Chlorofluorocarbons tropospheric concentration

Future changes in atmospheric concentration of other greenhouse gases (methane N2O, chlorofluorocarbons, tropospheric ozone). 

CO2, along with nitrous oxide, methane, chlorofluorocarbons, tropospheric ozone, and water vapor is a greenhouse gas. With the exception of water vapor, the concentration of all these gases is controlled more or less directly by human activities. CO2 is the most important greenhouse gas because it has an atmospheric life of about 100 years and therefore builds up in the atmosphere over long periods. While the preindustrial CO2 concentration was about 280 ppmv, its present concentration has increased 32% since preindustrial times to reach 370 ppmv today. Half of the increase has been since 1965 . 

Methane is removed continually from the atmosphere by reaction with OH radicals (Section 8.3). In contrast, chlorofluorocarbons and related volatile compounds are inert under the conditions of the lower atmosphere (troposphere), so atmospheric concentrations of these refrigerants and solvents will tend to increase as long as releases continue. The chief concern over chlorofluorocarbons is that they are a major factor in destruction of the stratospheric ozone layer (Section 8.3). They have been banned under the Montreal Protocol of 1988, but it is important that whatever substitutes (inevitably greenhouse active) are introduced to replace them degrade relatively quickly in the troposphere to minimize any contribution they may be capable of making to greenhouse warming. 

Estimates have been made of the annual emissions of HCl, HF, and SO2 from volcanic eruptions to the tropo- and strato-spheres. The results indicate that man-made chlorofluorocarbons are potentially more important in stratospheric chemistry than halides of volcanic origin. Lovelock has listed the concentration and concentration profiles of halocarbons in the troposphere and the lower stratosphere over the U.K. and the mid-Atlantic he has also estimated the total quantity of chloro-species transferred to the stratosphere by halocarbon sources. The interest in such materials, and especially in chlorofluorocarbons, e.g. CFCI3 and CF2CI2, used as propellants and refrigerants, is that they are photolysed to give chlorine atoms in the stratosphere the Cl then destroys ozone by reactions (part of the CIO cycle) such as (1). 

While ozone is a good molecule high in the stratosphere, its reviews in the lower troposphere are decidedly mixed. It is the source of minuscule concentrations of hydroxyl radical (OH, 10 molecules/ cm ). Hydroxyl is so extraordinarily active that it reacts with hydrocarbons (methane, benzene, etc) and most atmospheric compounds. Some extremely stable molecules, including chlorofluorocarbons like CFCI3 and CF2CI2 and N2O (nitrous oxide from fertihzers, a source of stratospheric NO), do not react with OH and migrate to the upper stratosphere (see chapter 8 for the consequences). 

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