Ok, let me make sure that I fully understand your complaint...

You are stating that someone is smoking outside, no windows or doors are open, and somehow smoke is getting into your unit? Do you otherwise have a serious problem with drafts and other insulation issues?

Smoke is going to follow the path of least resistance. The amount of smoke that could possibly enter your unit (unless there are serious drafts) should not be enough to give you headaches, serious fatigue or a higher risk for cancers. Even with serious drafts, the person would have to be literally smoking right next to the draft area.

What you might want to do is see if you can figure out what the point of entry is. If there is a draft area somewhere that could be rectified it might not only solve that problem, but might reduce your heating and cooling costs as well.