This segment is part of The State of Science, a series featuring science stories from public radio stations across the United States. This story, by Michael Elizabeth Sakas, originally appeared on Colorado Public Radio.

Between water and electricity, Colorado’s legal cannabis industry already has a big environmental footprint. But what about Front Range air quality? Could the plant itself be contributing to air pollution?

No, it’s not the pot smoke. Colorado Department of Public Health and Environment is conducting a study of terpenes, the organic compounds that make the cannabis plant smell so strong.

Terpenes are classified as volatile organic compounds. Many consumer products release VOCs, like acetone in nail polish remover and butanal from barbecues and stoves. VOCs from terpenes are harmless until they combine with combustion gases to create ozone.

That’s why the state is studying marijuana emissions—it’s about where it’s grown. Unlike other VOC-emitting crops, like lavender, cannabis is often cultivated in greenhouses in the industrial areas of cities, near highways and lots of cars.

“Here in Colorado, as far as air quality concerns go, ozone is our largest pollutant of concern. We are not meeting the national ambient air quality standards for ozone,” said CDPHE’s lead researcher on this project, Kaitlin Urso.

Denver’s ozone problem is especially bad. According to the American Lung Association, it has the nation’s 12th worst air quality. Usually, it’s the Environmental Protection Agency that studies emissions from new industries. Since marijuana is still a federally controlled substance, it can’t.

With the feds on the sideline, Urso said it’s now up to the state to figure out, essentially, “how many pounds of VOCs are emitted into our atmosphere per pound of marijuana grown?”

Indoor and outdoor air samples were taken from four volunteer cannabis companies during different stages of cultivation, including processing. It’s that final stage where “you get a lot higher VOC emission rates.”

“They’re cutting [marijuana] all up, sending them through roto machines that are flinging plant material everywhere,” Urso said.

The state’s study will be the most robust of its kind and builds on the research of William Vizuete, an associate professor at the University of North Carolina Chapel Hill. His study found cannabis grows could contribute anywhere from 66 to 657 tons of emissions per year. Compared to the total VOCs found in the state, that’s about a half a percent to 3.5 percent increase.

Vizuete’s final findings are in the review process and haven’t been published yet, although he shared his results with CPR News in advance.

He acknowledges the range of VOCs is broad. He’s now working with CDPHE and Urso in hopes of narrowing how much gas is released by marijuana grows.

Vizuete’s work has helped identify what types of gases cannabis emits. He said he was surprised to find it “really varied by the strain.” The plant’s life cycle matters as well, “as it grew older and matured, the types of gases that it was releasing also changed,” Vizuete said.

With more than 600 strains of cannabis in Colorado, he said there could be a wide range and volume of gas emitted by these plants.

Research is hard without government support, so it’s up to “states with limited budgets and limited research to fill the role of what the federal government would do in determining the basic science and developing the tools that are needed to make decisions,” he said.

When Vizuete came to Colorado, he teamed up with the National Center for Atmospheric Research in Boulder. He thought that in a legal state his work would be in the clear. He then found out he wasn’t allowed to grow pot in federally-supported research labs, so he had to improvise.

“We grew them in a garage. We set up some grow lights. We had to choose several strains of marijuana. And we had friends that helped out, to water and take care of the plants,” he said.

Vizuete’s research was done without any big federal money, which he argues is needed to better understand the cannabis industry’s health impacts. He might work with Canada, who’s expressed interest in his research now that the country has legalized marijuana.

Without federal guidance, it’s also up to states to set emission standards on the cannabis industry. In Colorado, there aren’t any.

Even if the state’s study does expose a pollution problem, state law says regulators can’t do anything about it. Of course, lawmakers could always step in. That’s why Scott Brady, the grow operations manager at Smokey’s 420 dispensary, was at first hesitant to participate in Colorado’s study. For him, anytime cannabis opens itself up to scrutiny, it’s unclear where it could lead.

“But it’s important to know, either way, good news or bad news, what is it that we’re doing? And then, to be able to have conversations with them about what we can do to help that?” Brady said.

The state notes that carbon filters, which lots of grows already use to control smell, also do a great job of absorbing VOCs. Researchers hope to share more solutions like this and educate the cannabis industry about their possible environmental impact. Brady said he’s listening.

Smokey’s grow operation is in the small town of Garden City, which is less than one square mile across and tucked right up in the southeast corner of Greeley. During prohibition, this was the “wet” town while Greeley was “dry.” Fitting to its name, there are three cannabis grow houses within Garden City limits.

Smokey’s tries to be an environmentally-friendly business. Their goal is zero waste, sustainable packaging and what Brady calls “living soil”—worms and bugs, and lots of other organic matter, to grow their plants. That’s why Smokey’s volunteered to be part of the state study.

“We have an obligation to make sure that we are in addition to our communities, and not a drag on our communities,” Brady said.

The results of the CDPHE study are expected to be released in 2020.