Ozone is technically a greenhouse gas, but ozone is helpful or harmful depending on where it is found in the earth's atmosphere. Ozone occurs naturally at higher elevations in the atmosphere (the stratosphere) where it forms a layer that blocks ultraviolet (UV) light, which is harmful to plant and animal life, from reaching the earth’s surface. The protective benefit of stratospheric ozone outweighs its contribution to the greenhouse effect and to global warming. However, at lower elevations of the atmosphere (the troposphere), ozone is harmful to human health.
There are human-made industrial chemicals that break down ozone in the stratosphere and create holes in the ozone layer. The United States and countries all around the world ban and control production and use of several of these industrial gases under the Montreal Protocol. In the United States, emissions of air pollutants that result in ozone formation in the troposphere, or ground-level ozone, are regulated under the Clean Air Act.
Last updated: July 15, 2019