Numerical simulation of air pollution mitigation by means of photocatalytic coatings in real-world street canyons

Motivated by the increasing interest on passive control solutions to lower pollutant concentrations in cities, this paper introduces a novel methodology to demonstrate the potential of photocatalytic coatings in abating air pollution in real-world urban environments. The methodology introduced in this paper is based on an original application of Computational Fluid Dynamic (CFD) modelling to simulate the effect of photocatalytic coatings in real yet simplified urban setting. The numerical approach is validated against observations gathered during an ad-hoc designed intensive experimental campaign performed in a real urban area in the city of Bologna, Italy (44.5075 N, 11.3514E), under semi-controlled conditions. Comparison of the model output with observations show a concentration reduction in the range 10–20%. After validation and choice of the proper model set-up, numerical simulations are analyzed by focusing on the mechanisms enhancing the flow circulation within the canyon, an effect that may increase the effect of coatings within street canyons. Results show that application of photocatalytic coatings can give pollutant reductions up to 50% in a confined region close to the walls. A parametrization for the pollutant reduction within the street canyon is suggested to summarize these results, providing a characterization of the photocatalytic coatings performances as a function of the geometric char-acteristic of the street canyon.