A L T E R N A T I
-
TRANSPORTATION FUELS AND AIR QUALITY The use of alternative fuels h received much attention in cent years as a method to mi mize this country’s reliance foreign energy sources a way to minimize comb
..
programs ha nandated in the 1990 Cle 4ir Act Amendments whi have natio implicati
,
(NAAQS) for carbon monoxi: le and ozone well into the next century. Due to these concerns the use of alternative fuels has become a prominent cornerstone in air pollution reduction programs, as evidenced by their inclusion in the 1990 Clean Air Act Amendments (CAAA),even though quantitative assessments of the air quality benefits of such fuels have not been completed ( I ) . Three different alternative fuel programs have been mandated in the 1990 CAAA which have nationwide implications. The first is a summer reformulated gasoline program which will be required after 1995 in the nine worst ozone nonattainment areas. Gasoline available in the summer (the season when ozone levels are the highest] in these areas will have to be reformulated to be less polluting, including requirements for 2% by weight oxygen content, and a benzene limit of 1% by volume. Second, there are provisions for a winter oxygenated gasoline program, requiring 2.7% fuel oxygen content, which is aimed at reducing CO emissions in areas of 1190 Environ. Sci. Technol., Vol. 25, No. 7. 1991
.
Tai Y.Chang Robert € Hammerle I. Steven M. Japar Irving T. Salmeen Ford Motor Company
Dearborn, MI 48121 CO noncompliance. Finally, there is a clean-fuel fleet program that will impact about 20 current ozone nonattainment areas, starting in 1998. Under this program, new motor vehicle fleets must include some percentage of low-emission vehicles, specifically those which can operate on reformulated gasoline, metha n o l , compressed n a t u r a l gas (CNG), liquid petroleum gas (LPG), or other clean fuels. In addition to federally mandated programs, a number of states are phasing in their own clean-fuel initiatives. California has established low-emissions vehicleslclean fuels requirements which are designed around conventional vehicles (CV), transitional low-emission vehicles (TLEV),low-emissionvehicles (LEV)
and ultra low-emission vehicles (ULEV) (see Table I), and zero emission vehicles (ZEV). For 1994 and beyond, manufacturers will be required to meet an annually decreasing yearly fleet-average nonmethane organic gases (NMOG) standard using any combination of CV, TLEV, LEV, ULEV, and ZEV.In addition, clean fuel programs affecting fleet operators, mainly of government fleets, have been adopted by Texas, Oklahoma, Louisiana, and Colorado. A number of assessments of the impact of alternative fuels on vehicle emissions have been carried out (2-8).Because vehicles designed to use such fuels have not yet been optimized and tested, all of these studies suffer from a paucity of reliable emissions data, especially on in-use emissions. Nevertheless, the environmental impact of probable emissions from alternative-fuel vehicles on air quality can be estimated from knowledge of atmospheric chemistry ( g ) , the general impact of vehicle emissions on that chemistry, and the reactivity of NMOG emissions in the atmosphere (10-1 3). Alternative-fuel emissions Because emissions data are currently available only from initial prototype alternative-fuel vehicles, we will not try to summarize the available data in detail. Instead, in Table 2, we present a qualitative summary of emissions from alternative-fuel vehicles relative to those from gasoline-fuel vehicles. These estimates are based on available data, our knowledge regarding
0013-936W91/0925-1190$02.50/0 0 1991 American Chemical Society
available technology, and some educated guesses about technological advances. The discussion will be limited to NMOG and nitrogen oxides (NO,), primarily of importance in the formation of urban ozone, and carbon monoxide (CO), air toxics, and carbon dioxide (CO,). Emissions of sulfur dioxide will not be considered because motor vehicles, including diesels, do not contribute substantially to the national sulfur dioxide emission inventory. Particle emissions will be considered within the context of air toxics.
/I
1
Air quality impact
Urban ozone. Ozone is the most pervasive and persistent urban air quality problem. In spite of significant reductions in vehicular hydrocarbon and NO, emissions in the past two decades, more than 90 urban areas currently violate the NAAQS for ozone (14). With the current emission control schedule, many areas are projected to continue to violate the NAAQS into the next century. One of the ozone air quality benefits of alternative-fuel vehicles is that their NMOG emissions have lower photochemical reactivity for ozone formation than the NMOG emissions from conventional gasoline-fuel vehicles (12,23, 25). The photochemical reactivity of vehicle emissions can be compared in terms of an “ozone-forming potential,” which is defined as the increase in ozone level calculated to occur when the NMOG emitted by a vehicle are added to a typical urban air parcel and exposed to sunlight. This ozoneforming potential is calculated using a mathematical model of an urban area which includes an emissions inventory, meteorology, and a representation of the appropriate atmospheric chemistry (10-13). The data needed to evaluate the ozone-forming potential of emissions are NMOG emission rates and chemical compositions. The emission information presented in Table 2 is inadequate for the task because it only represents trends in total NMOG emissions. At this time, only limited speciated emissions data are available for alternative-fuel vehicles, and considerable judgment is necessary in projecting these data to future vehicles, This situation will improve considerably in the near future, especially for vehicles operating on reformulated gasoline, methanol, and methanol blends, because of a number of ongoing research programs, in-
1 ---
1
cluding the AutoIOil Air Quality Improvement Research Program. (The Auto/Oil Air Quality Improvement Program, jointly sponsored by the automotive industry and the oil companies, is currently under way. Phase I test fuels include reformulated gasolines, methanol, and oxygenated fuels. Phase I1 testing will include other alternative fuels.] A comparison of ozone-forming potential of future NMOG emissions from alternative-fuel vehicles relative to current gasoline-fueled vehicles is presented in Figure 1. Both exhaust and evaporative emissions have been considered in deriving ozone-forming potentials for the various motor vehicles. The ozone-forming potentials cited here were calculated using estimated NMOG emissions for the various alternative-fuel vehicles and estimat-
ed reactivities (13)of the NMOG species at typical urban environmental conditions, particularly the NMOG/NO, ratios observed in urban areas. These ratios depend on emissions from both mobile and stationary sources. Because the alternativefuel vehicles may have somewhat higher or lower NO, emissions than gasoline vehicles, their use may tend to change the atmospheric NMOG/NO, ratios. However, because all of these alternative-fuel vehicles emit significant amounts of NO,, either directly or during fuel production, and because the observed NMOGINO, ratios are highly variable, both temporally and spatially, as a first approximation we have calculated the ozone-forming potentials at current average urban NMOGINO, ratios. The estimated
Environ. Sci. Technol., Val. 25, No. 7,1991 1191
values are highly uncertain; conseauentlv, ranges of values are given cn Figure 1. Reformulated easoline. There is a signkcant oppo&mity for reducing exhaust and evaporative emissions through changes in gasoline composition. However, the estimated ozone-forming potential for reformulated gasoline is very uncertain because such fuels are currently being developed. Reductions of about 15-20% in ozone-forming potential per vehicle may be possible compared to current gasoline, with the benefit coming both from reduced fuel volatility, that is, lower running loss and evaporative emissions, and from exhaust composition changes leading to lower exhaust reactivity. Data soon to be available from the ongoing AutolOil program will add considerably to our knowledge of the environmental impact of reformulated gasolines. Methonol. NMOG emissions from pure methanol (M100) Fuels will be significantly lower than those from gasoline, due to large reductions in evaporative and running loss emissions and reductions in tailpipe emissions. For methanol blends using 15% gasoline (M85), these reductions are significantly smaller. However, MlOO is currently not a practical automotive fuel because of cold start difficulty and safety problems such as the flame invisibility. Nearly all photochemical modeling studies ( 1 6 ) show that methanol fuel has a lower ozone-forming potential than gasoline, and currently we estimate that the reduction is likely to be only in the range of 2550% because of relatively high emissions of very reactive formaldehyde. Formaldehyde emissions from current methanol-Fuel vehicles are on the order of 5-50 mglmile, or, at the high end, an order of magnitude higher than those from gasoline vehicles (17. 18).The possibility of reduction of the ozone-forming potential from methanol-fuel vehi. cles beyond 25% is dependent on the magnitude of the in-use formaldehyde emissions. Ethonol. Emissions data from vehicles fueled with neat ethanol (E100) or high-percentage ethanol blends such as E90 are too limited to reliably estimate ozone-forming potentials. Available emissions data indicate that a reduction of about 20% in ozone-forming potential may be possible, with the major benefit associated with a reduction in evaporative emissions. A special developmental effort may be need-
-
-
vehiclea exhaust emission standards” NMOG
co
0.41‘ 0.25 0.125
3.4
0.39 0.25 0.125 0.075
0.040
1.7
iond lowemission vehicle; LEV = low-emission vehicle:
ed to minimize emissions of acetaldehyde, a highly reactive species under certain atmospheric conditions ( 1 9 , Z O ) . Diesel. The estimated ozoneforming potential for light-duty diesel vehicle emissions is highly uncertain because the composition of tailpipe emissions for a modern diesel vehicle with an oxidation catalyst is unknown. Oxidation catalysts are assumed necessary to meet particulate emission standards. However, because evaporative and running-loss emissions are essentially zero, a reduction of about 20% in ozone-forming potential should be possible. CNG. Because the primary emissions-methane and ethane-are very unreactive, the CNG ozoneforming potential may be as much as 60%, or more, lower than that of gasoline. LPG. Although NMOG tailpipe emissions will be higher than those for CNG, there appears to be a significant opportunity to reduce vehicular ozone-formingpotential relative to gasoline. However, currently available data for propane-LPG vehicles show that the emissions contain high levels of reactive olefin compounds. A reduction of ahout 35% in ozone-forming potential appears possible. Hydrogen and electric vehicles. Currently, hydrogen is made commercially from natural gas and steam. Hydrogen-fuel vehicles have no direct NMOG emissions, but NO, emissions may be significant. Electric vehicles do not emit NMOG and NO, directly, but associated power plant NO, emissions may be substantial ( 4 ) . NO, emissions. Because NO, emissions play a significant role in the urban ozone problem, a brief de-
1192 Envimn. Sd. Technol., VoI. 25, NO.7. 1991
scription of NO, emission trends is necessary. Based on currently available data, vehicles using CNG or LPG will have higher NO, emissions than gasoline- or reformulated gasoline-fuel vehicles. It may be possible to calibrate methanolfueled vehicles to lower NO, emission levels, but light-duty diesel vehicles appear fundamentally incapable of meeting the 0.2 g NOJ mile 1990 CAAA Tier I1 standard, regardless of v e h i c l e i n e r t i a l weight. Electric vehicles have no direct NO, emissions, but power plant NO, emissions could increase significantly with the implementation of electric vehicles. In order to relate alternative fuel ozone-forming potentials to changes in urban ozone levels, additional information is required about the emissions from all manmade and natural sources in that area, including the vehicle fleet, manufacturing facilities, and vegetation. Because vehicular NMOG emissions are only a part of the total NMOG emissions in urban areas, it is clear that reductions in the urban ozone levels as a result of alternative-fuel vehicle usage are much less than reductions i n per-vehicle ozoneforming potentials. For example, if the pre-1987 emission control scenarios with moderate growth of source population are continued, average percentages of the total NMOG emissions inventories for mobile sources and light-duty vehicle (LDV) emissions in urban areas are projected to change from 45% and 30%, respectively, in 1985 to 20% and lo%, respectively, in 2015 (16).
In the Los Angeles Basin, the percentage of the total NMOG emission inventories for LDV emissions is projected to be 12% in 2015,if the
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wuaiitawe summary Envlmnmental Issues
Gasolined
01 emissions from
Reformulated gasoline
Diesel
arernanve-ruei venicies VS. gasoline-ruei venicies MathanoP
Tailpipe, evaporative emission levelsd NMOG Base Lower Lower Lower co Base Lower Lower Equal NO, Base Equal Equal Impact on urban ozone relative to gasoline Ozone-forming . " " I " potential 1.00 Reduction in peakozone* 2.4% 1.4% 1.4% in Los Angeles 0% Level of concern over alrborne toxlc ernisdons Particles LOW LOW High LOW 1.3-Butadiene Medium Medium Unknown LOW Benzene High M e d i u r ' ow-Medium LOW High Formaldehyde Medium Mediur Medium LOW LOW LOW Low Acetaldehyde Global warming factors 0.09: g COdBTU 0.094 0.09 Fuel economy 22 (miledgal) 34 Energy economy 2923 (BTUimile) 3353 272 g Codmile 31 5
M8Sa
Ethanol
Lower
Lower
Equal Equal
Equal Equal
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Compressed
gas
gas
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natural
Lower Lower Higher
Hydrogen' ElectricC
None None Higher
None None Lower
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pre-1987 emissions control regulations are continued. A photochemical model estimate shows that, when all NMOG emissions from LDV are removed in 2015, peak ozone levels will be reduced by 6.6% (0.323 ppm to 0.301 ppm) in the Los Angeles Basin. Using this maximum reduction value (relevant to LDV) in ozone levels and the ozone-forming potentials per vehicle, reductions in peak ozone levels for full penetration of alternativefuel vehicles can be estimated. In Table 2 only emissions directly from the vehicles have been considered: increased electric utility emissions have not been included. Reductions in ozone levels range from 1.4% for reformulated gasoline and ethanol to 6.8% for hydrogen and electric vehicles. Although these results are consistent with those of other studies (13,21, 22),it should be noted that these estimates are highly uncertain, and reduction percentages change when additional stationary source controls are taken into account. Carbon monoxide. Urban CO air quality is determined mainly by mobile sources and has been im1194 Environ. Sci. Technol.,VoI. 25, No. 7, 1991
proving steadily as vehicular CO emissions have been decreasing (23).However, more than 40 urban areas currently are not meeting the NAAQS for CO. As newer vehicles replace older ones and local inspection-maintenance programs ensure proper operation of emission control systems, the downward trend of CO levels is expected to continue for some years, and the NAAQS for CO are likely to be attained in most urban areas early in the next century. This trend could be accelerated through the use of some alternative hydrocarbon fuels, particularly diesel and CNG. Electric and hydrogen vehicles would have the most impact in urban areas because they do not emit CO directly. Air toxics. The impact of alternative fuels on the health effects of vehicle emissions needs to be assessed cautiously for three reasons: First, today's criteria for determining which health effects are "of concern" may change. In principle, EPA is currently using the term "air toxics" to encompass all adverse health effects caused by airborne pollutants. In practice, the major concern in 1990 is the contribution
of airborne chemicals to the incidence of human cancer, and "air toxics" means airborne carcinogens. There is no reliable way to assess when, if ever, any of the noncancer health effects will become environmental issues. Second, many hundreds of different types of organic compounds have been detected in sparkignition and diesel engine exhaust. The toxicology of only a small number of these has been thoroughly evaluated. The same general types of compounds will be produced by combustion of any of the alternative carbon-containing fuels, but quantitatively their distribution may vary considerably. Moreover, fuel and lubricant additives may produce new types of emissions. Third, the health effects of direct vehicle emissions may be less important than those of the atmospheric reaction products of these emissions. Because of the above uncertainties, and the controversial nature of this issue, this discussion has been limited to emissions of five of EPA's listed mobile source air toxics: particles, including their associated
TTT
organic matter; formaldehyde; benzene: 1,3-hutadiene; and acetaldehyde (24).There is a large body of data concerning emissions of the listed air toxics from spark-ignition gasoline and heavy-duty diesel engine exhaust, but there are very few measurements of these components from vehicles operating on other alternative fuels. Nevertheless, it is possible to make reasonable guesses about what to expect for the alternative fuels, and these are presented in Table 2. It is likely that LPG and CNG fuels will result in lower emissions of the five air toxics compared to gasoline. Reformulated gasoline will prohably have lower benzene emissions because aromatics are the main component likely to be minimized through reformulation, but levels of other emissions will not be significantly different. Formaldehyde emissions from methanol and acetaldehyde emissions from ethanol will be considerably higher than those from gasoline engines. Increased aldehyde emissions from alcohol fuels, particularly formalde-
T
hyde, under semi-enclosed situations such as public parking garages (25) and highway tunnels (26),may be a concern. Diesel vehicles emit substantially more particulate matter than gasoline vehicles (27),and that particulate material may be a human carcinogen. This concern has already led to the proposal of a stringent 0.08 glmile particulate emissions standard for passenger vehicles. Because the average particle mass emission rate of passenger cars (between 0.02 and 0.04 glmile for the 1986 fleet) may be reduced below 0.01 glmile by the year 2000,a diesel-powered passenger car fleet meeting a 0.08 glmile standard would emit 3-6 times more particulate matter than the 1986 sparkignition fleet and perhaps 10 times more particulate matter than the year 2000 spark-ignition fleet. There is much less concern over the other toxic compounds emitted by the diesel vehicles. Because future diesel vehicles will be catalystequipped, formaldehyde and henzene emissions will be lower than for
similarly equipped gasoline vehicles. Emissions of 1,3-butadiene from diesel vehicles have not been measured. Global climate change. CO, and methane (CH,)are the two principal greenhouse gases, and both are components of vehicle exhaust. However, with the exception of CNG-fueled vehicles, methane emissions are quite low and can be ignored. CO,, the principal greenhouse gas, is emitted both from the direct combustion of fuels and from the processes used to make and transport the fuels. The latter factors can add 15-50% to the total CO, emissions for many alternative fuels, so that both sources must be considered in comparing the alternative fuels. The potential global climate impact of the alternative fuels, with the exception of CNG, is proportional to their relative CO, emissions on a gram per mile basis, as presented in Table 2. Of the liquid fuels, diesel presents a potential 20% benefit over gasoline and reformulated gasoline. The alcohols may present a small benefit, but the magEnviron. Sci. Technol., Vol. 25, No. 7, 1991 1195
nitude will depend on the manufacturing process. Methanol made from natural gas has a small CO, benefit, whereas methanol from coal leads to higher GO, emissions. Ethanol derived from grain fermentation presents a net CO, benefit only if the side products from its production, which account for perhaps 25% of the initial grain mass, are used in other production processes. The processing needed to produce hydrogen and electricity produce sufficient CO, so that neither fuel will likely present a global climate benefit. Ethanol. Ethanol has 10% higher combustion CO, emissionsIBTU than methanol, but if the ethanol is made from biomass, the combustion GO, emissions are reabsorbed by the growing biomass. Therefore, the GO, emissions from the combustion of biomass ethanol are zero. On the other hand, ethanol requires more processing energy than methanol made from natural gas. Estimates vary, but the energy expended to plant, fertilize, harvest, and ferment corn or sugar cane, and then to distill and transport the ethanol is about equal to that in the ethanol produced: that is, almost all of the ethanol produced must be used to process the next batch of ethanol. Hydrogen. Hydrogen is made commercially from natural gas and steam, with substantial CO, emissions. Combustion of hydrogen releases no CO,, but processing emits 0.15 g C0,IBTU of energy produced, or twice that for natural gas combustion. Therefore, converting natural gas to hydrogen is impractical. The only way to make hydrogen with low GO, emissions is through the electrolysis of water, with solar or nuclear power to generate the electricity. Electricity. In the United States, electricity is made by boilers fired with coal (54%), natural gas (10%). and fuel oil (5.4%),and by nuclear and hydroelectric plants (28). Electricity generation currently emits 0.21 g CO, per BTU of electrical energy distributed to homes and offices: in the year 2000 this will likely drop to 0.18 g GO, per BTU because of changes in the energy mix. These numbers are about twice those for combustion of gasoline, leading to the near equivalence in GO, emissions on a gram-per-mile basis. CNG. A global climate accounting for CNG requires the inclusion of its methane emissions. To account for the global warming effects of methane, its emissions can be converted 1196 Environ. Sci. Technol.. Vol. 25, No. 7. 1991
into equivalent CO, emissions using their relative global warming potentials. On a mass basis, methane has approximately a 10 times higher global warming potential than carbon dioxide (291, if the atmospheric lifetimes of methane (10 years) and GO, (250 years) are considered. Using this factor, tailpipe methane emissions from CNG do not contribute significantly to the greenhouse warming potential of the exhaust. Greenhouse warming potentials that ignore lifetime arguments may be as large as 50 to 100 (30). If a value of 50 is used, CNG vehicles would have approximately the same global warming impact (CO, plus methane) as gasoline vehicles. Although we believe that 10 is approximately the correct value to use for the global warming potential of methane, this remains a subject of considerable debate.
Conclusions It is clear from the above discussion that the selective use of alternative fuels will likely lead to air quality benefits. However, the magnitude of those benefits is uncertain and does not appear to be large. This is especially true for urban ozone, because of its indirect dependence on vehicle NMOG and NO, emissions, and the fact that vehicles will likely continue to decrease in importance as sources for these emissions in urban areas. Nevertheless, the reduction in urban ozone levels may be significant in comparison t o other ozonereduction options. Concerns about GO and air toxics will likely be significantly affected by the use of alternative fuels, but when viewed in the context of mandated emissions reductions for gasoline-fueled vehicles, the impact will be muted. When urban air quality issues alone are considered, widespread use of CNG-fueled vehicles appears to have the most significant impact among the carbon-containing fuels. Only widespread use of electric vehicles would have a major impact on urban air quality, with the exception of urban ozone, but even in this case the impact would depend on the type of energy used to produce the electricity. References (1) Schwarz. M. J.: S h i h , J. W. Presenled a1 the 1991 Annual Meeting ofthe
Air and Waste Management Association, Vancouver. British Columbia. June 1991: Paper X91-155.6. (2) "Replacing Gasoline: Alternative Fuels for Light-Duty Vehicles": U.S. Can-
gress Office of Technology Assessment: Report OTA-E-364. Sept. 1990. (3) DeLuchi. M. A,: Johnson, R. A,: Sperling. D. "Methanal vs. Natural Gas Vehicles: A Comparison of Resource Supply, Performance. Emissions, Fuel
(continued on next page) A / / authors are members of the research staff of Ford Motor C o m p a ny, in Dearborn, MI.
Tai Y . Chang (11. staff scientist, received B S c . and M.Sc. degrees in chemistry from the Seoul Notional University. Seoul. Korea. and a Ph.D in theoretical chemistry from the University of Wisconsin. His research interests are in air quality and photochemical modeling associated with urban, regional, and globo1 air quality.
Robert H. Hommerle (r), head of the emissions research group, received B.S. and M.S. degrees in physics from Wayne State University and o Ph.D in physics from the University ofMichigan. His research interests ore in the physical chemistry of the formation and control of gaseous and porticulote emissions from vehicles, and the reactions of these emissions in the otmosphere.
.. Steven M. lopor (I), is the head of the atniosplirric rhemistry group. He received a B.S. degree in chemistry from the Citv College ofNew York and a Ph.D in physical chemistry from Case Institute of Technology. His research interests include kinetics and mechanisms of atmospheric reactions and physics and chemistry of atmospheric aerosols.
Irving T.Snlmeen (r), head ofthe monufacturing emissions group, received B.S.E. degrees in engineering physics and mothemoficsfrom the University of Michigan and a Ph.D in biophysics from the University of Michigan. His research interests include the health effects of air pollutants and applications of biological methods for controlling emissions from manufacturing processes.
Storage Safety, Costs and Transitions”; Society of Automotive Engineers Paper #881656; SAE: Warrendale, PA, 1988. Wang, Q.; DeLuchi, M. A,; Sperling, D. J. Air Waste Manage. Assoc. 1990, 40, 1275. Bruetsch, R. I. “Emission, Fuel Economy, and Performance of Light-Duty CNG and Dual-Fuel Vehicles”; U.S. Environmental Protection Agency. Office of Mobile Sources: Ann Arbor, MI, 1988; Report EPAIAAICTAB-8805. Milkins, E. E. et al. ‘Comparison of Ultimate Fuels-Hydrogen and Methane.” Society of Automotive Engineers Paper #871167; SAE: Warrendale, PA, 1987. Nichols, R. J. et al. “A View of Flexible Fuel Vehicle Aldehyde Emissions’’; Society of Automotive Engineers Paper #881200; SAE: Warrendale, PA, 1988. Hammerle, R. H.; Shiller, J. W . ; Schwarz, M. J. Presented at the 14th Annual Energy-Sources Technology Conference and Exhibition, American Society of Mechanical Engineers, Jan. 1991. Atkinson, R. Atmos. Environ. 1990, 24A, 1-41. (10) Carter, W.P.L.; Atkinson, R. Environ. Sei. Technol. 1989, 23, 864-80. (11)Carter, W.P.L. “Development of Ozone Reactivity Scales for Volatile Organic Compounds”; Report to the U.S. Environmental Protection Agency, cooperative agreement no. CR814396-01-0, Statewide Air Pollution
Research Center, University of California, Riverside, CA, Nov. 1990. (12) Chang, T.Y.; Rudy, S. J. Atmos. Environ. 1990,24A, 2421-30. (13) Chang, T. Y.; Rudy, S. J, “Impact of Organic Emissions from AlternativeFueled Vehicles on Urban Ozone Air Quality”; Proceedings of the International Specialty Conference on Tropospheric Ozone and the Environment, Air and Waste Management Association, Pittsburgh, PA (in press). (14) “Ozone and Carbon Monoxide Air Quality Design Values, 1987-89 Air Quality Update”; U S . Environmental Protection Agency; Research Triangle Park, NC; Aug. 1990. (15) Lowi, A. L.; Carter, W.P.L. “A Method for Evaluating t h e Atmospheric Ozone Impact of Actual Vehicle Emissions”; presented at the Society of Automotive Engineers International Conference and Exposition, Detroit, MI, 1990. (16) Chang, T. Y.; Rudy, S. J. In Methanol as an Alternative Fuel Choice:An Assessment; The Johns Hopkins Policy Institute: Washington, DC, 1990. (17) Williams, R. L.; Lipari, F.; Potter, R. A. J. Air Waste Manage. Assoc. 1990,40, 747-56. (18) Gabele, P. A. J. Air Waste Manage. ASSOC. 1990, 40,296-304. (19) Swarc, A.; Branco, G. M. “Automotive Use of Alcohol in Brazil and Air Pollution Related Aspects”; Society of Automotive Engineers Paper #850390; SAE: Warrendale, PA, 1985. (20) Bailey, E. M.; Meagher, J. F. J. Air Pollut. Control Assoc. 1986, 36, 808-12.
(21) Russell, A. G.; St. Pierre, D.; Milford,
J, B. Science 1990,247,201-5. (22) Chang, T. Y. et al. Atmos. Environ.
1989,23,1629-44. (23) “National Air Quality and Emissions Trends Report, 1989”; Report EPA45014-91-003, U.S. Environmental Protection Agency: Research Triangle Park, NC, 1991. (24) Adler, J, M.; Carey, P. M. “Air Toxics Emissions and Health Risks from Mobile Sources”; 82nd Annual Air and Waste Management Association Meeting, June 1989; Paper #89-34A.6. (25) Kuntasal, G.; Venkatram, A. “Air Quality Impacts of Methanol-Fueled Vehicles in Micro-Environments”; prepared for South Coast Air Quality Management District, El Monte, CA, April 1990. (26) Chang, T. Y.; Rudy, S. J. Environ. Sei. Technol. 1990, 24,672-76. (27) IARC Monographs on the Evaluation of Carcinogenic Risks to Humans: Diesel and Gasoline Engin e Exhausts and Some Nitroarenes, Volume 46; World Health Organization; International Agency for Research on Cancer: Lyon, France, 1989. (28) “Annual Energy Outlook, 1989With Projections to 2000”; U S . Department of Energy: Washington, DC, 1989; Report DOEIEIA-0383(89). (29) Lashof, D. A.; Ahuja, D. R. Nature 1990,344,529. (30) Unnasch, S. et al. “Comparing the Impact of Different Transportation Fuels on the Greenhouse Effect,” Report to the California Energy Commission, Sacramento, CA, 1989.
Oxidations in Organic Chem
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