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The Ozone (O 3 ) Shield

Learn about the Ozone Shield, the Ozone Hole, its formation, effects on humans, animals & plants, and global efforts to protect it, like the Montreal Protocol. Discover how CFCs contribute to ozone depletion and its long-lasting impact.

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The Ozone (O 3 ) Shield

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  1. The Ozone (O3) Shield • Ozone layer: layer of the atmosphere at an altitude of 15 to 40 km where ozone absorbs UV radiation • Shields the Earth’s surface from most of the sun’s UV light • UV light can damage the genetic material in living cells.

  2. Chemicals That Cause Ozone Depletion • Chlorofluorocarbons (CFCs): hydrocarbons with some/ all of the hydrogen atoms replaced by chlorine and fluorine. • used in coolants (refrigerators, air conditioners), cleaning solvents, propellant in spray cans of everyday products (deodorants, insecticides, paint) • use now restricted • at the Earth’s surface, chemically stable • break apart high in the stratosphere, destroy ozone molecule

  3. The Ozone Hole • Thinning of stratospheric ozone that occurs over the poles during the spring • First noted in 1985, in Antarctica • Ozone levels over the Arctic have decreased as well. • In March 1997, ozone levels over part of Canada were 45 percent below normal

  4. How Does the Ozone Hole Form? • Products of CFCs are converted to molecular chlorine • In the spring, molecular chlorine is split into two chlorine atoms • Chlorine atoms rapidly destroy ozone • Ozone is very chemically reactive. Ozone produced by pollution breaks down or combines with other substances long before it can reach the stratosphere.

  5. Effects of Ozone Thinning on Humans • As ozone decreases, more UV light able reach Earth’s surface • UV light damages DNA • Exposure makes the body more susceptible to skin cancer • May cause other damaging effects to the human body.

  6. Effects of Ozone Thinning on Animals & Plants • High levels of UV light can kill phytoplankton, • disrupt ocean food chains • cause an increase in the amount of carbon dioxide in the atmosphere • Believe especially damaging for amphibians • kills many eggs of some species by damaging unprotected DNA • amphibians an indicator of environmental change due to their environmental sensitivity • Interferes with photosynthesis in plants, lowers crop yields

  7. Protecting the Ozone Layer • 1987, Montreal Protocol, to sharply limit their production of CFCs. • The United States pledged to ban all substances that pose a significant danger to the ozone layer by 2000 • Because many countries were involved and decided to control CFCs, many people consider ozone protection an international environmental success story. • Battle not over, CFC molecules remain active in the stratosphere for 60 to 120 years.

  8. Protecting the Ozone Layer • However, the battle to protect the ozone layer is not over. • CFCs released 30 years ago are still destroying ozone today, so it will be many years before the ozone layer completely recovers.

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