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John Wheeler, WDAY, Published August 09 2012

Weather Talk: Human noses sensitive to smell of geosmin in rain

Have you ever noticed that rain seems to have a smell? Have you noticed that the smell is at its most intense when the rain is first starting? Or even just before it rains?

Rain, itself, is water, of course. Raindrops also contain various minerals and other impurities, but these are not the reason for the rain smell. It turns out this smell actually has a name. It is called petrichor.

When soil is disturbed by raindrops, various bacteria within the soil produce a compound called geosmin, which translates from Latin as “Earth smell.” Human noses are particularly sensitive to geosmin and are able to detect it at levels as low as 10 parts per trillion.

Outflow winds ahead of a summer thunderstorm will often transport geosmin well ahead of the heavier raindrops. This is why we can sometimes smell the rain well before it falls.


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