What is the reason for the distinctive smell that appears after the rain

Weather of Arabia - We all notice a distinctive smell that spreads in the air after rain, and some call it "the smell of rain." What is this smell? And what is the cause?

There are three main sources of smell that usually appear after it rains:

1. A pleasant “cleanliness” smell:

When you notice this smell during rain, know that ozone gas is the cause of the smell, as ozone is characterized by being remarkably pungent and has a very sharp smell often described as smelling like chlorine, as the normal human nose can distinguish the smell of ozone at a concentration of less than 10 parts per billion ( parts per billion) .

Ozone is known scientifically as trioxygen because it consists of three oxygen atoms ( _O3 ), and some people notice the distinct smell of ozone in conjunction with rain, especially after a severe thunderstorm, because lightning sometimes works to disperse nitrogen and oxygen molecules in the atmosphere into atoms, this can eventually lead to the formation of a small amount of ozone, which descends with the wind near the surface of the earth, and ultraviolet rays in the atmosphere also work to split the binary oxygen molecules ( O ₂ ) into atoms, uniting the liberated oxygen atoms With oxygen molecules to form ozone .

Despite the pleasant smell of ozone, pure ozone is dangerous to human health, especially when it is present in high concentrations, as it can destroy cells in the lungs, but the ozone concentration before or after a thunderstorm does not rise to the extent that it can cause any permanent health damage. .

2 . Earthy smell:

Another pleasant smell caused by rain is the earthy smell, which is stronger after a drought or after heavy rain. This smell is caused by bacteria present in the soil , as these bacteria produce spores during periods of excessive drought, and the longer the soil remains without rain, The number of spores present increased, and there is a chemical substance that is secreted during the production of these spores by bacteria, this substance is known as ( Geosmin ), and this substance is what we smell after rain or after wetting the soil, and the human nose is very sensitive to distinguish this smell even at a low concentration (0.1 parts per million), and it is possible that the sensitivity of the human nose to this chemical is the reason that the smell is so strong in wooded areas in particular, but the smell is less in areas where there is less soil, and the smell of ozone prevails there.

3 . Aroma of plants:

The third reason for the distinctive smell after rain is largely due to the oils secreted by different plants, as these oils gather in the environment around the plants, and when it rains, the chemicals that make up these oils are released into the air, causing the appearance of the distinctive pleasant smell. Research has shown that this oily substance stunts the growth of some plants, leading researchers to believe that plants produce these oils to stop the seed release process in dry and imperfect conditions.

Why does the smell of rain make us happy?

This may be due to the hypothesis developed by scientists, which is that the feeling of happiness that was associated with smell after rain was transmitted to us from our ancestors who considered rain a symbol of survival. That rain brings with it goodness for humans, and works to improve the quality and abundance of food, and this relationship may have been entrenched in our brains without our realizing it.