There are a number of methods by which LNG from a cargo ship or storage vessel is regasified. Open-loop vaporizers (OLVs) at sea terminals utilize the thermal energy in seawater to vaporize LNG. The primary environmental question associated with the use of OLV technology is the potential impact of seawater intakes on fish eggs and larvae. 
Ambient air vaporizers (AAVs) are used to vaporize LNG into natural gas by using the thermal energy in the ambient air. In the process of removing the necessary amount of heat to vaporize LNG, the air can cool to below its dew point, in which case, fog is formed. As the AAVs are used, frost forms on the heat exchanger fins, reducing the effectiveness of the system. Typically, a facility will utilize a large field matrix of AAVs and cycle the LNG flow to different quadrants to improve efficiency.
Exponent has developed a modeling approach to quantify the fog generation, dispersion, and dissipation caused by the cold-air effluent from a large field of AAVs. Exponent used both integral models (SLAB, DEGADIS) and CFD models (Fluent) to predict the dispersion of a dense gas release, and coupled them with a psychometric model to quantify the fog density. The frequency of occurrence of AAV-induced low-visibility conditions along the abutting transportation routes was estimated. Mitigation techniques, to allow extended operation of the AAVs without affecting transportation, were also analyzed. Exponent developed this modeling approach to successfully address questions and concerns from regulatory agencies with regard to the potential effects on visibility from the fog cloud due to the AAV operation.