A 3D Lagrangian particle model has been presented for the atmospheric dispersion of the toxic pollutants released from industrial stacks. As the mean wind speed and direction is changed with height in a real atmosphere, the height of the exhaust stack may have a strong impact on the pollutant dispersion and ground concentrations. An elevated continuous release of non-buoyant gas in a neutrally stratified atmosphere has been simulated, for various stack heights. The turbulent atmospheric parameters like vertical profiles of fluctuating wind velocity components and eddy lifetime were calculated using a semi-empirical mathematical model. The numerically calculated horizontal and vertical dispersion coefficients (sigma(y) and sigma(z)) are compared with the Pasquill's empirical sigma's. The ground concentration as a function of downwind distance has been compared with the Green glow data. The ground concentrations for various release heights were compared with the Gaussian plume model. The comparison indicated a need for using either a modified Gaussian model or a 3D numerical mathematical model for pollutant dispersion and ground concentration calculations. Copyright (C) 2002 John Wiley Sons, Ltd.