Recently, California and other states have legalized the use of cannabis in licensed stores (subject to state-specific limitations), giving people who cannot consume cannabis in their homes a safe and legal place to consume it. However, on-site consumption may expose customers and workers to particulate air pollution. Consumption methods that use temperatures below combustion to aerosolize cannabis are a way to reduce exposure to toxicants (Gieringer et al. 2004). In vaporization of cannabis flower, an aerosol is formed by passing heated air through finely ground, dried flower. Cannabis concentrates can be consumed by dabbing, where a small amount of concentrate is applied to a heated surface to create an aerosol. Like smoking, vaporizing and dabbing create aerosols that contain particles [less than or equal to] 2.5 pm in aerodynamic diameter (P[M.sub.2.5]) (Jaques et al. 2018) that can penetrate deep into the lung. To assess the effects of on-site consumption of cannabis on P[M.sub.2.5] concentrations, we measured P[M.sub.2.5] in the retail and consumption space of a cannabis store (a dispensary), where smoking was banned, but vaporizing and dabbing were permitted.
P[M.sub.2.5] concentrations were measured continuously, using two, colocated laser photometers (model AM510; TSI Inc.), placed 80-100 cm above the floor, for 5 wk in 2019. Room occupancy was not monitored. In Wk 1, the instruments were located 30-122 cm from the sources (vaporizers and dab rigs). During Wk 2 and Wk 3-5, they were 6-9 and 2-4 m from the nearest sources, respectively. Photometers were operated with impactors to exclude particles >2.5 pm in diameter. The photometers were zeroed once a day and calibrated gravimetrically using a controlled cigarette smoke generation system (Schick et al. 2012) before and after each experiment. Gravimetric data from 20 cigarette smoke experiments, when plotted against the matching photometric data and forced through zero, yielded a calibration factor of 0.31 ([R.sup.2] = 0.84), which was applied to the dispensary photometric data. Cannabis P[M.sub.2.5] samples were also collected in the dispensary on filters (Emfab; Pall Corporation) for 1 wk in December 2019, and a preliminary photometer calibration factor was calculated as above. P[M.sub.2.5] concentrations in outdoor air were estimated using data from a U.S. Environmental Protection Agency monitoring station located 2.5 km (1.5 mi) from the dispensary in an area with similar ambient pollution sources.
The retail and consumption space was a single room of ~400 [m.sup.3]. Cannabis consumption occurred at three tables in one corner of the room, with sales counters located in the opposite corner. The room was served by the building heating, ventilation, and air conditioning (HVAC) system and by four window air conditioners that did not admit fresh air. The air conditioners had dust filters, and we were unable to examine filtration in the building HVAC system. The dispensary provided...