Inherited chain smoker in multi-unit.

[Troy B.]

I'm closing on a 5 unit in a few days. The one tenant is a 68 year old veteran that smokes like a chimney. The apartment is already covered with brown walls and ceilings and can't really get much worse. The previous landlord was charging him significantly more then the other tenants because of the smoking. 

In my other properties I only permit smoking outside and inspect often. My question is would it be ok to permit one tenant to smoke and but forbid the other new tenants from smoking in theirs. The building has a shared hallway so it's pretty hard to hide to the others that he is smoking. Has anyone had to deal with a situation like this or what would you do?