5.6 Depletion of Stratospheric Ozone

1. 5.6 Depletion of Stratospheric Ozone

2. Depletion of Ozone

3. Composition of Atmosphere

4. Troposphere • 0-12km thick; • 75% of all gases in atmosphere; • All weather happens here; • Temperature falls with altitude

5. Stratosphere • 12-50 km thick • Temperature increases with altitude (gets warmer!) • Horizontal winds (jet stream) • Contains ozone layer

6. Mesosphere • 50-80km thick • temperature falls with altitude • meteor showers happen here

7. Thermosphere • Aurora borealis and aurora australis • Ionosphere here (reflects radio waves for communications) • Very hot (2000 C+) !

8. Exosphere • Outermost layer of earth’s atmosphere • 550km+ above earth’s surface • Satellites orbit here

9. Ozone • 3 oxygen molecules • UV (ultraviolet) radiation is absorbed during the formation and destruction of ozone into oxygen (O2)

10. Ozone and UV light • Allows UVa and UVb through, but blocks UVc waves • UVa - causes wrinkles • UVb - causes skin cancer • UVc - worst one because of damage to organisms/tissues • O2 + O + UV → O3 • The energy provided by incoming UV light changes O2 → O3

11. Atmosphere

12. Ozone and HOGS (Halogenated Organic Gases) • HOG’s are usually stable but break down into halogen atoms (F, Cl, Br, I, At) which are highly reactive • Ex. (CFC = chlorofluorocarbon • Cl and F are halogens • Organic = contains carbon

13. HOGS cont. • How ozone is depleted by CFC’s: • UV radiation breaks off a chlorine atom from a CFC molecule. • The chlorine atom attacks an ozone molecule (O3), breaking it apart and destroying the ozone. • The result is an ordinary oxygen molecule (O2) and a chlorine monoxide molecule (ClO). • The chlorine monoxide molecule (ClO) is attacked by a free oxygen atom releasing the chlorine atom and forming an ordinary oxygen molecule (O2). • The chlorine atom is now free to attack and destroy another ozone molecule (O3). One chlorine atom can repeat this destructive cycle thousands of times. • sources of HOG’s - fire extinguishers, refrigerators, AC units

14. UV light and ozone

15. UV radiation on Life • Reacts with melanin in skin to cause sunburn & skin cancer • Overexposure degrades immune system (but how?)

16. UV radiation and life • Required for production of vitamin D (GOOD!) • Interferes with photosynthesis in producers (esp. phytoplankton) • Zooplankton then gain less energy from phytoplankton, and food chain suffers (i.e. productivity decreases)

17. Pollution Management of CFC’s and HOGS • Reduce-Regulate-Restore model • Reduce: • Replace CFC’s with CO2, propane, or air • Replace aerosol propellants • Replace methylbromide pesticides with something other than GHG’s • Don’t use aerosol hair products or deodorant

18. Regulate: • Require a switch to HCFC’s because they don’t persist as long in the atmosphere; • (They are still harmful to the ozone layer…just less so) • Create laws to require refrigerators returned to manufacturers to recover harmful materials inside • Capture CFC’s from scrap cars AC units

19. Restore: • Remove chlorine from the stratosphere or add ozone (not exactly feasible!) • Ozone layer is slowly replenishing itself as long as we continue the ban

20. National and International Policies • UNEP (United Nations Environment Program) forges agreements on: • ITIHC (International Trade in Harmful Chemicals) • air pollution • contamination of international waterways • provide information to countries and public on disadvantages of pollution

21. Policies Continued • 1987 Montreal Protocol • international agreement on the emission of ozone-depleting substances • froze production and consumption of CFC’s with goal of zero production by year 2000 • LEDC’s granted a longer time to implement the treaty • China and India have not met their quotas under the MP because of their rapid economic growth and high demand for refrigeration & AC’s • good example of a successful international cooperative effort to alter human impact on the environment

22. Hair Bands Ruined the Ozone Poison 1983… so much hairspray