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1960 1980 2000 2020 2040 2060 2080 2100 Year

FIGURE 13.1 Estimated equivalent effective stratospheric chlorine for a continued 3% growth per year, for controls contained in the Montreal Protocol, and for those in the Copenhagen amendments (adapted from World Meteorological Organization, 1995).

surface reach the stratosphere, in addition, the effectiveness of compounds in destroying stratospheric ozone depends on how readily they dissociate to form chlorine or bromine. As discussed in Chapter 12.D, bromine contributes significantly to ozone destruction as well and, indeed, is more efficient than chlorine under the current atmospheric conditions by about a factor of 60 (World Meteorological Organization, 1999). The contribution of bromine can be translated into equivalent chlorine by taking this increased efficiency into account. The net effect of chlorine and bromine is then expressed as "equivalent effective stratospheric chlorine" and it is this quantity that is shown in Fig. 13.f.

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.

The Montreal Protocol was first modified in June f990 in what is known as the London Amendments. These amendments speeded up the phaseout of CFCs and halons to 50% by 1995, 85% by 1997, and 100% by 2000, or 2010 for the developing countries (e.g., see Chatterjee, 1995; and Parson and Greene, 1995). Carbon tetrachloride was to be fully phased out by 2000 and methylchloroform (CH3CC13) by 2005. Included in the controls were a variety of additional CFCs, including CFC-13, -111, -112, -211, -212, -213, -214, -215, -216, and -217, not covered in the original protocol. A non-

binding portion of the agreement included phasing out the interim replacement compounds for CFCs, the HCFCs (hydrochlorofluorocarbons), with a target date of 2020, but not later than 2040. (See International Legal Materials, 1991, for details.)

A further amendment was subsequently signed in November f992 in Copenhagen. This speeded up the complete phaseout of CFCs, CC14, and CH3CC13 to 1996 and the halons from 2000 to 1994. The phaseout target for developing nations continued to be the year 2010. The HCFCs were to be reduced by 35% by 2004, 65% by 2010, 90% by 2015, and 99.5% by 2020, with full phaseout by 2030. Starting in 1995, the production of methyl bromide in developed countries was held at 1991 levels. In mid-July 1994, most countries had agreed to the restrictions; approximately 40 countries, with ~6% of the world's population, had not agreed to the controls (Holmes and Ellis, 1996).

Figure 13.1 also shows the estimated equivalent effective stratospheric chlorine content as a function of year under the Copenhagen Amendments. Chlorine is expected to peak around the year 2000 and then decrease. As discussed by Holmes and Ellis (1996), noncompliance and allowed exemptions could lead to a much slower decline than projected in Fig. 13.1.

In November 1995, it was agreed that CH3Br usage would be eliminated by 2010 in developed countries; in developing countries, its use is frozen in the year 2002 at the average 1995—1998 levels. Furthermore, HCFCs would be phased out in developed countries by 2020, with some production allowed until 2030 for application in existing refrigeration and air conditioning units. In developing countries, the use of HCFCs will be frozen at 20f5 levels in the year 2016, with complete elimination by 2040 (Zurer, 1995).

Figure 13.2 summarizes these international agreements for developed countries through ~ f995 (Parson and Greene, 1995). in September 1997, it was agreed that the use of methyl bromide by developed countries would end earlier, in 2005, and in developing countries by 2015 (Spurgeon, 1997a). In addition, steps to try to reduce smuggling of CFCs, which had become a problem (Spurgeon, 1997b), were taken.

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).

When first developed as refrigerants in 1928 by the DuPont chemists Midgley and Henne (1930), CFCs appeared to have ideal properties for this application

1960 1980 2000 2020 2040 2060 2080 2100 Year

FIGURE 13.1 Estimated equivalent effective stratospheric chlorine for a continued 3% growth per year, for controls contained in the Montreal Protocol, and for those in the Copenhagen amendments (adapted from World Meteorological Organization, 1995).

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