A Lagrangian particle model for marginally heavy gas dispersion

A simple approach within the framework of Lagrangian particle models was formulated to deal with gas vapours which are marginally affected by gravity and are also subjected to entrainment. For the model discussed in this study, a plume particle represents a small parcel of air and the pollutant. This parcel is subjected to the downward acceleration due to its excess of density over the surrounding. The mean downward motion of each particle was accounted by considering the Langevin equation with buoyancy correction term (Van Dop, 1992, Atmospheric Environment 26A, 1335–1346). Further, the effect of entrainment was considered in a simple statistical way similar to the method considered by Cogan (1985, Atmospheric Environment 21, 867–878). As an example, the formulation was used to study the dispersion of methyl isocyanate (MIC) that was accidentally released from the Union Carbide pesticide plant (Bhopal). A series of computer runs suggests that the particle model with the new formulation that accounts for heaviness and entrainment mechanisms simulates the transport and diffusion of marginally heavy gas vapours realistically.