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AIR ENVIRONMENT

AIR ENVIRONMENT. CHAPTER 20 Climate Change and Ozone. WHAT IS OZONE?. Oxygen At sea level, 21% of air is diatomic oxygen Two oxygen atoms bonded together = O 2 Ozone Triatomic form of oxygen (O 3 ) Three atoms of oxygen bonded together

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AIR ENVIRONMENT

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  1. AIR ENVIRONMENT CHAPTER 20 Climate Change and Ozone

  2. WHAT IS OZONE? • Oxygen • At sea level, 21% of air is diatomic oxygen • Two oxygen atoms bonded together = O2 • Ozone • Triatomic form of oxygen (O3) • Three atoms of oxygen bonded together • Reactive molecule that is a strong oxidant and reacts with many materials in the atmosphere

  3. WHAT IS OZONE? • The Ozone Layer • About 90% of ozone in the atmosphere is found in the stratosphere • Absorbs most (about 99%)of the ultraviolet radiation heading towards Earth • UV radiation comes in three forms • UVC • Shortest wavelength • Most energetic • Absorbed strongly in atmosphere • Negligible UVC reaches surface of Earth

  4. WHAT IS OZONE? • UVA • Longest wavelength • Least energetic • Can cause some damage to living cells • Not affected by ozone and is transmitted to Earth • UVB • Intermediate wavelength • Fairly energetic • Strongly absorbed by ozone layer • Damaging to living cells • THIS IS THE OZONE PROBLEM

  5. THE PROBLEM • British Antarctic Survey began measuring ozone in 1957 • From 1957 to 1970 the ozone concentration was fairly stable • In 1984, the concentration took a sharp decline • Their research indicated that stratospheric ozone concentration has been decreasing • Additional studies confirmed their reports • Since then, this decline has been named the “Ozone Hole” • Not actually a hole • Relative depletion in the concentration of ozone that occurs during the Antarctic spring

  6. THE PROBLEM • Antarctic Hole • Each spring, the ozone in the Antarctic atmosphere decreases • Amount of depletion has varied from 15% to 80% • In general, the thickness of the ozone layer above the Antarctic each spring has been declining • Geographic area covered by the ozone hole continues to increase • Covered 1 million or so square kilometers in 1970 • Today it covers over 22 million square kilometers • Larger than the entire U.S. and Canada combined • In 2000, it covered over 28 million square kilometers • Arctic Hole • Ozone depletion occurs over North Pole as well • Troublesome because it tends to spread

  7. CAUSES • Hypothesis that ozone is being depleted by the presence of CHLOROFLUOROCARBONS (CFCs) was first suggested in 1974 • CFCs have a long residence time in the lower atmosphere • CFCs eventually make their way to the upper atmosphere • Here, they are destroyed by solar UV radiation • This process produces chlorine, a highly reactive atom • Chlorine destroys ozone

  8. CAUSES • CFCs come from a variety of sources • Aerosol propellants in spray cans • Working gas in refrigeration and air-conditioning units • Foam-blowing process for production of styrofoam • Cleaning computer parts during manufacture • Even if all manufacture, use and emission of ozone depleting chemical occurred today, the problem would not be solved • CFCs remain in atmosphere between 74 and 140 years • About 35% of certain types of CFCs will still be in air until 2100 • Another 15% will be around till 2200 • Some CFCs have not been emitted yet

  9. EFFECTS OF DECREASED OZONE • Marine Ecosystems • Phytoplankton form the foundation of aquatic food webs • Exposure to solar UVB radiation has been shown to negatively affect phytoplankton • One study has indicated a 6-12% reduction • This results in reduction in the size of the population of animals that eat these smaller creatures

  10. EFFECTS OF DECREASED OZONE • Plants • Plant growth can be directly affected by UVB radiation • May result in decreased production

  11. EFFECTS OF DECREASED OZONE • Biogeochemical Cycles • Increases in solar UV radiation could affect terrestrial and aquatic biogeochemical cycles • May result in increased levels of carbon dioxide (CO2), and carbon monoxide (CO) • Could increase effects of global warming

  12. EFFECTS OF DECREASED OZONE • Materials • Synthetic polymers, naturally occurring biopolymers, as well as some other materials of commercial interest are adversely affected by solar UV radiation • Any increase in solar UVB levels will therefore accelerate their breakdown, limiting the length of time for which they are useful outdoors

  13. EFFECTS OF DECREASED OZONE • Human Health • Increases in type of skin cancer • 1% decrease in ozone = 1% - 2% increase of UVB • This will result in about 2% increase of skin cancer • Increase in a variety of diseases • Eye damage • Damage or reduce efficiency of human immune system

  14. http://www.epa.gov/ozone/science/missoz/index.html • On The Trail of the Missing Ozone……

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