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化学污染与防治5
* * * * * FIGURE 9.18 A false-color satellite image of the ozone hole over Antarctica on September 24, 2006. * * * * * * * * * * * * * * * * * * * * * * * * * * * * FIGURE 9.17 Annual concentration of atmospheric CO2 since 1850. * * * * * * * * ozone layer A layer in the stratosphere containing a relatively high concentration of ozone. The ozone layer absorbs 97-99% of the suns high frequency ultraviolet light , light which is potentially damaging to life on earth. A number of consequences can result from increased levels of UV(ultraviolet radiation) striking the earth, including: genetic damage, eye damage and damage to marine life. Increased UV radiation in the troposphere, can result in increased amounts of photochemical smog. A false-color satellite image of the ozone hole over Antarctica on September 24, 2006. The chemistry of Ozone depletion Researchers now know that chlorine creates the hole by devouring ozone molecules. The source of the chlorine: human-made chemicals called chlorofluorocarbons (CFCs) that have been used in spray cans, foam packaging (such as fast-food containers), and refrigeration materials (fridge). CFCs react with atomic oxygen and ultraviolet light to form chlorine atoms, which catalyze the decomposition of ozone. CF2Cl2 + ultraviolet light → CF2Cl? + Cl? Cl? + O3 → ClO + O2 ?ClO + O → Cl? + O2 The last step results in the formation of another chlorine atom that can break down another molecule of ozone. The second and third steps are repeated many times; thus, the decomposition of one molecule of chlorofluorocarbon can result in the destruction of many molecules of ozone. Each different CFC is identified by a numbering system which describes the CFC structure. In the hundreds place, the number represents the number of carbons, less one. In the tens place the number represents the number of hydrogens, plus one. In the ones place the number represents the number of fluorines. For
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