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Response to Comment on “Life-Cycle Analysis of Alternative Automobile Fuel/Propulsion Technologies” SIR: We thank Seager and Brown (1) for their comments. We agree that “LCA can be an objective, scientific approach to testing certain hypotheses ...,” that “The greatest value in [our article] ... is not conclusions, per se, but the methodology employed” and that the value of abating air pollutants ...”vary widely”. In particular, our valuation of air pollutants displays a wide range of values (2). The other points require discussion. We translate emissions of NOx, VOC, and HC into a pollution index and then into a dollar value. This is an important step in making the analysis tractable. Seager and Brown suggest that our approach is too simplistic because it uses aggregate values whereas the relative contributions of CO, HC, and NOx to ozone formation can be calculated for a specific area. We agree that the specific values vary with the precise location and season. However, vehicles are used year-round and, given economies of scale in manufacture, must be appealing to consumers (or regulators) in many areas. Thus, the evaluation of emissions abatement should be based on aggregate values with ranges to reflect different locations and seasons, uncertainties, and different valuations. We appear to have accomplished our goal of making the analysis transparent, which Seager and Brown say is most important, since they have examined our assumptions and data sets to arrive at their own judgments. Seager and Brown call for full disclosure of LCI data. Length constraints force us to list references rather than spell out the material. Seager and Brown suggest that we are “us[ing] the term [GWP] somewhat recklessly, interchanging it with greenhouse gas emissions (GHG)”, “not reference[ing] any publications from which the details of the computation might be gleaned ...”, and leaving CO2 emissions out of Table 3. As above, it is helpful to simplify by translating the vector of GHG into a scalar, following the method of the UN Intergovernmental Panel on Climate Change. References providing additional detail on the method are included (3, 4), as well as details in related documents referenced (3, 5-8). Since CO2 is not a pollutant, it is not included in Table 3. Tons of CO2 equivalent versus GWP is a distinction without a difference. We did not try to collapse the vector of objectives considered by policy-makers in Table 1 into a scalar index.
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We see no merit in placing equal weights for all the goals listed as Seager and Brown suggest. Equal weights are arbitrary; breaking a goal into several categories enhances its importance under equal weighting. The goal of our study is to inform policy-makers and to improve the quality of decisions, not to praise or denigrate a particular vehicle option.
Literature Cited (1) Seager, T. P.; Brown, R. L. Environ. Sci. Technol. 2001, 35, 16961697. (2) Matthews, H. S.; Lave, L. B. Environ. Sci. Technol. 2000, 34 (8), 1390-1395. (3) MacLean, H. L.; Lave, L. B.; Lankey, R.; Joshi, S. J. Air Waste Manage. Assoc. 2000, 50, 1769-1779. (4) Inventory of U.S. Greenhouse Gas Emissions and Sinks 19901997; Office of Policy, U.S. Environmental Protection Agency: Washington, DC, 1999. (5) Lankey, R. L.; McMichael, F. C. Environ. Sci. Technol. 2000, 34 (11), 2299-2304. (6) Lave, L. B.; MacLean, H. L. An Environmental Economic Evaluation of Hybrid Electric Vehicles Based on the Toyota Prius; Working Paper, Green Design Initiative; Carnegie Mellon University: Pittsburgh, PA, 1999. (7) MacLean, H. L.; Lave, L. B. Environ. Sci. Technol. 2000, 34 (2), 225-231. (8) MacLean, H. L.; Lave, L. B. Environ. Sci. Technol. 1998, 32, 322A-330A.
Lester B. Lave* Department of Engineering and Public Policy Carnegie Mellon University Schenley Park Pittsburgh, Pennsylvania 15213-3890
Heather L. MacLean Department of Civil Engineering University of Toronto Toronto, Ontario, Canada
Chris Hendrickson and Rebecca Lankey Department of Civil and Environmental Engineering Carneige Mellon University Schenly Park Pittsburgh, Pennsylvania 15213-3890 ES010534F
10.1021/es010534f CCC: $20.00
2001 American Chemical Society Published on Web 03/17/2001
