This paper investigates the flow and pollutant dispersion in the recirculation cavity behind an ‎isolated building immersed in a neutrally stratified rough-walled turbulent boundary layer flow ‎using Computational Fluid Dynamics (CFD) models. A gas pollutant was emitted from a point ‎source within the recirculation cavity. The CFD models used for the simulation were based on ‎the steady-state Reynolds-Average Navier-Stoke equations (RANS) with κ-ε turbulence models; ‎standard κ-ε and RNG κ-ε models. Inlet conditions and boundary conditions were specified ‎numerically to the best information available for each fluid modeling simulation. The flow and ‎diffusion fields in the boundary layer in an urban area were investigated using an isolated ‎rectangular high-rise building model. The accuracy of these simulations was examined by ‎comparing the predicted results with a wind tunnel experimental data. It was confirmed that ‎simulation using the model accurately reproduces the velocity and concentration diffusion fields ‎with a fine-mish resolution in the near wake region. Results indicated that a good agreement ‎between the results of numerical simulation and the wind tunnel experiment for both wind flow ‎and concentration diffusion. Moreover, the results of this work can be used to help develop and ‎improve the modeling of pollutant transport in the recirculation cavity behind the high-rise ‎building. ‎