Earth (ESD)
NASA Knows: The Ozone Hole
This is the story of the hole in Earth’s protective ozone layer: what it is, how it formed, and the decades-long effort to repair it.
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Why is there an ozone hole?
Ozone 101 shows the ABCs of CFCs and the atmospheric problem they created.
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Key takeaways
The ozone layer shields Earth from ultraviolet (UV) radiation from the Sun that can harm plants, animals, and humans. The ozone layer forms in the stratosphere 7-31 miles (11–50 km) above the Earth’s surface.
Chlorofluorocarbons (CFCs) and halons are human-produced chemicals, used in products in refrigerants, spray cans, and fire extinguishers. The breakdown of these chemicals causes a reaction with ozone molecules that thins the ozone layer over the poles, most notably Antarctica.
An international decision to phase out CFCs has slowly reversed the trend of thinning ozone. The Montreal Protocol, an international partnership begun in 1987 with signatories from around the world, controlled the consumption and production of ozone-depleting substances, so that the levels of these have stopped growing in the atmosphere.
If the progress caused by the Montreal Protocol and subsequent amendments continues, the Antarctic ozone hole could be restored to 1980 levels by 2070.
NASA and its partners—government agencies, universities, and private sector entitites—develop and operate systems to measure ozone in the atmosphere, using numerous optical methods, which measure the intensity of UV light as it passes through the atmosphere.
The basics
What is ozone?
Oxygen exists in two forms in the atmosphere: O2, a molecule with two oxygen atoms, is the air we breathe, and it makes up 21% of the Earth’s atmosphere; and O3, or ozone, a molecule with three oxygen atoms, makes up 0.001% of the atmosphere. Ozone is created when solar UV radiation breaks down oxygen molecules in our air.UV radiation is more intense at higher altitudes because it has not yet passed through much of the atmosphere, so it hasn’t yet been absorbed. The ozone layer forms in Earth’s stratosphere, about 7 to 31 miles (11 to 50 km) above the surface. Ozone also forms at the surface, where it is a harmful pollutant.
What does the ozone layer do for Earth?
The UV index is a measurement of the strength of the UV rays reaching Earth’s surface from the Sun. UV is measured on a scale of 1 to 11+, in which 1 indicates a low risk of overexposure and 11+ means a high risk to humans and the environment. Too much UV light can lead to sunburns, skin cancer, and cataracts in humans. It can reduce yields from our farm crops and harm aquatic plants and animals. Ozone controls the UV level, acting as a sunscreen for our planet. It absorbs UV-B—the most harmful form of UV radiation that reaches Earth’s surface—which can damage DNA in plants and animals.The ozone layer in Earth’s atmosphere is critical to healthy life on Earth. Thin places exist at both poles, but the “hole” is bigger in the Antarctic (see the Arctic, at left). Losing ozone there is such an enormous threat that, when scientists discovered that the ozone layer was thinning, they prompted the international community to act collectively in response to the news, enacting the Montreal Protocol to curb the chemicals that were causing the problem.
What is the ozone hole?
The ozone “hole” is not a hole, but rather a thin patch of depleted ozone in the stratosphere over Antarctica. This thinning is caused by molecules that result from the breakdown in CFCs and other ozone-depleting compounds. These include chlorine and bromine, which are so inert (nonreactive) that they can stay in the atmosphere long enough to be carried up to the stratosphere, where they react with polar cloud particles that ultimately deplete ozone.
Vital info
Where is the ozone layer?
The ozone layer forms in the stratosphere 7-31 miles (11-50 km) above Earth, and encompasses the entire planet. Most stratospheric ozone is produced at tropical latitudes, and high-altitude winds spread it over the planet. It is constantly forming and breaking down. Distribution is not uniform. In different places around the world, …