Depletion of ozone

Measurements of ozone (O3) concentrations in the atmosphere are of particular importance. Ozone absorbs strongly in the ultraviolet region and it is this absorption which protects us from a dangerously high dose of ultraviolet radiation from the sun. The vitally important ozone layer lies in the stratosphere and is typically about 10 km thick with a maximum concentration about 25 km above the surface of the earth. Extreme depletion of ozone in a localised part of the atmosphere creates what is known as an ozone hole. 

A smaller factor in ozone depletion is the rising levels of N2O in the atmosphere from combustion and the use of nitrogen-rich fertilizers, since they ate the sources of NO in the stratosphere that can destroy ozone catalyticaHy. Another concern in the depletion of ozone layer, under study by the National Aeronautics and Space Administration (NASA), is a proposed fleet of supersonic aircraft that can inject additional nitrogen oxides, as weU as sulfur dioxide and moisture, into the stratosphere via their exhaust gases (155). Although sulfate aerosols can suppress the amount of nitrogen oxides in the stratosphere... 

J. C. Farman discovered the ozone hole (substantial seasonal depletion of ozone) over Halley Bay, Antarctica. 

Thus, the mean temperature of the atmosphere, which is about 20°C at sea level, falls steadily to about —55° at an altitude of 10 km and then rises to almost 0°C at 50 km before dropping steadily again to about —90° at 90 km. Concern was expressed in 1974 that interaction of ozone with man-made chlorofluorocarbons would deplete the equilibrium concentration of ozone with potentially disastrous consequences, and this was dramatically confirmed by the discovery of a seasonally recurring ozone hole above Antarctica in 1985. A less prominent ozone hole was subsequently detected above the Arctic Ocean. The detailed physical and chemical conditions required to generate these large seasonal depletions of ozone are extremely complex but the main features have now been elucidated (see p. 848). Several accounts of various aspects of the emerging story, and of the consequent international governmental actions to... 

The CIO radical in particular is implicated in environmentally sensitive reactions which lead to depletion of ozone and oxygen atoms in the... 

Several authors (8,9) suggested that PSCs could play a major role in the depletion of ozone over Antarctica by promoting the release of active chlorine from its reservoir species, mainly by the following reaction ... 

The catalytic cycle described earlier (reactions 8 and 9) cannot explain the rapid depletion of ozone over the South Pole, because reaction 9 requires free oxygen atoms, which are too scarce in the polar stratosphere to react at any appreciable rate with QO. Several catalytic cycles that do not require oxygen atoms have been suggested as being at work over Antarctica. 

Nitrous oxide (N2O) is an important greenhonse gas with a radiative forcing effect 310 times that of CO2 and a lifetime in the troposphere of approximately 120 years. Part of the N2O is converted to NO in the stratosphere, and so contributes to depletion of ozone. Nitric oxide (NO) is very reactive in the atmosphere and has a lifetime of only 1-10 days. It contribntes to acidification and to reactions leading to the formation of ozone in the troposphere, and so also to global warming. 

Nitrous oxide contributes severely to global warming and the depletion of ozone in the stratosphere (Crutzen 1981, Bouwman 1996). Almost 90% of the global atmospheric N2O is formed during the microbial transformation of nitrate (NO ) and ammonia (NH ) in soils and water. In OECD countries the agricultural contribution to N2O emissions is estimated at 58% (IPCC 2001). Soils fertilised with inorganic fertilisers and manure stores are seen as the largest sources (Chadwick et al. 1999, Brown ef al. 2002). 

In connection with the study of the role Freon compounds play in the depletion of ozone in the atmosphere, a demand has arisen for 13C-labeled fluorinated hydrocarbons in infrared spectroscopic examination. For this purpose,13C-isotopically enriched trichlorofluoromethane, dichlorodifluoromethane, chlorotrifluoromethane, trifluoromethane, chlorodifluoromethane, and dichlorofluoromethane have been prepared from 13CC 4 and 13CHC13.73... 

In waste water ozonation experiments with high concentrations of (highly reactive) contaminants it is recommended that the ratio of QG to VL not be too low, i. e. the liquid volume not be too large (VL= 1-5 L) and an appropriate ozone generator be used. This is important because of the high reaction rates which may be achieved and which may cause a total depletion of ozone in the off-gas, causing problems in balancing the ozone consumption in the systems. 

In the presence of ozone in water, ozone diffuses through the membrane into the reaction chamber. The rate of flow is dependent on the partial pressure of ozone. In order to avoid a depletion of ozone molecules at the surface of the membrane, the electrode should be immersed into a continuous flow. 

The depletion of ozone in the stratosphere can be summarized by the net equation 2 03(g) - 3 02(g). (a) From values in Appendix 2A, calculate the standard reaction free energy and the standard reaction entropy for the reaction, (b) What is the equilibrium constant of the reaction at 25°C What is the significance of your answers with regard to ozone depletion ... 

The significant depletion of ozone, near-global in extent, which has been observed in recent years has raised concern primarily because of its direct effect of allowing more harmful solar ultraviolet radiation to penetrate to the Earth s surface. However, through its effect on the atmospheric temperature structure, it is possible that the effects of ozone depletion could be far more wide-ranging. 

The ozone layer around the Earth has provided us all a natural ring of protection from harmful UV radiation. However, multiple anthropogenic activities have acted as barriers and often caused damage to this shield. Less protection from UV light will, over time, lead to increased health problems and crop damage. Major health problems linked to overexposure to UV radiation by the depletion of ozone include skin cancer (melanoma and nonmelanoma), premature aging of the skin and other skin problems, cataracts and other eye damage, and suppression of normal immune system function.29... 

Prepare a concept map to explain the depletion of ozone in the atmosphere. Include details on the different chemicals responsible. Also, make sure you include information on how this depletion occurs. 

Figure 29 shows a recent picture of the ozone hole taken from space. Strictly speaking the use of the word hole to describe what happens to ozone in the Antarctic is an exaggeration. There is undoubtedly a massive depletion of ozone, particularly between 12 and 20 km in the Antarctic stratosphere (up to 100%) but the total column of ozone is depleted rather than removed altogether (see Figure 28). The exact location and size of the hole varies with meteorological conditions, but the area covered has increased over the past 10 years or so (see Figure 30). Currently, in the austral spring the hole extends over the entire Antarctic continent, occasionally including the tip of South America, covering an area equivalent to the North American continent (ca. 22 million km ) (see Figure 31).

Oxidizer Chemical substance that causes oxygen to combine with another chemical substance examples include oxygen and hydrogen peroxide Ozone depletion Destruction of the stratospheric ozone layer that protects the Earth from harmful effects of ultraviolet radiation. Depletion of ozone layer is due to the breakdown of certain chlorine- and/or bromine-containing compounds (chlorofluorocarbons or halons), which break down when they reach the stratosphere and then catalytically destroy ozone molecules Ozone layer Protective layer in the atmosphere, about 15 miles above the ground. The ozone layer absorbs some of the sun s ultraviolet rays, thereby reducing the amount of potentially harmful radiation that reaches the Earth s surface PAHs Polycyclic aromatic hydrocarbons... 

The movement of atmospheric constituents within a region and between regions is a key process in atmospheric chemistry. For example, the transport of chemicals from the troposphere to the stratosphere sets off the depletion of ozone. Conversely, the downward transport from the stratosphere increases ozone in the troposphere. The phenomenon that most distinguishes the troposphere from the stratosphere is the rate of vertical mixing. The time scale for the vertical transport of air and other chemical species in the troposphere can be of a few hours, whereas vertical transport in the stratosphere can last months or years. 

These catalytic cycles are largely responsible for the depletion of ozone. One chlorine atom may destroy more than 100,000 ozone molecules before it is transformed into a non-reactive species. Despite the substantial reduction of chlorine and bromine compounds released into the atmosphere as a result of the Montreal Protocol, this has not shown any significant impact on the reduction of the size of the ozone hole. If such a trend continues, it may still take some half a century for the recovery of ozone to the levels it had prior to 1984. 

In the upper atmosphere the presence of nitric oxide has the opposite effect—the depletion of ozone. The series of reactions involved is... 

All of the trace species discussed in this paper (CChF, CCI2F2, CCIa, CH3CCI3, CHa) are increasing in concentration in the atmosphere, primarily because of increasing use by man. Further increases in these and other trace chemical species will certainly occur in the coming decade and for the foreseeable future. These increases are connected with potentially important alterations of the environment through depletion of ozone at... 

The comparison that Jim showed between 1979 and 1981, the depletion of ozone at the altitude of around 40 kilometers was almost unchanged, that down around 20 kilometers one has the change from a substantial loss to an appreciable gain of ozone. One then has to ask why one is worried about a... 

Although Rowland and Molina had predicted depletion of ozone concentrations by these reactions, there were many who doubted their conclusions. The phenomenon that finally brought the problem to the attention of the world was the discovery of the ozone hole over the Antarctic in 1985. During the winter, a combination of air flow pattern and low temperature create stratospheric clouds of ice particles. The surface of these particles is an ideal location for reaction of NO2, OCl, and O3. These clouds contain nitric acid hydrate, formed by... 

Recent data from both ground-based and satellite measurements indicate that after decades of continual increase, concentrations of chlorine in the stratosphere are starting to plateau. The concentrations of bromide, however are continuing to increase and the depletion of ozone as a result of halides has been as great as 30% over the last decade. However, if halide and CFC concentrations continue to fall as directed by the Montreal Protocol, computer models predict that Antartic ozone concentrations should begin to increase in 2010. 

A model can he tested and used to make predictions. Mohna and Rowland s model predicted the formation of chlorine and the depletion of ozone, as shown in Figure 1-13. Another research group found evidence of interactions between ozone and chlorine when taking measurements in the stratosphere, but they did not know the source of the chlorine. Mohna and Rowland s model predicted a source of the chlorine. They came to the conclusion that ozone in the stratosphere could he destroyed by CFCs and that they had enough support for their hypothesis to publish their discovery. 

When the ozone hole was reported in 1985, scientists had made measurements of CFC levels in the stratosphere that supported the hypothesis that CFCs could be responsible for the depletion of ozone. The pure research done only for the sake of knowledge became applied research. Applied research is research undertaken to solve a specific problem. Scientists continue to monitor the amount of CFCs in the atmosphere and the annual changes in the amount of ozone in the stratosphere. Applied research also is being done to find replacement chemicals for the CFCs that are now banned. Read the Chemistry and Society feature at the end of this chapter to learn about research into the human genome. What type of research does it describe ... 

Because Cl atoms speed up the depletion of ozone and are first used and then re-formed, they function as a catalyst. The net result of these reactions is the conversion of ozone into O2. 

REGULATION OF CFCs PRODUCTION Depletion of Ozone Layer... 

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