CFCs emissions

It should be noted that prior to 1987, total CFC emissions were made up from aerosol sprays, solvents and foam insulation, and that refrigerant emissions were about 10% of the total. However, all the different users have replaced CFCs with alternatives. 

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) ... 

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... 

An atmosphere with a relatively intact ozone layer (left) compared to one with an ozone layer compromised by chlorofluorocarbon (CFC) emissions. Illustmtion by Hans Cassidy Courtesy of Gale Group. 

Prior to the discovery of heterogeneous chemistry, models suggested a strong anti-correlation between estimates of the calculated future midlatitude ozone changes to be expected at steady state due to CFC emissions and that predicted for NOx emissions from supersonic aircraft, as illustrated in Figure 6.8. For a period of more than a decade (roughly 1974 to the mid-1980s), when the estimated future NOx impact on ozone increased, the calculated CFC-related ozone depletion decreased. Of particular importance is the reaction ... 

What level of stratospheric ozone depletion will result from projected global chlorofluorocarbon (CFC) emissions ... 

Thus the prediction of a threat to stratospheric ozone by CFCs was made in 1974, and as early as 1978 the use of CFCs as aerosol propellants was banned in North America. International consensus on the need to restrict CFC emissions emerged with the discovery of an Antarctic ozone hole (see above) that correlated with an... 

Discuss the CFCs emission abatement strategy. Why is this strategy significantly different for developed and developing countries ... 

Recent research data suggest that, as a result of the control of CFC emissions, the chlorine levels in the stratosphere are stabilizing, and the growth of the ozone hole may be slowing down. 

Current elevated levels of CFCs in the troposphere will provide a source of chlorine to the stratosphere for decades, such that the recent actions taken to reduce CFC emissions (through the Montreal Protocol) will have a delayed impact. 

It is true that volcanoes emit vast amounts of chlorine, much more than chlorine in CFC emissions. However, only chlorine that makes it to the stratosphere depletes ozone. The chemical stability of CFCs allows them to drift to the stratosphere, where they do their damage. In contrast, chlorine ftom volcanoes is primarily in the form of HCl, a very reactive and water-soluble compound. Veiy little of the HCl emitted by volcanoes gets beyond the troposphere because it is rapidly washed out by rain and condensed steam from the eruption itself. Indeed, measurements of chlorine levels in the stratosphere showed little change after the eruption of Mt. Pinatubo in 1991. CFCs, on the other hand, are not water-soluble and are not washed out of the atmosphere by rainfall. They have long atmospheric lifetimes and eventually make it to the stratosphere. Further, the amount of chlorine in the stratosphere is about five times 1950 levels, which correlates well with CFC usage. 

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