Assessment of urban air pollution related to potential nanoparticle emission from photocatalytic pavements

Abstract

The main objective was to evaluate whether wearing and weathering of nanofunctionalized photocatalytic pavement in real urban environment can lead to undesirable emission of potentially toxic nanoparticle aerosols in urban air. The photocatalytic material was thoroughly tested before its application for conformity criteria in terms of photocatalytic effectiveness, intrinsic performance and undesired secondary effects, and then applied on a pilot scale in downtown Madrid. The aerosol monitoring on the pilot street before the coating applications as well as on the neighbouring streets during 10 months was used as a benchmark for evaluation of spatial and temporal variations. Analysis of the experimental data did not reveal any statistically significant variations in the aerosol concentrations on the pilot street in comparison with the benchmark. The concentration of Ti-containing particles was assessed by aerosol sampling and yielded values below 10 cm−3 that is more than three orders of magnitude below the toxicological limits. A theoretical model was developed to assess the upper bound of nanoparticle aerosol concentration in air. These findings indicated that photocatalytic pavement materials, which comply with conformity criteria under laboratory tests, can have low impact on the particulate contamination of urban air.