Local and non-local effects of building arrangements on pollutant fluxes within the urban canopy

This work investigates the vertical and horizontal mass (scalar) flux of a contaminant emitted from an area source located in an array of blocks representing an urban environment. Arrays consisting of buildings with random and uniform heights and staggered and aligned arrangements were tested. Results shows that the vertical scalar flux close to the source can affect downwind clean zones. It is also shown that taller buildings increase the vertical scalar flux and the fluctuations of the vertical velocity above the smaller buildings. The vertical advective scalar flux was found to have an effect on dispersion in the vicinity of the building (a local effect), while the vertical turbulent fluxes are associated with pollutant transportation downwind above the smaller buildings (a non-local effect).