Have you ever noticed the smell of rain?

That distinctive smell you notice before it starts raining.

This smell is called “petrichor,” and it’s produced through the following mechanism:

When sunny, dry days continue, plants release oil to protect their seeds, and this oil adheres to nearby soil, stones, and rocks.

When raindrops hit the ground, tiny bubbles (aerosols) are released. When these bubbles come into contact with the oil, they absorb its components and float into the air.

That’s the source of that distinctive scent: petrichor.

It’s that earthy smell, isn’t it?

Because of this mechanism, you smell it when it starts raining, but if you smell it even when it’s not raining, it’s because the bubbles are being carried by the wind.

It’s evidence that it’s raining nearby.

Incidentally, the smell after the rain also has a name; it’s called “geosmin.”

The source of this smell is organic compounds produced by bacteria in the soil.

The scent intensifies as it is washed away from the soil by rainwater, diffuses, and begins to evaporate, creating the distinctive smell of after the rain.