There is a very particular smell that happens when it rains, and it has a name: petrichor. It actually isn’t just one smell. There are three, and they come from totally different places. 

What are the three smells?

The term petrichor was coined by Australian scientists in 1964 to describe the earthy and recognizable smell linked to rain. 

Let’s break down the three smells you are experiencing: 

Ozone: This almost metallic smell occurs when lightning strikes split oxygen and nitrogen molecules. These recombine into nitric oxide and ozone. The ozone molecules are brought down to the surface by downdrafts from powerful storms. 

Geosmin: The earthy note comes from bacteria in the soil. They create compounds that our noses detect. There can barely be any geosmin in the air, and yet we can smell it. 

Plant oils: During dry spells, plants produce fatty acids that linger on rocks and in soil. When rain falls, it releases them back into the air. 

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It is a combination of these smells that comes together to create petrichor. 

How it reaches you

For decades, the release mechanism was a guess. Then the Massachusetts Institute of Technology did a very interesting study with a high-powered camera. 

A raindrop hits porous ground and traps a tiny bubble of air. The bubble bursts and releases the smell into the air as an aerosol, which is carried away by breezes. 

The intensity of the smell depends on several factors. If it rains too hard, it can actually make the smell less noticeable. If it's a thunderstorm with lots of lightning, the ozone smell could dominate. The longer the dry spell, the stronger the plant oil component. 

The best-smelling rain in my opinion is a gentle one after a dry spell. Maybe add one or two lightning strikes high in the atmosphere for a little bit of ozone.