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Science Magazine 1.24.19 Jason Plautz klmn�
As legal pot farms expand, so do air pollution worries
BOULDER,COLORADO—Atmospheric scientist William Vizuete grew his dozen pot plants in a garage here,on
shelves tucked between some bicycles and a lawn mower. The researcher at the University of North Carolina in Chapel
Hill wasn't looking for a high just data. His team aimed to measure the volatile organic compounds(VOCs)released
into the air by four varieties of cannabis—including strains dubbed Lemon Wheel, Elephant Purple, and Rockstar Kush—
as they grew,rather than when they were smoked.
Those measurements, recently published in Atmospheric Environment,are just one product of an emerging effort to
understand how expanding pot farms in Colorado and the nine other U.S.states and Washington,D.C.,that have
legalized recreational marijuana might be affecting air quality.
Vizuete's study, for instance, suggested the more than 600 indoor pot farms in Denver could be worsening the city's air
pollution,which sometimes violates federal limits.Next month, in a bid to understand that issue, Colorado officials will
launch one of the largest studies to date of pot farm emissions.
Those findings could also aid regulators across the nation,who face a dearth of data as they try to evaluate the pot
industry's potential effects on indoor and outdoor air quality as well as worker health. "To be able to permit [pot farms],
we have to at least estimate their emissions," says Mike Wolf, a regulator in Washoe county in Nevada.
Such estimates have been scarce, largely because the federal government still considers cannabis an illegal industry. That
has made it difficult for researchers to obtain funding from federal agencies, including the Environmental Protection
Agency(EPA)and the Occupational Safety and Health Administration. Vizuete,for example, had to work in a garage
because cannabis plants aren't allowed in the federally funded National Center for Atmospheric Research here,where he
had hoped to run the study. Scientists wanting to study pot, he says, "are stuck in a position where we have to cobble this
together on our own."
Researchers have long known that VOCs emitted by plants can contribute to smog.VOCs can mix with nitrogen
oxides—produced by cars and industrial sources—in sunlight-driven reactions that produce ground-level ozone,a
pollutant.Vizuete's study confirmed that pot plants are a rich source of potent VOCs called terpenes,which give
cannabis its dank smell.And it suggested the tens of thousands of plants in Denver's indoor farms—which are
mostly found along two busy highways—could,under a worst-case scenario,double the city's volume of smog-
forming VOCs.If the farms "are putting out a significant amount of terpenes,there is not a worse place to put
them," Vizuete says. "If I was designing an ozone reactor,this is what I'd do."
Vizuete's team notes its study—one of the first of its kind—was not definitive. It was small:just three plants each of four
of the 620 available cannabis strains. And the plants were "pathetic," says study co-author Christine Wiedinmyer, an
atmospheric chemist at the University of Colorado here—nothing like the lush crops grown by professionals.
The Denver study, funded by a state program, will collect more data.
It will measure VOC emissions at four farms—two large and two small—over the months long cultivation cycle,
from planting to processing.The goal is to track emissions across pot varieties,growing conditions,and plant size
and age,says project leader Kaitlin Urso of the Colorado Dept of Public Health and Environment in Denver.
Ultimately, researchers will plug the findings into computer simulations that help scientists and regulators understand the
factors driving air pollution.Normally, EPA provides those numbers for industrial emissions. But it doesn't recognize pot
growing and Urso says agency officials don't like to discuss the matter, leaving states to fill the gap. "EPA has left us
holding the bag," Urso says.
If pot farm emissions do pose air quality problems, it's not clear what regulations would require growers to do. Farms are
exempt from many clean air rules,although worker safety regulations and some state rules could apply.Placing carbon
filters on grow house exhausts could capture up to 98% of volatile emissions,but so far the filters aren't required.
The industry,meanwhile, is eager to work with researchers. "We want more data,we want to know how we can promote
best practices and be good neighbors," says Morgan Fox of the National Cannabis Industry Association in Washington,
D.C.
Some help could soon come from Canada, which recently legalized pot—opening the door to studies that don't have to
hide in a garage. But Vizuete says there also "needs to be some leadership from federal agencies" in the United States,
including EPA. "Nobody is helped," he says, "by refusing to acknowledge that this is a public health issue."