could also affect the relative amounts of evaporative and exhaust emissions from motor vehicles and thus the chemical composition of the VOCs emitted by these vehicles. Controversy arose over whether the nation's traditional approach to assessing emissions, based on the mass of VOC emitted, was adequate to assess and regulate various RFG blends. With the use of ethanol as an oxygenated additive, such regulation proved to be especially contentious (e.g., EPA 1994). When compared with typical RFG blends using MTBE, blends using ethanol tend to have more evaporative VOC emissions but, it was argued, with a lower net ozone-forming potential. Accordingly, Senator Richard G. Lugar suggested that EPA establish a procedure to certify ethanol blends of RFG as equivalent to non-ethanol blends based on ozone-forming potential (see Appendix B, letter from Senator Richard G. Lugar dated October 17, 1995). EPA has not done so because it was unsure that there was an appropriate method for making such an assessment. Instead, EPA has commissioned this report to address the scientific and technical bases for such an assessment.

Charge to National Research Council Committee

Does RFG with ethanol as the oxygenate result in vehicular emissions with a lower ozone-forming potential than a blend with MTBE? Can a metric based on ozone-forming potential be reliably and robustly used to quantify the relative impacts of different RFG blends with different oxygenates on ozone pollution in the United States? As outlined above, these are the questions that motivated the formation of the National Research Council Committee on Ozone-Forming Potential of Reformulated Gasoline and this report. More specifically, the committee was given the task to assess whether the existing body of scientific and technical information is sufficient to permit a robust evaluation and comparison of the emissions from motor vehicles using different RFG blends based on their relative ozone-forming potentials; and the concomitant impact on air-quality benefits of the RFG program. The committee was asked to focus its assessment on the use of oxygenates in RFG, with specific attention to RFG blends using MTBE and ethanol.

The committee was asked to address the following specific issues:

  1. Assessment of the technical soundness of various approaches


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