From: Emily Sohn via Discovery News
Published January 14, 2014 03:19 PM

Why Cold Air Smells Different

Pine needles. Wood smoke. Snow. These are the smells of winter, and for people who live with distinct seasons, wintry weather brings its own set of olfactory experiences.
But why does the cold of winter smell different from the heat of summer?

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One reason is that odor molecules move much more slowly as the air temperature drops, said Pamela Dalton, an olfactory scientist at the Monell Chemical Senses Center in Philadelphia. That means that there are simply fewer smells to smell on a cold, crisp day than there are on a hot and humid one.

It's the same reason why hot soup smells more than cold soup does and why the garbage truck leaves behind the strongest odors on steamy summer days.
What's more, our noses don't work quite as well when the ambient air is cold, Dolan said. In experiments that require biopsies of olfactory receptors that lie deep inside the nose, researchers at Monell have discovered that the receptors "bury themselves a little more deeply in the nose in winter," she said, possibly as a protective response against cold, dry air.

"We're not as sensitive to odors in winter," she added. "And odors aren't as available to be smelled."
Cold air also stimulates the irritant-sensitive trigeminal nerve, said Alan Hirsch, a neurologist and psychiatrist in Chicago. The trigeminal nerve is what makes you cry when you chop an onion and delivers a hit of spiciness when you inhale a whiff of strong mint.

When odors stimulate both the trigeminal nerve and the olfactory nerve, the experience of smell becomes more intense.

There is a strong psychological component to our sense of smell, Hirsch added, and what we expect to smell has a big influence on what we actually smell.

Read more at Discovery News.

Winter image via Shutterstock.

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