Which layer of the atmosphere contains the ozone layer?
Quick answer
Most of Earth’s ozone is in the stratosphere, the second layer of the atmosphere, about 15–35 km (9–22 miles) above the ground. This ozone layer absorbs most of the Sun’s harmful ultraviolet (UV-B and UV-C) radiation, protecting life on Earth.
The layers of the atmosphere
| Layer | Height (approx.) | Key features |
|---|---|---|
| Troposphere | 0–12 km | Weather, clouds and almost all the air we breathe |
| Stratosphere | 12–50 km | Ozone layer; calm air where jets cruise near its base |
| Mesosphere | 50–85 km | Where most meteors burn up |
| Thermosphere | 85–600 km | Very hot but thin; the International Space Station and auroras |
| Exosphere | 600 km + | Fades into space |
What is ozone?
Ozone is a molecule made of three oxygen atoms (O₃), unlike the oxygen we breathe (O₂). In the stratosphere, ozone is helpful, blocking UV rays that can cause sunburn, skin cancer and cataracts and harm crops and plankton. Near the ground, ozone is a pollutant in smog.
The ozone hole
In 1985, British scientists reported a dramatic thinning of ozone over Antarctica each spring, now called the ozone hole. The cause was CFCs (chlorofluorocarbons), chemicals once used in fridges, air conditioners and aerosol sprays, which release chlorine that destroys ozone.
A global success story
| Year | Milestone |
|---|---|
| 1987 | The Montreal Protocol agrees to phase out CFCs |
| 2009 | It becomes the first UN treaty ratified by every country |
| Today | Ozone is slowly recovering |
Scientists expect the ozone layer to return to 1980 levels around 2040 for most of the world, and around 2066 over Antarctica, if current policies continue.
The stratosphere is also where thunderstorm clouds flatten into anvils. For what the air is made of, see the most abundant gas in Earth’s atmosphere.
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