Measuring PM concentrations from secondhand tobacco vs. marijuana smoke in 9 rooms of a detached 2-story house.

The widespread legalization of recreational marijuana raises growing concerns about exposure to secondhand marijuana smoke. An important location for marijuana smoking is the home, but few measurements of air pollutant concentrations in the home are available for a marijuana joint fully smoked in one of its rooms. We used research grade calibrated real-time continuous PM air monitors in controlled 5-hour experiments to measure fine particle concentrations in the 9 rooms of a detached, two-story, 4-bedroom home with either a tobacco cigarette or a marijuana joint fully smoked in the home's living room. The master bedroom's door was closed, and the other bedroom doors were open, as was the custom of occupants of this residence. In two experiments with a Marlboro tobacco cigarette smoked by a machine in the living room, the 5-hour mean PM concentrations in 9 rooms of the home were 15.2 μg/m (SD 5.6 μg/m) and 15.0 μg/m (SD 3.7 μg/m). In contrast, three experiments with pre-rolled marijuana joints smoked in the same manner in the living room produced 5-hour mean PM concentrations of 38.9 μg/m (SD 10.6 μg/m), 79.8 μg/m (SD 25.7 μg/m) and 80.7 μg/m (SD 28.8 μg/m). In summary, the average secondhand PM concentrations from smoking a marijuana joint in the home were found to be 4.4 times as great as the secondhand PM concentrations from smoking a tobacco cigarette. Opening 3 windows by 12.7 cm reduced the high PM concentrations from marijuana smoking by 67 %, but the PM levels still exceeded those produced by tobacco smoking with the windows closed.