Calculation of Heavy Gas Spreading Over the Earth Surface by a Three-Dimensional Model

A mathematical model is constructed for motion of a heavy gas along the underlying terrain on the basis of equations of gas dynamics with allowance for the force of gravity, transfer by air masses, and turbulent diffusion. With the use of the method of coarse particles, the time dependences of the coordinates of the fore front, upper boundary, and volume of the cloud of a heavy gas in the presence and absence of wind are analyzed. It is shown that turbulent diffusion leads to a linear increase in cloud volume in time. Three-dimensional shapes of the heavy gas cloud are obtained for various ambient conditions. It is shown that, despite diffusion, the heavy gas spreads predominantly along the underlying terrain.