(WMC) - Have you ever noticed how sometimes when it's about to rain or just after it rains, there is this earthy but pleasant smell in the air?
I have, and my next thought is always "Why is that and what causes that smell?"
Here is the answer.
This smell actually comes from the moistening of the ground. Australian scientists figured this out in 1964 and scientists from MIT further studied it further in the 2010s.
Petrichor is a combination of plant oils and the chemical compound geosmin, which are released from the soil when it rains. Geosmin is a type of alcohol, similar to rubbing alcohol.
When it has been dry for several days, the air becomes more humid and the ground begins to moisten. This process helps to speed up the activity of the actinobacteria and more geosmin is formed.
The main contributor to petrichor are actinobacteria. These tiny microorganisms can be found in rural and urban areas as well as in marine environments. They decompose dead or decaying organic matter into simple chemical compounds which can then become nutrients for developing plants and other organisms.
When raindrops fall on the ground, especially porous surfaces such as loose soil or rough concrete, they will splatter and eject tiny particles called aerosols. The Geosmin and other petrichor compounds that may be present on the ground or dissolved within the raindrop are released in aerosol form and carried by the wind to surrounding areas. If the rainfall is heavy enough, the petrichor scent can travel rapidly downwind and alert people that rain is soon on the way.
The scent eventually goes away after the rain passes and the ground begins to dry. This leaves the leftover bacteria lying in wait and ready to help us know when it might rain again. And that is the breakdown on why rain sometimes has a smell.