Author: Jerry A. Havens

Publisher:

Published: 1985

Total Pages: 183

ISBN-13:

Mathematical modeling techniques use to predict atmospheric dispersion of heavy gases are reviewed and critiqued. These dispersion processes are characterized by three phases: (1) near field, negative buoyancy-domainated flow regime; (2) intermediate field, stably stratified shear flow regime; and (3) far field, passive turbulent diffusion regime. Mathematical models of laboratory and natural gravity currents are used to describe the negative buoyancy-dominated regime flow and dilution processes. A laboratory investigation of instantaneous heavy gas releases in calm air demonstrates scaling from small release volumes (0.5 cu m) to large field (2000 cu m) field releases, and is used to develop a mathematical model for the buoyancy-dominated regime. Laboratory data from stratified shear flow mixing experiments are used to develop a model for vertical diffusion of heavy gases in the atmospheric surface layer. The model concepts are consistent with the limiting passive behavior of demonstrated air pollution models. An interactive computer model for heavy gas dispersion (DEGADIS) is developed. The DEGADIS model accounts for the three regimes of heavy gas dispersion processes and can be used to simulate instantaneous, steady state, and transient releases. The model provides predictions of downwind concentration decay which are in good agreement with the full range of field experimental data currently available, and is recommended for incorporation in the Coast Guard hazard assessment computer system.