Recognizing Cannabis Intrusion
Cannabis plants, smoke, and vape give off emissions - in some cases unusually high levels of emissions - that can travel long distances (1 mile documented). This creates the potential for secondhand and thirdhand exposure from personal use and cannabis grow and processing operations. If airborne cannabis emissions enter buildings, ventilation systems are unable to eliminate smoked or vaped cannabis, according to ASHRAE, the organization of engineers who develop standards for building ventilation.
Am I Exposed?
Just because you're not smelling that classic skunky smell doesn't mean you're not exposed to cannabis.
Terpenes
​It used to be that you could recognize cannabis fairly consistently by the skunky or musky smell. Much of the modern cannabis, however, is infused with different smells and flavors that come from the variety of naturally occurring terpenes in the plant, as well as an enhanced amount of terpenes added during processing. Cannabis might have that classic skunky smell, or it might smell like mint, garlic, citrus, sewer, saffron, coffee, and more - or it might be odorless.​
Processing Agents
In the cannabis extraction process, butane, propane, and hexane are commonly used as solvents. Because of the heating involved in the extraction process, both the cannabis as well as the extraction agents (solvents, etc.) can become airborne; odors from solvents or other processing agents may also be a sign of cannabis exposure. A study by Desert Research Institute, also highlighted on the homepage, has more detail about butane and other emissions from cannabis grow and processing facilities.