The Nasal Ranger helps investigators track strong odors, whether of chemical contaminants or just "bad smells."

Machines are talented at detecting poisons or at purifying air, but humans are still better at tracking smells.

Dynamic olfactometry means diluted smelly air is passed to trained human panelists. The Nasal Ranger is a limited mobile version.

The tiny city of Bessemer, in Michigan’s remote Upper Peninsula, has spent $3,400 on a marijuana-sniffing instrument called the Nasal Ranger. City officials say that while recreational use is legal in the state, individuals are limited in how many plants they can grow, and the city’s strong odor indicates people aren’t obeying that part of the law. How does this device, which looks like a combination vape and bullhorn, help an investigator find the source of a smell?

The Nasal Ranger is a field olfactometer, and it uses a method called dilution to threshold: stinky air is sealed and then diluted with purified air that has no odor particles. In lab and manufacturing settings, this air is passed through a panel of qualified human smellers. The NIH explains, “[O]nly assessors who meet predetermined repeatability and accuracy criteria are selected as panelists.” The way we sense smells is logarithmic, the same as decibels, meaning our sense of “smelliness” doesn’t follow in a linear relationship with the amount of smelly particulate in our air.

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Sometimes, a specific odor at, say, a construction site or a workplace can be “bagged” and brought back to a lab environment to be analyzed and presented to panelists. But for use cases like trying to locate a concentrated marijuana plant odor, a field olfactometer lets testers roam and continue to smell on the go. Operators still must qualify as smellers, and the NIH says tracking odors in situ is challenging because of how quickly a skilled smeller can get overwhelmed by surrounding smelly air instead of the isolation of a lab.

The company that makes the Nasal Ranger, St. Croix Sensory, offers a trademarked Odor School program so people using the Nasal Ranger are qualified to operate it. Users should also each have their own custom nose-covering mask portion, because the Nasal Ranger has to make an airtight seal. This all sounds very methodologically mushy, and invites the question: Why don’t we just use machines?

Machine olfaction has come a long way, the NIH says , using “Gas Chromatography coupled with Mass Spectrometry.” For measuring poisonous compounds in the air, this level of straightforward detection can work really well and help to protect workers or local residents threatened by pollution or mishandling of dangerous materials.

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A complex mixture of chemicals makes up almost everything we smell. Have you ever caught a whiff of something that smelled good, before catching a second whiff and realizing it was something nasty? Our brains race to translate olfactory receptor information into smell messages, but scientists don’t yet understand how that process works or what’s really going on. They’re also not sure why certain smells disgust us so much.

Marijuana plants in particular have a strong stench that reminds people of skunk spray. “The smell from commercial cannabis farms, which brings to mind a mixture of rotting lemons and sulfur, is nothing like the wafting cloud that might hover over a Phish show, pot farm detractors say,” the New York Times reported from California in 2018.

In that piece, the creator of the Nasal Ranger said that flowering cannabis “easily” rates a level 7 on the Nasal Ranger’s scale. “Charles McGinley, the inventor of the device, says a Level 7 is the equivalent of ‘sniffing someone’s armpit without the deodorant — or maybe someone’s feet — a nuisance certainly,’” the Times reported.

In Bessemer, Michigan, the culprits are likely “hobby farmers” growing more than their legal share. The Nasal Ranger could lead to investigators busting these illegal farms, and residents could have better air quality in return.



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