Marijuana stinks. Here’s what cities, businesses and neighbors can do about it.

Even the most ardent marijuana lovers can’t deny it: The plant, at least to some noses, stinks.

Marijuana odors have triggered lawsuits against cannabis companies. They’ve also led residents to try to block commercial operations from coming to California and the other eight states where recreational cannabis is legal and, increasingly, big business.

Odor has sparked some neighborhood friction, too, as marijuana smoke drifts from one apartment or yard to the next.

There are products on the market that claim to test for smells, block all odors from wafting out of indoor operations, and even help control the stench of outdoor marijuana farms.

Long before legalization, the cannabis industry grew accustomed to working underground — making growers and processors and distributors pretty good at hiding the smells associated with their businesses. While that might ease the possibility of odor-related friction, it doesn’t foster industry-wide communication about new ideas for tackling the issue, even as new anti-odor technologies are coming to market.

Only now — with odor control an area that’s both problematic and ripe for technical solutions — are marijuana entrepreneurs starting to share ideas about their industry’s stink factor.

“That’s probably the biggest hurdle now, for everybody involved, is knowing what’s available as best practices, and what’s feasible,” said Dana Pack with Fogco, an Arizona-based company that makes systems to neutralize unwanted smells.

Cities can mandate odor-control systems for home growers, or as a condition for approval of marijuana-related business permits.

But some in the industry note that odor requirements aren’t yet universal, and that odor control is yet another element of the marijuana business in which regulators aren’t keeping pace with the spread of legalization.

“The licensing agencies are still in a learning curve,” said Chuck McGinley, technical director of St. Croix Sensory, a lab in Minnesota that tests for odors and makes products that help others do so in the field. “This is a very young industry.”

Neighbors fight back

Residents claim the stench of weed disrupts their quality of life, lowers their property values and causes problems for people with respiratory issues such as asthma.

In June, after the city of Palm Springs issued what might be the first permit for a cannabis lounge in Southern California, the owner of a spa next-door threatened to leave town.

Since January 2016, the South Coast Air Quality Management District — which monitors air quality issues for most of Los Angeles, Orange, Riverside and San Bernardino counties — has received 11 complaints of odors allegedly created by marijuana growers, dispensaries or processing facilities, according to spokesman Sam Atwood.*

Santa Barbara County and cities in its boundaries have received more permits to grow marijuana than any other county in California. Now residents of the beach town Carpenteria say they’re stuffing pillows under their doors to block odors coming from nearby cannabis farms.

In Colorado, three years ago, owners of residential property sued a marijuana farm that was set to open next-door, claiming cannabis-related odors would ruin their horse rides and harm their property values. The lawsuit cited racketeering laws, typically used to prosecute organized crime rings, since marijuana remains illegal under federal law.

A federal district court initially dismissed the Colorado claim, but an appeals court in 2017 cleared the case to move forward. That paved the way for a number of other lawsuits that raise racketeering charges while also citing odor and other nuisance concerns, and similar suits have been filed in Massachusetts and Oregon.

Some of those suits have been settled or dismissed. Others are pending, raising concerns within the industry about how state-legal marijuana programs might be upended by legal battles that often start with simple complaints about smell.

Solutions are out there

Most odor control solutions for the marijuana industry involve tweaking products that are already used by landfills, wastewater treatment plants and other businesses that generate offensive smells.

The most common fix is to add carbon filters, or “scrubbers,” to ventilation systems. As air passes through, odor molecules bind to the activated charcoal. As long as everything is properly installed and maintained, McGinley said the air that comes out of the vents should be virtually odorless.

But carbon filters have to be replaced often, making them pricey for large operators. Carbon filters also rely on a lot of electricity, making them less than ideal for many environmentally conscious greenhouse owners. And, of course, air filters can’t do anything about the smell generated by outdoor farms.

That’s where fog systems might come into play.

These systems involve placing nozzles at the spot where air from a grow operation will be expelled. The system mixes water with an odor-neutralizing chemical and forces that mixture through the nozzles at high pressure. The water instantly evaporates, leaving the chemical in the air to attract and neutralize any cannabis smells.

“The idea is to build a barrier of fog between the odorous air and community,” said Pack with Fogco.

Such systems don’t need to be in constant use, so Pack said energy use and maintenance are “a fraction” of what’s required to use carbon filters.

Mark Stanley, a vice president with Palm Springs-based MicroCool, which also makes a fog odor-control system, said marijuana growers are showing enough interest in his company’s products that it’s hard to keep up with demand.

Pack, of Fogco, said that while greenhouse operators are his company’s biggest clients, his company also sets up systems to control odors from outdoor farms. They line the perimeter of the farm with nozzles, which they can turn on when plants are flowering and monitors show that wind speed and direction might carry the scent to neighbors.

Some online grower forums recommend “ozone generators,” which can disrupt smells by converting oxygen into ozone. But the California Air Resources Board advises against using the devices with people around since, to remove odors, they have to create ozone molecules at levels that aren’t safe for humans to breath.

Local law rules

With such a wide range of techniques available, Santa Monica-based cannabis attorney Michael Jensen said it’s key to write odor-control regulations that leave room for innovation.

Currently, California law doesn’t do much to address odors, requiring only that marijuana businesses limit emissions from generators and from the solvents used in the extraction of certain marijuana compounds. Otherwise, state agencies overseeing cannabis have said odor control is a local issue.

Most California jurisdictions ban all marijuana businesses. And many cities and counties that do permit them simply include a line or two in their regulations that say marijuana odors can’t be noticeable.

Los Angeles’s marijuana regulation rules run 33 pages, only three sentences of which address odor control. The rules state that air vented from marijuana businesses must be filtered so that odors can’t be detected outside, or in adjoining sites, by a person with a “normal sense of smell.”

Long Beach requires businesses to submit odor control plans when they apply for local permits, and the system must be certified by a licensed engineer.

Local authorities are also the go-to source for complaints about marijuana odors.

While it’s legal in California for adults 21 and over to consume marijuana, and grow up to six plants at home, residents bothered by the smell can report it as a nuisance to their local code enforcement office. If the neighbor lives in an apartment, under a homeowner’s association or has a landlord, residents might have better luck reporting complaints through those entities, since they can ban smoking and cultivation in their units.

Enforcement challenges

Odor complaints are tricky to investigate, according to Alan Abbs, executive director of the California Air Pollution Control Officers Association. Smells tend to dissipate quickly, and the offensiveness of certain smells can be subjective.

One way to remove some of that subjectivity is to use devices called field olfactometers, which offer science-backed data about the intensity of odors.

McGinley’s lab makes a field olfactometer called the Nasal Ranger. It looks like a telescope with a mask on the skinny end and a rotating dial on the fatter end. Users adjust that dial, then hold the Nasal Ranger up to their nose and breath in. Carbon filters purify some of the air. Then, based on the dial’s setting, the device mixes the filtered air with the air coming in from outside before it gets to the user’s nose. The more dilution required to get rid of the smell, the stinkier the outside air would be.

Denver has set odor standards for marijuana and other stinky businesses based on the measurements tracked by the Nasal Ranger and similar devices. But for now, many California cities and counties rely on repeated complaints as evidence of a problem.

In Santa Barbara County, for example, if county authorities get three odor complaints from a business in a year, the company must take steps to fix the problem. And if the business doesn’t stop the stench, the county may revoke local permits.

“There’s going to be a tough learning curve,” Jensen said. “Time will tell whether this becomes an issue.”

*An earlier version of this story misstated the number of recent complaints to South Coast Air Quality Management District related to marijuana odors due to incorrect information provided to the Orange County Register. The story has been updated.