Evaluation of GRAL for the Pollutant Dispersion under Low Wind Speed Conditions from Two Road Tunnel Portals in Nanjing

A Lagrangian atmospheric dispersion model GRAL dealing with the dispersion of pollutants from a roadway tunnel portal has been introduced, with its application in Nanjing. The results show the dispersion characteristics under local meteorological conditions, especially in low wind speed conditions. A comparison with a Gaussian point source model and a CFD model (FLUENT), has been made. Under the low wind speeds and parallel-to-the-road wind conditions, GRAL has advantages over the Gaussian and CFD models, while the latter two overestimate concentrations as a result of neglecting the influence of the ambient wind fluctuations on position of the jet flow from the portal. The cases here might be useful in someway for pollution controlling, environment impact assessment and project design.