Summary of topic 6.2
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The document discusses stratospheric ozone and its depletion by chlorofluorocarbons (CFCs). It explains that ozone in the stratosphere absorbs ultraviolet light and protects life from its harmful effects. CFCs were used widely but break down ozone when they reach the stratosphere. This led to the discovery of the Antarctic ozone hole in 1985. Increased UV radiation can cause skin cancer, eye damage and lower crop yields. International agreements like the Montreal Protocol have phased out CFC use, reducing ozone depletion, though some developing nations still use CFCs and a black market exists.
Summary of topic 6.2
- 1. Topic 6 Atmospheric Systems and Societies 6.2 Stratospheric Ozone http://www.youtube.com/watch?v= t5w9eIPYodg http://edroness.blogspot.mx/2014/ 02/ozone-depletion.html
- 2. Structure of the Atmosphere Pressure(mb) OZONE LAYER
- 3. 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
- 4. The Effect of CFCs • CFCs are stable industrial products of by- products 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
- 5. 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
- 6. 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
- 7. 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 • There is also still an illegal market in CFCs • Some of the chemicals used to replace CFCs (e.g. HCFCs) are greenhouse gases
- 8. Questions 1. Describe the role of ozone 2. Explain the effect of ozone depleting substances 3. State the effects of increased UV(B) radiation on humans, animals and plants 4. Describe the efforts of international organisations in reducing the effects of ozone depleting substances and evaluate their effectiveness