States are moving quickly to legalize adult use of cannabis and many permit on-site consumption of cannabis products in retail outlets or marijuana lounges. All the inhaled forms of cannabis (smoking, vaping, dabbing) generate an aerosol of ultrafine particles that carries the THC (the psychoactive agent in cannabis) deep into the lungs where it is absorbed. Unfortunately, all these forms of consumption also pollute the air.
Morgan Murphy, Able Huang and Suzaynn Schick measured the air pollution levels in a cannabis retailer that provided electric herb vaporizers and dab rigs and allowed the use of vape pens, but did not allow smoking combusted cannabis or tobacco. Their results, published in “PM2.5 concentrations in a cannabis store with on-site consumption” in Environmental Health Perspectives, revealed unhealthy levels of air pollution (chart above).
With the collaboration of the dispensary management, they monitored ultrafine particles, 2.5 micrometers in diameter and under (PM2.5 ), in the dispensary 24 hours a day, for five weeks in 2019. They found that the average PM2.5 was 84 micrograms per cubic meter during business hours. In other words, on-site inhaled cannabis consumption, even without combustion.
And these are averages, the peak exposure levels are higher.
For perspective, during the day the PM2.5 was 28 times higher in the dispensary than outdoors. On busy days, the average concentration was over 100 µg/m3. When the air outside has been this polluted for 12 hours, sensitive people are advised to reduce the duration and intensity of exercise outdoors (chart above). When the air outside has been this polluted for 24 hours, everyone is advised to reduce the duration and intensity of exercise and sensitive people are advised to consider staying indoors . 12 hours at 84 translates to the orange. 24 hours at 84 translates to the red.
Levels would likely been higher had smoking combusted cannabis been allowed.
The pollution levels Murphy and colleagues found are well above the US Environmental Protection Agency standard for outdoor air:
Currently, the EPA has primary and secondary standards for PM2.5 (annual average standards with levels of 12.0 µg/m3 and 15.0 µg/m3, respectively; 24-hour standards with 98th percentile forms and levels of 35 µg/m3) and PM10 (24-hour standards with one-expected exceedance forms and levels of 150 µg/m3).
As during debates over tobacco smoke-free restaurants and bars, one hears the argument that people are not required to go into these smoky unhealthy environments. The same facts that overcame this resistance applies to cannabis:
- Not everyone who works in a dispensary smokes cannabis. Some workers don’t use or only use edibles or tinctures.
- Even smokers benefit from workplaces that protect them from air pollution. Right before smoking was banned in California bars, researchers surveyed the health of bartenders(5). Then they went back months after the ban to look for any changes in their health. They found that even the bartenders who smoked had better lung function and fewer incidents of eye irritation and respiratory symptoms. 40 hours or more of exposure to other people’s PM2.5 adds an extra level of risk on top of being a regular smoker.
- Cannabis is used as a medicine and some dispensary customers are ill and elderly, making them especially vulnerable to the health effects of air pollution.
The bottom line: Allowing on-site consumption of inhaled cannabis creates unhealthy air for everyone. Onsite cannabis consumption, if allowed at all, should be limited to edibles and other non-inhaled forms that do not impact non-users.