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7.20: Ozone Depletion

Difficulty Level: Basic Created by: CK-12
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Why can't the children in Punta Arenas go outside in the spring?

Punta Arenas, Chile is the world's most southern city. At such a high latitude winters are exceedingly cold and dark. Children must stay inside to avoid the cold. Of course, they look forward to spring. But some years, it is too dangerous for the children to go outside. The ozone hole has moved north. Too much of the sun's harmful UV radiation gets through.

Loss of High-Level Ozone

Ozone near the ground harms human health. Ground-level ozone is a pollutant. But the ozone layer in the stratosphere protects us from harmful solar rays. That’s why people were alarmed in the 1980s to learn that there was a hole in the ozone layer.

Cause of Ozone Loss

What’s destroying the ozone layer? The chief cause is chlorofluorocarbons (CFCs). These are human-made chemicals that contain the element chlorine (Cl). In the past, CFCs were widely used in spray cans, refrigerators, and many other products. CFCs are stable compounds that can remain in the atmosphere for hundreds of years.

Once CFCs are in the air, they float up into the stratosphere. What happens next is shown in Figure below. Sunlight breaks apart the molecules. This releases their chlorine ions (Cl). The free chlorine ions may then combine with oxygen ions in ozone. This breaks down the ozone molecules into an oxygen molecule and an oxygen ion. One CFC molecule can break down as many as 100,000 ozone molecules in this way! These forms of oxygen do not protect the planet from ultraviolet radiation.

CFCs break down ozone in the stratosphere.

Ozone Hole

Most ozone loss it taking place over the South Pole and Antarctica. This is the location of the ozone hole. The ozone hole is a region in the stratosphere where there is less ozone than normal. Conditions are just right for ozone destruction because it is exceedingly cold. The ozone hole is also seasonal. The hole forms during the early part spring in the Southern Hemisphere and then grows northward. You can see the hole in Figure below. The ozone layer is also thinner over the Northern Hemisphere.

The hole in the ozone layer occurs over Antarctica. How do you think the hole in the ozone layer could affect life on Earth?

Effects of Ozone Loss

With less ozone in the stratosphere, more UV rays reach the ground. More UV rays increase skin cancer rates. Just a 1 percent loss of ozone causes a 5 percent increase in skin cancer. More UV rays also harm plants and phytoplankton. As a result, they produce less food. This may affect entire ecosystems.

Protecting the Ozone Layer

The Montreal Protocol is a worldwide agreement on air pollution. It focuses on CFCs. It was signed by many countries in 1987. It controls almost 100 chemicals that can damage the ozone layer. Its aim is to return the ozone layer to its normal state.

The Montreal Protocol has been effective in controlling CFCs. By 1995, few CFCs were still being used. But the ozone hole kept growing for several years after that because of the CFCs already in the atmosphere. It peaked in 2006. Since then, it has been somewhat smaller. The Montreal Protocol is a shining example of how nations can come together to solve a global environmental problem.


  • ozone hole: A region around Antarctica in which ozone levels are reduced in springtime because of the action of ozone-destroying chemicals.


  • CFCs float up into the stratosphere where they break apart. The chlorine pulls an oxygen ion off of an ozone molecule and destroys it.
  • The ozone hole forms over Antarctica in the spring.
  • Ozone loss increases the amount of high-energy ultraviolet radiation that strike Earth. This can cause ecological and health problems.


Use these resources to answer the questions that follow.

Fear of Ozone Loss Launched UARS Satellite at http://www.youtube.com/watch?v=xDOFJ5xoGmw (2:21)

  1. What is the purpose of the ozone layer?
  2. Why is the ozone layer so fragile?
  3. How much did ozone decrease between 1979 and 1993?
  4. Which satellite was launched to study the ozone? When?

Unprecedented Arctic Ozone Loss in 2011 at http://www.youtube.com/watch?v=NvtUYQ_eAwY (1:38)

  1. What caused this ozone loss?


  1. How do CFCs destroy ozone?
  2. What is the ozone hole and where is it found?
  3. What effect does the ozone hole have on life, especially human life?

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ozone hole Region around Antarctica in which ozone levels are reduced in springtime because of the action of ozone-destroying chemicals.

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Date Created:
Jan 04, 2013
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Aug 29, 2016
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