Regulatory agencies increasingly require use of air dispersion and deposition modeling to evaluate the environmental risk of facility remediation, construction, or operation. Mathematical models calculate air contaminant (plume) dispersion and deposition — the changes in concentration of substances from the source to some location at a given distance from the release point. Typical air emission sources evaluated by regulatory agencies include superfund and hazardous waste sites undergoing groundwater or soil remediation; municipal solid-waste incinerators and landfills; industrial source operations that use various chemicals in the manufacturing process; industrial and municipal wastewater treatment facilities; and microelectronics industries which use specialty gases and chemicals.