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This study is the second in a series of three EPA studies to investigate the effect of fuel reformulations and modifications on exhaust emissions. Both the first and second study in this series of studies were used to support the development of EPA's complex model for the certification of reformulated gasolines. Phase I of the study tested eight fuels on forty vehicles. This study, termed Phase II, tested twelve fuels on a separate fleet of 39 light-duty vehicles. The Phase II fuel parameters studied included Reid Vapor Pressure (RVP), the 50% and 90% evaporated distillation temperatures (T50 and T90), sulfur content, aromatics content, olefin content, oxygenate type and oxygen content. Measured exhaust emissions included total hydrocarbons (THC), oxides of nitrogen (NOx), carbon monoxide (CO), carbon dioxide (CO2), benzene, 1,3-butadiene, acetaldehyde and formaldehyde.

This study was the first of three EPA studies to investigate the effect of gasoline fuel parameters on hydrocarbon, nonmethane hydrocarbon, nitrogen oxides, benzene, formaldehyde, and acetaldehyde exhaust emissions of 1990 model year or equivalent vehicles. The fuel parameters tested in this program were oxygen concentration, Reid Vapor Pressure (RVP), ninety percent evaporative distillation temperature (T90), and sulfur concentration. Sulfur concentration was found to have the greatest effect on hydrocarbon and nitrogen oxide emissions. Increasing oxygen concentration and RVP reduction was found to reduce hydrocarbon emission more for high-emitting than normal-emitting vehicles. Oxygenate concentration was found to have a significant effect on aldehyde emissions.