Using large eddy simulation to investigate pollutant dispersion over stepped roofs

Abstract

This study used the LES model PALM to investigate the effects of roof structures on turbulence and pollutant dispersion within urban street canyons, focusing on how different roof shapes influence airflow and pollution patterns. The analysis shows that stepped roofs, compared to flat roofs, significantly modify pollutant distribution, with accumulation and dispersion patterns affected by roof geometry. Stepped roofs result in variations in pollutant concentrations at various heights along the canyon sides and in different directions from the pollution source. Unlike flat roofs, stepped roofs primarily transport pollutants into the layer above the urban canopy through turbulence rather than advection, especially in areas distant from the windward wall. The simulation results indicate that a greater number of steps leads to increased pollutant accumulation. Thus, roofs with more steps are less favourable for pollutant dispersion. These findings highlight the critical role of roof shape in influencing urban air quality, particularly its impact on pollutant dispersion and concentration.