Chlorofluorocarbons and ozone First plenary lecture at Jekyll Island meeting
By Mack McFarland Chlorofluorocarbons (CFCs) were developed in the 1930s as safe alternatives to ammonia and sulfur dioxide refrigerants (ammonia is &"able and both are toxic). Since then the uses of CFCs have teen expanded to include air conditioning, cleaning of critical electronic and mechanical components, and expansion of plastics for energyefficient foams. Because of the many essential needs they serve, CFC use should be restricted only if there is sound scientific justification for doing so. CFCs have proved to be one of the most useful class of compounds ever developed because of several d e s i b l e properties mostly related to their chemical stability. CFCs promote worker and consumer safety because they are nontbmmable, noncorrosive, nonexplosive, and very low in toxicity. They can be used in a wide variety of applications because of physical properties including convenient vapor pressure and temperahue characteristics, low vapor phase thermal conductivity, desirable solubility characteristics, compatibility with many construction materials, and high stability. These properties have led to the widespread use of CFCs in consumer products. One of the more critical uses of CFCs is in refrigeration of perishable foods and medical supplies. In the W13.926X189~23.1203l.EOlO
United States, about 75% of the food supply depends on CFC refrigerants for processing, storage, or distribution. Blood, medicines, and donated organs are stored and transported under refrigeration. Other uses are also valuable to society. Air conditioning of our offices and houses leads to comfort and increased productivity. The reliability of electronic and mechanical components for communications equipment, computers, and navigation and conml instruments for aircraft depends on CFC cleaning agents. Because of their low vapor phase thermal conductivity, CFCs contribute to the efficiency of plastic insulating foams for refrigerators, freezers, buildings, and refrigerated railway cars and trucks; even if the foams could be expanded with air or carbon dioxide, the thermal efficiency would be reduced by about a factor of two.
CFCs provide significant advantages in uses that many consider nonessential. Aerosol propellants are one example. In spite of the fact that they are more expensive than other alternatives, CFCs were the propellant of choice for many applications because they are nodamnable, very low in toxicity, and provide efficient dispersion. In the United States, their use as a propellant was banned in 1978 except for a few applications. CFCs are used to expand plastic foams for packaging and cushioning for safety and health reasons. The low toxicity and nonflammability of CFCs make work places safer, and their high stability eliminates possible contributions to the formation of photochemical oxidants in urban areas. Estimated global production and consumption by application are shown in Figure 1. Total consumption increased until 1974, when the owne depletion theory was 6rst proposed; it decreased
I In May 1989, the 19th tal Analytical Chemi bered years the sym
1989 American Chemical Society
Island, GA. In even-numnext year's meeting will se symposia is a series of
Envimn. Sci.Teohnoi., Val. 23,No. 10, lgag 1205
and then remained approximately constant until the mid-1980s when it again began to increase. The use pattern changed significantlybetween 1974 and 1988. In 1974 CFCs were used primarily as aerosol propellants, but with an almost total elimination of that application in the United States and decreases elsewhere, they are now used mainly as refrigerants and blowing agents. Although developed countries currently account for 85-90% of global use, consumption rates are increasing in developing countries as they strive to improve their standard of living. There is some concern that developing countries might choose to continue to use CFCs outside the Montreal protocol agreement and become the major consumer as developed countries reduce their consumption.
mals now or in the future.”
As a result of that industry symposium, a research program was estab lisbed to investigate the fate and impact of CFCs in the atmosphere. Nineteen companies formed the Chemical Manufacturers Association’s Fluorocarbon Program Panel. The panel has funded well over $20 million in research at academic and government laboratories worldwide, including partial support of the recent Arctic and Antarctic expedi-
tions.
Lovelock’s measurements also initiated the researcb of S h e r w d Rowland and Mario Molina into the atmospheric fate of CFCs. Their study resulted in 1971). A c g q ” s o n of estimated re- the ozone depletion theory published in leases of the compound with its concen- Nafure in 1974 (Molina and Rowland, hation indicated that very little, if any, 1974). Stated briefly, they postulated had been destroyed. This led to studies that CFCs would remain in the atmosof the atmospheric fate of the CFCs. phere until transported to the shatoHistory of ozone h e In 1972, Du Pont invited CFC prc- sphere where they would be photoThe chemical stability of CFCs that ducers to a “Seminar on the Ecology of lyzed, releasing chlorine atoms. Then, leads to the desirable safety characteris- Fluorocarbons.” Quoting from the invi- through a series of catalytic reactions, tics also contributes to environmental tation written by Ray McCarthy: the chlorine atoms might cause a reducconcerns. There are no known destruc“Fluorocarbons are intentionally or ac- tion in the total amount of ozone. Betion mechanisms for the CFCs in the cidentally vented to the atmosphere cause ozone absorbs most of the solar lower region of the atmosphere, the troworldwide at a rate approaching one ultraviolet radiation in the 280-31Onm posphere. Thus, once released into the billion pounds per year. These com- region (UVb), a net ozone decrease troposhere, they will remain there until pounds may he either accumulating in could lead to increases in UVb. Altransported to the stratosphere and dethe atmosphere or returning to the sur- though many uncertainties remain r e composed by solar ultraviolet radiation. face, land or sea, in the pure form or as gardiig potential effects, increases in The first evidence of possible condecomposition products. Under any of UVb could lead to adverse effects on cern about these compounds was Love- these alternatives it is prudent that we plants and animals. lock‘s measurement of the atmospheric investigate any effwts which the comThere were insufficient data to test concentration of CFC-11 (Lovelock, pounds may produce on plants or ani- the theory at the time it was proposed. For examvle. the chlorine comwunds involved &e catalytic ozone destruc’ tion cvcleihhad never been observed in FIGURE 1 the s&tosphere. Estimated world pmductii and msumptlon 0fchbmRuomcarbOns Led by government agencies but with significant input from industry, scien(a) Production m tists from government, academia, and industry undertook the enormous task of developing the science with the goal of predicting future ozone amounts. Developing a predictive capabdity is important because, once in the atmosphere, the CFCs remain there for about - low 100 years. If policies controlling the use of CFCs were not implemented un500 til there was evidence of harm to plants or animals, the effect would persist for decades. However, the available scienI 1980 tific information indicated that any sigYear (b) Consumption (by application) nificant ozone depletion would probably not occur for decades, if at all, and 1988 (2510million Ik) 1974 (2025 million Ibs) time was available to develop the scierowls Refrigerants ence. I Then as now, the industry position was that any CFC policies should be based on sound scientific information. Du Pont’s position on the issue was based on its environmental policy adopted in the late 1930s. That policy commits Du Pont to “determine that each product can be made and disposed of safely and consistent with appropriate safety, health and environmental
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tion of the Ozone Layer adopted in March 1985. The convention was designed so that protocols could be added requiring specific control measures, and plans were outlined for a series of workshops to further evaluate the need for such controls. During December 1986 international negotiations on the development of regulations began. With the forecasts of growth in the use of CFCs and the science indicating that significant growth could lead to appreciable ozone depletion, there was a growing consensus to limit global consumption of CFCs. The basis for consensus was a shared goal of protecting the environment, commitment to advancing scientific understanding, and agreement that regulations should be based on sound scientific information. The result of the negotiations was the signing of the Montreal Protocol on Substances That Deplete the Ozone Layer in September 1987. The protocol was ratified by the required number of countries and took effect on January 1, 1989. The protocol requires developed countries to reduce their consumption of CFCs to 50% of 1986 rates over a 10-year period. Developing countries are allowed to increase consumption for 10 years (their consumption cannot exceed 0.3 kg/person). Given the scientific information incorporated in the atmospheric models used for forecasting ozone concentrations, it could be argued that these reductions provided a margin of safety for ozone protection. Model forecasts based on these consumption reductions indicated that ozone might actually increase over the next century. However, there had been two developments in the science that provided the basis for an argument that the reductions might be justified. During 1985 an article was published reporting significant and unexpected ozone decreases over the Antarctic continent each spring since the mid to late 1970s (Farman et al., 1985). There were also preliminary reports based on measurements by a satellite instrument The Montreal Protocol that global ozone amounts were deBecause CFCs are used worldwide creasing at the rate of about l % per and because they have equal potential year. Although ground-based measureto affect ozone regardless of where they ments indicating no persistent change in are emitted, any effective regulations to ozone conflicted with the satellite control emissions must be global. results, and the cause of neither the Therefore, the CFC issue requires in- Antarctic ozone decreases nor the possible global ozone decreases were unternational solutions, In 1977 the United Nations Environ- derstood, both were clearly cause for ment Programme (UNEP) formed the concern and further investigation. The Coordinating Committee on the Ozone Antarctic ozone decreases led to a seLayer, which prepared periodic scien- ries of measurement campaigns (two tific assessments. In 1981 UNEP ground-based campaigns, the National formed an ad hoc group to consider de- Ozone Expeditions; and an aircraft velopment of a global convention. A campaign, the Airborne Arctic Ozone result of these international efforts was Experiment) to establish the cause. The the Vienna Convention for the Protec- reports based on the satellite ozone
quality criteria.” For CFCs, this meant that Du Pont’s position was based on the best available science. From 1975 through the early 1980s, global production of CFCs was almost constant, and the available information indicated that there had been no persistent trend in ozone and none was expected. However, because there was still significant scientific uncertainty, both research and assessments of the need for controls was continued. Available information indicated that significant ozone changes were unlikely unless there were a significant increase in consumption of CFCs. This information is summarized in the following sentences taken from a 1985 international assessment report (World Meteorological Organization, 1986): “Time dependent scenarios were performed using one-dimensional models assuming C02, CH4, and N 2 0 annual growth rates of 0.5%, 1% , and 0.25 %, respectively, in conjunction with CFC growth rates of 0%, 1.5% and 3% per year. The ozone column effects are relatively small ( < 3 % over the next 70 years) for CFC increases of I 1.5% per year, but with CFC growth rate of 3% per year the predicted ozone depletion is 10% after 70 years and still rapidly increasing.” During the mid-l980s, global consumption of CFCs began to increase. Furthermore, forecasts indicated that demands for CFCs would continue to increase, primarily because developing countries would require CFCs to provide essential services such as refrigeration and insulation. These growth forecasts coupled with available scientific information indicated that global limits to CFC consumption were warranted. We at Du Pont came to this conclusion after one of our periodic reviews of the science during the summer of 1986. Led in September 1986 by Du Pont and the Alliance for Responsible CFC Policy, the worldwide CFC industry advocated international efforts to limit growth of CFC emissions.
measurements led NASA to organize an international assessment of ozone data, the International Ozone Trends Panel.
Basis for a phase-out The results of the Antarctic experiments and the findings of the Ozone Trends Panel significantly changed our understanding of the processes that control ozone and the involvement of CFCs in those processes. This new understanding provides the scientific basis for a phase-out of the production and consumption of CFCs. The Executive Summary of the Ozone Trends Panel Report (NASA, 1988) was released on March 15, 1988. Three major conclusions of the report are: There have been small but measurable decreases in the amounts of ozone at high northern latitudes during winter over the last 17 years. The decreases appear not to be due to known natural effects, and although the cause or causes have not been established, the pattern of decreases fits the calculated pattern of decreases that CFCs might cause. Also, if the chemistry contributing to the Antarctic decreases is having an effect in the Northern Hemisphere, the effect would be predicted to occur at high latitudes during winter and early spring. “The weight of evidence strongly in; dicates that man-made chlorine species [primarily CFCs] are primarily responsible for the observed decreases in ozone within the polar vortex [the region of the Antarctic ozone decreases].” “While the column ozone depletion is largest in the Antarctic springtime, normalized TOMS [Total Ozone Mapping Spectrometer] data indicate that total column ozone has decreased since 1979 by more than 5 % at all latitudes south of 60 degrees throughout the year. At this time it is premature to judge if this is caused by dilution of the air from the region of very low ozone, a changed meteorology, or some other unidentified phenomenon. However, at least some of the decrease is likely due to dilution [of air from the region of the Antarctic ozone decreases].” Of all the findings, the most significant is the discovery of a mechanism capable of converting inactive forms of chlorine into active forms. Once CFCs reach the stratosphere, photolysis by solar UV releases their chlorine atoms. Through a series of reactions, these chlorine atoms are converted back and forth between active forms that can participate in the catalytic reactions destroying ozone and inactive forms. Environ. Sci. Technol., Vol. 23, No. 10, 1989
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Throughout the region of maximum owne concentrations the ratio of inactive to active forms is about 100:1. The results of the measurement campaigns and laboratory studies have shown that reactions on particles of water ice and on nitric acid and water within the cold region of the Antarctic stratosphere during winter and spring can convert the inactive forms of chlorine into the active forms. Measurements of the primary active form of chlorine, chlorine monoxide, over Antarctica during the time of observed ozone decreases show that its concentrations are elevated by about a factor of 100 above what would be predicted based on previously accepted chemical mechanisms (Anderson, 1989). These concentrations are large enough to account for at least most of the Observed ozone losses during the Antarctic spring. The combination of these new results and projections of atmosphere concentrations of chlorine from CFCs that could occur with the current control provisions of the Montreal Protocol leads to the conclusion that it would be prudent to take linther steps. Calculated atmospheric chlorine from CFCs based on six assumptions of future consumption is shown in Figure 2. In all cases, it is assumed that worldwide compliance to control measures is achieved. Curve A shows chlorine under the current provisions of the Protocol and curve B shows the effect of moving the required reductions forward in time by one control period-the curves are essentially the same. Curve C shows the effect of an immediate reduction of CFC consumption by 85 %the reduction required to stabilize chlorine from CFCs. Curves D, E, and F show the effect of the timing of an 1206 Environ. Scl. Technol., Vol. 23, No. 10, 1989
eventual 95% reduction of emissions. This analysis shows that if the goal is a reduction in the contribution of chlorine from CFCs, the degree of reduction is much more important than the timing of that reduction. Based on the new information, on March 24, 1988, Du Pont announced a commitment to an orderly transition to the total phase-out of CFC praiuction. After further evaluation of the time required for a transition, we have stated that the phase-out would occur as m n as possible but not later than the turn of the century. An orderly transition is required to allow the time necessary for the development of alternative compounds and technologies so that the essential needs currently ~ ~ by CFCs e d continue to be met. An important provision of the protocol calls for periodic reviews of the adequacy of the control provisions every four years beginning in 1990. Based on those reviews, the parties to the protocol have the option of modifying the controls. International reviews of the scientific, environmental, technical, and economic aspects of the issue are under way and should be complete by September 1989. The parties to the protocol will meet in April 1990 to decide on any changes in the control provisions. Even though many of the details will need to be worked out, there appears to be an international consensus that the use of CFCs should be eliminated as substitutes become available.
Alternatives to CFCs A variety of options will probably be implemented to achieve a phase-out of CFCs. Dn Pont’s analysis of methods that might be employed in the year Zoo0 to replace CFCs is based on feed
back from customers in over 100 countries and on Du Pont’s experience as the world’s largest CFC producer (about one-fourth share of global production, with manufacturing sites in seven countries). The options include conservation, not-in-kind substitutes (i.e., alternatives outside the fluorocarbon family), hydrofluorocarbons (HFCs), and hydrochlorofluorocarbons (HCFCs). ’ ConsAation includes better maintenance practices to prevent leaks from refrigeration and air conditioning equipment, recovery during servicing of that equipment, and recovery and recycling of material used for cleaning. It appears likely that conservation programs currently being implemented for CFCs will be continued for the alternatives. These improved conservation practices could decrease demand for CFC alternatives by about 30%. Most of the aerosol propellant uses will probably be supplied by other products as happened in the United States during the 1970s. Nonfluomcarbon alternatives will also be used as cleaning and blowing agents. Another 30% of CFC demand will probably be met by not-in-kind alternatives by 2ooO. At this time it appears that the best options for meeting remaining demands are HFCs and HCFCs. These compounds appear to retain many of the desirable safety and performance characteristics of the CFCs, but, because they contain hydrogen, they are decomposed in the troposhere through reaction with hydroxyl. This decomposition shortens the atmospheric lifetimes of HFCs and HCFCs to 2-20 years, depending on the compound, compared to about 100 years or longer for the CFCs. Because the HFCs contain no
chlorine, they have no potential to de- bly a major contributor to the seasonal plete ozone. The tropospheric decom- Antarctic ozone decreases. Small ozone position of the HCFCs limits the decreases have occurred at high latiamount of chlorine that can reach the tudes in the northern hemisphere durstratosphere and reduces their ozone ing winter. Although the cause of these depletion potentials to only 2-10% of decreases is not established, there is a possibility that they could be due to those of CFCs. Another advantage of the shorter chlorine, primarily from CFCs. The lifetimes of these compounds is a re- CFCs have atmospheric lifetimes on duction in global warming potential the order of 100 years and, hence, their compared to CFCs. Concern has been concentrations will decay only slowly expressed over the 20% contribution of after emissions are stopped. This the CFCs to calculated global warming means action should be taken. On the other hand, the ozone deduring the 1980s. With their reduced lifetimes, HFCs and HCFCs would crease that has been observed has occontribute about 90% less on a pound- curred at high latitudes during winter for-pound basis. Considering that only and spring when a low sun angle results about 40% of the CFC demand will be in exposure of plants and animals to satisfied with these compounds, over very low UVb levels. This argues that the next century they would contribute actions taken now will be taken in adonly about 4% as much toward global vance of potential harm to plants and warming as CFCs would if their use animals. There is a consensus within governwere to continue. We project that about 10% of the de- ments and industry that protective meamand for CFCs could be met with sures should be taken, and progress is HFCs in 2000, primarily in the refrig- being made. Industry is aggressively eration applications. Elimination of the developing options so that the essential chlorine from these compounds in- needs served by CFCs will continue to creases their vapor pressures and de- be met safely. Du Pont’s goal is to decreases their solubility properties com- velop options that will meet the needs pared to CFCs. These two property of CFCs in a safe and environmentally changes limit their use for many appli- acceptable manner while achieving a long-term reduction in atmospheric cations. The HCFCs appear to be the best op- chlorine from the compounds meeting tion for meeting the remaining 30% of those needs. CFC demand. The primary uses of these compounds will probably be in Acknowledgments expanding plastic foams for insulation, The atmospheric science community decleaning of critical electronic and metal serves credit for developing the basis for on this important issue. I would components, refrigeration, and air con- consensus like to thank those at Du Pont, especially ditioning. C. B. Catanach, who provided the estiIndustry is aggressively developing mates of CFC production and consumption and testing all of these options to and of alternatives forecasts. achieve a rapid but orderly transition to the phase-out of CFCs. A critical part Reading list Anderson, J. G. In Ozone Depletion, Greenof these programs is safety and envi- house Gases and Climate Change; National ronmental testing. Three industry- Research Council: Washington, DC, 1989. Farman, J. C.; Gardiner, B. G.; Shanklin, sponsored programs are under way to D. Nature 1985, 314, 207-10. ensure that the options employed do not J.Lovelock, J . E. Nature 1971,230, 379. pose other problems. Two programs Molina, M. J.; Rowland, F. S. Nature 1974, (Program for Alternative Fluorocarbon 249, 810-12. “Present State of Knowledge of the Upper Toxicity Testing I and II) are doing the 1988: An Assessment Report”; studies required to ensure worker and Atmosphere, NASA Reference Publication 1208; 1988. consumer safety. Another program (AlWorld Meteorological Organization Global ternative Fluorocarbon Environmental Ozone Research and Monitoring Project; “Atmospheric Ozone 1985, Assessment of Our Acceptability Study) is being sponsored Understanding of the Processes Controlling its to ensure that the products are environ- Present Distribution and Change”; Report mentally acceptable. Although spon- Number 16; 1986. sored by 15 potential producers of alternatives, leading scientists from Mack McFarland is a research associaround the world are conducting the ate in the Freon Products Division of study under the guidance of Robert the Du Pont company in Wilmington, DE. He has been studying the science Watson of NASA. of atmospheric ozone since 1974 and is Conclusions science coordinator of environmental Many questions remain regarding the programs for Du Pont. McFarland has CFC/ozone issue, but there appears to a B.S. degree in chemistry from the be a consensus that enough is known to University of Exas at Austin and a begin an orderly phase-out of CFC pro- Ph.D. in chemical physics from the duction. Chlorine from CFCs is proba- University of Colorado.
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Environ. Sci. Technol., Vol. 23,No. 10, 1989 1207
