Researchers at the University of California, Berkeley, published this study in JAMA Network Open. They positioned an aerosol monitor in the living room of a bong smoker to measure the quality of air a visitor might be exposed to. The monitor measured the delicate particulate matter (PM2.5) in the living room while the room’s occupant and his friends smoked bongs for about 120 minutes. After eight sessions, the instrument noted the precise PM2.5 levels before, during, and after each session.