Ozone stratospheric

The ozone balance in the stratosphere is determined through complex interactions of solar radiation, meteorological movements within the stratosphere, transport to and from the troposphere, and the concentration of species based on elements other than oxygen that enter the stratosphere by natural or artificial means (such as flight of aircraft). 

It is not difficult to see that ozone initially forms from the oxygen present in the air. Chapman [115] introduced the photochemical model of stratospheric ozone and suggested that the ozone mechanism depended on two photochemical and two chemical reactions  

Reactions (8.149) and (8.150) are the reactions by which the ozone is generated. Reactions (8.151) and (8.152) establish the balance, which is the ozone concentration in the troposphere. If one adds reactions (8.151) and (8.152), one obtains the overall rate of destruction of the ozone namely, 

The rates of reactions (8.149)—(8.152) vary with altitude. The rate constants of reactions (8.149) and (8.151) are determined by the solar flux at a given 

Only an excited singlet oxygen atom could react with water at stratospheric temperatures to form hydroxyl radicals. 

The stratospheric ozone layer is situated at an altitude of between 17 and 50 km. It contains 90 % of the ozone content of the Earth s atmosphere. Ozone absorbs the sun s UVB radiation (280-310 nm) this fact can be easily demonstrated in the laboratory. Stratospheric ozone is therefore of major importance as a protective screen for the Earth against the sun s radiations. Thus, in the Antarctic, at each austral spring, a sharp decrease in the total ozone layer is observed with respect to the value in the summer correlatively, a significant increase in the UVB radiation at ground level is observed. 

the UVB radiation is likely to have harmful effects on the health of human beings causing melanomas, cataracts, erythemas, by decreasing the effectiveness of the immune system and causing genetic mutations it also affects animals and plants and is a cause of the ageing of plastics, paints and varnishes. 

It is difficult to establish precise relationships on the one hand, between the total quantity of stratospheric ozone and the intensity of the UVB radiation which reaches the Earth s surface, and on the other hand, between the doses of UVB radiation and in particular the effects on human health. Nevertheless, there is an important and lasting decrease in the stratospheric ozone layer which is a subject of worry to planetary ecologists. 

Measurements of the local ozone concentration, at a given latitude and altitude, can be integrated to give the total concentrations at a given instant. These measurements are carried out from the Earth, using balloons, aeroplanes or satellites. 

But since the beginning of the 1980s, this seasonal phenomenon has worsened. More than 65 % of the ozone disappears in the spring over a surface of 20 million km, about 90 % of which is at an altitude of between 18 and 25 km. 

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Straight-run asphalts Straight run naphthas Strain gauges Strainmaster S. strain NRRL 15496 Stratosphere Stratospheric ozone... 

Perfluorinated ethers and perfluorinated tertiary amines do not contribute to the formation of ground level ozone and are exempt from VOC regulations (32). The commercial compounds discussed above have an ozone depletion potential of zero because they do not contain either chlorine or bromine which take part in catalytic cycles that destroy stratospheric ozone (33). 

Depletion of the Ozone Layer. As a constituent of the atmosphere, ozone forms a protective screen by absorbing radiation of wavelengths between 200 and 300 nm, which can damage DNA and be harmful to life. Consequently, a decrease in the stratospheric ozone concentration results in an increase in the uv radiation reaching the earth s surfaces, thus adversely affecting the climate as well as plant and animal life. Pot example, the incidence of skin cancer is related to the amount of exposure to uv radiation. 

Stratospheric Ozone Review Group, Stratospheric O ne 1993, HMSO Books, London, 1993. 

Because of the expanded scale and need to describe additional physical and chemical processes, the development of acid deposition and regional oxidant models has lagged behind that of urban-scale photochemical models. An additional step up in scale and complexity, the development of analytical models of pollutant dynamics in the stratosphere is also behind that of ground-level oxidant models, in part because of the central role of heterogeneous chemistry in the stratospheric ozone depletion problem. In general, atmospheric Hquid-phase chemistry and especially heterogeneous chemistry are less well understood than gas-phase reactions such as those that dorninate the formation of ozone in urban areas. Development of three-dimensional models that treat both the dynamics and chemistry of the stratosphere in detail is an ongoing research problem. 

The demand for trichloroethylene grew steadily until 1970. Since that time trichloroethylene has been a less desirable solvent because of restrictions on emissions under air pollution legislation and the passage of the Occupational Safety and Health Act. Whereas previously the principal use of trichloroethylene was for vapor degreasing, currentiy 1,1,1-trichloroethane is the most used solvent for vapor degreasing. The restrictions on production of 1,1,1-trichloroethane [71-55-6] from the 1990 Amendments to the Montreal Protocol on substances that deplete the stratospheric ozone and the U.S. 

Trichloroethylene is being evaluated by the industry as a precursor in the production of hydrochlorofluorocarbons (HCEC), the replacement products for the chlorofluorocarbons impHcated in the depletion of the stratospheric ozone. At this time it is too early to project any estimates or probabihties for potential volume changes as a result of this opportunity (23). 

Chlorofluoro- Used in refrigeration and production of Refrigeration, plastic foam production, Attacks stratospheric ozone layer green-... 

The other global environmental problem, stratospheric ozone depletion, was less controversial and more imminent. The U.S. Senate Committee Report supporting the Clean Air Act Amendments of 1990 states, Destruction of the ozone layer is caused primarily by the release into the atmosphere of chlorofluorocarbons (CFCs) and similar manufactured substances—persistent chemicals that rise into the stratosphere where they catalyze the destruction of stratospheric ozone. A decrease in stratospheric ozone will allow more ultraviolet (UV) radiation to reach Earth, resulting in increased rates of disease in humans, including increased incidence of skin cancer, cataracts, and, potentially, suppression of the immune system. Increased UV radiation has also been shown to damage crops and marine resources."... 

Stratospheric ozone is in a dynamic equilibrium with a balance between the chemical processes of formation and destruchon. The primary components in this balance are ultraviolet (UV) solar radiation, oxygen molecules (O2), and oxygen atoms (O) and may be represented by the following reactions ... 

The discovery of ozone holes over Antarctica in the mid-1980s was strong observational evidence to support the Rowland and Molina hypothesis. The atmosphere over the south pole is complex because of the long periods of total darkness and sunlight and the presence of a polar vortex and polar stratospheric clouds. However, researchers have found evidence to support the role of CIO in the rapid depletion of stratospheric ozone over the south pole. Figure 11-3 shows the profile of ozone and CIO measured at an altitude of 18 km on an aircraft flight from southern Chile toward the south pole on September 21, 1987. One month earlier the ozone levels were fairly uniform around 2 ppm (vol). 

Fig. 11-3. Stratospheric ozone and CIO concentrations at an altitude of 18 km measured by aircraft flying south over Antarctica on September 27,1987. The dramatic decrease in ozone at a latitude of 71 degrees is attributed to the role of CIO in catalytic destruction of ozone. Adapted from Anderson et al. (13).

An important effect of air pollution on the atmosphere is change in spectral transmission. The spectral regions of greatest concern are the ultraviolet and the visible. Changes in ultraviolet radiation have demonstrable adverse effects e.g., a decrease in the stratospheric ozone layer permits harmful UV radiation to penetrate to the surface of the earth. Excessive exposure to UV radiation results in increases in skin cancer and cataracts. The worldwide effort to reduce the release of stratospheric ozone-depleting chemicals such as chlorofluorocarbons is directed toward reducing this increased risk of skin cancer and cataracts for future generations. 

The EPA summary (4) for stratospheric ozone and global climate protection lists the basics of the title ... 

Title VI Stratospheric Ozone and Global Climate Protection - The law builds on the market-based structure and requirements currently contained in EPA s regulations to phase out the production of substances that deplete the ozone layer. 

Title VI - Stratospheric Ozone and Global Climate Title VII - Provisions Relating to Enforcement... 

Chlororocarbon (CFG) refrigerants are inherently safer with respect to fire, explosion, and acute toxic hazards when compared to alternative refrigerants such as ammonia, propane, and sulfur dioxide. However, they are believed to cause long term environmental damage because of stratospheric ozone depletion. 

Deals with issues that affect the quality of our air and protection from exposure to harmful radiation. OAR de >el-ops national programs, technical policies, and regulations for controlling air pollution and radiation exposure. Areas of concern to OAR include indoor and outdoor air quality, stationaiy and mobile sources of air pollution, radon, acid rain, stratospheric ozone depletion, radiation protection, and pollution prevention. 

Problems that rank relatively high in duee of the four typos, or at least medium in all four, include criteria air pollutiuits, stratospheric ozone depletion, pesticide residues on food, and other pesticide risks (runoff and air deposition of pesticides)... 

The decrease is continuing due to global adherence to the provisions of the Montreal (1989) and London (1990) Protocols, and it is hoped that the most deleterious CFCs will eventually be phased out completely. As a result of their work, Rowland and Molina were awarded the Nobel Prize for Chemistry for 1995 (together with P. Crutzen, who showed how NO and NO2 could similarly act as catalysts for the depletion of stratospheric ozone). Several excellent accounts giving more details of the chemistry and meteorology involved are available. 

Ozone has received increased attention for its occurrence and function in the Earth s atmosphere.For example the decreasing ozone concentration in the stratospheric ozone layer, becoming most obvious with the Antarctic ozone hole. 

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