After the dry periods, the sun and the heat regularly give way to rainy episodes.
The contact between the ground and the drops of water releases a pleasant fragrance, called petrichor.
This neologism comes from the Greek meaning "
blood of stone
" and was coined by chemist Isabel Joy Bear, and mineralogist Roderick G. Thomas in 1964 when they were trying to explain this famous "
smell of rain. "
It wasn't until the 2010s that its mechanism was unraveled by researchers at the Massachusetts Institute of Technology (MIT).
More than 50 different substances
This odorous emanation is the result of the interaction of around fifty substances, two of which are the main aromatic compounds.
During dry periods, plants secrete an oily liquid absorbed by soil sediments.
At the same time, some soil bacteria release a compound called geosmin.
When it rains, these two molecules combine and are propelled into the air in the form of an aerosol.
"
Petrichor is in fact the mixture of geosmin and the oily liquid secreted by certain plants, released when it rains, after a dry period
", deciphers Alice Lebreton, doctor at the Institute of Biology of the École Normale Supérieure. .
Read alsoA worrying drought with no sign of improvement
Olfactory hypersensitivity
Beyond the scientific explanation of this smell, researchers have also succeeded in highlighting the reason why it is appreciated by a large majority.
Human beings show an astonishing hypersensitivity to this effluvium because its proportion in the air is comparable to the addition of a drop in an Olympic swimming pool but it remains detectable by our sense of smell.
According to them, it is an ancestral heritage because the rain has always embodied a strong symbolism: that of life and survival announcing the end of the drought.
The scents diffused are regularly associated with undergrowth or freshly plowed land.
However, there are as many petrichors as substrates beaten by the rains.
The bitumen of a road, for example, will emit other aromatic compounds than the soil of a forest.
