Stratosphere ozone layer degradation

The Stratospheric Ozone Layer Its Photochemical Formation and Degradation... 

Due to its gaseous nature it may have an effect on the stratospheric ozone layer [281, 402, 404]. After injection into soil for fumigation, methyl bromide rapidly diffuses through the soil pore space to the soil surface and then into the atmosphere [159,162,163,405,406]. Since a plastic sheet typically covers the soil surface, the rate of emission into the atmosphere depends upon the thickness and density of the plastic, if other conditions are the same [159, 406]. Other routes of disappearance from soil include chemical hydrolysis, methylation to soil organic matter through free radical reactions, and microbial degradation [ 136,159,405,407]. Several reports appeared on the study of the microbial transformations of methyl bromide, summarized as follows ... 

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. 

While this type of experiment has never been reported, it can provide unique and useful information. For instance, it can be useful in determining the effects of slightly increased levels of UV radiation in sunlight on its potential for increased polymer photodegradation. Levels of UV-B in terrestrial sunlight are expected to increase as a result of the partial depletion of the stratospheric ozone layer. The effect of this spectrally altered, UV-B-rich sunlight on polymer degradation can also be ascertained from activation spectra, subject to several assumptions mentioned earlier. 

Photochemical stability also can play an important role in solvent selection. Ethers are for instance easily attacked by UV light, to form in the presence of oxygen explosive peroxides a well-known industrial hazard. Fully halogenated solvents are on the other hand so stable, that, once evaporated, they remain a long time in the atmosphere without being degraded by sunlight. In this way they indirectly, finally affect the stratosphere ozone layer around the earth. 

Depletion of Stratospheric Ozone Layer from Photochemical Degradation... 

Because of their extreme stability against all kinds of aggressive chemical agent, for example radicals, perfluorocarbons and halofluorocarbons are not degraded in the lower layers of the atmosphere as are other pollutants. After several years, or even decades, they finally reach the stratosphere at altitudes of 20 to 40 km [26, 27]. In this layer, under the influence of short-wave UV irradiation, ozone is formed continuously (Scheme 1.2). This stratospheric ozone plays an essential role in preserving life on earth by absorbing the short-wavelength UV which would otherwise lead to an increase of photochemically induced mutations in most life-forms. For humans, over-exposure to short-wave UV irradiation results in a dramatically increased risk of skin cancer. Many crops and other plants also react rather sensitively towards an increase of UV exposure. 

Due to the volatility of the linear VMS fluids, the most likely route for environmental exposure is through evaporation. These fluids degrade quickly via ongoing natural photo-oxidation and have an atmospheric half-life of just 4-9 days (3-5). Ultimate degradation products include water-dissolved silica, water, and carbon dioxide, all abundant, naturally occurring, benign compounds. Because VMS fluids are rapidly and effectively oxidized before reaching the stratosphere, they are believed to have no impact on the earth s protective ozone layer and... 

---