Correspondence Comment on “Life-Cycle Analysis of Alternative Automobile Fule/Propulsion Technologies” SIR: The recent appearance of Life-Cycle Analysis of Alternative Automobile Fuel/Propulsion Technologies by Lave et al. (1) may have marked a significant milestone in the development of the scientific body of literature suggested by industrial ecology. Life-cycle analysis (LCA) approaches have not been without controversy or criticism (2, 3). Some writers have suggested that methodological shortcomings ensure that LCA will either be a subjective, value-laden process or a practical impossibility because of the paucity or inconsistency of the data sets required to build a reliable life-cycle inventory (LCI). Nevertheless, it is our position that LCA can be an objective, scientific approach to testing certain hypotheses provided that the shortcomings are addressed in an obvious, transparent manner that allows separate researchers to examine the boundaries of study, assumptions, data sets employed, etc. to the extent that the LCA results may be reproduced and corroborated by the scientific community. Therefore, it is with some disappointment that we submit this letter in criticism of the above referenced study when we would like nothing more than to see wider adoption, publication, and discussion of innovative methods of investigation like LCA in a journal that is still dominated by traditional laboratory experiments. It is widely recognized that the conclusions of any LCA may be extremely sensitive to the boundary conditions under which the study is conducted (4, 5). In this case, the authors contend that hybrid and fuel cell cars are “not attractive in the near term”, presumably because the financial costs including an estimate of social (or external) costs under present economic conditions exceed those of traditional internal combustion technologies. While the study purports to employ a life-cycle perspective, in fact the discussion is dominated by financial considerations that may rest on dubious assumptionssto the abject exclusion of the healthrelated constraints that have presumably motivated both the research into alternative technologies and this very study. Automobile exhaust is responsible for over half the smogforming VOCs and nitrous oxides, half the hazardous air pollutants, and 90% of the carbon monoxide found in urban air (6, 7). But it is unclear whether urban, rural, or aggregated data should be employed to do such seemingly simple tasks as determining the average gasoline mileage of the baseline and alternative vehicles or establishing the social costs of air pollution. The latter figures vary widelysparticularly in the case of carbon monoxide, a better figure may be 300-1000 times less than the value actually cited (8-10). Discrepancies or inconsistencies in LCI data are notorious for undermining the credibility of LCA studies (11). For this reason, it is essential that LCI data be fully disclosed. In this case, portions of the LCI data appear in tables distributed throughout the article, but critical aspects or assumptions may be missing altogether (such as air pollutants from hybrid vehicles, CO2 emissions in Table 3, or miles driven per year in Table 6, etc.). The global warming potential calculations provide a detailed example. GWP has a specific definition and calculation methodology as reported in refs 12 and 13. However, the authors use the term somewhat recklessly, interchanging it with greenhouse gas emissions (GHG). The purpose of the GWP index is to compare the radiative forcing effects of various pollutants taking into account primarily 1696
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two factors: radiative absorption spectra (for the pollutant in question and a reference atmosphere) and atmospheric lifetime. Methane, for example, is represented by an atmospheric lifetime on the order of 1/10th carbon dioxide but is a much more effective infrared wavelength energy absorber. The 20-, 50-, and 100-year GWP of CH4 are reported as 56, 21, and 6.5 respectively, although other studies have produced results that vary slightly depending upon the assumptions employed (12). It may be surmised, although it is not explicitly stated in the study, that Figure 3 is constructed by multiplying the emissions (measured in kg released over the lifetime of the vehicle) of any particular pollutant by a respective 100year GWP, resulting in an estimate of the kg of CO2 release that would produce an equivalent effect. While such an approach may be methodologically sound, the result should not be reported as GWP but as GHG emissions in equivalent kg of CO2 for the time horizon in question. To the authors’ credit, they note units of kg of CO2 equivalents in the subtitle of the figure but make no mention of the time horizon serving as the basis for computations, do not reference any publications from which the details of the computations might be gleaned, nor report the GWP employed for the aggregated categories of air pollutants reported in Table 3. The last point is particularly egregious as GWP computations for VOCs and nitrogen oxides are problematic (12). It should also be noted that the GHG emissions attributable to electric vehicles are not reported at all, except in Table 1 where they are listed as comparable to the 1998 Ford Taurus, which serves as the baseline vehicle. Some simple calculations confirm that this may indeed be the case (5). The greatest value in a paper of this type is not conclusions, per se, but the methodology employed. That is, the boundary conditions appropriate for such a study may vary both temporally and geographically (e.g., the price of gasoline). For an LCA study of this type to be fully informative, it should not be motivated solely by the question “which technology is most attractive?” but also by the question “under what conditions are they most attractive?”. We believe the authors’ understand this point and have attempted to recognize the importance that must be placed on valuation of various criteria in their discussion. It is clear from a cursory examination of Table 1 that if all the listed attributes were weighted equally, hybrid and fuel cell vehicles would be equally the most attractive technological alternatives. However, there remains little scientific basis for weighing the benefits of energy independence vs air toxins, and none should be presumed by this study. It may be that for urban areas that experience acute air pollution problems, under driving conditions that favor the hybrid’s regenerative braking and idle shut off features, when gasoline is expensive, the hybrid vehicle is the most sensible economic choicesif not from the individual consumer’s perspective, at least from the perspective of society as a whole. The purpose of this type of analysis should be to provide decision-makers the objective information necessary to create incentives for consumers to employ more environmentally responsible technologies that minimize total costs to society. This paper falls short of that goal.
Literature Cited (1) Lave, L.; MacLean, H.; Hendrickson, C.; Lankey, R. Environ. Sci. Technol. 2000, 34, 3598-3605. (2) Owens, J. B. J. Ind. Ecol. 1997, 1 (1), 37-49. (3) Ehrenfeld, J. R. J. Ind. Ecol. 1997, 1 (2), 41-49. 10.1021/es001734e CCC: $20.00
2001 American Chemical Society Published on Web 03/17/2001
(4) Graedel, T. E. Streamlined Life Cycle Assessment; Prentice Hall: Englewood Cliffs, NJ, 1998. (5) Seager, T. P. J. Ind. Ecol. 1998; http://www.yale.edu/jie/ w97f1a.htm. (6) Idling Vehicle Emissions; United States Environmental Protection Agency, Office of Transportation and Air Quality: Washington, DC, 1998; EPA 420-F-98-014. (7) General Information for Motor Vehicles; United States Environmental Protection Agency, Region 3 Air Protection Division: Washington, DC 1996; http://www.epa.gov/reg3artd/ oldweb/airqual/pegcaa04.htm. (8) Desvousqes, W. H.; Johnson, F. R.; Banzhaf, H. S. Assessing Environmental Externality Costs for Electricity Generation; TER General Working Paper No. G9402; Triangle Economic Research and Radian Corporation: Research Triangle Institute, NC; 1994. (9) Arthur D. Little., Inc. Total Cost Assessment Methodology; American Institute of Chemical Engineers and the Center for Waste Reduction Technologies: 1999. (10) Minnesota Public Utilities Commission. Environmental Costs of Electricity; Minnesota Regulatory Proceeding, Docket No. E-999/CI-93-583, 1997.
(11) Ayres, R. U. Resour., Conserv. Recycl. 1995, 14, 199-223. (12) Climate Change 1995: The Science of Climate Change; Houghton, J. T., Meira Filho, L. G., Callander, B. A., Harris, N., Kattenberg, A., Maskell, K., Eds.; Intergovermental Panel on Climate Change by Cambridge University Press: New York, 1996. (13) Seinfeld, J. H.; Pandis, S. N. Atmospheric Chemistry and Physics: From Air Pollution to Climate Change; Wiley and Sons: New York, 1998.
Thomas P. Seager* and Randy L. Brown Center for Environmental Management Box 5715 Clarkson University Potsdam, New York 13699-5715 ES001734E
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