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Atmosphere

Atmosphere. Composition Ozone Layer Human Impact. Our Atmosphere. Is fixed – i.e. closed system for matter, but not energy! Has many functions Protection from cosmic rays Keeping us warm Oxygen. Its all relative. Is a very thin layer of gas Is small compared to Earth itself.

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Atmosphere

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  1. Atmosphere Composition Ozone Layer Human Impact

  2. Our Atmosphere • Is fixed – i.e. closed system for matter, but not energy! • Has many functions • Protection from cosmic rays • Keeping us warm • Oxygen

  3. Its all relative • Is a very thin layer of gas • Is small compared to Earth itself

  4. Composition & Layers

  5. Troposphere • The lowest layer • Home of life • Home of weather • Home of pollution – mainly from human impact

  6. Sources of pollution • Humans – industry, transport and domestic • Is particulate (carbon, dust and metals) and gaseous (carbon dioxide, smog, unburnt hydrocarbons, etc. • Can be natural • Chief source is volcanic activity

  7. Stratosphere • Home of the ozone layer • Where the Concorde once flew • Where global warming originates

  8. What is ozone • Allotrope of oxygen • Formed naturally • Oxygen molecule split by UV radiation • Unstable Oxygen atom forms • Atom joins with molecule to form ozone

  9. The oxygen free radical • This is another name for the unstable oxygen atom • contains an unpaired electron in its outermost shell of electrons. • This is an extremely unstable configuration, • radicals quickly react with other molecules or radicals to achieve the stable configuration of 4 pairs of electrons in their outermost shell

  10. How can Ozone be stable? • Simply put, a special bond forms • It is called a co-ordinate covalent bond • One of the oxygen molecule atoms has to share two electrons with the atom!

  11. How the bond forms

  12. Decomposing ozone • Ozone is readily split apart to form oxygen molecules • This is a natural process occurring in the atmosphere

  13. CFC’s the real villains! • CFC = chloro fluoro carbons • CFCs were developed in the early 1930s and are used in a variety of industrial, commercial, and household applications • Used as coolants for commercial and home refrigeration units, aerosol propellants, electronic cleaning solvents, and blowing agents

  14. Halons are also to blame • Are compounds of bromine, fluorine and carbon • The halons are used as fire extinguishing agents, both in built-in systems and in handheld portable fire extinguishers

  15. CFC and ozone • In 1973 chlorine was found to be a catalytic agent in ozone destruction • It essentially cleaves the ozone to produce oxygen molecules – see decomposing ozone

  16. The chemistry – we think

  17. Simply put • Human activity puts chlorides and bromides into the atmosphere. • Cold conditions are present in the Polar Regions that allow the accumulation of the CFC’s. • Sunlight breaks down the CFC’s. • Under certain conditions atomic chlorine forms and this has a major part in the breakdown of ozone. • The breakdown products destroy ozone. • The ozone is broken into oxygen molecules. • No more Ozone protection in the stratosphere.

  18. So what’s being done • The CFC problem may be hard to solve because there are already great quantities of CFCs in the environment.  • CFCs would remain in the stratosphere for another 100 years even if none were ever produced again • In the Montreal Protocol, 30 nations worldwide agreed to reduce usage of CFCs and encouraged other countries to do so as well

  19. Montreal Protocol • The governments of the world got together to try to stop the problems that were clearly evident – the major push was the gradual phasing out of CFC’s. • The Montreal Protocol was a convention signed in 1987 by many countries to greatly reduce the production and use of CFCs which had been shown to be responsible for damage to the ozone layer. • Since 1987, further amendments to the protocol have imposed even greater restrictions of the production and use of potentially damaging compounds.

  20. What’s it mean to me? • Small steps are being taken to reduce CFCs including the use of alternate propellants in: • Refrigeration units • Air conditioning units • Propellants for spray cans • Using pump action instead of gas propellants

  21. But surely there are alternatives! • You bet! In place of CFCs and Halons we now use: • Two CFC replacements have been developed for medical uses; they are referred to as hydrofluoroalkanes (HFAs) or as hydrofluorocarbons (HFCs), and contain only carbon, hydrogen and fluorine. • They are non-flammable and chlorine-free, so they have no impact on the stratospheric ozone layer.

  22. Being more specific • Cyclopentane and cyclohexane have been put forth as replacements for coolants • Nitrogen gas can be used as a blowing agent

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