1. Replacement fuels include alternative fuels as well as other fuels. As defined in EPACT, “the term 'replacement fuel' means the portion of any motor fuel that is methanol, ethanol, or other alcohols, natural gas, liquefied petroleum gas, hydrogen, coal-derived liquid fuels, electricity (including electricity from solar energy), ethers, or any other fuel the Secretary of Energy determines, by rule, is substantially not petroleum and would yield substantial energy security benefits and substantial environmental benefits.”

2. As defined in EPACT, “the term 'alternative fuel' means methanol, denatured ethanol, and other alcohols; mixtures containing 85 percent or more (or such other percentage, but not less than 70 percent, as determined by the Secretary of Energy, by rule, to provide for requirements relating to cold- start, safety, or vehicle functions) by volume of methanol, denatured ethanol, and other alcohols with gasoline or other fuels; natural gas; liquefied petroleum gas; hydrogen; coal- derived liquefied fuels; fuels (other than alcohol) derived from biological materials; electricity (including electricity from solar energy); and any other fuel the Secretary determines, by rule, is substantially not petroleum and would yield substantial energy security benefits and substantial environmental benefits.” Subsequent to the passage of EPACT, the Secretary of Energy determined that biodiesel, in neat form, was an alternative fuel.

3. The fuel cycle of any transportation fuel includes several stages, such as recovery, processing, transportation, and end- use. See Argonne National Laboratory, Center for Transportation Research, Emissions of Greenhouse Gases from the Use of Transportation Fuels and Electricity, ANL/ESD/TM- 22, prepared by Dr. Mark Delucchi, Vol. 1 (Argonne, IL, November 1991) and Vol. 2 (Argonne, IL, November 1993) and Energy Information Administration, Alternatives to Traditional Transportation Fuels 1993, DOE/EIA-0585/(93) (Washington, DC, June 1994), pp. 29-33, 49-53.

4. Energy Information Administration, Alternatives to Traditional Transportation Fuels: An Overview, DOE/EIA-0580/O (Washington, DC, June 1994), and Alternatives to Traditional Transportation Fuels 1993, DOE/EIA-0585(93) (Washington, DC, January 1995).

5. Energy Information Administration, Alternatives to Traditional Transportation Fuels: An Overview, pp. 93-101.

6. Energy Information Administration, Alternatives to Traditional Transportation Fuels 1993, DOE/EIA-0585/(93) (Washington, DC, June 1994), pp. 29, 45.

7. Energy Information Administration, Alternatives to Traditional Transportation Fuels 1994: Volume I, DOE/EIA-0585(94)/1 (Washington, DC, February 1996).

8. Intergovernmental Panel on Climate Change, The IPCC Scientific Assessment (Cambridge, United Kingdom: Cambridge University Press, 1990), p. xxxvii.

9. Nitrogen oxides represent a family of gases, generically written as NOX.

10. Data are not currently available for NMHC and ozone.

11. Emissions from electric vehicles occur largely in manufacturing and recycling batteries. This information will be available in a subsequent report.

12. One mole of a gas is equal to the amount of substance that contains as many elementary units (6.023 x 1023 molecules or atoms) as there are atoms in 12 grams of carbon-12. Normally, emissions are reported in grams per VMT. However, reporting in moles is preferable because greenhouse gas heat absorption is directly related to the number of molecules of a gas, i.e., its volume.

13. The actual concept here is the ability of gases to absorb infrared (heat) energy radiated from the Earth's surface. The more common term, “global warming potential,” is used to refer to this concept. Strictly speaking, however, global warming potential includes other factors.

14. Public Law 102-486, Section 503, 42 U.S.C. 13253, “Energy Policy Act of 1992” (Enacted October 24, 1992).

15. Replacement fuels include alternative fuels as well as other fuels. As defined in EPACT, “the term 'replacement fuel' means the portion of any motor fuel that is methanol, ethanol, or other alcohols, natural gas, liquefied petroleum gas, hydrogen, coal-derived liquid fuels, electricity (including electricity from solar energy); ethers, or any other fuel the Secretary of Energy determines, by rule, is substantially not petroleum and would yield substantial energy security benefits and substantial environmental benefits.”

16. As defined in EPACT, “the term 'alternative fuel' means methanol, denatured ethanol, and other alcohols; mixtures containing 85 percent or more (or such other percentage, but not less than 70 percent, as determined by the Secretary of Energy, by rule, to provide for requirements relating to cold- start, safety, or vehicle functions) by volume of methanol, denatured ethanol, and other alcohols with gasoline or other fuels; natural gas; liquefied petroleum gas; hydrogen; coal- derived liquefied fuels; fuels (other than alcohol) derived from biological materials; electricity (including electricity from solar energy), and any other fuel the Secretary determines, by rule, is substantially not petroleum and would yield substantial energy security benefits and substantial environmental benefits.” Subsequent to the passage of EPACT, the Secretary of Energy determined that biodiesel, in neat form, was an alternative fuel.

17. The date, October 1, 1993, was subsequently modified to October 1, 1994.

18. The date applicable to Section 503 (b) (2) was changed from October 1, 1994, to December 31, 1995, and the date for other data collection activities was modified to December 31, 1995.

19. V. Senthil and P. Warnken, “Estimating Greenhouse Gas Emissions from Replacement Fuels: Fulfilling the Energy Policy Mandate,” The Emissions Inventory, 1995, pp. 98-107.

20. Argonne National Laboratory, Emissions of Greenhouse Gases from the Use of Transportation Fuels and Electricity, ANL/ESD/TM-22, Vol. I (Argonne, IL, November 1991) and Vol. II (Argonne, IL, November 1993).

21. Mark A. Delucchi, “Revisions to the Greenhouse Gas Emissions Model Used in Emissions of Greenhouse Gases from the Use of Transportation Fuels and Electricity, ANL/ESD/TM-22, November 1991,” draft report submitted to the Energy Information Administration in June 1996. Also, see Energy Information Administration, Alternatives to Traditional Transportation Fuels: An Overview, pp. 25-29, and Energy Information Administration, Alternatives to Traditional Transportation Fuels 1993, DOE/EIA-0585/(93) (Washington, DC, June 1994), pp. 49-53, and Decision Analysis Corp., “Measurement of Emissions: Greenhouse Gas Estimates for Alternative Transportation Fuels,” unpublished final report prepared for the Energy Information Administration (Vienna, VA, December, 1995), and V. Senthil and P. Warnken, “Estimating Greenhouse Gas Emissions from Replacement Fuels: Fulfilling the Energy Policy Mandate,” The Emissions Inventory, 1995, pp. 98-107.

22. The results in Table 1 imply that weighted greenhouse gas emissions (including water vapor) from gasoline will be less than for all ATF's, except LPG, if water vapor's GWP is less than 4.8. If water vapor's GWP is greater than 0.55, total weighted greenhouse gas emissions for CNG and alcohol fuels will be less than for gasoline. Although a GWP per se for water vapor has yet to be determined, researchers have calculated similar properties to GWP (i.e., “positive feedback” and “direct radiative forcing”) which leads to speculation that water vapor's GWP lies between 0.5 and 3.0. For further details, see Decision Analysis Corporation, Measurement of Emissions: Greenhouse Gas Estimates for Alternative Transportation Fuels, unpublished final report prepared for the Energy Information Administration (Vienna, VA, December 1995). For information on water vapor positive feedback, see V. Ramanathan and A. Raval, “Observational Determination of the Greenhouse Effect,” Nature 342 (1989):758-761 and D. Lubin, “The Role of Tropical Super Greenhouse Effect in Heating the Ocean's Surface,” Science 265 (1994): 224-227 and R.D. Cess, “Gauging Water Vapor Feedback,” Nature 342 (1989): 736-737.

23. Intergovernmental Panel on Climate Change, The IPCC Scientific Assessment (Cambridge, United Kingdom: Cambridge University Press, 1990), p. xxxvii.

24. The radiative greenhouse effect alone would lead to temperatures of 77 oC. However, non-radiative processes, such as evaporation and convection, cool the Earth, leading to its average temperature of 15 oC.

25. Infrared absorptivity is a dimensionless quantity equal to the ratio of the absorbed infrared radiation to the infrared radiation incident on a given surface.

26. Encyclopedia of Science and Technology, 5th Ed. (New York: McGraw Hill Book Co., 1982), p. 381.

27. R.P. Wayne, Chemistry of Atmospheres (Oxford, United Kingdom: Clarendon Press, 1991).

28. D.L. Hartmann, Global Physical Climatology (New York: Academic Press, 1994), p. 8.

29. Human activity is sometimes referred to as “anthropogenic” activity.

30. Chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), and perfluorocarbons (PFCs) are not directly related to the internal combustion engine operations.

31. S.J. Oltmans and D.J. Hoffman, “Increase in Lower- stratospheric Water Vapor at a Mid-latitude Northern Hemisphere Site from 1981-1994” Nature 374 (1995):146-149.

32. R.S. Lindzen, “Some Coolness Concerning Global Warming,” Bulletin of the American Meteorological Society 71 (1990):288- 299, and D.G. Sun and R.S. Lindzen, “Distribution of Tropical Tropospheric Water Vapor,” Journal of Atmospheric Science 50 (1993):1643-1660.

33. K.P. Shine and A. Sinha, “Sensitivity of the Earth's Climate to Height-Dependent Changes in the Water Vapor Mixing Ratio,” Nature 354 (1991):382-384, and D. Lubin, “The Role of Tropical Super Greenhouse Effect in Healing the Ocean Surface,” Science 265 (1994):224-227.

34. On a 100-year basis. See Table 5.

35. U.S. Climate Action Report, Submission of the United States of America Under the United Nations Framework Convention on Climate Change, 1994, p. 8.

36. R.D. Prinn and others, “Global Average Concentration and Trend for Hydroxyl Radicals Deduced from ALE/GAGE Trichloroethane Data for 1978-1990,” Journal of Geophysical Research 97 (1992):2445-2461.

37. B. Weinstock, “Carbon Monoxide: Residence Time in the Atmosphere,” Science 166:224-225, and World Meteorological Organization, Scientific Assessment of Ozone Depletion (Geneva, Switzerland, 1991).

38. As ozone is transported to the lower stratosphere and to high latitudes, it lasts many months (possibly years) and is stored there until destroyed or transported down into the troposphere.

39. Light trucks include certain automobiles (e.g., minivans) and trucks having a gross vehicle weight rating of less than 8,500 pounds.

40. Energy Information Administration, Renewable Energy Annual 1995, DOE/EIA-0603(95) (Washington, DC, December 1995), p. 9.

41. Energy Information Administration, Annual Energy Outlook 1996, DOE/EIA-0383(96) (Washington, DC, January 1996), p. 24.

42. Oak Ridge National Laboratory, 1990 NPTS Data Book (Oak Ridge, TN, 1993), pp. 1-2, was used for non-U.S. countries.

43. U.S. Climate Action Report, Submission of the United States of America Under the United Nations Framework Convention on Climate Change, 1994, p. 8.

44. Argonne National Laboratory, Emissions of Greenhouse Gases from the Use of Transportation Fuels and Electricity, ANL/ESD/TM-22, Vol. I (Argonne, IL, November 1991) and Vol. II (Argonne, IL, November 1993).

45. R.G. Prinn and others, “Atmospheric Trends and Lifetimes of Methyl Chloroform and Global Hydroxyl Radical Concentration,” Science 269 (1995):187-192.

46. A.R. Ravishankara and D.L. Albritton, “Methyl Chloroform and the Atmosphere,” Science 269 (1995):183-184.

47. Assuming current vehicle fuel combustion technology.

48. Energy Information Administration, Annual Report to Congress 1994, DOE/EIA-0173(94) (Washington, DC, April 1995), p. 7.

49. Argonne National Laboratory, Emissions of Greenhouse Gases from the Use of Transportation Fuels and Electricity, ANL/ESD/TM-22, Vol. I (Argonne, IL, November 1991) and Vol. II (Argonne, IL, November 1993).

50. The “Mobile 5a” calculates most emissions, uses regulatory maxima for others, and uses measured values for the remainder (e.g., carbon monoxide).

51. Ibid.

52. Energy Information Administration, Alternatives to Traditional Transportation Fuels 1993, DOE/EIA-0585/(93) (Washington, DC, June 1994), pp. 29-36.

53. One mole of a gas is equal to the amount of substance that contains as many elementary units (6.023 x 1023 molecules or atoms) as there are atoms in 12 grams of carbon-12. Normally, emissions are reported in grams per VMT. However, reporting in moles is preferable because greenhouse gas heat absorption is directly related to the number of molecules of a gas.

54. Decision Analysis Corporation, Measurement of Emissions: Greenhouse Gas Estimates for Alternative Transportation Fuels.

55. Evaporative emissions occur when a portion of the liquid fuels vaporizes as opposed to being combusted.

56. There are 188 million vehicles in the United States and 582 million vehicles in the world (from the 1992 Motor Vehicle Manufacturers Association Fact Book). Average consumption is approximately 619 gallons per vehicle annually.

57. Although some data indicate that CNG emits lower levels of carbon monoxide than gasoline, the regulatory maximum is used for all the fuels considered in this report.

58. D.W. Fahey and others, “Emission Measurements of the Concorde Supersonic Aircraft in the Lower Stratosphere,” Science 270 (1995):70-74.

59. In radiation no mass is exchanged, and no medium is required. Pure radiant energy moves at the speed of light. In conduction no mass is exchanged, but a medium is required to transfer heat by diffusion. In convection mass is exchanged. Energy may be exchanged without a net movement of mass.

60. For a rigorous approach, use “The Lambert-Bouguet-Beer Law Approach” found in D.L. Hartmann, Global Physical Climatology (New York: Academic Press, 1994).

61. National Aeronautics and Space Administration, The Detection of Climate Change Due to the Enhanced Greenhouse Effect (Columbia, MD, July 1991).

62. V. Ramanathan and others, “Climate and the Earth's Radiation Budget,” Physics Today 42 (1989):22-33.

63. V. Ramanathan and others, “Cloud Radiative Forcing and Climate: Results from the Earth Radiation Budget Experiment,” Science 243 (1989):57-63.

64. L.I. Grossweiner, The Science of Photobiology, ed. K.C. Smith (New York: Plenum Press, 1989), pp. 1-77.

65. R.B. Withrow and A.P. Withrow, Radiation Biology, Volume 3, Chapter 3, ed. A. Hollander (New York: McGraw-Hill, 1956).

66. The mesosphere is the coldest region of the atmosphere extending from the stratopause (50 kilometers) to about 90 kilometers from the Earth's surface.

67. The stratosphere is the region of the upper atmosphere extending from the tropopause (8 to 15 kilometers altitude) to about 50 kilometers. The thermal structure is determined by its radiation balance and is generally very stable with low humidity.

68. The troposphere is the inner layer of the atmosphere below about 15 kilometers within which there is normally a steady decrease of temperature with increasing altitude. Its thermal structure is caused primarily by the heating of the Earth's surface by solar radiation, followed by heat transfer by turbulent mixing and convection. Nearly all clouds are formed and weather conditions manifest within this region.

69. A. Nolle and others, “Temperature Dependent UV Absorption Spectra of Carbonyl Chloro-fluoride,” Geophysical Research Letter 20 (1993):707-710.

70. H. Rhode, “A Comparison of the Contribution of Various Gases to the Greenhouse Effect,” Science 248 (1990):1217-1219.

71. U.S. Department of Energy, A Primer on Greenhouse Gases, DOE/NBB-0083 (Washington, DC, March 1988).

72. Intergovernmental Panel on Climate Change, The IPCC Scientific Assessment (Cambridge, United Kingdom: Cambridge University Press, 1990), pp. 179-180.

73. A.S. Grossman and D.J. Wuebbles, “Global Warming Potential for SF6,” UCRL Report, ID# 112944 (1992), pp. 1-3.

74. The radiative forcing is expressed as a change in the flux of energy in watts per square meter.

75. K.C. Cho and R.A. Greenkorn, Thermodynamics of Fluids (New York: Marcel Dekker, 1975), p. 2.

76. The interaction is radiative for the atmosphere and chemical for the oceans.

77. V. Ramanathan and A. Raval, “Observational Determination of the Greenhouse Effect,” Nature 342 (1989):758-761.

78. V. Ramanathan and W. Collins, “Thermodynamic Regulation of Ocean Warming by Cirrus Clouds Deduced from Observations of 1987 El Nino,” Nature 351 (1991):27-32.

79. V. Ramanathan and others, “Warm Pool Heat Budget and Shortwave Cloud Forcing: A Missing Physics,” Science 267 (1995):499-503.

80. R.D. Cess and others, “Absorption of Solar Radiation by Clouds: Observations Versus Models,” Science 267 (1995): 496- 499 and Y Baskin, “Under the Clouds,” Discover (September 1995), pp. 62-69.

81. D. Lubin, “The Role of Tropical Super Greenhouse Effect in Healing the Ocean Surface,” Science 265 (1994):224-227.

82. D.D. Davis and others, “A Photostationary State Analysis of the NO2-NO System Based on Airborne Observations from the Subtropical/Tropical North and South Atlantic,” Journal of Geophysical Research 98 (1993):23,501-23,523.

83. C.A. Cantrell and others, “Branching Ratios for the Singlet Oxygen and Nitrous Oxide Reaction,” Journal of Geophysical Research 99 (1994):3739-3743.

84. Lefevre and others, “Chemistry of the 1991-1992 Stratospheric Winter: Three Dimensional Model Simulations,” Journal of Geophysical Research 99 (1994):8183-8195.

85. H.B. Singh, M. Kanakidou, P.J. Crutzen, and D.J. Jacob, “High Concentrations and Photochemical Fate of Oxygenated Hydrocarbons in the Global Troposphere,” Nature 378 (1995):50-53.

86. S.E. Schwarzbach, “CFC Alternatives Under a Cloud,” Nature 376 (1995):297-298.

87. J.H. Butler, “Methyl Bromide Under Scrutiny,” Nature 376 (1995):469-470.

88. A.S. Campbell, Thermodynamic Analysis of Combustion Engines (New York: John Wiley & Sons, 1992), Table E.4, p. 357.

89. The heat of combustion can be measured either at constant pressure using a constant flow calorimeter or at constant volume using a batch calorimeter.

90. Decision Analysis Corporation, Measurement of Emissions: Greenhouse Gas Estimates for Alternative Transportation Fuels, unpublished final report prepared for the Energy Information Administration (Vienna, VA, December 1995).

91. J. Schirmer and others, “K-shell Excitation of the Water, Ammonia, and Methane Molecules Using High-resolution Photoabsorption Spectroscopy,” Physical Review A 47 (1993):1136-1147.

92. B.E. Priloglou and others, “On the Atmospheric Water Vapor Transmission Function for Solar Radiation Models,” Solar Energy 53 (1994):445-453.

93. S. Elliott and others, Kinetics Programs for Simulations of Tropospheric Photochemistry on the Global Scale, Report No. LA-12539-MS, (Los Alamos, NM: Los Alamos National Laboratory, August 1993).

94. D.P. Kratz and others, “Infrared Radiation Parameterizations for the Minor CO2 Bands for Several CFC Bands in the Window Region,” Journal of Climate, 6 (1993):1269-1281.

95. M.D. Di Rosa and R.K. Hanson, “Collision-broadening and -shift of NO Absorption Lines by H2O, O2, and NO at 295o K,” Journal of Molecular Spectroscopy 164 (1994):97-117.

96. J. Heidberg and others, “Polarized FTIR--Spectra of C60 Layers and the Adsorbates of CO and CO2 on C60,” Journal of Electron Spectroscopy and Related Phenomena 64/65 (1993):883-892.

97. P.J. Medvecz and K.M. Nichols, “Experimental Determination of Line Strengths for Selected Carbon Monoxide and Carbon Dioxide Absorption Lines at Temperatures Between 295 and 1250oK,” Applied Spectroscopy 48 (1994):1442-1450.

98. Sadtler Research Laboratories, Infrared Spectra of Organic Compounds (1979), pp. 51, 585.

99. Snell-Ettre, Encyclopedia of Industrial Chemical Analysis, Vol. 8 (1966), p. 252.

100. N.V. Sidgewick, The Chemical Elements and their Compounds, Vol. 11 (Oxford, UK: Clarendon Press, 1950), pp. 859-863.

101. D.P. Kratz and others, “Infrared Parameterizations for the Minor CO2 Bands and for Several CFC Bands in the Window Region,” Journal of Climate 6 (1993):1269-1281.

102. R.G. Ellingson and others, “The Intercomparison of Radiation Codes in Climate Models (ICRCCM): Long Wave Results,” Journal of Geophysical Research 96 (1991):8929-8953.

103. M.D. Chou and others, “Infrared Radiation Parameterizations in Numerical Climate Models,” Journal of Climate 4 (1991):424-437.

104. R.G. Ellingson and others, “The Intercomparison of Radiation Codes in Climate Models (ICRCCM): Long Wave Results,” Journal of Geophysical Research 96 (1991):8929-8953.

105. V. Ramanathan and J.A. Coakley, Jr., “Climate Modeling Through Radiative-Convective Models,” Review of Geophysics and Space Physics 16 (1978):465.

106. S.M. Freidenreich and V. Ramaswamy, “Solar Radiation Absorption by Carbon Dioxide, Overlap with Water, and a Parameterization for General Circulation Models,” Journal of Geophysical Research 98 (1993):7255-7264.