What gives fall its signature smell?
What we are actually smelling involves another signature component of the season: leaves that have fallen to the ground.
What's the science behind that familiar fall smell?
In addition to crisp air and fall foliage, autumn brings with it a signature smell. Theresa Crimmins, director of the U.S. National Phenology Network, joined FOX Weather on Sunday to explain where the smell comes from.
In addition to changing leaves and crisp, cool air, autumn brings with it a signature smell.
The scent of fall can be described as organic and earthy with a little bit of sweetness to it, according to Theresa Crimmins, director of the U.S. National Phenology Network. Phenology is the study of seasonal changes in plants and animals.
How plants and animals, particularly fallen leaves and bacteria, respond during autumn is one of the main reasons behind the season’s notable perfume.
Sunbeams through a forest in fall.
(Johannes Plenio / Unsplash / FOX Weather)
"As the leaves are beginning to be digested and decomposed by bacteria in the soil and the surrounding environment, as those things break down, they release volatile organic compounds and other molecules," Crimmins said. "That's what we actually are smelling."
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How our noses are able to detect this scent is due to a couple of weather-related factors that happen during this time of year.
Fall leaves on the ground.
(Greg Shield / Unsplash / FOX Weather)
One factor involves the drier atmospheric conditions that are associated with fall.
With less moisture in the air, Crimmins said, the organic molecules that humans are able to detect with our noses are able to move more easily through the air. In contrast, the air during summer is more humid. With more moisture in the air, scent molecules are more muddled.
Once fall arrives and the amount of moisture in the air drops, the air is cleaned out.
Blue sky and bright fall leaves.
(Joyful / Unsplash / FOX Weather)
"A lot of people will say, ‘It smells fresher. It smells brisk and clean and clear,’" she said. "I think all of that is associated with the fact that there's really less of that muddle of a lot of different kinds of organic molecules in the air for our noses to try to differentiate among."
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Cooler temperatures also play a role, as the colder air cannot hold as much moisture as warmer air can, she added.
For Crimmins, understanding the science behind the smell of fall and other experiences related to the seasons can help increase our awareness of what plants, animals and ecosystems provide.
Boy lays in pile of fall leaves.
(Annie Spratt / Unsplash / FOX Weather)
"They're responsible for cleaning our water for us, cleaning the air, and it’s providing habitat for all the other animals or plants that we might eat as our food," she said. "So, appreciating and understanding what's going on there benefits us in a lot of indirect ways, but ways that are really important for our everyday lives."
Nature lovers are encouraged to report their observations of plants and animals, such as when leaves in their area fall, in the U.S. Phenology Network’s Nature’s Notebook. Observations contributed to the online notebook help the Phenology Network better understand the cycles of nature.