The photocatalytic degradation of nitrogen oxides (NOx) employing concrete paving stones with titanium dioxide is studied experimentally and theoretically. Experiments were carried out in a laboratory photoreactor designed according to the standard ISO 22197-1 (2007) [7] to assess photocatalytic materials. A kinetic model is proposed to describe the photocatalytic reaction of NO and NO2 as well as the influence of several parameters that can affect the performance of the stones, such as NO inlet concentration, reactor height, flow rate, relative humidity and irradiance. The proposed kinetic model is in good agreement with the experimental results, for instance the prediction of the NO and NO2 concentration at the reactor outlet. (C) 2010 Elsevier B.V. All rights reserved.