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The effect of gasoline olefin composition and content on urban ozone was estimated using the Urban Airshed Model (UAM), emission measurements for a base fuel, and projected emissions for two hypothetical fuels with reduced olefin content. The projected emissions for the hypothetical fuels were developed using regressions developed from Auto/Oil Air Quality Improvement Research Program (AQIRP) Phase I testing, a vapor headspace model and other information. Ozone modeling was conducted for Los Angeles in year 2010 and Dallas-Fort Worth and New York in year 2005. When all olefins were removed from the base fuel, the light-duty vehicle contribution to peak hourly ozone was reduced by 8 to 12%. This corresponds to a projected reduction of 0.6 to 0.8% in total peak ozone from all sources. Removing only light (C5) olefins provided 67 to 78% of the peak ozone benefit from removal of all olefins.

The effect of gasoline sulfur content on urban ozone was estimated using the Urban Airshed Model (UAM) and exhaust emission measurements from the Auto/Oil Air Quality Improvement Research Program (AQIRP) Phase II sulfur study. Ozone modeling was conducted for Los Angeles in year 2010 and Dallas-Fort Worth and New York in year 2005. Reducing fuel sulfur content reduced predicted ozone formation in all three cities. The light-duty vehicle contribution to predicted peak hourly ozone was reduced by 9, 16, and 8% in Los Angeles, Dallas-Fort Worth, and New York, respectively, when fuel sulfur content was reduced from 450 to 50 ppm. This corresponds to a reduction in total peak ozone from all sources of 0.8, 0.7, and 0.5% in Los Angeles, Dallas-Fort Worth, and New York, respectively, in year 2005/2010. There is uncertainty in these predicted effects; in particular, the effect of sulfur reduction expressed as a percentage of total peak ozone from all sources may be larger.