The Dankest Weed Could Also Be the Most Polluting

Researchers stress the importance of proper air filters to keep terpenes from interacting with outside air.
Researchers stress the importance of proper air filters to keep terpenes from interacting with outside air. Jacqueline Collins
While the cannabis industry's appetite for energy use is already widely documented, we're still learning more about other forms of legal pot's impact on the environment, such as packaging and extraction waste, as well as how growing nutrients affect soil.

One environmental factor we didn't see coming? Terpenes.

Terpenes are molecules responsible for the smells and flavors of cannabis, hops, pine trees and every other plant aroma. As growers began to breed cannabis to achieve flavor profiles that taste more like oranges, grapes or pine than weed, terpenes quickly became all the rage in legal cannabis — to the point that they're now extracted and mixed with THC concentrate for a more flavorful dab.

But according to the Colorado Department of Public Health and Environment, terpenes also have quite the carbon footprint. Classified as a volatile organic compound (VOC), terpenes can mix with other VOCs and eventually create gases that harm the environment. As the department finishes up research into how many VOCs metro Denver's pot industry produces, we caught up with CDPHE environmental protection specialist Kaitlin Urso, who's helping lead the study.

Westword: What exactly are VOCs, and how can mixing them with other atmospheric gases lead to more emissions?

Kaitlin Urso: They are volatile organic compounds, and when they're released into the atmosphere and interact with other pollutions, like nitrous oxide from combustion activities, you get ground-level ozone formation. The third ingredient is sunlight, and we get lots of that in Colorado. We are also not meeting the EPA's standard for ambient ozone levels [in Colorado]. There is a very large spectrum of them; there can be man-made VOC sources, like paints and solvents, or organic sources, like trees and plants.

We want to find out out how much VOCs are produced per pound of marijuana grown, so we're using state Marijuana Enforcement Division tracking to figure out the cannabis industry's influence on ozone in the state. Carbon filters can actually catch these VOCs and filter them out. Like a sponge, they have a lot of openings, so those VOC molecules get trapped into the pores of the carbon.

Pueblo has a lot of cannabis grows, but nowhere near the same density of people. Are VOCs more dangerous in Denver or other dense environments with a lot of concentrated emissions?

It is a locational issue, and this happens more in the Denver area, or other more populated areas. Those nitrous oxide-rich areas of the state, where there's more population and industry, actually stretch up north to Fort Collins. The Front Range has a lot of ambient nitrous oxide sources.

Down south in Pueblo or on the eastern plains, where there is more agriculture, ozone isn't as big of an issue, because there's not as much nitrous oxide concentration. With the way we legalized in Colorado, we forced most regulated grows indoors. Then, with local zoning regulations and so on, that meant about 70 percent of [Colorado] grows are located in these high-ozone areas.

click to enlarge CDPHE researchers Kaitlin Urso and Dr. Daniel Bon in front of their study subjects. - COURTESY OF CDPHE
CDPHE researchers Kaitlin Urso and Dr. Daniel Bon in front of their study subjects.
Courtesy of CDPHE
Are these types of studies done on other forms of agriculture that produce high terpene amounts? Hops, lavender, citrus, etc.?

You could very closely compare marijuana to hops in terms of terpene emissions,  but we haven't really looked at this indoors and in a hydroponic environment. The types of terpenes that cannabis puts off the most — myrcene, pinene, limonene and terpinolene — are in the "highly reactive" VOC category. And we've essentially relocated a forest of cannabis into the heart of our city center.

We typically let the EPA do this research, but because marijuana isn't federally legal, the EPA hasn't provided that to us. It kind of left this gap in environmental knowledge, so that's where the state stepped in.

How can the findings of this study help cannabis growers evolve?

We can design better odor control and carbon filtration systems if we know which terpenes to look for on a large scale. There are also some HVAC factors and other things that we'll have to work backwards to find, including how many pounds of VOC per pound of marijuana grown are emitted, and what the resulting influence is on ozone.

It's all about seeing odor through a new lens: that it's not just a nuisance, but there are also public-health impacts. It's a good piece of information for the cannabis industry — that this is a little bit more than an odor your neighbors down the street complain about.

Agricultural facilities are exempt from air-quality regulations, so I hope the cannabis industry sees that and receives that message. I think some first reactions could be, "Why are you picking on cannabis?" But we do focus on a lot of other sources of emissions. We just see this as one more service that needs to be provided to the community.

How far along are you on the study?

We've finished conducting sampling at cultivations, so we're going through the data process right now. Soon we'll take those results and marry them to room conditions, like the size, strains and number of plants in the room. We'd like to publish the results by the summer of this year. We want it in a peer-reviewed publication, because having that outside affirmation from outside entities is important.
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Thomas Mitchell has written about all things cannabis for Westword since 2014, covering sports, real estate and general news along the way for publications such as the Arizona Republic, Inman and Fox Sports. He's currently the cannabis editor for westword.com.
Contact: Thomas Mitchell