A method for eliminating ground fog which results from vaporizing cryogenic fluids using ambient air. The method includes the steps of drawing an ambient air stream through an ambient air vaporizer thereby cooling the air stream and vaporizing the cryogenic fluid, and then passing the cooled air stream through a vent stack. The method further includes isolating the inlet air stream from the cold outlet air stream and dispersing the cold air into the atmosphere upon leaving the stack. The method further controls the relationship of the stack exit location and the ambient air vaporizer to prevent a temperature depression in the air surrounding the vaporizer which depression causes reduced vaporizer performance.