Ozone Contribution (Before the Rain)

Sometimes, people can smell a distinct, sharp scent in the air just before it rains, especially during thunderstorms. This is caused by ozone. Lightning can split oxygen molecules (O₂) into individual atoms, which can recombine to form ozone (O₃). Winds from the storm carry this ozone to ground level, where people may smell its crisp, clean scent.

Why Do We Like the Smell of Rain?

The pleasant association many people have with the smell of rain might be due to an evolutionary trait. Since rain is critical for life, especially for plants, crops, and drinking water, humans may have developed a sensitivity to the smell of petrichor as a way to sense and appreciate rainfall, which would signal good conditions for survival.