International Halocarbon Usage and Global Ozone Depletion Trends

By Clifford Szu

Ozone depletion as evidenced by the area of low ozone concentration over Antarctica.

Continued ozone depletion resulting from the catalytic destruction of ozone has caused an area of low ozone concentration over Antarctica to increase in size. Recent measurements and studies of ozone depleting substances have shown the rate of increase of ozone depletion in the lower stratosphere is slowing. At current rates of decrease, quantitative evidence shows the ozone layer column over Antarctica will begin recovery in the next decade and will continue to recover into the 21^st century.

The column of ozone in the lower stratosphere covering Antarctica received attention beginning in the mid 1980's. Scientists at the British Antarctic Society's (BAS) Halley Bay station reported abnormally low levels of ozone between the months of August and December (Farman et al., 1985), and similar reports continued through-out most of the 1980's and 199’s. While fluctuations in ozone levels occur on a biannual, monthly and even daily basis, the overall rend of ozone depletion is apparent from longitudinal displays (Jones and Shanklin, 1995; see Figure 1). Ozone layer fluctuations are common (Kley, 1997; Edouard et al. 1996) and can result from shifts in wind patterns, solar activity, volcanic eruptions and human activities such as biomass combustion. However, the major source of the ozone depletion trend in the lower stratosphere has been attributed to the extensive use of man-made halocarbons and related compounds. When released into the atmosphere, halocarbons such as chlorofluorocarbons are broken down by ultraviolet light. The resulting free chlorine and bromine atoms function as catalysts in the breakdown of ozone:

Cl + 03 -> C10 + 02 C10 + 0 -> Cl + 02

Net Result: 0 + 03-> 2 02

Since it is a catalyst in the reaction, the chlorine atom is not consumed in the reaction and is free to destroy other ozone molecules. Bromine has several pathways to catalyze the breakdown of ozone; its overall effect on the ozone layer is a fraction of chlorine's due to its relatively low levels in the stratosphere. The bromine reactions with ozone have a similar result as chlorine's (see Solomon, 1990 for more information) . The net result of the catalysts is a substantial thinning in the ozone over Antarctica, which has been termed a "hole" in the ozone layer.

Since virtually all stratospheric chlorine is of anthropogenic origin, curtailing the production and use of chlorofluorocarbons will reduce the levels of chlorine in the atmosphere. Bromine compounds such as methyl bromide have both natural and man-made sources, but man-made bromine compounds account for a large fraction of the stratospheric bromine levels (World Meterological organization, 1994) , and the net effect of chlorine on the ozone layer is greater than that of bromine. The key effort to reduce and eliminate the emissions of CFC's has been the Montreal Protocol (Montreal Protocol on Substances that Deplete the Ozone Layer). It was devised in 1987 and revised in 1990 to eliminate

CFC, halon, and related substance emissions by the year 2000. Efforts to reduce emissions have been successful, and the leading models predict an ozone hole reduction in both diameter and depth, as well as a general increase in stratospheric ozone levels.

Exact predictions vary, but most models predict a peak in halocarbon levels in the stratosphere near the end of this century. Both Hofmann (1996) and Montzka et al. (1996) place the years of halocarbon peaks between 1997 and 1999, and other estimates coincide with their estimates (Elkins et al. 1993) . Current estimates of thorough ozone hole recovery are in the mid 21st century (World Meterological organization, 1994), and Hofmann predicts noticeable signs of ozone hole reduction should appear around 2008.

These predictions are based, in part, on the elapsed time associated between halocarbon emission and ozone depletion (Prather et al. 1996) . The elapsed time difference between emission and depletion is 10-20 years. This time difference must be taken into account when analyzing reports such as Gleason et al.'s "Record Low Global Ozone in 1992" (Gleason et al. 1993) and similar reports (Jiang and Yung, 1996; Jones and Shanklin, 1995); high levels of ozone depletion in the present decade are the result of high halocarbon emissions during the 1970's and 1980's. Similarly, curtailment of halocarbons in the present deca e can prevent future ozone layer damage and growth of the ozone layer hole over Antarctica; it will not have an immediate effect on ozone levels and the ozone hole.

With this established observation, measurements of halocarbon emissions in past years can be used to predict the future status of the ozone hole and ozone layer. Montzka's group measured air samples from remote locations in the troposphere (as to prevent skewed data from local halocarbon sources) and concluded that concentrations are decreasing by 25 ± 5 parts per trillion per year. Hofmann found that global monitoring of the troposphere's ODP (ozone destroying potential) peaked in 1994, and will be transported to the stratosphere by 1997. Elkins's research group used flask samples from monitoring stations in Alaska, Hawaii, American Samoa, Colorado, Canada, Australia and the South Pole; they reported a significant recent decrease in the growth rate of specific CFC compounds that comprise the majority of stratospheric chlorine (see figure 3 [at end of document]).

With this consistent evidence of CFC emission reductions, accurate predictions of the ozone hole and ozone layer's future status can be made. Substantial and consistent evidence has been collected to support the assertion of halocarbon and related substance emission reduction. Furthermore, empirical evidence provides a framework for predicting the future state of the ozone layer, given current levels. However, a central assumption made in the above cited research is that produces and consumers of ozone depleting substances will continue to decrease their emissions. The Montreal Protocol has been the driving force behind the reduction of halocarbon and related substance emissions. Whether nations and corporations choose to abide by it is a condition that cannot be predicted by science alone.

The Revised Montreal Protocol and the Cooperation of Nations

The Montreal Protocol was revised to eliminate halocarbon emissions into the lower atmosphere by the year 2000. Overall ozone depletion in the upper atmosphere, which is most clearly evidenced in the area of low ozone concentration over Antarctica, will continue due to the peaking concentration of past emissions diffusing into the upper atmosphere.

Fortunately, scientific assessment shows that the total concentration of halocarbons and other ozone-depleting chemicals is declining. overall, the production of chlorofluorocarbons and other depleting substances has decreased by 86% in the last ten years. In terms of worldwide production, the peak was reached inl987, where over 1200 tons of chlorofluorocarbons were produced. This was also the same year that the Montreal Protocol was signed. Following the adoption of the Protocol and its revisions, worldwide production has declined sharply to less than 200 tons per year in 1997.

In these respects, the Montreal Protocol is a success. Although upper atmosphere halons and CFCs will continue to deplete the layer as they propagate from the lower atmosphere, the trend of their production and consumption will allow for upper atmosphere ozone layer recovery later in the 21't century. The full recovery of the ozone layer can take place as early as the middle of the 21 t century with the full participation of all countries and their full adherence to the Montreal Protocol.

From this diagram, it is clear that the Montreal Protocol was formed at a crucial stage in CFC usage and production. Almo s t immediately following the signing of the protocol, there was a sharp decline in the global production of CFCs. While the levels have yet to reach zero, the benefits of bringing global attention to the problem cannot be denied.

While CFCs and halons were key elements in industrial production, the public pressure on chemical producers such as DuPont and Dow to research and implement the use of viable alternatives has proven invaluable.

Specific Regions' Responsibility for Ozone Depletion

All countries can be divided into three groups with respect to their Montreal Protocol adherence. Most countries have signed the treaty. There are also countries in the CEIT group, primarily in Eastern Europe, which have received funding from the United Nations and the Global Environment Facility to help shoulder the costs of implementing the Montreal Protocol. Countries included in the CEIT group are Belarus, Bulgaria, the Czech Republic, Hungary, Poland, the Russian Federation, Slovakia, Slovenia and Ukraine.

In the 1980's industrialized nations such as the United States were responsible for the great majority of CFC production. As the detrimental effects of CFCs on the upper atmosphere ozone layer were explored and publicized, the gradual decline of their production was led by industrialized nations. CEIT nations were slower to adopt the phasing out due to their heavier dependence on the chemicals and their lack of capital to upgrade and phase out CFCs.

As the phasing out reached the mid 1990's, CEIT nations were following the lead of the industrialized nations. Much of this was made possible by the funding provided by groups such as the Global Environment Facility. Funding from the CETT has reached over US$115 million dollars to the eleven nations in this group.

The pattern of CFC consumption follows a similar trend, with industrialized nations using the bulk of the damaging chemicals. However, as depicted in the above graph, CEIT and developing nations use a larger proportion of the chemicals compared to their proportion of CFC production (previous graph). In other terms, developing and CEIT nations were proportionally more reliant on the usage of CFCs than the industrialized nation states. For most applications, it is a simpler adaptation to change production of raw chemicals than it is to adapt industrial capital to be compatible with new materials. Deep-pocketed chemical giants such as DuPont were able to shoulder the costs of production changes more easily than developing and CEIT nations were able to change their production lines to be compatible with CFC substitutes.

The production of halons exhibits a similar decline regarding the involvement of industrialized nations and CEIT nations. However, developing nations take on a much larger proportion of halon production and actually surpassed the total production of industrialized nations by mid 1993. Unfortunately, the trend of decreasing halon production was reversed by developing nation by 1994, and production actually begins to increase in later years. This can be attributed to the general lack of availability for halons and their perceived necessity in developing nations' heavy and light industries. In order to understand the trend, it is necessary to examine the consumption behavior of halons.

As shown above, the consumption level of halons for developing nations is proportionally higher when compared to their CFC production and consumption. It should be noted that the ramping up of halon consumption by developing nations is closely followed by a similar increase in halon production by the same group of countries. Due to the Montreal Protocol, halons became scarce in the mid 1990's, forcing developing nations to fulfill their own halon demands through production of the ozone-depleting chemicals. As shown in the graph, halon production and consumption were Closely linked at roughly 40,000 ODP tonnes in 1996. It is clear, then, that developing nations were the sole producers and consumers of halons after 1994.

When examined separately, the production trends of the developing nations is disturbing.

While essentially all industrialized and CETT nations are cutting back on CFC production, developing nations are dramatically increasing CFC production. Again, this trend is linked to the consumption pattern of the developing nations and the relative scarcity of suitable CFC sources. The production of halons shows a similarly unsettling trend.

The Future of the Ozone Layer

Future challenges to the protection of the ozone layer primarily stem from the existing dependency on ozone depleting halocarbons. In addition, there still are over twenty countries in the world that have-, not ratified the Montreal Protocol and its original revision.

The Earth Without Ozone Protection

Although many sacrifices have been made to help protect and preserve the ozone layer, it is important to keep in perspective the consequences of not implementing the Montreal Protocol.

By 2050 it was projected that over half of the protective upper atmosphere ozone would have been depleted in the northern hemisphere, and over 70% would have been depleted over the southern hemisphere. The overall concentration of ozone depleting halocarbons would have been over seven times higher. The weakened ozone layer, which normally shields earth's inhabitants from extremely destructive ultraviolet radiation, would have allowed millions of additional cases of skin cancers and hundreds of millions of eye cataracts to have developed.

By bringing public awareness to the destruction of the ozone layer, scientists and policy makers have averted what would have been one of the most dramatic disasters caused solely by the activities of humans. While much progress has been made in the elimination of ozone depleting chemicals, we must wait several decades before the ozone layer repairs itself. Furthermore, the lack of cooperation from developing nations is an issue that mixes diplomacy, economies and global ecology. only with time and further support from industrialized nations will the ozone layer fully recover.