Ozone-Forming Potential of Reformulated Gasoline (1999) / Chapter Skim
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Executive Summary
Executive Summary
Pages 1-10
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From page 1... ...
The RFG program attempts to lower motor-vehicle emissions through re-engineering gasoline blends. For example, the Clean Air Act mandates a specified minimum oxygen content in RFG blends to help reduce emissions of ozone precursors from gasoline-fueled motor vehicles and to reduce the need for some toxic compounds, such as benzene, in the fuel.
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In addition, the committee was not charged or constituted to address relevant, but separate, issues about domestic sources versus foreign sources of fuel, relative energy and cost implications for the production of different RTG blends, relative health and global environmental impacts, or the use of renewable versus nonrenewable fuels.
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After accounting for the effects of meteorological fluctuations, data from EPA's Aerometric Information Retrieval System indicate that peak ozone concentrations in 41 metropolitan areas in the United States decreased by about 10% overall from 1986 to 1997 despite growing fuel usage. Nevertheless, ozone pollution remains a problem; in 1997, about 48 million people lived in areas of the United States that were classified as ozone "non-attainment" areas, and promulgation of the new 8-fur National Ambient Air Quality Standard (NAAQS)
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If correct, this would imply that the potential impact of using RFG on near-ground ozone concentrations will decrease with time. In fact, air-quality models suggest that implementation of the RFG program reduces peak ozone concentrations by only a few percent.
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The great majority of emissions testing of motor vehicles using RFG has been performed on normally functioning vehicles, and there is substantial uncertainty over how RFG affects emissions from high emitting vehicles. Therefore, it is difficult to quantify total motor-vehicle emissions for an entire motor-vehicle fleet and to assess the efficacy of the use of RFG for the full driving cycle.
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Further, as VOC emissions from mobile sources continue to decrease in the future, CO emissions might become proportionately an even greater contributor to ozone formation. The committee did not conclude that the various RFG oxygenates affected CO emissions to such a degree that they substantially altered reactivity comparisons between RFG blends.
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From page 7... ...
In addition, such blends can lead to reductions in emissions of CO and some air toxics. Despite such emission reductions, however, the overall effect of the RFG program on ozone air quality is expected to be difficult to discern.
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There is also no statistically significant difference between MTBE and ethanol blends in the reactivity of VOC exhaust emissions. No evidence supports the claim that reactiv~ty-weighted VOC emissions from properly operating motor vehicles using RFG with ethano} would be significantly less than those from motor vehicles using RFG blended with MTBE, even if the ethanol-containing fuel had more oxygen than the MTBE-containing fuel.
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12. MODELS USED TO CHARACTERIZE EMISSIONS FROM RFG BLENDS The models currently used to inform regulatory decision making by quantifying emissions from motor vehicles that use RFG bZends are probZematic.
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From page 10... ...
For example, the Complex Model, developed by EPA, does not account for temperature variations when calculating evaporative emissions. The Predictive Model, developed by the California Air Resources Board, excludes consideration of evaporative emissions.
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