2.4.2. Nitrogen oxides

Two different setups were used—one under static conditions [39] and the other under flowing conditions [40]. A chemiluminescence NOx monitor (Teledyne API, Model 200E, San Diego, CA, USA) provided online detection of NO and NO2 concentrations. The batch reactor consisted of a Pyrex glass cylinder of volume of 25 L; this is described elsewhere [39]. The tile (2 20 cm) was located at the bottom of the cylinder and an overhead 500-W iron halogenide lamp (HG 500, 315–400 nm, UV-A, Jelosil, Milan, Italy) provided irradiation of 20 W/m2 . The inlet gas consisted of NO2 (0.6% in N2) mixed with air of relative humidity (RH) 40%, which allowed equilibration between NO and NO2 to be reached quickly. The NO2 concentration was set at 1000 ppb (static) or 250 ppb (flowing) and tests lasted 6 h each. The continuous flow reactor allowed testing of larger tiles (60 60 cm) [40]. A Thermo-Hygro Meter (HT-3006A, Metravi, Calcutta, India) measured both temperature and relative humidity, which ranged between 40 and 50%. Two iron halogen lamps (Jelosil, model HG 500), at 770-mm center-tocenter distance, which was designed to irradiate the sample surface with the same 20 W/m<sup>2</sup> light intensity, were used. The total NOx gas flow was in the range of 140–180 NL/h, which is in accordance with the standard concentration based on the limiting values specified in Directive 2008/50/EC of the European Parliament and of the Council on Ambient Air Quality and Cleaner Air for Europe (range 100–200 ppb).
