The effect of canyon aspect ratio on flushing of dense pollutants from an isolated street canyon

► Aspect ratio strongly affects pollutant flushing mechanism and canyon flow regime. ► In flushing process, decreasing canyon aspect ratio causes longer trapping times. ► Decreasing canyon aspect ratio results in strong stratification within the canyon. ► For all geometric configurations three different flow regimes were observed. ► The regime transition Richardson numbers are a function of the canyon geometry.