How the Ozone Layer Protects Life
Ozone near the ground can be an air pollutant, but high in the stratosphere it performs an important protective role. The ozone layer absorbs much of the Sun's ultraviolet radiation before it reaches Earth's surface. Its chemistry depends on a continuing cycle of creation and destruction.
Ozone forms and breaks apart naturally
An ordinary oxygen molecule contains two oxygen atoms. High-energy ultraviolet radiation can split some of these molecules into separate oxygen atoms. A free oxygen atom can then join another oxygen molecule to form ozone, which contains three oxygen atoms.
Ozone absorbs ultraviolet radiation and can split back into an oxygen molecule and a free oxygen atom. These reactions create a moving balance. Ozone is continually formed, destroyed and formed again rather than remaining as one permanent shield.
Most atmospheric ozone is found in the stratosphere, roughly above the weather-filled lower atmosphere. Its concentration is small compared with ordinary oxygen, but it is enough to absorb much of the most damaging ultraviolet radiation.
Some chemicals accelerated ozone loss
Chlorofluorocarbons, often called CFCs, were once widely used in refrigeration, aerosols and foam production. They are stable in the lower atmosphere, so they can persist long enough to reach the stratosphere.
There, ultraviolet radiation can release chlorine atoms from the molecules. A chlorine atom can react with ozone and later be regenerated, allowing it to destroy many ozone molecules through a catalytic cycle. Bromine-containing chemicals can cause similar damage.
The strongest seasonal ozone loss developed over Antarctica. Extremely cold conditions help form polar stratospheric clouds, while isolated winter air allows reactive chemicals to build up. When sunlight returns in spring, rapid reactions produce the region known as the ozone hole.
Protection requires long-term cooperation
Less stratospheric ozone allows more ultraviolet B radiation to reach the surface. Higher exposure can increase skin cancer and eye damage and can affect crops, plankton and other living things.
Countries responded through the Montreal Protocol, which reduced the production and use of many ozone-depleting substances. Because these chemicals can remain in the atmosphere for decades, recovery is slow even after emissions fall.
Keep the main story clear:
- •Ultraviolet light helps create ozone from oxygen.
- •Ozone absorbs ultraviolet radiation.
- •CFCs can release reactive chlorine in the stratosphere.
- •Chlorine repeatedly destroys ozone molecules.
- •Reducing harmful chemicals allows gradual recovery.
The takeaway
The ozone layer protects life by absorbing harmful ultraviolet radiation in the stratosphere. Human-made chemicals disrupted its natural balance, but coordinated international action reduced the main sources of damage. Separate protective stratospheric ozone from polluted ground-level ozone, and the issue becomes much easier to understand.