CFD simulation of the stratified atmospheric boundary layer: Stack gas dispersion under different thermal stabilities

ABL stratification can have an important adverse effect on pollutant dispersion. Following earlier work by the authors on horizontally homogeneous CFD simulations for the Monin–Obukhov similarity theory (MOST) stratified ABL, this paper tests this framework by CFD simulations of dispersion of a passive tracer from an isolated stack under four stability conditions. Two stable conditions, the neutral condition and one unstable condition are considered with ¹/_L equal to 1/150, 1/1000, 0 and −1/300 m⁻¹, respectively, with L the Monin-Obukhov length. A new procedure for employing the MOST-based boundary conditions is proposed, allowing a better comparison of different stability conditions. The results show a good reproduction of the dispersion under different stabilities, such as a more consistent plume trajectory (a continuous rise from a height of 100 m at the stack exit to 130.8 m at 900 m downstream) due to a constrained dispersion under stable conditions and an immediate drop of the plume centerline height (from a height of 113.8 m at 150 m downwind of the stack) due to a stronger dispersion under unstable conditions. The influence of different atmospheric stabilities on plume behavior and the associated convective and turbulent pollutant fluxes is evaluated and discussed.