan, X., Zhao, L. & Sun, M., Photocatalytic oxidation of NOx over visiblelight-responsive nitrogen-doped TiO2. Korean Journal of Chemical Engineering, 24(6), pp. 1017–1021, 2007.