Influence of TiO2-based photocatalytic coating road on traffic-related NOx pollutants in urban street canyon by CFD modeling

The use of titanium dioxide (TiO2) photocatalytic nanoparticles as road coating to trap and decompose air pollutants provides a promising technology to mitigate the harmful effects of vehicle emissions. However, there are few studies on computational fluid dynamics (CFD) simulations of the effect of NOx photocatalytic oxidation in street canyon with TiO2 nanoparticles as pavement coating. This study develop a CFD model with photocatalytic oxidation (PCO) reaction implemented for numerical simulation of NOx abatement in an urban street canyon with TiO2 coating, considering the effects of relative humidity (RH) (10–90%), and irradiance (10–40W ⋅ m−2). Results show that TiO2 coating road can effectively reduce nitrogen oxide (NOx) concentration in the street canyon. The average nitric oxide (NO) and nitrogen dioxide (NO2) concentrations in street canyon with TiO2 coating road were reduced by 3.70% and 4.31%, respectively, comparing with street canyon without TiO2 coating. The irradiance and relative humidity had great effect on PCO reaction in street canyon with TiO2 coating road. When the irradiance increased from 10W ⋅ m−2 to 40W ⋅ m−2, average NO conversion rose from 1.35% to 3.70%, and average NO2 conversion rose from 2.43% to 4.31%. The average conversion of NO and NO2 decreased from 5.11% to 2.54% and from 5.60% to 3.25%, respectively, when the relative humidity is varied from 10% to 90%. Results are useful to transport planners and road engineers who need to reduce NOx concentrations in urban streets travelled by fossil fuel-powered vehicles. Method of the study can be considered by future research faced with different pavement construction and traffic environment.