In 2017, a Colorado State Trooper pulled over a car to the side of Interstate 70 for a minor traffic infraction. The police officer, who works on highway narcotic smuggling, claims he immediately sensed a strong marijuana odor once he approached the car. He proceeded to conduct a probable cause search based on the strong smell and “other indicators”, which revealed two vacuum duffle bags filled with 52 pounds of marijuana, a wad of thousands of dollars in cash, and a secondary phone.

Later, in court, the defendant pleaded guilty for possession with intent to distribute. However, he challenged the motive of the search and did so in a highly unusual way for this kind of offense. His lawyer hired Dr. Avery Gilbert, a self-described “smell scientist” and “sensory psychologist”, and Dr. Joseph Diverdi, a professor of chemistry at Colorado State University, who examined the evidence and took samples of air inside the evidence bags holding the vacuum packs.

“There’s long tables just filled with bagged weed. I’d never seen anything like it,” Gilberg told Leafly. The marijuana was still in the double vacuum-sealed bags. “Coming as close as we could to sniffing those packages, I couldn’t smell a damn thing.”

In the lab, the two researchers examined the air samples with a gas chromatography machine, focusing on the concentrations of six terpenes known to give marijuana its conspicuous odor. The examination confirmed the researchers’ initial subjective assessment of the sealed marijuana — the odor molecules were in a far too low concentration to be detected by people.

Although the case was over (the man found with the marijuana in his possession received a two-year deferred sentence, a fine, and community service), the two researchers thought that marijuana odor concealment merits more scientific attention.

Back in the lab, they set up an experiment with 21 participants familiar with the smell of cannabis. The participants had to select the correct packaging that contained marijuana from ten sample pairs. Four different packaging methods were used: Ziploc bags, thin plastic produce bags, pop-top canisters, and a vacuum-sealed heavy plastic bag inside another vacuum-sealed bag. An open glass bowl was also used to act as a control.

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The participants immediately recognized the package containing marijuana when it placed in an open glass bowl, the Ziploc bag, and the produce bag. The pop-top dispensary canister yielded mixed results.

However, vacuum-sealed marijuana seems to have been the least conspicuous out of all the packaging methods. According to the results, which were published in the journal Science & Justice, the “material packaged in doubly vacuum-sealed plastic was correctly identified at rates no different from chance.”

Since the experiment showed that people with experience handling marijuana had great difficulty identifying it in a double-sealed vacuum bag, what would be the odds that the officer could smell it (from outside the car while the bag was inside a suitcase)? That’s extremely unlikely.

The findings “may help address issues involving the detectability of cannabis aroma in law enforcement and other scenarios,” the researchers concluded.

Tibi is a science journalist and co-founder of ZME Science. He writes mainly about emerging tech, physics, climate, and space. In his spare time, Tibi likes to make weird music on his computer and groom felines.

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