Numerical investigation of possible role of local meteorology in bhopal gas accident

Two numerical models were coupled in this study; a three-dimensional mesoscale meteorological model and a three-dimensional Monte Carlo dispersion model. The dispersion of methyl isocyanate gas from the Bhopal accident was examined using the coupled models. A series of numerical experiments were performed to investigate the possible role of the surface induced mesoscale circulations and various environmental parameters on this industrial gas episode. The temporal and spatial variations of the wind and turbulence fields were simulated by the mesoscale model. The dispersion of the accidentally released methyl isocyanate gas was then evaluated by the Monte Carlo model using these wind and turbulence fields. The numerical experiments suggest that the reported complex dispersion of the gas at Bhopal could have resulted from the interaction of thermally forced mesoscale circulations. Results especially point to the effect of the Bhopal urban heat island which dominated the local circulation and trapped the gas over Bhopal city. The calm ambient winds, clear skies, and stable nocturnal atmospheric conditions that prevailed during the accident are consistent with the formation of an urban heat island effect over Bhopal.