TCDD is strongly retarded on fly ash surfaces. Other results presented at the workshop indicated that surprisingly large fractions of PCDDs in the atmosphere exist in the vapor state, although significant amounts also are sorbed on particulates. These results, however, are possibly influenced by some analytical artifact that leads to overestimates of the vapor-phase component. Several factors influence the kinetics of PAH transformations on coal fly ash surfaces. PAH photooxidations are slower on coal fly ash with high carbon and iron content. This retardation may be attributable to an inner-filter effect that shields PAHs from the light. PCDDs are believed to be easily degraded in the vapor phase, but the measurement of vapor-phase photolysis rates of low volatility compounds is difficult due to their strong tendency to sorb onto surfaces. Experimental designs that minimize the wall effects while maintaining adequate concentrations in the vapor phase are essential for evaluating vapor-phase processes. Preliminary results presented at this workshop indicated that the quantum yield for direct photolysis of 2,3,7,8TCDD in the vapor state is of the same order of magnitude as in organic solvents. As mentioned earlier, the direct photolysis half-life for 2,3,7,8-TCDD in hydrocarbon solvents exposed to midday sunlight is less than one hour.
Evaluative fate models An overview was presented at the workshop of state-of-the-art land surface models that simulate the transport and transformation of environmental contaminants. The fate of pesticides and other environmental pollutants may be evaluated through simulation using models that mathematically describe mass transport and transformation processes in the dissolved and adsorbed states. Various agricultural models, such as the Hydrological Simulation ProgramFortran model and the Pesticide Root Zone Model, have been useful in simulating pesticide fate on land surfaces. In developing such models, it is very important to integrate research on physical, chemical, and biological processes with model development and subsequent validation through field and laboratory studies. The Pesticide Root Zone Model is now being modified to take into account the new results presented at the workshop. There was general agreement, however, that modeling the fate of compounds at the air-soil interface will require a better understanding of these processes before any secure predictions can be made on exposure to humans.
References ( I ) Paustenbaeh. D. 1.: Shu. H. P: Murray, E J . Regulatory Taxicoiogy ond Pharmacology 19%. 6, 284-307. ( 2 ) Cohen. Y. Environ. Sci. Technol. 1986.20, 538-44.
Glenn C. Miller is an associate professor of biochemistry at the University of Nevada, Reno. Since 1978 he has taught at UNR and conducted research on the photochemistry of medium-weight pollutants on soil surfaces and in the vapor phase.
Vince R. Heberr is a research associate and graduate student in the department of biochemistry at the University of Nevada, Reno. He has a B.S. from Humboldt State University. His research interests are in examining the factors that affect the photolysis of pollutants on environmental surfaces. Richard G. Zepp is ajiliared with the €PAS Environmental Research Laboratory at Athens. Go. He is a research chemisr specializing in the kinetics of photochemical and oxidation processes in aquatic environments. He is a member of the ES&T advisory board.
The ozone layer Its protection depends on international cooperation
/ w i n g M . Mintxr
By Irving M. Mintzer and Alan S. Miller Governments around the world will soon make decisions on policies that could determine the fate of the ozone layer-the Earth’s shield from harmful ultraviolet radiation. The Vienna Convention for the Protection of the Ozone Layer, signed on March 22, 1985, created a framework for scientific cooperation and information exchange that will form the basis for a protocol for controlling substances thought to threaten the ozone layer. As of mid1987.29 countries had signed the Convention, including the major producers and users of chlorofluorocarbons (CFCs), the most important of the suspect chemicals. Recent scientific developments make governmental deliberations more urgent. In 1985 British scientists reported that springtime losses of ozone in the Antarctic were far greater than current atmospheric models can explain. National Aeronautics and Space Administration (NASA) satellite measurements have confirmed these ozone measure-
M)13936W87/0921-1167501.5010 @ 1987 American Chemical Societv
Alan S. Miller
ments, the lowest ever recorded over the Earth. Whether, when, and even where depletion occurs depends on numerous assumptions about the relative growth rates of different chemicals and the sensitivities of the model used to simulate what happens when the atmospheric chemistry is changed. The possible interaction between chlorine and stratospheric odd nitrogen (NO,) makes modeling even more complex. Even though ozone depletion caused by CFCs may be offset by emissions of C02, CH4, and NO,, the atmosphere may be radically altered at certain altitudes. Another contributing factor is the “selfhealing” effect-the accelerated production of ozone from molecular in the lower stratosphere oxygen (02) due to the increased ultraviolet rays that pass through the depleted upper and middle stratospheres. Even when depletion estimates can be unequivocally established, the role of human activities in ozone depletion cannot readily be traced. But significant effects have been clearly associated with high levels of depletion. Environ. Sci. Technol.. Vol. 21. NO.12. 1987 1167
According to a recent analysis, a 1 % increase. in ultraviolet-B band (W-B) would increase malignant melanoma mortality in the United States by 0.8 to 1.5 % . Soybean yields could decline by up to 25% with a comparable increase in UV-B. Ozone depletion could harm aquatic organisms, exacerbate smog in some cities, and accelerate the degradation of some plastics and paints. CFCs profile CFCs are used primarily in the Western industrialized nations as aerosol propellants, refrigerants, agents for foam blowing, and solvents. The United States, Canada, and Sweden banned most aerosol uses in the late 1970s. But because other countries did not, aerosols still represent almost onethird of CFC-11 and CFC-12 use by countries surveyed in the Chemical Manufacturers Association’s annual report. The United States and Japan also use large amounts of CFC-12 for automobile air conditioning. Foam blowing is the major use of CFC- 1 1, and almost all CFC-113 is used as a solvent. Global use of CFC-I1 and CFC-12 has increased steadily over time, although growth rates vary markedly by use and country. Between 1958 and 1983, average annual production of CFC-I1 and CFC-12 grew approximately 13%. In theory, such growth could continue. Supplies of raw materials-mainly fluorspar-will last at least through 2030. Aerosols create emissions virtually immediately, whereas most other uses emit CFCs gradually. Emissions from rigid foams may be glacially slow because the CFCs remain stored until the foam is cmshed-in effect “banking” large amounts of CFCs for future re*I. Emissions of CFCs can be reduced through four basic methods: Equipment can be designed and operated to reduce losses-which can range upward of 25% of total usage in some applications. The compound can be recovered and cleaned for reuse. Formulations of CFCs that present little or no threat to the ozone layer can be substituted for those that do. (DuPont, the largest U.S. manufacturer of CFCs, announced in Se.ptember 1986 that it could produce substitute CFCs in commercial quantities within five years, given adequate regulatory incentives.) Non-CFC Dloducts can be substituted for CFCS. Althoueh the cost and feasibilitv of substitutes for many uses of CFCd are known, major gaps remain in our knowledge of how CFCs are used. More important, there is little incentive 1168 Envimn. Sci.Technol., Vol. 21. NO.12, 1987
FC113
CCbCls
to produce most of the substitutes. Yet much as opportunities to improve energy efficiency magically appeared once energy prices tripled, CFC price increases could produce new CFC substitutes as well. The key to innovation is to increase the price of CFCs by taxation or regulation.
Regulatnry policy issues The Vienna Convention for the hotection of the Ozone Layer is the most recent stage of decade-long international deliberations on ozone depletion. The Convention-some 21 articles and two technical annexes-spells out the general obligations of the states to cooperate in scientific programs on risks to the ozone layer and to control activities that “have or are likely to have adverse effects” on the ozone layer. It could enter into force, perhaps in 1988, once as few as nine countries ratify it. Participants at the Vienna Convention meetings also tried unsuccessNly to adopt a protocol for controlling CFCs. A quick resolution seemed unlikely, so the parties agreed to complete the Convention and continued to discuss protocol issues. By October 1986, unofficial discussions had produced some progress. US.and European trade associations representing CFC users and producers now support limits (so far unspecified) on CFCs. In November 1986, the united states announced support for an immediate cap on CFC emissions at current levels and a long-term commitment to phase out all CFCs that threaten the ozone layer. In April 1987 representatives of 30 countries attending an inter-governmental negotiating session on the Ozone Convention in Geneva provisionally agreed to a protocol that would freeze production and use of the most dangerous CFCs (CFC-11, -12, and -1 13) at 1986 levels two years after the Vienna Convention enters into force. This move would be followed in two years by an alttomatic 20% reduction in the production of these same cbemicalS. A further reduction of 30%could occur six years later if the majority of signatories approve. Alternatively, the draft proposes a 30% reduction in eight years unless two-thirds of the countries oppose its implementation. Decisions about control of CFCs
hinge on three key issues: the policy implications if growth in other trace gases offsets ozone depletion caused by CFCs, the risk of delaying regulation, and the most workable and effective policy strategies. So far, discussions held internationally have focused on the limits that should now be placed on CFC prcduction and use, the allocation of responsibilities for meeting such limits among nations, and the necessity of national policies to implement global limits. Domestically, the issues differ because eacb country will have to decide how to &ce its CFC use to stay within negotiated limits.
Limiting prnduction and use Phasing out all uses of CFCs immediately would offer the most protection from ozone depletion and climate change. But a more politically realistic approach is adopting different strate.gies to meet short-and long-term goals, both international and domestic. Policies implemented in the next few years will greatly affect the long-term cost of controls. At the very Least, a short-term plan is needed to reverse recent growth mends and begin steady reductions in CFC use, inviting producers and users to seek alternatives to CFCs. Neither the capacity cap proposed by the European Economic Community nor the U S . aerosol ban meets these objectives. The first approach would take too long, because Europe now has enough excess capacity to meet increased demand until perhaps 2010. As for the aerosol ban, the benefits of e l i i inating any specific uses of CFCs over time can be offset if other uses grow, and restrictions only on designated uses may strike remaining users as a license to use more and to take more time to look for alternatives. A better approach was suggested by Canada at the September 1986 workshop: an international cap on CFC consumption set at one-third less than estimated current global capacity for producing CFC-11 and CFC-12, which is about 1245 million kg. The global limit would be about 800 million kg, roughly equivalent to recent global use. Coi&nption may be harderio monitor than production, but this policy does not unfairly favor countries that happen to have more (or less) production in place.
The optimal approach is to set the allowable total limit at less than 85% of estimated current production of CFCs. At this level, the likelihood that any agreement may not take effect for several years is acceptable and the opportunity to expeditiously eliminate use of CFCs for aerosols, and food packing and with commercially competitive substitutes is maximized. At the same time credit (additional permitted consumption for amounts recaptured) should be allowed.
Allocating allowable production Whatever limit is imposed on CFC production or consumption, some allocation formula is needed to determine how much specific countries would be allowed. Canada proposes allocating 75% of permitted consumption to countries according to their GNP: CFC use would be allowed to increase greatly in developing countries, but the United States and Europe (which have already profited handsomely from CFCs and are largely responsible for the problem) would have to cut back immediately. The incentive to develop substitutes in the industrialized countries will also help produce alternatives for the developing countries, so they may not have to use much of their permitted allocations. National policies If global and national CFC limits other than a ban on new production capacity are established, further national policies to reduce emissions may or may not be necessary. Producers could limit demand by raising prices. But most producers will wait to see how the market responds before introducing products that can cost several times as much as current CFCs. The most effective means of assuring a minimum future price for CFCs is to tax them. A tax of $5 a pound, phased in over several years, would make substitutes appealing without noticeably raising the cost of most CFC uses. A tax would also allow governments to benefit from the increase in selling price that may occur if consumption or production limits are set. The revenues captured could support research on ozone depletion and climate change. Taxation of CFCs by international agreements is widely considered politically impossible. Nonetheless, adopting a domestic tax in addition to limiting consumption is in the interest of individual countries poised to lead in the development of CFC substitutes. Even as political concern over ozone depletion grows, so do opportunities to reduce CFC emissions. But building the international consensus necessary to phase out CFC emissions will take
time. In the short term it is more realistic to expect that participants in the Convention process can agree to reduce global CFC emissions by an amount roughly equal to one-half of current use. Even if an international protocol is adopted, however, individual nations may need to set more stringent controls. ntis article is an updated abridgment ofThe Sky is the Limit: Strategies for Protecting the Ozone Layer, World Resources Institute. November 1986.
Irving U.Uintzer is director of the energy and climate program at the World Resources Institute. His research focuses on long-term global energy strategies and global warming due IO the greenhouse ef fect, stratospheric ozone. and acid rain. Alan S. Miller is o Fulbright scholar spending 1987 at the University of Tokyo studying Japanese policies toward internorional environmental issues. Formerly a re. search attorney with WRI and o senior attorney with the Natural Resources Defense Council. he has been involved with en+ ronmental and regulatoq litigation /or 10 yeurs.
Glaze: ES&I "s new editor
William H. Glaze will become editor next month, He is director of the interdepartmental Environmental Science and Engineering Program at UCLA, a position he has held since 1984. There he is also professor in the Division of Environmental and Occupational Health Science in the School of Public Health. He has been a member of the ES&Tadvisory board since 1980. Earlier in his career, at the University of Texas at Dallas, he was professor of environmental science and chemistry, head of the Graduate Program in Environmental Sciences, and director of the Center for Energy and Environmental Studies. At North Texas State University in Denton, Texas, he was professor of chemistry, associate dean for the College of Arts and Sciences (19731975) and director of the Institute of Applied Science (1973-1980). He has been involved in a number of ACS programs. He served as a councilor and as a member of the Committee on Environmental Improvement, he canvassed for candidates for the ACS Award in Creative Advances in Environmental Science and Technology, and he held several offices in the Dallas-Ft. Worth section. Glaze was also the re-
cipient of the Zimmerman Award in Environmental Sciences in 1986 and has received a number of honors and awards for excellence in teaching. He has served on several advisory committees, including a subcommittee on disinfection byproducts of the Safe Drinking Water Committee of the National Research Council of the National Academy of Sciences. He was chairman of the NRC committee on Water Treatment Chemicals. Glaze follows in the footsteps of two previous editors who were chemistsJames Morgan and Russell Christman. His research originally concentrated on SttuCNre and mechanisms of organometallic compounds of main group elements. More recently, he has focused on the byproducts of chlorination and water treatment processes for the removal of water contaminants, including oxidation and adsorption processes. His group at UCLA is currently involved in studies of ozone byproducts, advanced oxidation processes for water treatment, and applications of advanced analytical methods for exposure assessments. As director of the UCLA Environmental Sciences and Engineering (ESE) Program, Glaze heads one of the unique professional doctoral programs in the environmental field. The ESE program, which was founded in the early 1970s. accepts post-master's students from the sciences and engineering into a two-year cumculum that combines research with courses in environmental science, engineering, and policy. The dissertation is developed in a two-year internship in industry or a government agency. Glaze indicates that he is committed to continuing the high standards of scholarship that his predecessors have established for ES&Tand the multipurpose format of the journal. Environ. Scl.Technol..MI. 21. NO. 12. 1987 1169
