What makes rain smell so good?


ARE you a pluviophile, a person who loves rain and the smell of rain? Did you know that the earthy smell when rain hits the ground is called petrichor? The word petrichor was coined from Greek which petros means “stone” and ichor means “the fluid that flows in the veins of the gods”.

Petrichor has a number of contributors such as compound secreted by bacteria, oils secreted by plants, and the splitting of atmospheric chemicals to form ozone.

The main contributor to petrichor is Actinomycetes, a group of soil-dwelling bacteria. They decompose dead or decaying organic matter into simple chemical compounds which can then become nutrients for developing plants and other organisms. A by-product of their activity is an organic compound called geosmin which contributes to the petrichor scent.

Geosmin is a type of alcohol, like rubbing alcohol. Alcohol molecules tend to have a strong scent, but the complex chemical structure of geosmin makes it noticeable to people even at extremely low levels. Our noses can detect just a few parts of geosmin per trillion of air molecules.

During a prolonged period of dryness when it has not rained for several days, the decomposition activity rate of the Actinobacteria slows down.

Just before a rain event, 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.