The objective of the present work is to propose a methodology to simulate hazardous gas dispersion in neutrally and stably stratified atmospheric boundary layer (ABL) flows. The profiles of velocity, temperature and turbulence quantities are set based on the stratification effect. Special emphasis is placed on the generation of a horizontally homogeneous turbulent boundary layer (HHTBL). FLUENT software is validated for simulating ABL flows by comparing the results obtained with available numerical data from the literature. The fully developed profiles of velocity, turbulent kinetic energy, turbulent dissipation rate and temperature are implemented as user defined functions in the commercial code FLUENT. The hazardous gas release is modeled using the convection diffusion equation. Four test cases from the classical Prairie Grass experiment are considered for validating the present approach. The predicted concentration of the SO₂ gas at various locations of the test field (50, 100, 200, 400 and 800 m) are in close agreement with the experimental data. The cases of neutral stratification compare quite well with the experimental data and there exist a slight discrepancy in the stably stratified cases. This mismatch can be attributed to measurement errors and the anisotropic nature of the ABL flows.