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This paper presents results derived from Phase I of the Auto/Oil Air Quality Improvement Research Program. The Clean Air Act-defined mobile source toxic air pollutants benzene, 1,3-butadiene, formaldehyde and acetaldehyde have been measured in exhaust from twenty current model vehicles and fourteen older model vehicles during testing with 18 gasolines of varying composition. The gasoline fuel compositional variables evaluated included aromatic content, methyl tertiary-butyl ether (MTBE) content, olefin content, and the 90% distillation temperature (T90). The four fuel parameters were varied at target values of 45 and 20 vol % total aromatics, 0 and 15 vol % MTBE, 20 and 5 vol % total olefins and 360 and 280 °F 90% distillation temperature. An industry average fuel and an emissions certification test fuel were tested as reference fuels. In the current fleet, benzene levels were lowered when either fuel aromatics or T90 were reduced.

Prior studies of the effect of gasoline composition and physical properties on automotive exhaust and evaporative emissions have been reviewed. The prior work shows that the parameters selected for investigation in the Auto/Oil Air Quality Improvement Research Program (AQIRP) - gasoline aromatics content, addition of oxygenated compounds, olefins content, 90% distillation temperature, Reid vapor pressure, and sulfur content - can affect emissions. Effects have been observed on the mass of hydrocarbon, CO, and NOx emissions; on the reactivity of emissions toward ozone formation; and on the emissions of designated toxic air pollutants. The individual effects of some of the AQIRP parameters have been studied extensively in modern vehicles, but the most comprehensive studies of gasoline composition were conducted in early 1970 vehicles, and comparing the various studies shows that fuel effects can vary among vehicles with different control technology.

In this portion of the Auto/Oil Air Quality Improvement Research Program, ten 1989 model vehicles were tested using two fuels with different sulfur levels. These tests were run to determine instantaneous effects on exhaust emissions, not long-term durability effects. The high- and low-sulfur fuels contained 466 ppm and 49 ppm sulfur, respectively. Mass exhaust emissions of the fleet decreased as fuel sulfur level was reduced. Overall, HC, CO, and NOx were reduced by 16, 13, and 9 percent, respectively, when fuel sulfur level decreased. This effect appeared to be immediately reversible. Engine-out mass emissions were unaffected by changes in the fuel sulfur content, therefore, tailpipe emissions reductions were attributed to increased catalyst activity as the sulfur level was reduced.