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The Science of the Ozone Layer

The ozone layer is an important part of Earth's atmosphere, shielding us from harmful ultraviolet (UV) radiation from the sun. But what would happen if the ozone layer gradually disappeared? About 30 years ago, atmospheric scientists predicted that this could happen—and that it was being caused by human activity.

The ozone layer protects the Earth by transforming UV radiation into thermal energy in the stratosphere. It contains oxygen gas in O2 (two atoms) and O3 (three atoms) states: UV strikes the O2 molecules and breaks them into individual oxygen atoms, which then each join up with existing O2 molecules, turning them into O3 (ozone). This chemical reaction repeats, stopping up to 99% of UV radiation from reaching the Earth's surface.

Screening out UV radiation is important as UV-C is harmful to all living things and UV-B radiation is capable of producing sunburn and DNA damage that can result in skin cancer. Most UV-A radiation reaches the surface of the Earth: though it is less harmful, but can still cause sunburn and skin cancer, explaining the importance of wearing sunscreen when outdoors.

Atmospheric scientists discovered several decades ago that the ozone layer was being destroyed by harmful human-created chemicals. The main culprits were chlorofluorocarbons (CFCs), used in aerosol products, and hydrochlorofluorocarbons (HCFCs), used in refrigeration and air conditioning. In response, the United Nations drafted the Montreal Protocol on Substances that Deplete the Ozone Layer in 1987, internationally banning or phasing out the use of these ozone-depleting chemicals. New, less harmful chemicals have been or are being developed to replace CFCs and HCFCs.

In 1994, the United Nations designated September 16 as the International Day for the Preservation of the Ozone Layer to commemorate the signing of the Montreal Protocol. As the ozone layer is expected to recover between 2050 and 2070, the Montreal Protocol and other efforts to ban ozone-depleting chemicals have been considered successful examples of international scientific diplomacy.

To learn more about the ozone layer and Earth's atmosphere, head to our Today in Science piece for additional Science NetLinks resources.

image credit: unep