What is the identity of a distinctive smell that suddenly happens when it rains?

When you go outdoors in the rainy weather, you may feel a smell like wet soil. BBC explains why the distinctive odor drifts around when rain falls.

Petrichor: why does rain smell so good? - BBC News
https://www.bbc.com/news/science-environment-44904298

In 1964 Australia Chemical and Industrial Research Organization Mr. Isabel Joy Bear and Richard Thomas (CSIRO), the "dry smell coming risen by rain on the ground," " PETRICHOR and (Petrichor)" I named it. Petri call is a combination of Petro (meaning stone in Greek) and ichor (meaning "liquid flowing through veins of the gods").

Petri calls also include the odor of ozone that occurs when thunder breaks the air, but the main ingredient is the substance called " geosmin ". Geosmine is produced by bacteria of the genus Streptomyces that inhabit many healthy soils. When rain falls and rain particles hits the ground, minute water particles called " aerosol " are generated. This aerosol is greatly related to the fact that geosmine originally contained in the soil is released into the air.

Massachusetts Institute of Technology has taken a picture in a slow movie of 1/250, showing how the aerosol scatters from droplets that fell to the ground.

Rainfall can release aerosols, high-speed video shows - YouTube


It is an appearance that droplets are dropped on the aluminum plate on the left and on the dry soil on the right.

Water droplets strike the ground, and shapes are greatly damaged. If you look closely, you can see the aerosol above the falling point.

You can see how aerosol flows as you hit the wind.

Aerosol scatters from the raindrop into the air in the state containing the geosmin in the soil By catching the aerosol containing the geosmin with the sense of smell, we feel the unique smell after rain.

In recent years, scientists have also pointed out that the " terpene " biological material produced by plants and insects may be related to the geosmin content in the air. If the drought continues for days, the metabolism of plants will be delayed, but as rain falls, the metabolism also gets faster and it is said that terpenes will be released from plants along with it. Terpenes may chemically react with other substances and change to geosmine. Professor Philippe Stevenson, senior researcher at the Royal Botanic Gardens in the UK, said, "There are times when the terpenes produced in plants are released as the hair on the plant leaves is damaged by water droplets." I will.

Although Geosmin is nontoxic, it is judged to be offensive odor and discarded if it is included in even a small amount in mineral water or wine. According to Professor Jeppe Nielsen of Aalborg University, human beings are very sensitive to this geosmine, even though they can be detected even if diluted to 1/1 billion, why humans are Geosmin's It is sensitive to smell and it does not seem to know whether it feels negative.

Bear and Mr. Thomas discovered that the perfume sold in India in the 1960s contains the main ingredient of geosmin, and it is generally 50 years that Geoschen is included in perfume It is getting. According to a perfumer Marina Barcenira, Geosmin is exactly "a scent like concrete after rain".