Depends what you're smoking on. If you're using a pipe or similar, the smell will dissipate within a few windows of opening the windows. If you have a sun roof and it's not too windy, just smoke with the roof open. If you're smoking a joint or blunt, the smell is much more dense. Blunts stink up my car for a good day or two and joints, for a few hours...and that's with the windows open!