A Numerical Study on the Effects of Building-roof Cooling on Flow and Reactive Pollutants Dispersion in street canyon

In this study, the effects of building‒roof cooling on flow and reactive pollutants dispersion were investigated using the coupled CFD‒chemistry model. Flow characteristics were analyzed first in street canyons with and without building‒roof cooling. In all the cases, a portal vortex was generated in street canyon, producing dominant reverse and outward flows near the ground. The building‒roof cooling decreased air temperature and increases horizontal wind speeds above the roof level by weakening the temperature gradient. Wind speeds strengthened at roof level enhanced the reverse and outward flows near the ground. The flow changed with building‒roof cooling affected the distribution of primary and secondary pollutants. High concentrations of primary pollutants occurred near the upwind building because the reverse flows were dominant at street level, making this area the downwind region of emission sources. O3 concentration was lower than the background near the ground, where NOx concentrations were high. Building‒roof cooling decreased primary pollutant concentrations in contrasted to those under non‒cooling conditions. In contrast, building‒roof cooling increased O3 concentrations by reducing NO concentrations in the street canyon compared to concentrations under non‒cooling conditions.