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5 Environmental Impacts of Alleviative Fuels AIR QUALITY, HEALTH, AND SAFETY EFFECTS The activity involved in producing, manufacturing, distributing, and us- ing fuels raises issues on a variety of adverse effects on the environment and on human health and safety. Environmental effects from liquid fuel production are presented in Chapter 4; only the end-use effect on the envi- ronment of using these alternative fuels is considered here (greenhouse gases are considered later). Pollutants, emissions, air quality, safety, and toxicity are addressed. Economic aspects of alternative fuels and vehicles are considered in Chapter 3. Currently, U.S. local, state, and federal governments are interested in reducing emissions from motor vehicles and stationary sources in those regions that fail to meet ambient ozone standards. One proposed strategy to reduce ozone is to decrease emissions from gasoline-powered vehicles of volatile organic carbon (VOC) compounds and nitrogen oxides (NO), pre- cursors to ozone formation. The California Air Resources Board (CARB) has established a hydrocarbon exhaust standard about 40 percent more strin- gent than the U.S. Environmental Protection Agency's (EPA) standard of 0.41 g/mile. Clean Air Act bills have been introduced to require a similar standard for the other 49 states. CARB is also considering an even more stringent emission standard for vehicles, as required by the air quality man- agement plan for the Los Angeles area. Efforts are also under way to design engines or use fuels that will meet the stricter diesel particulate standards in the 1990s. The U.S. government is encouraging the use of alternative fuels through the testing of demonstration fleets and research on alternative-fueled vehicles (U.S. Congress, 1988b). In addition, President 105

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106 FUEl~ TO DRIVE OUR FUTURE Bush's Clean Air Act proposals call for the introduction of such vehicles in urban areas that have unusually severe air quality problems. Important vehicle fuel options include compressed natural gas (CNG), methanol, and reformulated hydrocarbon-based fuels. Electric vehicles could potentially be used in niche markets and could certainly reduce automotive emissions (Wang et al., 1989~. Hydrogen vehicles are a potential long-term option (DeLuchi, 1988; Ogden and Williams, 1989~. Reformulated fuels, electricity, and hydrogen are not considered here in any detail. Analysis of alternative fuels and emissions requires the consideration of which fuel- engine-emission control technology combinations are capable of meeting emission standards with the least cost and inconvenience to motorists. These trade-offs are not considered in detail in this study. Automobile Exhaust Emissions and Air Quality There is a great deal of uncertainty in determining the impact on air quality of different fuels. A variety of air quality impacts between different fuels have been reported, especially for ozone (Arson et al., 1989; DeLuchi et al., 1988b; Dunker, 1989; Harris et al., 1988; Long et al., 1986; Moses and Saricks, 1987; Nichols and Norbeck, 1985; Sierra Research, 1988; Whitten et al., 1986~. First, actual emission rates are determined by trade- offs between emissions standards, costs, performance, and driveability. If a particular fuel offers the potential for easier emission control, then engines designed to emit the maximum allowed can gain other benefits such as reducing the cost and complexity of pollution control equipment and in- creased performance. Actual emissions will likely vary considerably across vehicle make and model. Also, there are limited emission data for alterna- tive-fueled vehicles at low mileage and virtually no data on performance of their emission control systems at high mileage and in actual use by typical motorists. Most pollutant production is sensitive to the air-to-fuel ratio of engines. If future engines are designed to run "lean" (using high air-to-fuel ratios) to achieve greater fuel efficiency, then for moderately lean mixtures the NOx levels would be higher and carbon monoxide and hydrocarbon emissions and engine power would be lower than those of engines operating at stoi- chiometric ratios, as do most of today's gasoline engines. However, almost all automobiles now (and for the foreseeable future) use three-way catalysts with the air-to-fuel ratio controlled to approximately stoichiometric condi- tions. This means that comparisons of the carbon monoxide production at lean fuel mixtures are valid but are irrelevant unless the catalysts and air-to- fuel ratios used in automobiles are changed. R&D is being conducted on lean-burn engines, but to date they have not been able to meet emission standards for oxides of nitrogen.

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ENVIRONMENTAL IMPACTS 107 A distinction must also be made between single-fuel fully optimized engines and multifuel engines, and the fuel used must be specified clearly since some methanol emission data are based on a fuel consisting of 100 percent methanol, while others contain 10 or 15 percent gasoline. Analysis becomes even more complicated for multifuel methanol-gasoline engines, since they will operate on various blends of methanol and gasoline. For improved cold starting and flame visibility, about 15 percent gasoline will probably be added to methanol. Moreover, specifying environmental ef- fects is complicated. The ozone formation process is highly complex; even the most sophisticated photochemical air quality models have error margins of 30 percent or more in predicting hourly averaged ozone concentrations (Russell, 1988; Tesche, 198X). Ozone formation also depends on the ratio of reactive hydrocarbons to oxides of nitrogen (RHCs/NO) in the atmos- phere, which varies greatly among urban areas. Only in the Los Angeles area have sufficient meteorological and spatial pollutant concentration data been collected to operate multiday photochemical airshed models; results from Los Angeles, however, cannot be generalized to other regions. Surveys of published data generally conclude that a reduction in peak ozone level of 0 to 20 percent might be attainable from complete substitu- tion of methanol for gasoline (Beyaert et al., 1989; DeLuchi et al., 1988b). Generally, more recent studies using more realistic assumptions predict less benefit than older studies. Even the recent studies assume catalytic reduc- tion of formaldehyde to low levels, which has not yet been demonstrated at high mileage or for public use. Emissions of formaldehyde, which is photo- chemically very reactive, are about three to six times higher from current methanol-fueled prototype cars than from those operated on gasoline, and technology to bring formaldehyde emissions down to gasoline fuel levels has not yet been demonstrated? though California has emission standards in place requiring major reductions before methanol vehicles can be sold, be- ginning in 1993. While not yet clearly established, it appears that, if the formaldehyde concentration in the methanol exhaust can be reduced to that produced by gasoline-fueled cars, some regions may reduce smog by using methanol. Present catalysts, optimized for gasoline, do not attain this goal. Whether new catalysts can (at high mileage in actual use) achieve the levels set by California is not yet clear. The problem is further complicated when multi- fuel cars are used it is more difficult to find a catalyst equally effective for both fuels. CNG vehicles emit very little carbon monoxide (if operated at a lean air- to-fuel ratio) and much less reactive hydrocarbons than gasoline vehicles. CNG will have less smog-producing reactive exhaust pollutants than gaso- line vehicles if NOX emissions can be controlled adequately. Most data to date indicate that CNG vehicles may produce as much, or more, NOX because

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108 FUELS TO DRIVE OUR FUTURE the current three-way catalyst technology is not effective unless carbon monoxide is present. It is too soon to have any air quality models of the impact of different reformulated gasolines on airsheds. In summary, there is considerable uncertainty about the air quality bene- fits of practical alternative fuel-engine-emission control combinations over present fuels. Methanol produces more formaldehydes in the exhaust, which can react immediately to produce smog. This will require development of effective and durable emissions controls. Methanol's ability to reduce smog depends on solving the cold-starting and engine durability problems of methanol vehicles, the development of catalysts more effective at reducing aldehyde emissions, and nontransportation factors that affect the RHC/NOX ratio in the atmosphere in different airsheds. Reformulated gasoline could also be used in all vehicles and may also produce air quality benefits with- out the cost, consumer acceptance, and other problems associated with es- tablishing a new fuel distribution system and redesigning vehicles, but no data are available to support this. Additional R&D is needed before valid judgments can be made about the comparative environmental effects of various fuels. Air Quality Impacts of Diesel Engines The U.S. diesel fuel market is about 0.58 billion bbVyear compared to 2.6 billion bbl/year of gasoline use for 1988. CNG and methanol may be used in modified compression ignition (diesel) engines. The conclusions on spark ignition engines are roughly the same for compression ignition en- gines. Use of methanol or CNG instead of diesel fuel dramatically reduces particulates emissions and, because there is no sulfur in these fuels, sulfur oxide emissions; methanol may also significantly reduce NOX emissions depending on the engine design (Arson et al., 1989; Unnasch et al., 19861. However, heavy-duty methanol engines emit substantially more methanol, formaldehyde, and carbon monoxide than do diesel engines and would re- quire oxidation catalyst systems and evaporative emissions controls that are not now needed for diesel engines. It is believed that satisfactory catalytic oxidation systems cannot currently be designed for the wide range of ex- haust temperature and composition encountered in diesel exhaust. How- ever, the continued use of diesel fuel will probably also require expensive changes and additional costs to meet 1991 and 1994 emission standards. Because of EPA emission regulations that take effect in 1991, diesel urban transit buses will probably be the first market penetrated by methanol and CNG, but this market is dispersed and small, representing a total of only about 30,000 bbl/day in the United States (ORNL, 1987~. Further penetration of the diesel market is likely to lag behind penetration of the

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ENVIRONMENTAL IMPACTS 109 gasoline market, because of high fuel costs and poor compression ignition characteristics and because diesel engines are not replaced as often. Safety There are different safety issues for the different alternative fuels. For example, leakage of natural gas from pressurized tanks in closed spaces creates the potential for explosions. Pure methanol burns with an invisible flame in daylight, although adding 15 percent gasoline makes the flame visible. Under normal ambient temperatures, methanol produces a flam- mable mixture in storage tanks, vapor control systems, and vehicle fuel tanks. Although there are different fire and safety issues for different fuels, proper engineering, handling, and education may adequately address these differences. Toxicity Methanol is toxic, as is gasoline. Ingestion of methanol is followed by a 12- to 24-hour latent period of no symptoms and then signs of poisoning, progressing to possible blindness, permanent neurological damage, and death without prompt medical attention. Since gasoline itself is toxic, combining gasoline and methanol raises questions about the toxicity of, and medical treatment for exposure to, the blends compared to each fuel alone (Beyaert et al., 1989~. There are also concerns about chronic toxicity from human absorption through skin or inhalation in atmospheres with low ambient con- centrations of methanol. Drinking water can be contaminated by either methanol or gasoline, but odor and taste thresholds for methanol are much higher and it may not be detected in water supplies unite significant human exposure has occurred. Methanol also has a significant cosolvent effect on water-insoluble hydro- carbons, possibly leading to increased concentrations of hydrocarbons in groundwater from releases of methanol and gasoline mixtures. Better under- standing is needed of the effects of exposure to methanol liquids and metha- nol and formaldehyde vapors. There are also concerns about the long-term effects of exposure to hydro- carbon vapors, particularly benzene and the other volatile aromatics. At an appreciable cost, aromatics can be converted to naphthenes by hydrogena- tion; however, the elimination of tetraethyl lead has made current gasolines and vehicles more dependent on the high octane number of aromatics. This removal would require replacement by other high-octane-number compo- nents such as oxygenated hydrocarbons at some increased cost and with uncertain impacts on air quality. An alternative is use of low-compression-

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110 FUELS TO DRIVE OUR FUTURE ratio engines that will tolerate low octane number. These engines would suffer from higher fuel consumption for the same power, since efficiency is reduced by reducing compression ratios. Another alternative is develop- ment of stratified charge engines, which are less sensitive to octane number. Except for diesel engines, stratified charge engines, despite considerable development effort, have not yet been successfully commercialized. Conclusions and Recommendations Because of different assumptions about vehicle emissions, vehicle re- placement rates, and ratios of RHCs to NOx ambient levels, air quality models incorporating substitution of gasoline-powered vehicles by metha- nol-fueled vehicles vary widely in predictions of tropospheric ozone reduc- tion. Using optimistic assumptions for the California South Coast Air Ba- sin and some other areas, significant potential improvements are predicted if formaldehyde emissions can be controlled adequately. These results are very sensitive to modeling uncertainties and to the ratio of RHCs to NOx in the ambient atmosphere, and they depend heavily on developing more ef- fective catalysts and other control technology. Actual effects may range from adverse to beneficial. Ozone benefits of CNG have received less research attention but are likely to be greater than those of methanol if NOx emissions can be controlled. Impacts of reformulated gasolines have not been extensively investigated, but ARCO recently introduced a reformu- lated regular gasoline in Los Angeles that is claimed to be significantly less polluting. Methanol has different health and safety impacts than gasoline, but it is not necessarily superior or inferior to gasoline. CNG is not toxic and may be generally safer than gasoline and methanol. The committee makes the following recommendations: The DOE should cooperate with the automobile and fuel industries and other government agencies such as the EPA and the National Institutes of Health (NIH) to investigate the opportunities for reducing automobile emissions with investigations using a total systems approach resource to disposalto adequately compare fuel-engine-emissions control combina- tions. This research would facilitate the design and production of cost- effective, environmentally acceptable fuel-vehicle combinations. . DOE, along with EPA and others, should try to resolve uncertainties about the air quality and health effects of fuel and vehicle options. Emis- sions quantities and compositions for advanced-technology vehicles need to be evaluated more extensively, simulating use by typical motorists and employing more accurate photochemical air quality models for different urban areas. This work should lead to a comprehensive data base, inde-

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ENVIRONMENTAL IMPACTS pendent of any decisions (government or private) to commercialize particu- lar engines or fuel types. GREENHOUSE GAS EMISSIONS 111 As mentioned previously, the accumulation of greenhouse gases in the atmosphere may lead to global warming. The extent of global warming, its timing, and its potential impacts are highly uncertain at this point. How- ever, because the impacts of changed climate and weather patterns could be so great, it is important to think through contingency planning. One strat- egy may be to significantly reduce greenhouse gas emissions from human activity. If this strategy becomes policy, a premium will be placed on energy conversion and end-use technologies that reduce these emissions. The committee has not extensively analyzed greenhouse gas emissions for different fuels and feedstocks. However, to give some perspective on the relative contributions of different alternatives, some data from the literature are presented. The raw material production, manufacture, transportation, and combus- tion of fuels produces greenhouse gases carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone (O3) in amounts depending on the fuel and technologies used. Calculations have recently been made of the production of greenhouse gases from different fuels and vehicles, consider- ing emissions from the entire fuel cycle (DeLuchi et al., 1989; DeLuchi, 1989~. The results are expressed in CO2 equivalents by converting the mass emissions of those gases other than CO2 into the mass amount of CO2 that would have the same temperature effect. Same temperature effect is de- fined in degree-years over a given period, where 1 degree-year is an in- creased surface temperature of 1C for 1 year. Differences in vehicle effi- ciency are also factored in. Results are expressed as CO2-equivalent emis- sions compared to those vehicles using gasoline and diesel derived from petroleum (Table 5-1~. Transportation fuels such as gasoline, diesel, alcohols, and CNG can be manufactured from plant matter such as wood. If no nonrenewable carbon fuel is used in growing, harvesting, or manufacturing these fuels, at steady state there should be no net contribution of the greenhouse gas CO2. How- ever, this is by no means the situation for energy-intensive crops such as corn that require major energy inputs for planting, fertilizing, harvesting, and drying. CNG vehicles using fossil methane have a lower production of green- house gases than gasoline-powered vehicles, although this result depends on assumptions about the relative contributions of CH4 and CO2 to global warming and on CH4 emissions from production and use (DeLuchi, 1989; Ember et al., 1986~. In this particular analysis, CNG is 19 percent better

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112 FUEL TO DRIVE OUR FUTURE TABLE 5-1 Approximate Greenhouse Gas Emission per Mile Relative to Pe~oleum-Powered Internal Combustion Engines Fuel and Feedstock Percent Change Current Technology CNG, gasoline, diesel, or methanol from biomassa Gasoline and diesel from crude oily CNG from natural gasC Methanol from natural gasC Gasoline from oil shale Methanol from coal (baseline)C Potential Advanced Technology -100 o -19 - 3 27 to 80 98 Gasoline from coal or shale using nonfossil 0 sources for process heat and hydrogene aPercent charge is for CO2 only. This is true only for biomass processes that do not use fossil fuel, that do not displace land from forest that would otherwise sequester carbon in its biomass, and that are grown every year so that carbon dioxide from fuel use is talcen up by the crops. bShould be increased by 25 to 33 percent for thermally en- hanced oil recovery. CThe analysis considered emissions of CH4, N2O, and CO2 from the production and transportation of the primary resource (coal, natural gas, or crude oil); conversion of the primary re- source to transportation energy (e.g., natural gas to methanol); distribution of the fuel to retail outlets; and combustion of the fuel in engines, except as noted. N2O emissions from vehicle engines were not included. Emissions of ozone precursors, chloro- fluorocarbons (CFCs) from air-conditioning systems, and water (H2O) were not considered (available data and models do not allow estimation of the greenhouse effect of emissions of ozone precursors; CFC emissions are independent of fuel use; and H2O emissions from fossil fuel use worldwide are a negligible per- centage of global evaporation). The composite greenhouse gas is actual mass emissions of CO2 plus CH4 and N2O emissions con- verted to mass amount of CO2 emissions with the same tempera- ture effect. dConsiders only CO2. eNonfossil sources could be biomass, nuclear, or solar energy devices. SOURCE: Adapted from DeLuchi et al. (1988a) and DeLuchi (1989~.

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ENVIRONMENTAL IMPACTS 113 than petroleum-based gasoline; however, the methane equivalency factor is uncertain, and varying it from 5 to 30 (instead of using 12) would cause the CNG impact to be ~ to -25 percent (DeLuchi et al., 1988~. Because of coal's lower hydrogen-to-carbon (H/C) ratio, using coal as a feedstock with current technologies for transportation fuels would increase greenhouse gas emissions significantly. However, if nonfossil sources of energy were used for hydrogen production and process heat for the conver- sion processes, the net effect of coal-based fuels would be about the same as for fuels from petroleum. CO2 emissions from shale conversion would vary widely depending on the process technology. Western oil shale kerogen has a higher hydrogen and lower oxygen content than coal, resulting in less CO2 emissions from hydrogen and heat generation. However, decomposition of shale carbonates can release CO2. Calculations indicate that carbonate decomposition of shale rock would be held below 10 percent from a hot solids retorting process, releasing about 24 gC/megajoule as CO2, a 27 percent increase over 19.2 gC/megajoule for burning petroleum. Modified in situ (MIS) processes decompose a large fraction of the carbonate rock and 100 percent decomposition releases about 35 gC(as CO2~/megajoule, about 80 percent more than petroleum. Thermally enhanced oil recovery would produce more CO2 than conventional petroleum recovery because it typically takes about 25 to 33 percent of the oil produced for thermal heating. This in- crease would not occur if nonfossil sources of heat were used. Schulman and Biasca (1989) calculated CO2 emissions for different fuels in terms of pounds of CO/million Btu. Their results also show significant increases of using coal in comparison to petroleum or natural gas but do not include the other greenhouse gases. There are significant uncertainties in all these calculations. However, in general, feedstocks of lower H/C ratios generate more greenhouse gas emis- sions. For conversion processes using coal for process heat and hydrogen production, coal-based fuels look the least attractive for limiting green- house gases. However, successful R&D on conversion processes and use of nonfossil energy for process heat and hydrogen production can reduce the impact to the equivalent of that from petroleum-based fuels and of methanol from natural gas. In any long-term evaluation of greenhouse gas strategies, consideration of the contribution of the entire transportation sector to the global effect and the various trade-offs involved in fuel manufacturing and in switching to alternative fuels, vehicles, or transportation systems is needed. Conclusion Because manufacture of transportation fuels from coal and oil shale re- sources produces more CO2 than processes based on oil, natural gas, or non-

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114 FUELS TO DRIVE OUR FUTURE energy-intensive biomass, a special effort should be made to identify and pursue opportunities for reduction in CO2 emissions from these sources. Biomass could supply the hydrogen or heat for fossil fuel conversion processes. Since biomass supply will probably limit its use, system studies of the optimum use of biomass for reduction of CO2 emissions from fossil fuel conversion are recommended. In the longer term other nonfossil en- ergy sources for heat and hydrogen production should also be investigated.