The Role of Roof Material in Diurnal Urban Air Quality: A Coupled Large-eddy Simulation and Surface Energy Balance Analysis

Due to the increasing and adverse effects of the urban heat island phenomenon, heatwave events, and high urban air pollution, it has become increasingly important to have an in-depth understanding of the urban microclimates for mitigation purposes. The main objectives of this study are to analyze the relationship between building roof types/materials and the diurnal urban flow characteristics to assess the diurnal urban microclimates and street ventilation capacities. Through a series of novel computational simulations, involving detailed surface energy balance analyses coupled with large-eddy simulations, this study compares the thermo-fluid dynamics and pollution dispersion effects of asphalt, reflective, and green roofs. The results have shown significant differences in street ventilation capacity and pollution dispersion between the different roof-type cases. While the use of green roof reduces the urban air temperatures, a decline in the urban street air quality due to pollutant trapping has been observed at particular times throughout the day.