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25
Nonenergy Emission Reduction

Nonenergy-related sources of greenhouse gases include manufactured halocarbons, methane and nitrous oxide from agriculture, and methane from landfills.

Halocarbons

"Halocarbon" is the general lable applied to chemicals such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), halons, and chlorocarbons (CCs). Halocarbons have the largest radiative impact per molecule of any of the greenhouse gases. However, halocarbon emission volumes are much lower than CO2 emission volumes, so that the total halocarbon contribution to global warming is less than that of CO2 from other sources. The CFCs also threaten the stratospheric ozone layer. Emissions of CFCs are scheduled to be eliminated under the Montreal Protocol, an international treaty signed in 1987 and strengthened in 1990, that commits nations to act to preserve the ozone layer. Positive action under the Protocol—including bringing additional nations under its umbrella—continues to be a visible demonstration of the possibility of global action on environmental questions.

Recent Trends

More than 1 Mt of CFCs and halons were produced and consumed on a worldwide basis in 1986.1 Figure 25.1 shows that the United States is the largest consumer of CFCs in the world (approximately one-third). Other developed countries also consume large amounts of CFCs. During the 1970s, scientists became concerned about the potential impact of CFCs on the



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Page 376 25 Nonenergy Emission Reduction Nonenergy-related sources of greenhouse gases include manufactured halocarbons, methane and nitrous oxide from agriculture, and methane from landfills. Halocarbons "Halocarbon" is the general lable applied to chemicals such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), halons, and chlorocarbons (CCs). Halocarbons have the largest radiative impact per molecule of any of the greenhouse gases. However, halocarbon emission volumes are much lower than CO2 emission volumes, so that the total halocarbon contribution to global warming is less than that of CO2 from other sources. The CFCs also threaten the stratospheric ozone layer. Emissions of CFCs are scheduled to be eliminated under the Montreal Protocol, an international treaty signed in 1987 and strengthened in 1990, that commits nations to act to preserve the ozone layer. Positive action under the Protocol—including bringing additional nations under its umbrella—continues to be a visible demonstration of the possibility of global action on environmental questions. Recent Trends More than 1 Mt of CFCs and halons were produced and consumed on a worldwide basis in 1986.1 Figure 25.1 shows that the United States is the largest consumer of CFCs in the world (approximately one-third). Other developed countries also consume large amounts of CFCs. During the 1970s, scientists became concerned about the potential impact of CFCs on the

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Page 377 ozone layer (Rowland and Molina, 1974). Concern continued, and in 1985 scientists detected unexpected seasonal losses in the stratospheric ozone layer above Antarctica (Farman et al., 1985). In 1987, these concerns resulted in the Montreal Protocol—an international agreement to reduce by 1998 the production and use of CFCs, in developed countries, to 50 percent of their 1986 levels and to freeze halon production at 1986 levels by 1993. By 1988, research had shown that chlorine from man-made sources, primarily CFCs and CCs, contributed to the temporary early spring ozone losses above Antarctica. The Montreal Protocol was amended in 1990 to require a total phaseout of CFCs, halons, and carbon tetrachloride by the year 2000 in developed countries (2010 in developing countries). Not all countries have agreed to sign the Montreal Protocol, however, and this fact, along with the possibility that some countries may not comply with the agreement, has caused concern. More than 100 countries with over 67 percent of the global population and about 10 percent of current CFC use—India and China included—have not yet signed the agreement. The United States has signed the Montreal Protocol. In addition, the 1990 amendment to the Clean Air Act will further regulate halocarbons in the United States. Figure 25.2 illustrates how CFC consumption will decline between now and 2010 because of the new Clean Air Act amendment. Besides having a role in ozone depletion, CFCs are also greenhouse gases. Unlike the other greenhouse gases, which began to increase during the Industrial Revolution (1850), CFCs were not introduced until the early image FIGURE 25.1 CFC and halon consumption by geographic region, 1985. SOURCE: Cogan (1988).

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Page 378 image FIGURE 25.2 Effect of Clean Air Act Amendment of 1990 on CFC usage. SOURCE: Data are from F. A. Vogelsberg, Du Pont, personal communication to Deborah Stine, National Academy of Sciences, 1990. 1930s. Future use rates, and hence emissions, of fluorocarbons will be driven by societal use of goods and services employing CFCs (Table 25.1),which can be found in everything from mobile air conditioners to fire extinguishers to plastic foams in residential, commercial, and industrial applications. Over the last decade, the fractional contribution of CFCs to greenhouse warming has been about 20 percent. Because CFC concentrations began to increase significantly only after 1960, their fractional contribution to the increase since 1940 is about 15 percent, and since 1850 about 10 percent. The fractional contributions of CO2, CH4,N2O, and CFCs are shown for the three time periods in the pie charts shown in Figure 25.3.These charts illustrate how the CFC contribution to greenhouse warming relative to the contributions of the other greenhouse gases changed between the beginning of widespread use of CFCs in the 1940s (14 percent) and the1980s (19 percent). The areas of the pies are proportional to the calculated warming over the time periods given (F. A. Vogelsberg, Du Pont, personal communication to Deborah Stine, Committee on Science, Engineering and Public Policy, 1990).

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Page 379 TABLE 25.1 Primary Uses of CFCs and Halons Application Primary Compound(s) Used in United States in 1986 (million pounds) Where or How Used Stationary air conditioning and refrigeration CFC-12 (68.5) 45 million homes and most commercial buildings   CFC-11 (14.5) 100 million refrigerators   CFC-115 (9.9) 30 million freezers   CFC-114 (2.2) 180,000 refrigerated trucks     27,000 refrigerated rail cars     250,000 restaurants     40,000 supermarkets     160,000 other food stores Mobile air conditioning CFC-12 (120.0) 90 million cars and light duty trucks Plastic foams CFC-11 (150.7) Rigid insulation for homes, buildings, and refrigerators;   CFC-12 (48.2) flexible foam cushioning, food trays, and packaging   CFC-114 (6.6)   Solvents CFC-113 (150.7) Microelectronic circuitry; computer and high-performance air- and space-craft, dry cleaning Sterilants CFC-12 (26.4) Medical instruments and pharmaceutical supplies Aerosols CFC-12 (15.6) Essential uses in solvents, medicines, and pesticides   CFC-11 (9.9)   Miscellaneous CFC-12 (22.0) Food freezants for shrimp, fish, fruit, and vegetables Fire extinguishing Halon 1301 (7.7) Computer rooms, telephone exchanges, storage vaults   Halon 1211 (6.2)   SOURCE: Cogan (1988).

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Page 380 image FIGURE 25.3 Contribution to calculated warming. SOURCE: Data are from Du Pont (1989). The goal of minimizing contributions to global warming should be considered in the context of other goals, including minimizing the potential for ozone depletion, maintaining safety standards for chemicals (low toxicity and low flammability), maintaining energy efficiency, and continuing to realize the substantial economic and societal benefits of CFC-using technologies while making the transition from CFCs to alternatives. Several alternatives are being evaluated in an attempt to balance these goals. As a group, the HCFCs and HFCs under evaluation have about one-tenth the global warming potential of CFCs, and less than one-twentieth the ozone depletion potential of CFCs, because the hydrogen in these two alternatives destabilizes these chemicals and lowers their residence time in the atmosphere and thus their potential to contribute to greenhouse warming and ozone depletion. Furthermore, because HFCs contain no chlorine, they cannot contribute to ozone depletion (see Table 25.2). Thus, even with emission rates comparable to those of CFCs, the contributions to calculated global warming and ozone depletion would be significantly reduced, as shown in Figure 25.4.

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Page 381 TABLE 25.2 Global Warming Potentials of CFCs Trace Gas Lifetimea (years) Ozone Depletion Potentialb Global Warming Potentialc dF for dC per Molecule Relative to CO2d Rate of Increase in 1986 (ppb/yr)e Carbon dioxide 120 NA 1 1 1.2 × 10-3 Methane 10 NA 21 58 13 Nitrous oxide 150 NA 260 206 0.7 CFC-11 60 1 2,000 12,400 9 × 10-3 CFC-12 130 1 6,200 15,800 1.7 × 10-2 CFC-113 90 0.8 2,800 15,800 4 × 10-3 CFC-114 200 0.7 7,900 18,300   CFC-115 400 0.4 14,000 14,500   HCFC-22 15 0.05 680 10,700 7 × 10-3 HCFC-123 2 0.02 38 9,940   HCFC-124 7 0.02 190 10,800   HCFC-141b 8 0.1 190 7,710   HCFC-142b 19 0.06 710 10,200   HFC-125 28 0 1,100 13,400   HFC-134a 16 0 550 9,570   HFC-152a 2 0 62 6,590   HFC-143a 41 0 1,400 7,830   Carbon tetrachloride 50 1.1 680 5,720 2 × 10-3 Methyl chloroform 6 0.15 45 2,730 6 × 10-3 aFrom Intergovernmental Panel on Climate Change (1990), Table 2.8. bAverage of values in World Meteorological Organization (1989), Table 4.3-3. cCalculated from lifetimes and change in radiative forcing (dF) for a change in molar concentration relative to CO2. dFrom Intergovernmental Panel on Climate Change (1990), Table 2.3 (Table 19.4 of this report). dF = change in radiative forcing; dC = change in temperature. eFrom National Aeronautics and Space Administration (1988), Table C-8.1. Table 25.2 shows the atmospheric lifetimes, ozone-depleting potentials, global warming potentials, calculated equilibrium warming, and rate of increase of atmospheric concentration for CO2, CH4, N2O, fluorocarbons, and chlorocarbons. The global warming potentials are calculated on a mass basis relative to a global warming potential of 1.0 for CO2. These global warming potentials are estimates of the total cumulative (over time) calculated warming due to emission of 1 kg of a compound relative to the total cumulative calculated warming due to emission of 1 kg CO2. All of the

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Page 382 image FIGURE 25.4 Calculated global warming contributions: (1) based on emission scenario in World Meteorological Organization (1985); (2) assumes unregulated use of CFC's with continued growth in worldwide demand; (3) assumes global compliance with a phaseout of CFCs by 2000 (2010 in developing countries), a phaseout of HCFC substitutes over the period from 2030 to 2070, and continued growth in demand for HFC substitutes throughout the next century. The curve represents the contribution of residual CFCs plus HCFCs plus HFCs. SOURCE: Data are from Du Pont (1989). compounds have large global warming potentials compared to that ofCO2,but this fact can be misleading because it does not account for relative emission rates. This method of calculating global warming potentials differs slightly from that used by the Intergovernmental Panel on Climate Change (1990). They computed relative effects over the first 20, 100, and 500 years after instantaneous injections of 1 kg of each of the compounds into the atmosphere to derive the values in Table 2.8 of IPCC(Intergovernmental Panel on Climate Change, 1990). The values in Table 25.2 of this reportare based on the same atmospheric lifetimes and values for radiative forcing as used in the IPCC report, but relative effects are computed from totalintegrated forcing by assuming a CO2 lifetime of 120 years. The last two columns of Table 25.2 can be used to estimate current contributions to calculated warming. Multiplying the values in these columns yields the 1986 contribution to global warming. Dividing the individual contributions by the sum of all the contributions yields an estimate of the relative contribution of each gas. This shows that although the global warming potential and calculated equilibrium warming for CO2 are small

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Page 383 per unit of CO2, it nevertheless contributed about 55 percent of the total calculated warming in 1986. Figure 25.4 shows the projected calculated warming from fluorocarbon substitutes based on options for meeting a growing demand for goods and services that currently rely on CFCs. A comparison of the curve for continued use of CFCs with the lower curve demonstrates the effects of the decreased demand for fluorocarbons due to conservation and replacement by nonfluorocarbon alternatives, and also the lower global warming potentials of the HCFCs and HFCs targeted to replace CFCs. Global compliance with a CFC phaseout by 2000 (2010 in developing countries) and an HCFC phaseout from 2030 to 2060 (not yet required by treaty, but in a nonbinding agreement) would stabilize the contribution of fluorocarbons to global warming even though the demand for goods and services they provide is projected to increase at about 3.5 percent per year. Emission Control Methods Production and use of CFCs will probably be eliminated over the next 10 years (20 years in developing countries) because of concerns about ozone depletion. A variety of options can be used to meet growing demands for the goods and services as CFCs are eliminated: • increased conservation of CFCs in the short term and of their replacements over the longer term, • nonfluorocarbon alternative compounds for technologies not requiring a gas, and • substitution of other compounds in the fluorocarbon family—HCFCs and HFCs. Figure 25.5 illustrates how the demand for services now provided by CFCs could be satisfied in the year 2000 (deadline for phaseout under the amended Montreal Protocol). Conservation and recycling measures can reduce worldwide demand for CFC production by 30 percent and provide environmental benefits by reducing the need for virgin CFC production. Replacement of certain applications, primarily aerosols in Europe, with nonhalocarbon substitutes (''not-in-kind" options) can reduce CFC demand by an additional 30 percent. Fluorocarbon alternatives can replace CFCs in the remaining 40 percent of applications (Du Pont, 1989). However, some of the substitute chemicals—developed to avoid reaction with ozone in the upper atmosphere—may have radiative properties that would result in significant contributions to greenhouse warming (Shine, 1990). Increased conservation and recycling of CFCs and their fluorocarbon replacements are initiatives that can provide benefits to consumers, industry, and the environment. United States tax legislation has more than doubled

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Page 384 image FIGURE 25.5 How CFC demand is satisfied in 2000. SOURCE: Adapted from Du Pont (1989). the price of CFCs since January 1, 1990. Escalating tax rates will raise the price of CFCs by approximately 500 percent in the next 10 years. These price increases are exclusive of additional increases from producers due to mandated production cuts and higher fixed costs, increased raw materials costs, and the need for revenue to invest in alternatives. In addition, fluorocarbon alternatives are expected to cost up to 5 times as much as present(untaxed) CFCs. Clearly, economic incentives for conservation and recycling will grow rapidly with these price increases. A review of the different industries that use CFCs illustrates the feasibility of each of the substitution options. The foam plastics industry uses CFC blowing agents in the insulation it produces. Conservation measures are difficult for this industry to implement because about 80 percent of the CFC blowing agent ends up in the bubbles of rigid foam insulation. The industry currently recovers 50 percent of the fugitive emissions that occur during manufacture (Aulisio, 1988). The best options for this industry are CFC substitutes such as HCFCs 22, 123, 141b and 142b, which will become available in increasing quantities in 1994 and 1995, when the market could be fully supported by HCFC alternatives. Higher prices may cause consumers to choose not-in-kind substitutes such as fiberglass and fiberboard insulation. Because these substitutes are less energy efficient, the net contribution to global warming may be adverse, a possibility that should be taken into account. Appliance manufacturers put insulating foam in refrigerators to increase their energy efficiency as required by statute. Manufacturers will be able to

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Page 385 use some CFC substitutes such as HCFC-123. However, until these products are widely available, manufacturers will have to balance the need for energy efficiency with the availability of substitutes. Whirlpool has estimated that refrigerators with the new CFCs would cost about $100 more per unit to produce. CFCs are also used in refrigerators as refrigerants. Used refrigerant is currently being recycled, and manufacturers of commercial refrigeration and air conditioning equipment are working to reduce fugitive emission losses in the field (Cogan, 1988). Mobile air conditioning is the largest market for CFC consumption in the United States; however, because new automobiles account for only 20 to 25 percent of the CFCs used in this sector, phaseout of CFCs by automobile producers will afford only a small reduction initially. Seventy-five percent of the consumption is in servicing the existing 125 million automobile air conditioners after the refrigeration fluid has leaked to the atmosphere (Putnam, Hayes, and Bartlett, 1987). Of the 120 million pounds used for replacement, 30 million pounds replaced fluid lost through normal operation, and 40 million pounds replaced fluids flushed out during servicing and repairs (Radian Corp., 1987). Therefore conservation and recycling of these CFCs are critical to reduce emissions from this industry. The automobile industry has examined numerous alternative refrigerants. After independent analysis, mobile air conditioner manufacturers have agreed that HFC-134a is the best replacement for CFC-12. Significant technical issues need to be solved before HFC-134a can be used in new mobile air conditioning systems, most notably the development of a new system lubricant, hardware and elastomer modifications, toxicological testing of HFC-134a, and development of feasible chemical HFC-134a synthetics. Excellent progress has been made in all areas, such that domestic automobile manufacturers plan to switch to HFC-134a over a several-year period, with conversion expected to be complete by 1996. However, HFC-134a is not a drop-in replacement for CFC-12 in mobile air conditioning systems, and it is not expected to be retrofit option. The automobile industry is making serious efforts to minimize the release of CFC-12 from these air conditioning systems; for example, one major domestic producer (General Motors) is requiring that all of its dealerships use refrigerant recovery and recycling equipment by October 1990. Conversion from CFC-12 to HFC-134a will reduce the greenhouse impact of mobile air conditioners by more than 90 percent. Serious efforts at refrigerant recovery and recycling in the mobile air conditioning industry can further reduce this greenhouse contribution to less than 5 percent of its present level. No nonfluorocarbon alternative air conditioning technology is currently suitable for this mobile market. The alternative technology most frequently considered is the Stirling gas refrigeration cycle (using helium or nitrogen), but there has been no demonstration of a high cooling capacity, energy

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Page 386 efficient, reasonably priced Stirling air conditioning system suitable for vehicle applications. The electronics industry accounts for roughly one-fourth of CFC demand in the United States. This industry currently uses CFC-113 solvent to clean semiconductors and circuit boards. Recovery and recycling technology is available, and equipment is already in place for an estimated 50 percent of the applications; implementation of the best available equipment technology in the remaining 50 percent could reduce emissions by 25 percent or more. Water-based solvents are alternative cleaning agents used by a number of companies (ICF, 1987). These systems afford a trade-off of longer-lived CFCs for shorter-lived volatile organic carbon (VOC) emissions and increased waste-water treatment loads for municipal and industrial waste treatment facilities. Halons are used to extinguish fires and are mainly contained within fire extinguishers, tanks, and so on, until released during testing or actual use. Seventy-five percent of halon emissions occurred during testing prior to the Montreal Protocol. Currently, the industry has ceased using halons as a requirement in the test. Not-in-kind substitutes are not yet available for these compounds (Cogan, 1988). Recently, two U.S. companies (Great Lakes Chemical Corporation and Du Pont) announced potential halocarbon substitutes for these halons. Large-scale demonstration of these substitutes has yet to be accomplished. Carbon tetrachloride (CCl4) and methyl chloroform (CH3CCl3) emissions are controlled in the amended Montreal Protocol because of their potential contributions to ozone depletion. The use of CCl4 will be eliminated by 2000, and the use of CH3CCl3 by 2005. As can be seen from Table 25.2, both compounds are relatively small contributors to calculated global warming (<1 percent in 1986). The primary use of CCl4 is as a feedstock to produce CFCs 11 and 12. Only very small amounts (less than 1 percent of the quantity consumed) are emitted to the atmosphere during CFC production. However, based on atmospheric measurements of the concentrations of CCl4 and its model-calculated lifetime, atmospheric emissions of CCl4 are estimated at about 10 percent of the amount used for CFC production. This indicates that significant emissions occur from other uses. Carbon tetrachloride was used extensively as a solvent. However, in the United States and most other developed countries, CCl4 is currently used as a solvent in only very specialized applications with tight control on atmospheric emissions due to concerns about toxicity. Thus it appears unlikely that the United States, Japan, Western Europe are major sources of CCl4 emissions. Based on analysis of measurements of CCl4 and CFCs on the coast of Ireland, Prather (1985) concluded that Europe and, in particular, Eastern Europe might constitute a significant source of CCl4 emissions; however, uncertainties in the

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Page 403 efficient extractors of atmospheric nitrogen) with grains. More organic waste recycling would also be helpful, and its use could be effectively increased. An alternative mitigation approach is the application of additional chemicals that reduce N2O emissions from soils. A summary of possible mitigation techniques includes the following: • controlling erosion, • improving crop varieties, • matching available nitrogen to crop needs, • using the lowest-emitting nitrogen fertilizers whenever suitable, • adding nitrification inhibitors to fertilizers, • limiting fertilizer use, and • extending no-tillage or low-tillage farming using nitrogen-fixing plants. Barriers to Implementation Fertilizer use has long been essential to efficient agricultural production. Many improvements in crop varieties have depended on an enhanced responsiveness to fertilizers to achieve greater productivity. For many less-developed countries a reduction in nitrogen fertilizer use would be seen as a strong and direct threat to their capacity to produce food. Many countries have been actively seeking to increase fertilizer use (Barker and Herdt, 1985; Hayami and Ruttan, 1985). In developed countries where there is an interest in controlling production of commodities as part of farm programs designed to achieve higher prices, a nitrogen tax, provided it applied to all farmers for all uses, would probably be politically feasible. The political feasibility of such programs is discussed in the section on "Methane" above. Policy Options Nitrogen fertilizer use is widespread, being heaviest in Europe. Some crops in some countries use little fertilizer (cassava and legumes), but cotton, paddy rice, and maize rely heavily on nitrogen fertilizer. A ban on nitrogen fertilizer would have a major impact on the production of these crops. Thus a tax to reduce N2O emissions could be quite costly. In most developing countries, extension advisors to farmers usually recommend more nitrogen fertilizer use than farmers actually apply. In general, the value of the increase in crops produced by nitrogen fertilizer—the "marginal product"—is higher than the price of the fertilizer applied (Hayami and Ruttan, 1985). Several studies of fertilizer demand estimate that a 10 percent increase in price (from a tax) would decrease use by roughly 5 percent (Gardner, 1987).

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Page 404 If such a tax were applied on all nitrogen fertilizer in the United States, it would have a cost of $25 million and would reduce N2O emission by 50,000 t N/yr at a cost of $500/t N. Research and Development Biological efficiency can be improved by supporting and strengthening agricultural research programs. CH4 reduction objectives can be incorporated directly into research programs. Specific programs for animal improvement can be implemented. Past experience with agricultural research programs indicates that most programs have been highly productive (Evenson, 1990). Expanded support for CH4 concerns is likely to be effective. Paddy rice production and consumption can be reduced by enhancing substitutes such as upland rice. The production of such rice could be improved through research programs. It should be recognized, however, that the substitute crops for upland rice are other upland crops, not paddy rice. More upland rice production will increase rice supplies and lower rice prices generally, however, thus having a small discouragement effect on paddy rice production. Ruminant products could be replaced with cereal-based substitutes with additional development. Given that substantial research and development activities directed toward this objective are in place, it is unlikely that a specific subsidy to such research and development would speed up the process significantly. Subsidies to substitutions for rice and ruminant products would reduce CH4 but could be more costly than other policies (see below). Naturally produced or fixed nitrogen by plants is quite important and may be enhanced by further research. Legumes (e.g., beans, soybeans, and lentils) fix nitrogen. The Azolla fern is used in parts of Asia to fix nitrogen in rice fields, but its use is limited by high labor requirements and temperature sensitivity. Conclusions The agricultural sector constitutes a major sink for sequestering of carbon, and because this carbon is constantly recycled, the sink is a long-term one. The sector is a major source of CH4 and N2O, and to the extent that agricultural production uses fossil fuels it is also a small source of CO2. Land use change also leads to direct emission of CO2. The political climate for policies (e.g., taxes, subsidies, and buyouts) to reduce CH4 and N2O emissions through reductions in supply of ruminant products and rice in the United States is favorable because farm interest groups seek higher prices; however, there is some concern regarding the efficiency and effectiveness of such mechanisms. For other industrialized

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Page 405 countries, the political situation is similar and would likely not constitute a major barrier to the implementation of greenhouse gas emission control options. Developing countries, on the other hand, offer quite a large scope for potential greenhouse gas mitigation. Political and distributional concerns are barriers to mitigation options in these countries because they often reduce production and consumption of vital goods. International mechanisms for sharing costs would be required to realize mitigation in many developing economies. Finally, although there are few impending breakthroughs in technology, the potential for improved technology from research and development in both food and biomass fuel production is good in the long run. Landfill Methane On a worldwide basis, municipal landfills are a relatively small but increasing source of CH4 emissions to the atmosphere. The EPA estimates that worldwide landfill emissions account for approximately 3 percent of total global CH4, but that this would increase to roughly 7 to 9 percent by 2025 in the absence of new abatement measures (Lashof and Tirpak, 1990). For the United States, however, landfills are the largest source of CH4 emissions, as seen in Chapter 19. Landfill CH4 is produced primarily by the decomposition of municipal and industrial solid wastes under anaerobic conditions (i.e., a lack of oxygen). The quantity and rate of CH4 production depend on a number of factors, including composition of the waste; age, moisture and oxygen content, temperature, and acidity (pH); and the presence of nutrients or biological inhibitors that either stimulate or repress the activity of bacteria responsible for decomposition. Biological decomposition in landfills is typically accompanied by other chemical reactions and by vaporization of some landfill constituents. Thus ''landfill gas" includes not only CH4, but CO2, nitrogen, and a variety of non-CH4 organic compounds. The average composition of waste at active U.S. landfills is shown in Table 25.5. Household waste at approximately 72 percent (by weight) is the largest contribution by far. Figure 25.7 depicts the typical evolution of landfill gas constituents, illustrating the dominant biochemical processes over time (U.S. Environmental Protection Agency, 1990a). Actual elapsed time is measured in decades and depends on landfill composition. As a rough approximation, most studies assume that landfill gas is 50 percent CH4 and 50 percent CO2 by volume, with trace amounts of other constituents. The time required for significant production of CH4 can vary from 10 to 100 years or more, depending on the landfill properties noted above. The

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Page 406 TABLE 25.5 Average Composition of Waste in Active Municipal Waste Landfills Waste Type Mean Waste Composition (wt %) Household waste 71.97 Commercial waste 17.19 Household hazardous waste 0.08 Asbestos-containing waste material 0.16 Construction/demolition waste 5.83 Industrial process waste 2.73 Infectious waste 0.05 Municipal incinerator ash 0.08 Other incinerator ash 0.22 Sewage sludge 0.51 Other waste 1.19 SOURCE: U.S. Environmental Protection Agency (1990b). EPA estimates typical rates of CH4 production at 1000 to 7000 cubic feet per ton of municipal solid waste deposited (Lashof and Tirpak, 1990). Recent Trends Estimates of landfill CH4 and CO2 generally are based on population estimates for a particular region, together with assumptions about the quantity and composition of refuse associated with that population. Table 25.6 summarizes the assumptions employed by Barnes and Edmonds (1990) in a study for DOE. These estimates are based on the work of Bingemer and Crutzen (1987), who estimate current landfill CH4 emissions at approximately 30 to 70 Mt/yr worldwide. Note that the model described by Barnes and Edmonds (Table 25.6) does not include a time lag between waste generation and landfill gas emissions. In the United States, more detailed estimates of CH4 generation rates have recently been developed by EPA as part of a proposal for controlling air emissions from municipal solid waste (MSW) landfills (U.S. Environmental Protection Agency, 1990a,c). Table 25.7 summarizes EPA estimates of CH4 and non-CH4 organic compound emissions for new and existing landfills in 1997 in the absence of any regulatory action. A simple two-parameter model is used to estimate CH4 generation rates as a function of the landfill opening and closing dates and of the annual average refuse acceptance. The two chemical parameters in the model reflect the type of

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Page 407 image FIGURE 25.7 Evolution of typical landfill gas composition. SOURCE: U.S. Environmental Protection Agency (1990a). refuse in each landfill and the various dependency factors (temperature, moisture, and so on) listed earlier. As noted earlier, CO2 emissions are roughly comparable in magnitude to CH4 emissions on a volume basis. Adjusting for the differences in molecular weight, CO2 mass emissions thus are approximately 2.75 times greater than the CH4 values in Table 25.7. Emission Control Methods Reduction of CH4 from active or inactive landfills requires that the gas first be collected and then utilized in an energy recovery system or simply burned (flared). Either alternative produces CO2 and water vapor, but a net benefit in terms of greenhouse effects still results because CH4 contributes more radiative forcing than CO2 (see Chapter 19, Table 19.4) and because with CH4 as an energy source, some use of an alternative fuel has been displaced.

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Page 408 TABLE 25.6 Parameters for Estimating Landfill Gas Emission Rates Region Waste Generated (kg/person/day) Fraction of Waste to Landfill Organic Carbon Fraction in Wastea United States, Canada, and Australia 1.8 0.91 0.22 Other OECD countries 0.8 0.71 0.19 USSR and Eastern Europe 0.6 0.85 0.175 Developing countries 0.5b 0.08 0.15 aHalf of this is assumed to produce CH4 and half CO2. bBased on urban population only, assumed to be 22 percent of total. SOURCE: Barnes and Edmonds (1990). In the United States, approximately 17 percent of the operating municipal landfills employ some form of CH4 recovery and mitigation system, although less than 2 percent of the sites recover CH4 for energy use (Lashof and Tirpak, 1990). Recently, however, EPA announced its intent to require the collection and control of landfill gases under Section 111 of the Clean Air Act (which pertains to new sources). The EPA standards (for new sources) and guidelines (for existing sources) currently being drafted would apply to all municipal landfills emitting more than 100 t/yr of non-CH4 organic compounds (U.S. Environmental Protection Agency, 1990c). Such facilities would be required to design and install gas collection systems and then combust the captured landfill gases (with or without energy recovery). The combustion control device would have to be capable of reducing non-CH4 organic compounds in the collected gas by at least 98 percent. As background to its draft regulatory proposal, EPA analyzed three regulatory options for new and existing landfills. The three alternatives were based on cutoff sizes of 25, 100, and 250 t/yr of non-CH4 organic compounds from a given landfill. The lowest cutoff level would influence the greatest number of facilities. For each regulatory alternative, engineering and economic models were used to estimate the overall emission reductions and costs of landfill gas mitigation. The assumed control technology was an active gas collection system coupled with either a flare or an energy

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Page 409 TABLE 25.7 National Baseline CH4 and Non-CH4 Organic Compound Emission Estimates, 1997 Landfill Category Number of Landfills Methane Emissions (t CH4/yr) Nonmethane Organic Compound Emissions (t CH4/yr) Existing municipal solid waste landfills (active and closed) 7,480 1.8 x 107 510,000 New municipal solid waste landfills 928 5.3 x 105 10,000 All affected landfills 8,408 1.8 x 107 520,000 SOURCE: U.S. Environmental Protection Agency (1990b). recovery system for gas combustion. Because the latter option entails higher capital costs, its economical viability depends on the site-specific nature of by-product energy use or markets, which EPA was not able to evaluate. Thus the costs reported by EPA are based on application of active gas collection systems and flares to all landfills above the specified emission level cutoffs (U.S. Environmental Protection Agency, 1990c). The control cost results for new and existing landfills are presented in Table 25.8. The average CH4 emission reduction encompassed by the three regulatory alternatives ranges from 39 to 82 percent at costs of $9 to $29/t CH4 removed. The current EPA draft proposal calls for implementing "regulatory TABLE 25.8 Landfill CH4 Reduction Control Costs   New Landfills Existing Landfills Regulatory Alternative CH4 Reduction (%) Costa ($/t CH4) CH4 Reduction (%) Costa ($/t CH4) 1 82 28 81 29 2b 65 22 60 23 3 43 9 39 20 aMethane control costs shown were derived from figures reported by EPA normalized on non-CH4 organic compound emissions. Those costs were adjusted by using the reported ratios of non-CH4 organic compounds to CH4 for each regulatory alternative. All costs are based on a 1992 reference year. bAs calculated in Appendix M, the cost for this regulatory alternative is approximately $1/t CO2 equivalent. SOURCE: U.S. Environmental Protection Agency (1990c).

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Page 410 alternative No. 2," which would reduce CH4 emissions by 60 to 65 percent over the life of U.S. landfills. Because emissions, as well as capital and operating costs, vary significantly over the life of a facility, EPA's analysis employs a two-stage discounting procedure to calculate cost-effectiveness. First, capital costs are annualized over the useful life of the equipment by using a 10 percent rate of return. Then, the annual capital costs, operating costs, and emission reduction are brought back to a reference year (1992) by using a 3 percent social discount rate. Cost-effectiveness is calculated by dividing the total annualized cost by the total annualized emission reduction. Landfill lifetimes employed in the calculation range from 64 to 119 years, depending on the type of facility and the regulatory stringency. Although this calculation procedure differs from one used earlier in this report for CO2 reduction measures (where emissions do not vary from year to year), the discount rate assumptions employed by EPA are similar to those employed in earlier chapters. Note, however, that 1992 (the effective date for regulation) rather than 1990 is used as the basis for EPA's cost results. The panel's analysis of landfill gas cost-effectiveness in terms of CO2 equivalence, which is based on the EPA results in Table 25.8, is presented in Appendix M. Barriers to Implementation Of primary interest here are barriers to the utilization of landfill gas as an energy resource. The economic viability of this option is hampered both by the quantity of gas available and by the fact that the energy content of landfill gas is only about half that of natural gas. Thus, under present conditions, landfill gas is economically viable as a fuel only if used close to the landfill site (e.g., within 2 to 3 miles). One such option could involve coupling directly to an electricity grid via a co-generation plant. Landfill operators have not traditionally been concerned with by-product recovery and utilization, however. Most landfills also tend to be in relatively remote locations. Another significant impediment to energy recovery is that some existing state regulations establish unlimited liability for any potential contamination problems at landfill resource recovery projects (Lashof and Tirpak, 1990). Policy Options As discussed above, EPA already plans to require collection and combustion of landfill gas from large facilities. This policy will reduce the emissions of greenhouse gases. The magnitude of the reduction will depend on a final determination of the size of facilities affected.

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Page 411 In the long term, landfill gas emissions can be reduced through increased recycling so that less waste is available for decomposition. Alternative methods of waste disposal also could be promoted. For example, an analysis could be conducted that evaluated the relative greenhouse gas benefits of incineration versus landfill disposal. Policy incentives to encourage wider use of energy recovery systems could also be devised and implemented. Other Benefits and Costs The U.S. Environmental Protection Agency (1990a,c) lists four major health and welfare effects that motivate the regulation of landfill gas emissions: (1) human health and vegetation effects caused by tropospheric ozone, which is formed from non-CH4 organic compound emissions; (2) carcinogenicity and other health effects associated with air emissions of toxic species; (3) global warming effects of CH4; and (4) gas explosion hazards. Additional consequences cited by EPA are odor nuisance and hazardous effects on soil and vegetation (U.S. Environmental Protection Agency, 1990a). Policies that reduce waste generation would also help communities that are running out of landfill space. Research and Development One important focus for research and development is to explore and improve techniques for enhancing CH4 gas production yield from landfills. Methods such as the controlled addition of nutrients and moisture, control of landfill acidity, and bacterial seeding could help improve the economic viability of landfill gas recovery as an alternative to flaring (Lashof and Tirpak, 1990). Conclusions Major conclusions emerging from the above discussion on the potential mitigation of landfill gas are the following: • Municipal landfills account for a small but growing fraction of CH4 emitted from the decomposition of organic materials in refuse worldwide. • In the United States, EPA is about to promulgate new measures that would require the collection and combustion of landfill gas from larger facilities, thus reducing overall emissions from new and existing landfill sites. • The utilization of landfill gas as an energy resource is currently quite low. Increased research and development could enhance the economic feasibility of this energy option.

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Page 412 Note 1. Throughout this report, tons (t) are metric; 1 Mt = 1 megaton = 1 million tons; 1 Gt = 1 gigaton = 1 billion tons. References Aulisio, L. 1988. Presentation at International Conference on CFC and Halon Alternatives, Washington, D.C., January 14, 1988. Barker, R., and R. Herdt. 1985. The Rice Economy of Asia. Washington, D.C.: Resources for the Future. Barnes, D. W., and J. A. Edmonds. 1990. An Evaluation of the Relationship Between the Production and Use of Energy and Atmospheric Methane Emissions. Report DOE/NBB-0088P. Washington, D.C.: U.S. Department of Energy. Bingemer, H. G., and P. A. Crutzen. 1987. The production of methane from solid wastes. Journal of Geophysical Research 92:2181–2187. Cogan, D. G. 1988. Stones in a Glass House. Washington, D.C.: Investor Responsibility Research Center. Crutzen, P. J., et al. 1986. Methane production by domestic animals, world ruminants, other herbivorous fauna and humans. Tellus 38B;184–271. DeCanio, S. J., and K. N. Lee. 1991. Doing well by doing good: Technology transfer to protect the ozone layer. Policy Studies Journal 19(2):140–151. Du Pont. 1989. An Industry Perspective on Technology Transfer and Assistance to Help Less Developed Countries (LDCs) Phaseout of Chlorofluorocarbons (CFCs). Wilmington, Del.: E.I. du Pont de Nemours and Company. Energy Information Administration. 1989. Potential Cost of Restricting Chlorofluorocarbon Use. Service Report SR/ESD/89-01. Washington, D.C.: Energy Information Administration, U.S. Department of Energy. Eicher, C. K. 1990. Building scientific capacity for agricultural development. Agricultural Economics 4:117–143. Evenson, R. E. 1990. Human capital and agricultural productivity change. In Agriculture and Government in an Interdependent World, A. Maunder, ed. Alderahot, England: Dartmouth Publishing Co. Farman, J. C., B. G. Gardiner, and J. D. Shanklin. 1985. Large losses of total ozone in Antarctica reveal seasonal ClOx/NOx interaction. Nature 315:207–210. Gardner, B. 1987. The Economics of Agricultural Policies. New York: Macmillan. Hayami, Y., and V. W. Ruttan. 1985. Agricultural Development, An International Perspective. Baltimore: John Hopkins Press. ICF. 1987. Regulatory Impact Analysis: Protection of Stratospheric Ozone. Volume III, Part 7, Solvents. Prepared by ICF, Inc., for the Office of Air and Radiation, U.S. Environmental Protection Agency. Intergovernmental Panel on Climate Change. 1990. Climate Change: The IPCC Scientific Assessment, J. T. Houghton, G. J. Jenkins, and J. J Ephraums, eds. New York: Cambridge University Press. Krause, F., W. Bach, and J. Koomey. 1989. Energy Policy in the Greenhouse, Volume 1. El Cerrito, Calif.: International Project for Sustainable Energy Paths.

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