Montreal Protocol stratospheric ozone

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. 

In the last decade, the refrigerant issue is extensively discussed due to the accepted hypothesis that the chlorine and bromine atoms from halocarbons released to the environment were using up ozone in the stratosphere, depleting it specially above the polar regions. Montreal Protocol and later agreements ban use of certain CFCs and halon compounds. It seems that all CFCs and most of the HCFCs will be out of produc tion by the time this text will be pubhshed. 

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. 

Recognition of the threat of stratospheric ozone depletion posed by chlorofluorocarbons and chloro-fltiorohydrocarbons led 131 countries to sign the Montreal Protocol in 1987. Production of chlorofluorocarbons was banned as of January 1, 1996, because of their potential to further deplete stratospheric ozone. Chlorofluorohydrocarboiis will be... 

An additional area of concern with respect to stratospheric ozone is possible direct emissions of NOj into the stratosphere by high-flying supersonic aircraft. This issue has come up repeatedly over the past 20 years, as air travel and pressure from commercial airlines has increased. However, despite substantial research effort to understand stratospheric chemistry, the question is complicated by the changing levels of stratospheric chlorine, first due to a rapid accumulation of tropospheric CFCs, followed by a rapid decline in CFC emissions due to the Montreal Protocol. To quote from the from the 1994 WMO/UN Scientific assessment of ozone depletion, executive summary (WMO 1995) ... 

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. 

While the growth in stratospheric chlorine should clearly be slowed by the Montreal Protocol agreements, it was still substantial and expected to lead to quite large losses of ozone. This recognition, bolstered by the dramatic appearance of the Antarctic ozone hole, led to further major amendments to the Montreal Protocol. 

As discussed in more detail in this chapter, detecting trends in stratospheric ozone and deconvoluting the causes are complex, particularly outside the polar regions. However, it is estimated that for the Antarctic, where the most dramatic loss of ozone has been observed, recovery may be experimentally observable by the year 2008 if the Montreal Protocol and associated amendments are followed (e.g., Hofmann et al., 1994). 

In short, the trends in the tropospheric concentrations of CFCs, halons, and their substitutes follow trends in their emissions. The effects of the controls imposed by the Montreal Protocol and its subsequent amendments are evident in the trends and have been used to show that the associated impact on ozone destruction is expected to begin about the turn of the century. The following section briefly describes the observed trends in stratospheric ozone. 

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. 

CFCs) and halons over the next decade, as mandated by the Montreal Protocol for the Protection of the Ozone Layer, will affect the chlorine burden of the stratosphere. Hydrochlorofluorocarbons (HCFCs) can be used as substitutes for the CFCs for a few decades without having a substantial impact on the chlorine burden of the stratosphere because they are primarily destroyed in the troposphere by reactions with OH before they are able to deliver the chlorine to the stratosphere. The elimination of CFCs and the temporary use of HCFCs into the early part of the next century must be carefully orchestrated to minimize the peak chlorine loading and promote the most rapid reduction of the chlorine burden of the stratosphere (56, 87). Another issue is the effects that perturbations to the reactive nitrogen abundances will have on the abundances of reactive chlorine. A better understanding and clarification of the direct heterogeneous conversions of chlorine species on both PSCs and sulfate aerosols are also needed. 

Montreal protocol Treaty signed in 1987 that governs stratospheric ozone protection and research, and the production and use of ozone-depleting substances. It provides for the end of production of ozone-depleting substances such as CFCS. Under the protocol, various research groups continue to assess the ozone layer. The multilateral fund provides resources to developing nations to promote the transition to ozone-safe technologies. 

The Montreal Protocol on Substances that Deplete the Ozone Layer requires each signatory nation to reduce its production and consumption of the CFCs 11, 12, 113, 114 and 115 to 80% of their 1986 levels by 1993 and to 50% by 1998. Figure 8 shows that production levels of the first three of these has indeed fallen dramatically since 1988, according to data reported in Reference 109 by the major industrial producers. However, the Montreal measures will have little effect on the current levels of stratospheric CFCs, which would still continue to rise for many years, as illustrated by Figure 9 for the example of CFC-12. It would be necessary to impose an 85% reduction in order to stabilize atmospheric concentrations at their 1989 level110. Even with a total cessation of CFC emission atmospheric concentrations will not be restored to their pre-1960 levels until well... 

By blending CFCs, it is possible to achieve appropriate vapor pressure, solvency and liquid density. However, CFCs have been linked with the depletion of the stratospheric ozone layer and will be phased out in accordance with the Montreal Protocol on Substances that Deplete the Ozone Layer . Current substitutes are the hydrofluoroalkanes (HFAs), e.g. 1,1,1,2-tetrafluoroethane (HFA-134a) and 1,1,2,3,3,3-heptafluoropropane (HFA 227) (Table 10.3). 

Title VI Stratospheric Ozone Protection Title VI of the 1990 Clean Air Act Amendments established a program to implement the provisions of the Montreal Protocol, a worldwide agreement to reduce the use and emission of ozone-depleting substances. EPA s regulations adopted in response to Title VI outline a series of requirements for facilities that use equipment containing ODS compounds. Facilities must be certain that they handle and manage ODS compounds as prescribed in the rules. Only certified technicians and staff may maintain... 

Under the agreements of the Montreal Protocol on Substances that Deplete the Ozone Layer, the production of chlorofluorocarbons (CFCs), halons and several other halocarbons has been prohibited [1,2]. Consequently, there is an interest in replacing these compounds [3]. As part of the development of such replacing compounds, it is necessary to consider and evaluate the potential environmental effects of their use, especially on stratospheric ozone [2],... 

Bromine-containing compounds have the potential to released Br atoms upon degradation in the atmosphere. Once in the stratosphere, Br atoms are about 45 times more effective than chlorine in destroying stratospheric ozone [22]. An important example of Br-containing compounds is 1-bromopropane, which is currently utilized as a industrial solvent and have been proposed as a replacement for CFCs, controlled under the agreements of fhe Montreal Protocol. 

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