Well, while "Ghosts" as such may not exist, the unknown phenomena we superstitiously CALL "Ghosts" certainly do. And do these "ghosts" occupy space?----- We don't know, however if they DO, not only would they displace air, other Phenomena associated with the phenomena would be explained.
Assuming these "ghosts" "pop in" and "pop out" via the 4th Dimension and displace air, we would also observe both small, localized "Hot spots" and "Cold spots" associated with the phenomena----As a "ghost" "popped in" and displaced air, the displaced air in the area would momentarily be Compressed and thus generate a short lived "Hotspot" around and near the location of the event. Conversely, Should one of these "ghosts" "pop out" , leaving a momentarily "void" which the air would expand into, and according to the principles or refrigeration, would generate a "Cold spot" of cooler air.
Also providing insight into the "physical displacement" properties in this "Ghost Phenomena", are the "Underwater "Ghosts" observed in water tanks, pools, etc., near where other Phenomena such as above happens. These "Ghosts" look like a mass of "bubbles"----But what is odd about them, is the bubbles do not RISE. Why not?, because they are not air bubbles, but actual voids in the water where the liquid has been displaced----And as long as the "ghost" doing the displacing, keeps it's place, so do the bubbles, which immediately collapse, when the "ghost" " Pops out".
So we ARE dealing with a real phenomena here, of an unknown nature, that has displacement properties, but appears to be made of a collection of small units, rather than a solid displacing mass---as evidenced by the "bubble appearance when it displaces voids in water.
So we may be dealing with some kind of 4th Dimensional Physics phenomena that is invisible, but can displace air and water. We don't know what it is yet, and it deserves study.----Forget that people claim its "spirits of the dead", there is no evidence of that, we can only observe the phenomena and speculate. for now.