Ozone chlorofluorocarbons, role

Evidence that many of these compounds can have adverse effects on the immune, endocrine and nervous systems and that some are carcinogenic has grown during the last decade. The role of chlorofluorocarbons (CFCs) and of methyl bromide in the ozone layer depletion is well established (ref. 3).It is therefore not surprising that many halogenated derivatives are cast as environmental and health villains by various concerned groups who call for total phase out of chlorine and chlorinated hydrocarbons. 

F. S. Rowland, Chlorofluorocarbons and the depletion of stratospheric ozone Am. Sci. 77, 36-45 (1989) T.-L. Tso, L. T. Molina, and F. C.-Y. Wang, Antarctic stratospheric chemistry of chlorine nitrate, hydrogen chloride and ice release of active chlorine. Science 238, 1253-1260 (1987) J. G- Anderson, D. W. Toohey, and W. H. Brune, Free radicals within the Antarctic vortex the role of CFCs in Antarctic ozone loss. Science 251, 39-46 (1991) P. S. Zurer, Complexities of ozone loss continue to challenge scientists. Chem. Eng. News June 12, 20-23 (1995). 

What role do chlorofluorocarbons play in the catalytic destruction of ozone ... 

Another important mutagen is ultraviolet light. Recent concern about the depletion of the atmospheric ozone layer by chlorofluorocarbon compounds (CFCs) is due to the role of the ozone in absorbing UV radiation before it can cause mutations in the organisms at the earth s surface. All the DNA bases efficiently absorb UV and become chemically reactive as a result. The formation of pyrimidine dimers from adjacent thymidine residues in DNA interferes with replication and transcription of DNA. See Figure 8-14. 

The radiatively active trace gases, which contribute most to atmospheric absorption, and hence play a key role in the energy budget of the middle atmosphere, are carbon dioxide, ozone, and water vapor. Other gases, whose sources are partly related to anthropogenic activity (such as CH4, N2O, and chlorofluorocarbons) also contribute to the radiation budget. 

This chapter has outlined the history and conceptual understanding of the processes responsible for ozone depletion by chlorofluorocarbons in the stratosphere. In brief, the long lifetimes of chlorofluorocarbons are reflected in their observed worldwide accumulation in the atmosphere. Their role in stratospheric ozone depletion depends critically on... 

The first step in the production of ozone, the photolysis of molecular oxygen [reaction (1)], is rate limiting. While ozone production is slow, there are chemical reactions that can rapidly destroy it. One of the major species that is efficient in the removal of ozone is chlorine. The role of chlorine species in the depletion of ozone has been investigated actively since 1974, when Rowland and Molina [2] drew attention to the potential impact of human-made materials known as chlorofluorocarbons (CFCs) on ozone produced in the stratosphere. Chlorofluorocarbons are widely used in our daily life as refrigerants, aerosol propellants, cleaning solvents, and in fire-extinguishing applications. CFCs are stable, chemically inert, and have low toxicity. These properties make CFCs ideal for many applications and account for their wide use. However, the release of chlorine from the photodissociation of chlorofluorocarbons poses a central threat to ozone produced in the stratosphere ... 

Ozone plays important roles in atmospheric chemistry and physics. Up to 5 x 10 molecules cm or 4-5 ppmv (10 mixing ratio by volume) of ozone is found in the stratosphere where the solar radiation intensity of shorter wavelengths is high. Ozone in the stratosphere has made it possible for animals to live on land by preventing harmful 200-300 nm UV radiation from reaching the Earth s surface. The absorption of UV radiation by ozone, however, heats the air, disturbing air convection and creating a layered structure in the stratosphere. As some useful and stable chemicals like chlorofluorocarbons (Fre-ons) and other substances were found to decompose in the stratospheric environment and to destroy the... 

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