How third-hand cigarette smoke is infiltrating even nonsmoking areas

A room occupied by a smoker can effectively expose the other occupants served by the same HVAC system to (thirdhand smoke), even if they do not share space directly. Photo: Shutterstock

Pop quiz: If you sampled the air in an empty college classroom where smoking is not permitted, what is the last thing you’d expect to find? If you guessed “cigarette smoke,” you’re in good company.

Peter DeCarlo, an air quality researcher at Drexel University in Philadel­phia, would have agreed with you. But when he examined the air from the unoccupied room, he discovered that 29% of the tiny particles suspended within it could be traced to the residue of cigarette smoke.