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Earth’s Changing Environment Lecture 5

Earth’s Changing Environment Lecture 5. Depletion of the Ozone Layer. The Stratospheric Ozone Layer. Begins where the troposphere ends at 50,000 feet (10 miles) above the Earth’s surface. The lower stratosphere is the location of most atmospheric ozone. Solar UV Radiation.

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Earth’s Changing Environment Lecture 5

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  1. Earth’s Changing EnvironmentLecture 5 Depletion of the Ozone Layer

  2. The Stratospheric Ozone Layer • Begins where the troposphere ends at 50,000 feet (10 miles) above the Earth’s surface. • The lower stratosphere is the location of most atmospheric ozone.

  3. Solar UV Radiation • UV Radiation is blocked by the ozone layer • But UV Radiation also forms the ozone layer.

  4. Solar Spectrum

  5. Regions of the Solar Spectrum

  6. Regions of the Solar UV Spectrum

  7. Chapman Reactions form O3 in the Stratosphere

  8. O3 absorbs most of the UVB radiation

  9. These two processes form the Ozone Cycle

  10. Depletion of the Ozone Layer

  11. Chlorine acts as a catalyst to destroy the Ozone layer

  12. How does Chlorine get into the Stratosphere? • chlorofluorocarbons (CFCs). • CFC-12 (CF2Cl2) (freon) • CFC-11 (CFCl3) • Have 100 year atmospheric lifetimes

  13. Mario Molina • Born in Mexico City • Won Nobel Prize in 1995 • In 1974 with Sherry Roland, he predicted that CFCs could destroy ozone layer

  14. Antarctic Ozone Hole • Normally, stratospheric reactions put chlorine from CFCs into inert forms (HCL and ClONO2) • Ice crystals in these antarctic polar stratospheric clouds (PSCs) act as sites for the conversion of the inert form of chlorine to the active form of chlorine.

  15. Antarctic Ozone Hole • Every spring, UVC radiation breaks CL2 formed on the PSCs into atomic chlorine. This active CL causes a very sharp decrease in the concentration of ozone in the Antarctic stratosphere, an ozone hole.

  16. US Ozone Depletion

  17. Health and Environmental Effects

  18. The Montreal Protocol • International treaty for the control on the production and consumption of ozone-depleting substances agreed on in 1987. • President Reagan signed the ratified Protocol in 1988. • 1994 Copenhagen Amendment and Vienna Adjustments called for a more rapid phase out of certain ODP chemicals.

  19. Montreal Protocol • 29 countries plus the European Union signed initially • All have agreed to a phase-out schedule • Globally emission of ODPs has been drastically reduced to around 10% of original levels.

  20. EPA – Ozone Depletion Program • Command and Control Strategy • Halt the production of ozone-depleting substances (ODS) • Ensure refrigerants and halon fire extinguishing agents are recycled properly • identifying alternative to ODS • banning the release of OD refrigerants

  21. US Phase-out of high ODP chemicals • chlorofluorocarbons (CFCs) • carbon tetrachloride • methyl chloroform • halons

  22. Will take 50 years to Recover

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