You must know that specific smell that is floating in the air after the rain has stopped, especially in summertime or after a long period of drought- the world just feels different, smells different. Have you ever wondered what causes that strange earthy aroma reminding us of freshness and cleanliness? People all over the world recognize it and scientists have several theories for its origin.
One part of that smell- more particularly the part people define as the smell of “cleanliness”- is due to the ozone. Usually oxygen atoms hang around in pairs. Ozone contains three oxygen atoms. It is made naturally in the upper layers of the atmosphere where the energy of the UV light divides the oxygen molecules and each of the single atoms connects to a different oxygen pair. The same process may occur near waterfalls or after a lightning strike.
The other specific aroma after rain is strongly earthy, just like freshly dug soil.
In almost all kinds of soils on Earth there is a kind of bacteria called actinobacteria. It is found in rich and humid soil. Actinobacteria is healthy as for earth, as it is for us. Scientists have extracted antibiotics from the soil and they have found that it is produced by that particular kind of bacteria.
When the earth dries, the actinobacteria releases spores which can survive in the dry soil. The spores are activated when it is raining as the dirt gets wet. The specific smell comes from bacteria that has got back to work in the soil and in the air.