It's worse than that. Some buildings have to be equipped with fans that maintain elevated air pressure in stairwells. They also have airtight stairwell doors to keep that extra pressure in. However some people like to hold the door open and smoke in that stairwell. The smoke is then pushed by the airflow into the building, and - since it retains positive pressure - it penetrates into apartments and escapes through the vents there. As result, apartments near the stairwells become filled with smoke.
I lived in one such building some time ago, and I had to hermetically seal the door after I come through it, otherwise the apartment would have more smoke than smokers themselves have - all *their* smoke is blown away by the fresh air.
I don't smoke. In most situations I can distance myself from someone who smokes, and there is no need to force the smoker to stop. He has his freedoms, I have mine. In that building, however, it was pretty bad. Once one smoker leaves, another shows up. I haven't signed up to live in an apartment that gets filled with tobacco smoke for most of the day by teams of smokers. I left the place as soon as I could.