Ozone layer halogen-containing

Trichlorofluoromethane is a member of a class of molecules called chlorofluorocarbons or CFCs, which contain one or two carbon atoms and several halogens. Trichlorofluoromethane is an unusual organic molecule in that it contains no hydrogen atoms. Because it has a low molecular weight and is easily vaporized, trichlorofluoromethane has been used as an aerosol propellant and refrigerant. It and other CFCs have been implicated in the destruction of the stratospheric ozone layer, as is discussed in Chapter 15. 

The halons are a class of halocarbons that contain bromine as well as hydrogen and other halogens. Their main use is in fire extinguishers. They are, however, significantly more active than CFCs in their effect on the ozone layer. The halocarbons are also thought to contribute to global warming. 

Only a relatively limited number of mechanisms are needed to describe the very large number of reactions in organic chemistry. Mechanisms enable us to understand how and why reactions occur, and what products are likely to form in them. In this chapter we ply mechanistic concepts to explain the effects of halogen-containing chemicals on the stratospheric ozone layer. We conclude with a brief discussion of alkane combustion and show how that process serves as a useful source of thermodynamic information about organic molecules. 

The stratospheric region of the atmosphere is located above 15—35 km from the surface of the earth. It contains a deep layer of ozone that acts as a filter of harmful UV radiation of sunlight to reach the earth s surface and thus protects us from hazardous effect of UV radiation. The massive loss of ozone in the stratosphere occurs daily by atmospheric pollutants, UV-induced photolysis of ozone in the presence of man-made chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons (brominated hydrocarbons), CCU, and methylchloroform (CH3CCI3). These halocarbons generate halogen radicals which have active roles for photolysis of ozone. These are also derived from gaseous chlorine and hydrochloric... 

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