I think there is a general misunderstanding about gas phase miscibility among many. Substances which exist in the vapor phase under ambient (existing) conditions are infinitely miscible. They will eventually form a complete gaseous solution (vial convectional mixing and Brownian motion) and will not separate or "settle out" after mixing unless they react to form a compound that is no longer a gas under the existing temperature and pressure (precipitation) or unless the existing temperature or pressure are changed, for example, in fractional distillation. One or more gas species in a gaseous solution could also preferentially adsorb onto a solid or liquid surface but I do not think this is something most people consider when dealing with gas releases. I have read that there are conditions of temperature and pressure under which gases may become immiscible but it does not appear to me that these would exist outside of an atmospheric chamber.