This is a molecule made of three oxygen atoms in succession. Ozone can be made when lightning flashes through air, zapping molecules of O2 to produce O3. The sun’s radiation can spark ozone production. And ozone can also be produced when oxygen reacts with pollutants in smog.
Between 15 and 30 kilometers (nine to 18 miles) above the Earth, the atmosphere has a relatively high amount of ozone. In this area — a part of the stratosphere — there’s between two and eight atoms of ozone per one million molecules of air. This layer — called the ozone layer — absorbs some of the ultraviolet light from the sun. That’s good, because ultraviolet radiation can be harmful to many organisms, including humans. But a lot of ozone lower in the atmosphere can be harmful. That’s because ozone can damage lung tissue in people and animals.
In a sentence
Trees can indirectly produce ozone when a chemical they produce, called isoprene, combines with pollutants such as nitrogen oxide from cars and trucks.