Presentation on theme: "By Narmada Harish & Daniel Cheng"— Presentation transcript:
1 By Narmada Harish & Daniel Cheng Discuss the problems associated with the use of CFCs and assess the effectiveness of steps taken to alleviate these problemsBy Narmada Harish & Daniel Cheng
2 What are CFC’s Chlorofluorocarbons Are haloalkane molecules in which all the hydrogen molecules have been replaced by chlorine or fluorine atoms.Are very stable and inert compoundsOrigins and Uses of CFCsRefrigerant Fluid (working fluid) in refrigerators and air conditionersAgents to make liquids form foams ( e.g. Expanded Styrofoam)The propellant gas in aerosol cansSolvent to clean circuit boards
3 Problems with CFC’sCFCs have a detrimental effect on the ozone layer as it damages it.
4 Ozone LayerOzone layer is located in the lower stratosphere at about km above the surface of the earthThe 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.
6 Effect of CFC’s on Ozone CFC’s pass through the troposphere into the stratosphere where they photo dissociate to produce chlorine radicals.CCl2F2(g) → CClF2(g) + Cl (g)
7 Effect of CFC’s on Ozone The chlorine radical then acts as a catalyst to convert O3 to O2 in two stepsCl(g) + O3(g) ClO(g) + O2(g)The chlorine radical is then reformedClO(g) + O (g) Cl(g) + O2(g)
8 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
9 Steps taken to alleviate problem International Agreements: e.g. Montreal and Kyoto ProtocolAgrees to limit and eventually phase out the production of Halons, CFCs and HCFCsAssist less developed countries to help them phase out CFCsHowever, countries can bypass the agreement by “paying” for their excess CFC use.
10 Use of alternative compounds to replace CFCs HCFC (hydrochlorofluorocarbons) were the first replacement for CFCsThe 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 stratosphereHowever they still contain chlorine therefore will do damage to the ozone layer (about 60% less damage)
11 Use of alternative compounds to replace CFCs HFC (hydroflourocarbons) replaced HCFC and does not contain chlorine therefore there's no damage to the ozone layerAlso it contains the CH bond which will be mostly decomposed in the troposphereHowever, HFCs are more expensive and are not as efficient – HFCs are also a greenhouse gas.
12 EffectivenessDespite 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.
13 EffectivenessBecause 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.