Summary of topic 5.6


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Environmental Systems and Societies

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Summary of topic 5.6

  1. 1. Topic 5 Pollution Management 5.6 Depletion of Stratospheric Ozone t5w9eIPYodg 02/ozone-depletion.html
  2. 2. Composition of Air carbon dioxide; argon; 0.93% 0.038% other gases, 0% oxygen; 20.9% nitrogen; 78.1%
  3. 3. Structure of the Atmosphere • It is a mixture of solids, liquids and gases held in place by the Earth’s gravity • Close to the surface (first 15 km the troposphere), the composition is fairly constant. It changes at higher altitudes • Certain gases are characteristic of different altitudes * • A layer of ozone occurs at an altitude between 10 – 15 km (this is called the stratosphere) Altitude (km) Most Significant Gas 10 - 50 ozone 100 - 200 nitrogen 200 - 1100 oxygen 1100 - 3500 helium > 3500 hydrogen
  4. 4. Pressure (mb) Structure of the Atmosphere OZONE LAYER
  5. 5. The Role of Ozone • Ozone (O3) is produced by the action of sunlight on O2 molecules • There are higher concentrations around the equator due to higher levels of sunlight, but it concentrates near the poles due to transportation by winds • Ozone is a greenhouse gas but also absorbs incoming (and some outgoing) UV light • Ozone production and destruction is at equilibrium (but it is destroyed by anthropogenic pollutants (e.g. chlorofluorocarbons (CFCs) and NOx) • Without the ozone layer, incoming UV radiation from the sun would destroy all life
  6. 6. The Effect of CFCs • CFCs are stable industrial products of byproducts that contain chlorine, fluorine or bromine (halogens) • They can persist for many years in the troposphere, however when they travel to the stratosphere, UV light breaks them down and release their halogen atoms • The halogens catalyse the breakdown of ozone • A hole in the ozone layer was first reported over Antarctica by the British Antarctic Survey in 1985 • The hole is seasonal – ozone thins during the Antarctic winter, since colder temperatures result in the formation of clouds of ice particles provide catalytic surfaces to accelerate ozone breakdown
  7. 7. • The Effects of Increased UV(B) Light Humans and other animals – Sunburn, skin cancer, immune deficiencies, eye damage and cataracts – Effects may be acute or chronic (chronic effects are often irreversible) – It may have effects on the success of vaccinations – Reduction of fish stocks – Fall in frog populations – Due to the Antarctic Ozone hole Australia tried to increase public awareness, but has seen an increase in skin cancer over the last decade • Plants – Reduced yield (although GM is producing UV(B) tolerant varieties) – Reduction in natural plant productivity, particularly phytoplankton
  8. 8. Regulation • Reduction in the use of CFCs – They have been discontinued as propellants in aerosol cans – They are being phased out as refrigerants – There are now programmes for the collection of old fridges and the recycling of the CFCs they contain • Reduction in the use of methyl bromide – Used as a soil insecticide, but phased out in Europe and the US in 2005. Still used in many countries
  9. 9. Regulation • There has been successful international cooperation, largely organised by the United Nations Environment Programme (UNEP) – Montreal Protocol (1987) • Europe banned the use of CFCs in 2000 • Developing countries are phasing out their use, but this will take considerably longer • A total worldwide ban should be in place by 2030 • However CFCs are very persistent in the troposphere and will continue to have effects well into the future • Some of the chemicals used to replace CFCs (e.g. HCFCs) are greenhouse gases
  10. 10. Questions 1. 2. 3. 4. Describe the composition of the atmosphere Describe the role of ozone Explain the effect of ozone depleting substances State the effects of increased UV(B) radiation on humans, animals and plants 5. Describe the efforts of international organisations in reducing the effects of ozone depleting substances and evaluate their effectiveness