Thursday, August 23, 2007

The smell test

Officer Kenneth Marrow smelled alcohol on 24-year-old Cody Schaaf at a fast food drive-in and arrested him for drunk driving. The arrest is being challenged because Officer Marrow detected the alcohol seven feet away from inside the restaurant.

Smell – our olfactory system – is so unquantifiable. For example, the only numbers oenophiles put on their wine is the price. Instead they use words like herbaceous, cloying, rustic, and buttery. Mathematicians don’t tend to use those words unless they’ve had too much wine.

So you just never hear numbers associated with smell, and there is no unit of smell, as in “wow that onion was strong, must have been at least three olfactors!”

Odorants – molecules that humans can smell – bind to receptors on the nose’s cilia. Each receptor can bind to several odorants and each odorant can bind to one or more receptors. The number of possible combinations is the number of different smells detectable by the brain: it’s in the millions although the best trained nose like that belonging to a master perfumer can distinguish – and name – 10,000 different smells.

Smells are stronger up close and fade inversely with the square of the distance from the source. This means that Office Marrow smelled 82% fewer of the molecules from Mr. Schaaf’s breath than he would have if he were just three feet away.

Time will tell if Officer Kenneth Marrow – or Cody Schaaf will pass the smell test. But the argument seems moot – Mr. Schaaf flunked the breathalyzer test.

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