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An extensive set of emission tests has been conducted in the Auto/Oil Air Quality Improvement Research Program on different fuel/vehicle systems. These emission tests have been used to model the impact of fuel/ vehicle changes on ozone formation in Los Angeles, Dallas-Fort Worth, and New York in 1995 and 2005/2010. Light-duty vehicles are estimated to contribute 28-37% of the peak ozone in 1980/1985, decreasing to 7-18% in 1995, and further decreasing to 5-9% in 2005/2010. Gasoline changes that show promise in reducing the contribution of light-duty vehicles to ozone formation are reductions in olefin content, 90% distillation temperature, sulfur content, and vapor pressure. Results for a methanol/gasoline blend (M85) used in prototype flexible/variable fuel vehicles depend on the assumptions used to project future M85 emissions. A research test gasoline produced less ozone than the M85 cases in Los Angeles and New York and either more or less ozone than M85 in Dallas-Fort Worth, depending on the assumptions. Sensitivity tests for Los Angeles addressed uncertainties in the overall magnitude of emissions from light-duty vehicles, in the biogenic inventory, and in the representation of the atmospheric chemistry.

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