Several of the residents have complained that the hallway on the third floor smells of cigarette smoke. In my experience, there's a moderately strong smell of smoke in the hallway, but it doesn't permeate into my unit. I've not heard of anyone complaining that they smell smoke in their unit, only in the hallway.
The source of the smoke has been traced to one specific unit on the floor, which is occupied by a renter. It seems that he's a chain smoker and a militant smokers' rights advocate. There is nothing in his lease which prohibits smoking, nor is there anything in the HOA bylaws that does so. I'm sure there are provisions for maintaining the cleanliness of common spaces, though I haven't read them since I moved in.
If you were on the board of directors, what strategy would you adopt?