The only really effective thing is ozone, as has already been posted, though an ozone generator in the living quarters comes with its own gotchas such as ozone being corrosive and harmful to your respiratory system.
Apart from that, we used to get the smell out of hair and clothes with a hairdryer set to hot. I’m not sure how you could apply that knowledge to an entire room, but there’s probably no harm in trying.
Having said that, if your roommate carries such a strong smell, does he really smoke outside, or does he just sorta-kinda stand in the half-open doorway and call this outside?