Laboratory investigation of the effect of mixed nitrogen dioxide and nitrogen oxide gases on titanium dioxide photocatalytic efficeincy in concrete pavements

Nitrogen oxides (NOx) emitted from vehicle exhausts are associated with adverse health effects on the public. Self-cleaning, airpurifying concrete pavement is a rapidly emerging technology that can be constructed by using a photocatalyst such as titanium dioxide (TiO2). The main objective of this study was to evaluate the environmental effectiveness of TiO2 coating in photodegrading mixed NO2 and NO gases from the atmosphere. Results of the experimental program determined that increasing the flow rate and NO2=NOx ratio negatively affect the effectiveness of the photocatalytic process. However, within the evaluated range, the titanium content and aggregate gradation had little effect on NOx removal efficiency. The highest photodegradation rate was observed at 25% relative humidity, which balances the availability of hydroxyl radicals at the surface with NOx contact with the photocatalytic surface.