Titanium dioxide is the most important photocatalyst used for purifying applications. The purpose of this study was to investigate the photocatalytic activity of the commercial product Protectam FN2, containing Evonik P25 titanium dioxide nanopowder, with regard to NO and NO2 abatement. Photocatalytic experiments on the photocatalytic coatings on concrete and plaster substrates were carried out in two types of flow reactors, namely one with laminar flow and another with ideally-mixed flow, under "real world conditions" of temperature, relative humidity, irradiation intensity and pollutant concentrations. The results showed that the photocatalytic process significantly reduced the concentration of both nitrogen oxides in the air. The reaction rate, i.e., the decrease in the concentration of NOx achieved in the steady-state for the inlet concentration of NO and NO2 of 0.1 ppmv, which corresponds to highly polluted urban air, was up to 75 and 50 mu mol m(-2) h(-1), respectively, at the flow rate of 3000 cm(3) min(-1) and relative humidity of 50%. Further, even two years after their application to the surface of concrete walls along a busy thoroughfare, the photocatalytic coating maintained high effectivity. (C) 2017 The Authors. Published by Elsevier B.V.