A 3-D Lagrangian stochastic model for the meso-scale atmospheric dispersion applications Original Research Article

A fully 3-D Lagrangian stochastic particle trajectory model is presented and applied to the meso-scale atmospheric dispersion and ground concentration calculations. The use of Gaussian plume model (GPM) with Pasquill–Gifford σʹs for downwind distances exceeding 10 km is critically viewed. Further, the effect of variation in release height on the ground concentration and dispersion parameters (σy,σz) is studied for continuous releases. A continuous release of a non-buoyant gas in a neutral stratified atmosphere is simulated for various stack heights. The turbulent atmospheric parameters like vertical profiles of the fluctuating wind component and the eddy lifetimes for the horizontal and vertical directions, etc. were calculated using a semi-empirical mathematical model and compared with a E–ϵ model. The numerically calculated horizontal and vertical dispersion coefficients (σy,σz) are compared with the Pasquill–Gifford empirical σʹs and with the Pasquill-modified σy. The ground concentration values as a function of downwind distance, have been compared with the Green Glow data and with a GPM for various release heights. The comparison of the results demonstrate a need of using a 3-D model over the simple GPM for meso-scale atmospheric dispersion applications. The GPM overpredicts the ground concentration because it cannot take into account the vertical wind shear, which is observed in the atmosphere under all stability conditions. A weak dependence on the release height in the numerically calculated dispersion coefficients σʹs, is also observed.