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Three-day diurnal SHED evaporative emissions were measured in a fleet of ten Auto/Oil current (1989) and 2 older (1984) vehicles using Auto/Oil Industry Average fuel. SHED temperature cycled each 24-hour period from 72 to 96 F (22.2 to 35.5C). Measurements included speciation of individual hydrocarbons in the SHED as well as total mass emissions at the end of each of the three 24-hour test periods. Previous evaporative emission studies provided evidence that permeation and/or fuel seepage could contribute significantly to the mass of diurnal and hot soak emissions. Data from this investigation were used to quantify the contribution of liquid fuel to total SHED emissions during diurnal testing. A calculation method, based on the concentration of 29 select hydrocarbons in the SHED, is presented to apportion SHED emissions between those associated with liquid fuel losses and those associated with fuel tank head space vapor losses.

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.

The annual mean diesel particulate concentrations in 1979 were estimated for four urban areas -- New York, Los Angeles, Washington, DC and Denver. These values were then compared with projections for the year 2000 under three different NOx emission scenarios. The particulate emission rates chosen for the three scenarios are best engineering estimates which include the implementation of advanced technology. It was found that diesel particulate concentrations remained about the same as the 1979 levels for the high NOx scenario, but doubled or more than doubled for the low NOx scenario. The low NOx scenario will also lead to a visibility deterioration of 5% or more compared to 1979 visibility. For all scenarios, the contributions of buses and heavy duty trucks to diesel particulate concentrations are comparable for all cities except Los Angeles, with a combined contribution of 65 to 85%.