Can You Really Smell Rain?

I grew up on a sheep and chicken farm, so naturally there were lots of smells.  One of the most interesting was what I sensed before a rain.  It was if I could actually smell the rain coming.

Was it just me?  No, according to the article “Why You Can Smell Rain” by Tim Logan of Texas A&M University ( http://earthsky.org/earth/what-is-smell-of-rain-petrichor? ), rain showers do produce a distinctive smell.

But of course this doesn’t come from water, which has no smell.  It’s from petrichor, a combination of chemicals — plant oils and actinobacteria, which are microorganisms that decompose dead organic matter into compounds that become nutrients for plants and other organisms.  In doing so, the bacteria release geosmin, a type of alcohol, as a byproduct.

During dry periods, the decomposition activity of the actinobacteria slows down.  Then just before it rains, humidity increases and the ground moistens, speeding up actinobacteria activity and the production of geosmin.

Actual raindrops then splatter and eject tiny aerosol particles.  The geosmin and other petrichor compounds that may be on the ground or dissolved within the raindrop are released as an aerosol and carried by the wind.  If the rainfall is heavy enough, the scent can quickly move downwind.  That’s how you can “smell rain” before it arrives.

This process of petrichor formation was first documented by Australian scientists in 1964; the Massachusetts Institute of Technology further studied the process in the 2010s.

So it really is possible to smell rain!

 

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