The Ozone Layer

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The Ozone Layer

• Laura McManus

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What is the Ozone Layer?

• A region of the stratosphere
• Contains relatively high concentrations of ozone
  located at altitudes of 12-30 miles (19-48 km)
  above the Earths surface.
• Ozone is a form of oxygen. It has 3 oxygen atoms
  bonded together to form O3.

3
The Facts

• Acts as a protective screen
• Prevents most UV light and other high-energy
  radiation from penetrating to the Earths surface
• CFCs cause ozone depletion

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Formation of Ozone

• Formed when an oxygen atom reacts with a dioxygen
  molecule
• One way to make oxygen atoms is to split up
  (dissociate) dioxygen molecules
• Requires a lot of energy to break the bonds

5
The Problems

• Depletion of ozone in the atmosphere has resulted
  in a hole being formed
• More UV light can penetrate through to the
  Earths surface
• More radiation can result in a greater risk of
  skin cancer

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The Ozone Hole
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The Ozone Hole

• Located over the Antarctic
• Satellite readings and measurements from balloons
  and high altitude planes have supported the
  measurements from the ground to confirm that
  there is a hole
• Measurements taken are for ozone concentration
  measured in Dobson units
• Discovered in 1984 by Joe Farman and his team

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The Ozone Hole

• The lower stratosphere over the South Pole is the
  coldest spot on Earth.
• From June to September cold winds blow around the
  region which prevent warmer air from entering.
• The small amount of water vapour in the
  stratosphere freezes and forms thin clouds of ice
  crystals.
• These ice crystals convert safe molecules like
  ClONO2 and HCl to more reactive ones like HOCl
  and Cl2. These two compounds release Cl atoms.
• The ice crystals are eventually melted by the
  warm air and by November the hole is virtually
  refilled.
• The problem exists because of the small amount of
  the hole that is not refilled each year

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What has been done?

• In 1978 the U.S. banned CFCs as propellants in
  aerosol products
• In 1990 in the U.S. the Clean Air Amendment was
  passed
• May 15th 1993, warning labels were printed on all
  products with ozone-depleting substances

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Radicals

• Highly reactive atoms or groups of atoms with
  unpaired electrons are known as radicals
• The key feature of a radical is its unpaired
  electron, which makes it particularly reactive

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The Future

• The ozone layer is expected to eventually recover
  if all nations maintain their efforts to reduce
  ozone-destroying chemicals
• The layer is still thinning at the poles and it
  could be at least the year 2050 before we begin
  to see definite signs of recovery

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The End