What the Nose Knows: The Science of Scent in Everyday Life by Avery Gilbert Page A

State Highway Patrol officer stopped a motorist for running a red light. When the driver rolled down his window, the officer smelled marijuana smoke. A search turned up rolling papers and joints in the driver’s pocket, and a stubbed-out doobie in the ashtray. The driver was arrested. At trial, he succeeded in having the charges dismissed on the grounds that a search based only on odor—without other visible, tangible evidence—was improper. The case made its way to the Ohio Supreme Court, which ruled that the “plain smell” of burning pot was, by itself, sufficient probable cause for a warrantless search. The supreme courts of Michigan, Colorado, Wisconsin, Arkansas, and at least fifteen other states have reached similar conclusions.
    How good a nose does a government agent need to claim probable cause for a drug search? The Ohio court relied on the fact that the arresting officer was trained and experienced in identifying the smell of marijuana smoke. Other jurisdictions aren’t so fussy. The degree of nasal prowess claimed by police officers can, at times, beggar belief. In New Jersey, for example, a driver was pulled over for a traffic infraction. The police officer claimed to smell fresh, unburned marijuana through the open driver’s window. A search revealed a brick of Mexican pot wrapped in a plastic garbage bag in the trunk, where it had been placed after a drug buy twenty minutes earlier. In California, police searched a house where they suspected pot was being grown. They didn’t obtain a warrant because they claimed they could smell marijuana plants—from several hundred yards away in the hot air and diesel exhaust venting from the chimney.
    These feats of nasal detection are all the more remarkable given the level of training most police officers receive. According to Jim Woodford, who serves as an expert witness in criminal trials, officers often learn drug smells by sniffing the real thing in the evidence room. Formal training is rudimentary. “Somebody comes in with a suitcase of stuff, everybody goes by and takes a sniff. That’s the training,” he says. The problem with this informal approach is that marijuana aroma is extremely variable, something potheads are well aware of. (Just ask the reviewer of the Beck concert in Costa Mesa…)
    Of course, police officers become familiar with drug smells while busting dealers and users. They cite this on-the-job experience when defending their skills in the courtroom. They testify that “I’ve been on so many busts, and I recognize it. Over the years I’ve learned it.” Woodford says, “That’s sufficient to be deemed an expert by the court.” He says it is rare for the defendant in a drug case to challenge the officer’s smell ability via a smell test or medical exam.
    Just how detectable is the smell of pot under circumstances such as these? Richard Doty and colleagues conducted some forensic sniff tests to find out, using experimental conditions modeled on the New Jersey and California cases. They found that untrained people can easily distinguish a Hefty bag containing 2.5 kilograms of Mexican pot from one holding an equal weight of shredded newspaper. But when the samples were placed in a car trunk, the panelists could not detect the smell from the driver’s window. Likewise, panelists could reliably identify mature female cannabis plants at close range by scent alone, and could distinguish immature pot plants from tomato plants by smell. But when the smell of marijuana plants was mixed with exhaust from a diesel generator, the panelists couldn’t detect it.
    When it comes to detecting drunk drivers, sniff-based forensics are on even shakier scientific ground. A study by the National Highway Transportation Safety Administration found large variability in the ability of police officers to smell alcohol on a person’s breath. As a group, cops picked up the scent consistently only when the drinker had a very high blood alcohol level (the