The smell of rain is one of those experiences almost everyone recognizes even if they do not know its name.
The earthy scent that often appears when rain hits dry ground is called petrichor.
The water itself is not doing most of the smelling.
Rain is helping release chemicals that were already on or in the ground.
Dry ground collects scent-producing compounds
During dry periods, plant oils and other organic compounds can collect on soil, rocks, pavement, and vegetation.
Soil microbes also produce compounds.
One especially important one is geosmin, which has a strong earthy smell.
Humans can detect very small amounts of geosmin, which helps explain why the scent can become noticeable so quickly.
Raindrops launch material into the air
When a raindrop hits a porous surface, tiny bubbles can form where the water meets the ground.
Those bubbles can rise through the droplet and burst.
When they burst, they can release microscopic particles and odor molecules into the air.
Now those compounds can reach your nose.
Rain did not create the geosmin at that moment.
It helped aerosolize it.
Why is the smell stronger after a dry spell?
A long dry period gives oils and other compounds more time to accumulate.
The first rain after that period can release a noticeable burst of scent.
Once heavy rain continues for a while, much of the loose material has already been washed away or diluted, so the smell may become less intense.
What about the smell before a storm?
Some people notice a sharper, cleaner smell before rain arrives.
That can involve ozone and other atmospheric chemicals.
Storm-related electrical activity and air movement can influence which compounds reach ground level.
That smell is different from the earthy petrichor that often becomes strongest when rain hits dry soil.
Why do people like the smell?
There is no single universal reason everyone likes petrichor.
Familiarity, memory, weather associations, and individual sensitivity all matter.
For some people, the scent may be tied to relief from heat, childhood memories, gardening, or the feeling that dry weather is ending.
For others, it is simply a pleasant earthy odor.
Is geosmin only found in soil?
No.
Geosmin can appear in water and foods too, which is why some water sources or vegetables can occasionally have an earthy taste or smell.
In the case of rain, though, soil microbes are a major part of the familiar scent.
So the smell of rain is not really the rainwater itself.
You are smelling chemicals that the rain knocked loose and carried into the air.
Rain basically turned the ground into a temporary air freshener.
A related part of the natural world appears in Why do we see lightning before thunder?, where the same kind of physical or biological reasoning answers another familiar question.
And that’s the short explanation.
Related explanations: Why do we see lightning before thunder?, Why does thunder rumble?, and Why do puddles disappear?