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

A fully 3-D Lagrangian stochastic particle trajectory model is presented an d applied to the meso-scale atmospheric dispersion and ground concentration calculations. The use of Gaussian plume model (GPM) with Pasquill-Gifford a's for downwind distances exceeding 10 km is critically viewed. Further, t he effect of variation in release height on the ground concentration and di spersion parameters (sigma (v),sigma (z)) is studied for continuous release s. A continuous release of a non-buoyant gas in a neutral stratified atmosp here is simulated for various stack heights. The turbulent atmospheric para meters like vertical profiles of the fluctuating wind component and the edd y lifetimes for the horizontal and vertical directions, etc. were calculate d using a semi-empirical mathematical model and compared with a E-epsilon m odel. The numerically calculated horizontal and vertical dispersion coeffic ients (sigma (y),sigma (z)) are compared with the Pasquill-Gifford empirica l sigma 's and with the Pasquill-modified sigma (y). The ground concentrati on values as a function of downwind distance. have been compared with the G reen Glow data and with a GPM for various release heights. The comparison o f the results demonstrate a need of using a 3-D model over the simple GPM f or 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 disp ersion coefficients sigma 's, is also observed. (C) 2001 Elsevier Science B .V. All rights reserved.