Photocatalytic degradation of NOx in a pilot street canyon configuration using TiO 2 -mortar panels Th. Maggos & A. Plassais & J. G. Bartzis & Ch. Vasilakos & N. Moussiopoulos & L. Bonafous Received: 27 July 2006 / Accepted: 18 December 2006 / Published online: 12 June 2007 # Springer Science + Business Media B.V. 2007 Abstract Titanium dioxide is the most important photocatalysts used for purifying applications. If a TiO 2 - containing material is left outdoors as a form of flat panels, it is activated by sunlight to remove harmful NOx gases during the day. The photocatalytic efficiency of a TiO 2 -treated mortar for removal of NOx was investigated in the frame of this work. For this purpose a fully equipped monitoring system was designed at a pilot site. This system allows the in situ evaluation of the de-polluting properties of a photo- catalytic material by taking into account the climato- logic phenomena in street canyons, accurate measurements of pollution level and full registration of meteorological data The pilot site involved three artificial canyon streets, a pollution source, continu- ous NOx measurements inside the canyons and the source as well as background and meteorological measurements. Significant differences on the NOx concentration level were observed between the TiO 2 treated and the reference canyon. NOx values in TiO 2 canyon were 36.7 to 82.0% lower than the ones observed in the reference one. Data arising from this study could be used to assess the impact of the photocatalytic material on the purification of the urban environment. Keywords Photocatalysis . TiO 2 building materials . Pilot street canyon . NOx degradation . Meteorology Introduction Advanced oxidation technologies and more specifical- ly heterogeneous photocatalysis represent emerging environmental control options for efficient removal of chemical pollutants. Among the various semiconduc- tors TiO 2 in the form of anatase has attracted wide interest, due to its strong oxidizing power under U.V irradiation, its chemical stability and the absence of toxicity (Fujishima et al. 1999; Agrios and Pichat 2005; Lewandowski and Ollis 2004; Pichat 2003; Ibrahim and Lasa 2002; Zhang et al. 2001). Environ Monit Assess (2008) 136:35–44 DOI 10.1007/s10661-007-9722-2 T. Maggos (*) : C. Vasilakos Environmental Research Laboratory, INT-RP, NCSR “Demokritos”, 153 10 Aghia Paraskevi, Athens, Greece e-mail: tmaggos@ipta.demokritos.gr A. Plassais : L. Bonafous CTG/Italcementi Group, Rue des Technodes, 78931 Guerville, France J. G. Bartzis Department of Energy Resources Engineering, University of Western Macedonia, 51100 Kozani, Greece N. Moussiopoulos Laboratory of Heat Transfer and Environmental Engineering, Aristotle University, GR-54006 Thessaloniki, Greece