If its doesn’t CHALLENGE you It Doesn’t CHANGE you

Petricore and geosomine: that’s why we love the scent of rain

You know that unmistakable smell that spreads after a storm? If you like this perfume too, you can exclaim: “What a good petricore!”

They are not the protagonists of a fairy tale or even the lines of a poem, but the scientific names of some of the components that determine the typical ” scent of rain ” that we feel after a downpour. That precise odor is not in fact due to the water itself, but to a mixture of  chemical substances : ozone, oils and resins, petricore and geosmin which, combined with each other, create this unmistakable aroma.

Petricore: the sap of the gods

The  discovery  of petricore was made public in the well-known scientific journal  Nature  about fifty years ago thanks to the studies of Australian chemists  Isabella Bear  and  RG Thomas . The two, to find out what were the causes of the scent of the rain, tried to dry some clay and then extract the oils found inside. The result was a yellowish substance with a smell that was reminiscent of rain. Bear and Thomas were the  ones who also devised  the term “petricore” to indicate this particular perfume: it is the union of two Greek words ” petros ” (stone) and ” ichor ” (blood of the gods).

In 2015, thanks to a team of scholars from the  Massachusetts Institute of Technology (MIT) , the mechanism  by which petricore is released into the air was also discovered  . With the arrival of the rain, in fact, scholars have seen how the drops of water falling on the ground are able to make the petricore retained by some plants and the clay of the ground spread in the air creating that characteristic odor.

 Thanks to high-frequency  cameras , the MIT scientists   studied  the impact of raindrops on some porous surfaces  and managed to capture the tiny particles of air and water (aerosols) as they rise from the ground shortly after the rain fall, that is, when they release the petricore which, thanks to the wind, spreads into the air.

Geosmina: irresistible earthy fragrance

The smell of  damp earth , on the other hand, even more intense when the rain occurs after a long period of drought, is due to a chemical compound called  geosmin . Geosmin is produced by different classes of microorganisms including  cyanobacteria  (blue algae -green) and actinomycetes  (  especially Gram positive aerobic bacteria of the genus  Streptomyces ): it is released when the  microorganisms  themselves die. The earthy odor caused by geosmin can sometimes mix with that of the  oils  and  resins  produced by plants which, with the humidity of the rain, tend to dissolve even more in the air, giving it an aroma. sweetish .
The name “geosmina” also derives from the  Greek  for a combination of the terms ” gea ” (earth) and ” osmé ” (smell).

The human body is very  sensitive  to this fragrance and is able to detect it even from very far away. Several  perfumes  on sale are formulated with solutions containing geosmin precisely because it is particularly  pleasant  for the human sense of smell.

Camels in the   desert are also able to perceive this substance. In fact, they would be able to hear it even at a distance of 10-15 kilometers in order to chase it to get to the oasis  that emanates it and where, of course, they can drink. Furthermore, during watering, the spores of streptomycetes (producers of geosmin) remain on the animals that carry them throughout the desert.

Feeling that it is about to rain thanks to the ozone

It happens that some people are able to “smell in the air”  the arrival of a storm . This is possible thanks to another little mystery easily revealed thanks to chemistry. In fact, the ozone molecules   released by  lightning  in the upper layers of the atmosphere are transported by currents at low altitudes where they give the air that particularly  pungent  and  garlicky smell  that can lead one to assume the arrival of a downpour.

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