Ozone-depletion problem

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. 

Volatilization of a low-boiling liquid, either by the heat liberated by an exothermic reaction, or by externally applied heat. Commonly used liquids are chlorofluoro-carbons (CFCs). This is the most widely used technique in the production of rigid polyurethane foams. However, due to the ozone depletion problem in the stratosphere, they must be phased out and industry is presently searching for alternative blowing agents. 

Fluorine chemistry in the stratosphere has also been considered and attention has been drawn to the atmospheric chemistry of the FOx radicals. The compounds with O-F bonds have gained interest in connection with the ozone depletion problem. It has been suggested that FO and F02 radicals formed in the atmospheric degradation of hydrofluorocarbons (HFCs) could destroy ozone in chain reaction processes. Experimental studies of this hypothesis led to the conclusion that catalytic cycles involving F, FO, and F02 are irrelevant with respect to the chlorine cycle.8 However, kinetic investigations of the reactions of fluorine atoms with 02 and NOx provide useful information on the fluorine chemistry in the polluted atmosphere. 

Awareness of the ozone depletion problem was reflected by signing in 1987 of the Montreal Protocol on substances that deplete the ozone layer . This international treaty initially set targets for CFC production to be cutback to 1986 baseline levels by mid-1989, cut to 80%ofbaselineby 1993, and to 50% of baseline by 1998. Subsequent information suggested that these cuts in CFC production would be insufficient to prevent substantial loss of stratospheric ozone over the first half of the 2T century. Consequently, amendments have been made to strengthen the original terms of the Montreal Protocol, so that a complete phase-out of the hard CFCs such as CFC-11 and CFC-12 (Figure 6) will be effected. 

This solution is based upon that presented by Sinha and co-workers (1999). A set of 12 molecular groups is selected upon which the search for solvent molecules is based. These are CHj—, —CH2—, Ar— (CgHj—), Ai= (QH4=), —oh, CH3CO—, —CHjCO—, —COOH, CH3COO—, —CHjCOO-, —CH3O, and —CHjO—. Note that chlorine is omitted to avoid ozone-depletion problems. 

In contrast to the paucity of action concerning the CO2 problem, appreciable headway has been made in combatting the ozone depletion problem. Most industrial nations that produce CFCs have agreed to curb production and examine substitute chemicals. Such action will take time, however, and the depletion of ozone corrtinues to be of concern. Atmospheric scientists researching the problem are now examining the dynamics that cause holes that periodically occur in the polar ozone layers. 

In response to the ozone depletion problem, chemists began looking for replacement refrigerants that didn t affect ozone. Substitutes were found and the environmental problem lessened. 

In the mid-1980s, a serious problem with ozone depletion became apparent. A springtime decrease in the concentration of stratospheric ozone (ozone holes) was observed at high latitudes, most notably over Antarctica between September and November. Scientists strongly suspected that chlorine atoms or simple chlorine compounds may be playing a key role in this ozone depletion problem. 

The CFC-ozone depletion problem has demonstrated that humankind is capable of seriously modifying the atmosphere on a global scale, it has also shown us that in... 

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."... 

The more common requirement to control routine disposal and dispersion of solid, liquid or gaseous pollutants is based upon different criteria, e.g. their persistence in the environment (as with the effects attributed to ozone-depleting gases, or the problem of heavy metal contamination... 

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)... 

Certainly, photochemical air pollution is not merely a local problem. Indeed, spread of anthropogenic smog plumes away from urban centers results in regional scale oxidant problems, such as found in the NE United States and many southern States. Ozone production has also been connected with biomass burning in the tropics (79,80,81). Transport of large-scale tropospheric ozone plumes over large distances has been documented from satellite measurements of total atmospheric ozone (82,83,84), originally taken to study stratospheric ozone depletion. 

Effect of UV on Productivity of the Southern Ocean. Has ozone depletion over Antarctica affected the productivity of the Southern Ocean There is no easy answer. First, one has to take into account the fact that the drastic decrease of ozone over Antarctica has been reported as recently as 1976, a relatively short time in the evolution of the organisms to develop mechanisms to cope with elevated UV. One of the most vexing problems in studying the effects of UV radiation on productivity, is a dearth of historical data on the level of UV. Without these baselines, normal fluctuations could easily be interpreted as decline in productivity. Second, there is a host of biotic and abiotic factors that play significant roles in governing the productivity of the Southern Ocean (40). Ultraviolet radiation is but one more complicating factor to be considered in an already stressful environment. 

Recently, there have also been some concerns over possible problems related to hydrogen gas leakage as the molecular hydrogen leaks from most containment vessels. It has been hypothesized that if significant amounts of H2 escape to stratosphere, FT free radicals can be formed due to ultraviolet radiation, which in turn can enhance the ozone depletion. However, the effect of these leakage problems may not be significant as the amount of hydrogen that leaks presently is much lower (by a factor of 10-100) than the hypothesized 10-20%. 

Ozone bleaching technology, 21 46 for recycled pulps, 21 51-52 Ozone contactors/dispersion devices, 17 801-802 Ozone decomposition in acidic solution, 17 773 hydroxyl ion initiated, 17 771—772 Ozone deficit problem, 17 785 Ozone delignification technology, 21 46 Ozone-depleting substances, in release agents, 21 598... 

The history of ozone depletion took a dramatic turn in 1985 when J. C. Farman at the BAS Halley Bay station announced that ozone levels over the Antarctic had decreased by more than 40 percent between 1977 and 1984. Farman explained that ozone levels had fallen so low that one could say that a "hole had formed in the ozone layer above the South Pole. In 1984, that "hole covered an area of more than 15 million square miles (40 million square kilometers), equal to the size of the continental United States. Clearly, ozone depletion was not a long-term problem about which scientists could debate for the next century or so. It was an issue that demanded quick attention and action. 

What does seem to be clear is that without the international agreements reached in Montreal, London, and Copenhagen, the problem of ozone depletion would probably have been much worse than it is today. The graph on page 79 shows the trends in ozone depletion (as measured by the concentration of chlorine in the stratosphere) that would have been seen in the absence of no agreement at all, with the Montreal Protocol alone, and with later amendments to that agreement. 

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