Near the ground, ozone is an air pollutant that causes lung damage and asthma attacks. But 10 to 30 miles above the Earth’s surface (16-48 km), ozone molecules protect life on Earth. They help shield our planet from harmful solar radiation.

The ozone layer, in the stratosphere, is where about 90% of the ozone in the Earth system is found. But ozone makes up only one to ten out of every million molecules in the ozone layer. (The rest of the molecules are mostly nitrogen and oxygen, like the air we breathe.) There isn't much of it, but ozone is powerful, able to block the most harmful radiation. 

Ozone absorbs the most energetic wavelengths of ultraviolet light, known as UV-C and UV-B, wavelengths that harm living things. Oxygen molecules absorb other forms of ultraviolet light, too. Together, ozone and oxygen molecules are able to absorb 95 to 99.9% of the ultraviolet radiation that gets to our planet. When UV light is absorbed by oxygen and ozone, heat is generated, which is why the stratosphere gets warmer with altitude.