Presentation on theme: "Discuss the problems associated with the use of CFCs and assess the effectiveness of steps taken to alleviate these problems By Narmada Harish & Daniel."— Presentation transcript:
Discuss the problems associated with the use of CFCs and assess the effectiveness of steps taken to alleviate these problems By Narmada Harish & Daniel Cheng
What are CFC’s Chlorofluorocarbons Are haloalkane molecules in which all the hydrogen molecules have been replaced by chlorine or fluorine atoms. Are very stable and inert compounds Origins and Uses of CFCs Refrigerant Fluid (working fluid) in refrigerators and air conditioners Agents to make liquids form foams ( e.g. Expanded Styrofoam) The propellant gas in aerosol cans Solvent to clean circuit boards
Problems with CFC’s CFCs have a detrimental effect on the ozone layer as it damages it.
Ozone Layer Ozone layer is located in the lower stratosphere at about km above the surface of the earth The ozone layer is vital to life on Earth as the ozone molecules that make up the layer absorb ultraviolet radiation (UVB and UVC) which is harmful to the cells of living organisms.
How the Ozone layer works? O 2 + UVB → O + O O 2 + UVB → O + O O + O 2 → O 3 O 3 + UVC → O + O 2
Effect of CFC’s on Ozone CFC’s pass through the troposphere into the stratosphere where they photo dissociate to produce chlorine radicals. CCl 2 F 2 (g) → CClF 2 (g) + Cl (g)
Effect of CFC’s on Ozone The chlorine radical then acts as a catalyst to convert O 3 to O 2 in two steps Cl (g) + O 3 (g) ClO (g) + O 2 (g) The chlorine radical is then reformed ClO (g) + O (g) Cl (g) + O 2 (g)
Effect of CFC’s on the atmosphere The chlorine atoms will continue to destroy ozone as the chlorine radical is constantly being reformed. It both destroys ozone and inhibits the formation of new ozone by reacting with single oxygen atoms that are needed to produce ozone. The destruction of ozone will then allow harmful UV rays to pass through the stratosphere into the troposphere to the surface of the earth
Steps taken to alleviate problem International Agreements: e.g. Montreal and Kyoto Protocol Agrees to limit and eventually phase out the production of Halons, CFCs and HCFCs Assist less developed countries to help them phase out CFCs However, countries can bypass the agreement by “paying” for their excess CFC use.
Use of alternative compounds to replace CFCs HCFC (hydrochlorofluorocarbons) were the first replacement for CFCs The CH bond in the HCFC is attacked by hydroxyl radicals (HO ) found in the troposphere causing a large percentage of HCFCs to decompose before they reach the stratosphere However they still contain chlorine therefore will do damage to the ozone layer (about 60% less damage)
Use of alternative compounds to replace CFCs HFC (hydroflourocarbons) replaced HCFC and does not contain chlorine therefore there's no damage to the ozone layer Also it contains the CH bond which will be mostly decomposed in the troposphere However, HFCs are more expensive and are not as efficient – HFCs are also a greenhouse gas.
Effectiveness Despite the efforts being undertaken to ban the use and production of ozone destroying chemicals, the Western world in 2003 was still responsible for half the global emissions of ozone-destroying chemicals.
Effectiveness Because of large volumes of CFC currently in the troposphere and the slow diffusion rate into the stratosphere, if all nations adhere to the current restrictions, it will take years before the ozone completely recovers.