A series of large-eddy simulation (LES) models consisting of two-dimensional (2D) idealised street canyons with building height variability (BHV) are examined. Building blocks with two different heights are placed alternately in the computational domains, constructing repeated street canyons of building-height-to-street-width (aspect) ratio (AR) = 1, 0.5, 0.25 and 0.125 together with BHV = 0.2, 0.4 and 0.6. LES results show that the air exchange rate (ACH) increases with increasing aerodynamic resistance. Apart from AR, BHV is another factor affecting the aerodynamic resistance and thus the ACH. The (vertical) dispersion coefficient
of plume transport is also closely related to the aerodynamic resistance, suggesting that introducing BHV in urban areas could help improve the air quality.
Keywords: air pollution, computational fluid dynamics, CFD, large-eddy simulation, LES, scalar dispersion