To leave a smoke screen
The Ghost Duster was a feature build into Ghost Buggy. When the driver, usually Tracy the Gorilla, would turn on the Ghost Duster, a trail of green smoke would be ejected from one of G.B.'s rear exhausts. The purpoise of this was to temporarilly blind any persuers so Ghost Buggy could make a clear getaway.
An unfortunate side effect was that the dust was so powerful and all encompassing, that the Ghostbusters and G.B. would most often also lose their sense of direction due to a lack of vision.