Pass the Sniff Test

Features - Compliance

Just because you like the smell of your flowers doesn’t mean your (nosy) neighbors will.

January 9, 2017

The Nasal Ranger odor-measuring tool. Charles McGinley, technical director for St. Croix Sensory, which produces the tool, says nearly 200 Nasal Rangers are in the hands of cultivators and their regulators.
Courtesy Nasal Ranger/St. Croix Sensory

Not long ago, odor management could keep cannabis cultivators out of jail. Now, it can keep you in business.

As cannabis reform sweeps the nation, growers face different regulatory situations, with states and cities varying significantly on rules subject to rapid change.

In some places, cultivators view odor management as optional. But in others, notably Colorado, limits exist and are actively enforced, with failure to control odor resulting in denial of a Denver facility’s license renewal, a fine for a Boulder grow and a close call for an Aspen-area business.

Investing in expensive equipment is not necessary if there’s enough distance from neighbors, but for greenhouses near a subdivision and warehouses downtown, a relatively small budget line could prevent big problems.

Cultivation experts who advise growers and sell the latest tools say that in addition to making wise decisions about location and facility design, it’s smart to be proactive to protect your business and avoid inviting new local rules.

There are three common approaches to odor management, each with its own advantages and pitfalls. In general, the choice is to trap (or catch), destroy or disguise the skunky aroma that drives certain people to dial 9-1-1.


Carbon filters probably are the most common odor management tools used by cannabis cultivators. Large fans generally blow air over the filters, which trap passing odor molecules.

High Valley Farms in Basalt, Colo., recently adopted carbon filtration for its greenhouse after facing complaints about smell, resolving the problem after tense relations with local authorities.

“Carbon filters at the present time [are] the standard method of filtering the air for cannabis growers,’ says Charles McGinley, who says he sold the company a Nasal Ranger odor measurement tool for self-testing.

“It appears when they’re using fresh carbon they’re well in compliance,” he says. High Valley farms did not respond to a request for comment, but did win a local vote allowing continued operations.

Downsides of carbon filters include that they can cost a few hundred dollars each (with fans costing hundreds themselves). Large rooms can require several filters, and when they fill up, they need replacement. The fans also use significant electricity and clutter rooms.

McGinley, the technical director of Minnesota-based St. Croix Sensory, travels the nation selling the $1,900 Nasal Ranger to landfills, refineries, wastewater plants, cannabis cultivators and government officials. He says nearly 200 are in the hands of cultivators and their regulators.

McGinley says the Nasal Ranger — or a more rudimentary “scentometer” sold by Calgon Carbon — can determine when it’s necessary to replace carbon filters to stay in line with odor limits. He says cultivators also can adopt the practice of recording “defensible data” from self-testing, which is done in other industries to mitigate any future problems.

“It’s an answer to the person who will complain even if the wind is in the other direction,” he says.

New carbon-based technologies are emerging that offer potential cost savings.

Washington-based Urban Agricultural owner Ben Barker, who supports the cannabis businesses with technology and industry expertise from two decades of cultivation experience, says lighter-weight carbon filters are emerging with greater surface area, lower cost and less weight.

Barker says his company has helped set up about 150-200 cultivation facilities, with odor management addressed on a case-by-case basis.

Urban Agriculture is beginning to sell a climate control system produced by Dutch company Opticlimate that has a built-in slot for carbon filters, eliminating the additional upfront and continuing electricity cost of fans for warehouse locations.

For many growers, carbon is a reliable go-to, which, although expensive, isn’t going to put pressure on the bottom line.

“Carbon filters do the trick 90 percent of the time. We’ve had zero issues with smell abatement. … They’re very, very effective,” says Aaron Herzberg of CalCann Holdings, a California marijuana real estate company.

“It did not reach a level where it was called to my attention,” he says about the cost.


Cultivators do have an increasing number of high-tech options that destroy odor, but these methods can introduce new occupational safety and horticultural health considerations.

Among the technologies are ozone machines that produce unstable molecules with three oxygen atoms and a similar technology that uses UV lights to create hydrogen peroxide vapor.

Both compounds oxidize odor molecules, eliminating their smell, says Kurt Parbst, an agricultural engineer at the large cultivation support firm Envirotech.

Odor-destroying technologies have been used in food-processing facilities and for other industrial purposes for years, and some growers are beginning to give them a try.

One new entry to the market is the Element Air machine developed by Urban-Gro. The hydrogen peroxide (H2O2) vapor generator is designed for use in grow rooms at both warehouse and greenhouse facilities. A commercial version was unveiled in late 2016 and sales of a home-grow option are expected through a yet-to-be-named retailer early this year.

John Chandler, Urban-Gro’s vice president for cultivation technologies, says the machine is safe for use because of the low concentrations of H2O2 it generates. Ozone machines, by contrast, are known to be unsafe when used within an actual grow room.

Chandler says the hydrogen peroxide vapor generator offers the potential for long-term cost saving by eliminating the need to constantly power large fans. And he says the bulbs last longer and are cheaper to replace over time than carbon filters.

The up-front cost of Element Air units may be more than the cost of carbon filters, but Chandler says it could pay off, and that the machines are surprisingly effective, allowing grow rooms to be nearly odorless.

Parbst of Envirotech, which serves companies across the United States and Canada, with many in California, says hydrogen peroxide and ozone leave no harmful residue on plants, though he’s not familiar with any of the firm’s dozens of clients using such a system.

Not everyone’s convinced that technology should be immediately pursued.

Barker says he’s most familiar with ozone, which he says should not be used with plants or near workers, requiring instead a separate “lung room” that draws air from a grow room, allowing a long enough contact time for deodorization before being sent out of the facility.

Using ozone in a grow room, rather than in a lung room, works less effectively because the concentration is insufficient and can “literally strip odor off plants and oxidize oils on the plant,” Barker says.

“There are so many people through the generations of growers who have purchased ozone machines, and they have not worked out as well as they hoped,” he says.

Although he’s not familiar with growers who have used a hydrogen peroxide machine, he worries they would pose a threat to plants or the safety of workers.

“Coming from a smoker’s perspective,” he says, it’s important not to deodorize the marijuana. “Like a great-tasting meal, you definitely want to smell it,” he says.

Chandler says he has supplied many growers with hydrogen peroxide machines and that there’s no need to fear for the safety of plants or people, though he does say the machines aren’t dummy-proof and must be calibrated, producing a scratchy throat if the output is too high.

The dozen growers to whom he’s supplied the machines — in Colorado, Nevada, Massachusetts, New Hampshire and California — have offered no complaints, he says, about the quality of their product.

“At this point they’re in a good dozen commercial facilities for up to four years now with no detrimental effects reported or seen,” he says.

Urban-Grow launched its commercial-grade hydrogen peroxide vapor generator, called Element Air (shown at left), in late 2016. The product is designed for use in both indoor grow rooms and greenhouses to eliminate odor.
Courtesy Urban-Gro


Odor-disguising liquid sprayed outside grow sites is a third major method of keeping smell under control.

This method neither traps nor destroys odor, but rather makes passersby believe they are smelling something else.

“The result, which is tried and true for decades in the market, is you deodorize the situation,” Parbst says.

The idea doesn’t have universal acclaim. McGinley says masking odor won’t fool the Nasal Ranger.

“It works a little, but it doesn’t work enough to take away the root cause, which is the compound being generated by the bud,” he says.

Chandler says it may be true that the odorous compounds remains, but that spraying outside facilities can accomplish important goals nonetheless by preventing inspection.

“The Nasal Ranger doesn’t make complaints,” he says; people do.


Experts contacted for this article say there are ways to avoid costs.

Parbst, the agricultural engineer at Envirotech, says, when practical, it’s important to pick a facility location far enough from neighbors that Mother Nature takes care of odor.

“This sounds corny, but the best treatment for this is distance, to have a distance between the cultivator and the neighbor for the air to mix,” he says.

Urban-Gro’s Environmental Air machine in use in an indoor cultivation site. John Chandler, Urban-Gro’s vice president of cultivation technology, says the machine is safe to use because of the low concentrations of hydrogen peroxide generated.
Courtesy Urban-Gro

Have your eye on an awesome downtown warehouse with the possibility of troublesome neighbors? Maybe it’s best to reconsider, Parbst says. He says his company works with dozens of growers and only a handful pursue odor management, generally because it’s not optional.

With up-front capital and ongoing maintenance costs, “odor control is expensive, and that’s why I think siting is very important,” he says. “Dilution is ideally the easiest way to do it.”

Barker says it’s also a good idea to consider facility design. Retrofitted warehouses that have a potential to ooze odor from every crack benefit from creation of negative pressure in grow rooms, achievable by sucking air from the room. With carbon filters it’s possible to make a closed loop, saving on energy, he says.

“You need to design your facility properly or you’re going back to basement status,” he says. “If you design your building where you can create negative pressure, you won’t have to chase down odor.”

Barker says that odor management hasn’t been a huge concern in Washington, but that localities are beginning to sniff out the issue and that he views regulation as inevitable.

“I believe they should regulate it,” he adds. “I love the smell of cannabis, but it would be rude to bombard someone’s neighborhood and make it smell like weed 24-7. The occasional whiff every now and then is fine, but I’ve seen some pretty obnoxious stuff.”