1. for evaluating and comparing the relative ozone-forming potentials of RFGs. Two prominent methods for assessing relative ozone impacts include relative reactivity factors and grid-based airshed models. Determine whether there is sound scientific basis for the use of reactivity factors, models, and/or any other approach(es) for evaluating the ozone-forming potential of RFGs in a nationwide program.
  2. Assessment of technical aspects of various air-quality issues when evaluating the relative ozone-forming potentials of RFGs. Air-quality issues to be considered include assessment of the ozone-forming potentials of RFGs for both peak (1-hr) and average (8-hr) ozone levels, inclusion or exclusion of CO as an ozone precursor, and consideration of changes in NOx emissions and the corresponding impact on ozone levels resulting from the use of different levels and/or types of oxygenates or other fuel composition changes.
  3. Assessment of the sensitivity of evaluations of the relative ozone-forming potentials of RFGs to factors related to fuel properties and the variability of vehicle technologies and driving patterns. Factors to be considered include assessment of effects of the fuel blending method (i.e., splash blending versus match blending), "distillation impact" and/or the "commingling effect," variability in fuel composition, engine operating conditions as they pertain to emissions, and changes in the exhaust-to-evaporative emissions ratio.6

The committee was asked to identify any gaps in the existing scientific and technical information, recommend how such gaps might be


"Splash blending" refers to a method of oxygenating gasoline by adding an oxygenate to the gasoline blend stock without any systematic control over the resulting Reid Vapor Pressure (RVP) of the RFG. (RVP is the constrained vapor pressure of the fuel at 100 degrees Fahrenheit.) When ethanol is splash blended into gasoline, the RVP of the finished blend could increase by I pound per square inch (psi) or more above the applicable RVP limit. "Match blending" refers to the preparation of an RFG blend with systematic control over the re-suiting RFG such that the finished blend meets the RVP standard for the appropriate RFG blend. "Distillation impact" refers to the possible effect of oxygenates on the volatility of RFG blends at temperatures greater than 100°F, which can occur in a vehicle's fuel tank. "Commingling effect' refers to an increase in the resulting vapor pressure when an ethanol-blended RFG is mixed with a non-ethanol blended RFG in a vehicle's fuel tank The increase in vapor pressure of the mixture is beyond that of either of the separate blends.

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