SLAB: a time-dependent computer model for the dispersion of heavy gases released in the atmosphere

The SLAB model describes the dispersion and gravity flow of a heavy gas released into the atmosphere at ground level, using a crosswind-averaged form of the conservation equations of mass, momentum, species, and energy. The model is time-dependent and one-dimensional in that the equations depend on only one spatial dimension, downwind distance. On the other hand, the model is quasi-three-dimensional since it contains equations to determine the crosswind dimensions of the dispersing cloud. Specific submodels are included to describe wind speed as a function of height, air entrainment into the cloud as the result of turbulent mixing, and heat and momentum flow between the cloud and the ground beneath it and the air surrounding it. The SLAB computer code determines the properties of the dispersing heavy-gas cloud by employing the method of lines to numerically integrate the partial differential equations that comprise the model.