Ozone Depletion and Chlorofluorocarbons CFCs

Other Important Radical Reactions 487 THE CHEMISTRY OF... Antioxidants 489 THE CHEMISTRY OF... Ozone Depletion and Chlorofluorocarbons (CFCs) 490... 

Global Warming and increased Climatic Variability due to Greenhouse Gas (GHG) Accumulation in the Atmosphere and Increased Radiation due to Ozone Depletion by Chlorofluorocarbons (CFC). 

Free-radical chain reactions also occur during the chlorination of methane (Chapter 10) and of the methyl group of methylbenzene. Ozone depletion by chlorofluorocarbons (CFCs), acid rain formation and formation of photochemical smog (Chapter 25 on the accompanying website) also involve free-radical reactions. (Free-radical reactions are also operating in unpolluted atmospheres and play an important role in all chemical reactions that occur in the gas phase.) The combustion of hydrocarbons, such as petrol, also proceeds via a free-radical mechanism, which has important consequences for the smooth running and performance of combustion engines. Chain reactions may also have ions as intermediates, as opposed to free radicals. 

Amorphous fluoropolymers have many applications in the areas of advanced materials where they are used in applications requiring thermal and chemical resistance. Their manufacture is hindered by their low solubility in many solvents. Many fluoropolymerizations cannot be carried out in hydrocarbon solvents because the radical abstraction of hydrogen atoms leads to detrimental side reactions. Chlorofluorocarbons (CFCs) were thus commonly used, but their use is now strictly controlled due to their ozone depleting and greenhouse gas properties. Supercritical carbon dioxide is a very attractive alternative to CFCs and it has been shown that amorphous fluoropolymers can be synthesized by... 

By law, chlorofluorocarbons (cfcs) used as refrigerants in refrigerators must be removed before the appliances are discarded. This solves only part of the ozone-depletion and global-warming problem attributed to refrigerators. Why ... 

While less harmful to the environment than CFCs, hydro-chlorofluorocarbons (HCFCs) are stiU ozone-depleting (they are classified as Class II ozone-depleters) and will be phased out by 2020. Hydrofluorocarbons appear to have little or no ozone-depleting effect and are replacing CFCs and HCFCs in refrigerants and aerosol propellants. 

Earlier, in Chapter 6, we discussed the catalytic cycle involving chlorine free radicals generated by the effect of ultraviolet radiation on chlorofluorocarbons (CFCs). This cycle results in the phenomenon of ozone depletion and the consequent polar ozone holes . CFCs are not the only compounds that cause this depletion. Nitrogen oxides (NO, ) are also responsible. 

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