CFD simulation of pollutant dispersion around isolated buildings: On the role of convective and turbulent mass fluxes in the prediction accuracy

► Pollutant transport can be decomposed into turbulent and convective fluxes. ► Accuracy of RANS and LES is explained by observing these fluxes. ► LES shows that turbulent mass flux obeys a counter-gradient mechanism streamwise. ► The RANS gradient-diffusion hypothesis is valid in lateral and vertical directions. ► In the 2 cases, convection is the dominant mechanism of mass transport streamwise.