Ozone-Forming Potential of Reformulated Gasoline (1999) / Chapter Skim
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7 Using Ozone-Forming Potential to Evaluate the Relative Impacts of RFGs: A Case Study
7 Using Ozone-Forming Potential to Evaluate the Relative Impacts of RFGs: A Case Study
Pages 175-202
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From page 175... ...
Because the mass of VOC emissions can be a misleading indicator of the ozone-forming potential of these emissions, the committee assessed the air-quality benefits of various RFG blends on the basis of the reactivity of these emissions as well as their mass. It should be noted at the outset, however, that this is a difficult task.
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From page 176... ...
In order to assess the role of oxygenates and, more specifically, the relative roles of MTBE and ethanol, the subset of fuels included in this analysis was selected to provide a range of oxygen contents from 0 to 3.4% by weight (recall that the federal RFG program calls for a minimum oxygen content of 2% by weight) , with this oxygen coming from MTBE or ethanol.
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From page 177... ...
RVP (psi) b AQIRP Phase Ic F 0 0 0 8.8 S 0 0 0 8.0 U 9.7 0 3.4 9.6 T 9.7 0 3.4 9.3 N2 0 14.5 2.6 8.8 MM 0 14.8 2.7 8.0 AQIRP Phase 110 C1 0 0 0 6.9 C2 0 11.2 2.0 6.8 California Ethanol Testing Programe 63 0 11.6 2.1 6.9 64 11.2 0 3.9 7.8 Wee Table 6-1 for a more detailed tabulation of the fuel properties.
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From page 178... ...
The magnitude of the uncertainty in these reactiv~ties is a crucial piece of information needed to decide whether one RFG blend is preferable over another from an air-quality point of view. The uncertainty in any measured parameter, including those related to LDV emissions, can arise from both random and systematic errors.
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From page 179... ...
US/NO OZONE-FORM/NO POTENT/A! TO EVALUA HE /MPACTS OF RUGS Oa5 0.4 hi_ it_ Oh Oa3 _ ~ 0.2 ct o Q 0~1 179 / / / / \ \ / To interval about men\ ·_^ #A /(~% probdl~ty Rhea lth Intel)
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From page 180... ...
If a decision maker uses a difference in the mean reactivities measured for two fuels to implement a given control policy (e.g., choosing fuel a over fuel b on the basis of experimental data) but, in fact, there is no difference in the real world, the decision maker has committed a Type ~ error (falsely concluding that a difference exists)
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From page 181... ...
On the other hand, when a large p value is obtained, a decision maker is likely to make a Type I error by choosing the fuel with the apparent, but not statistically significant lower reactivity. In general, as the probability of making a Type I error increases, the probability of making a Type II error (i.e., not choosing the lower reac
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From page 182... ...
Thus, low p values imply a high probability of a Type IT error if a decision maker decides to not choose the lower reactivity fuel, while high p values imply a low probability of a Type II error. FUELS AND EMISSIONS DATA FROM THE AQIRP STUDY As indicated in Table 7-l, eight fuels from the AQIRP study were selected for detailed analysis here: six from AQIRP Phase ~ and two from AQIRP Phase II.
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From page 183... ...
It also should be noted that all of the vehicles in the AQIRP study were well-maintained and properly functioning and thus the data do not address the probable substantial contributions from high-emitting vehicles to overall precursor · ~ emissions. Tables listing the LDV emissions from each of these fuels derived from the AQIRP data are presented in Appendix D
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From page 184... ...
Given the substantial variability in emissions of the various vehicles tested with fuels A and B the committee used logarithm Remissions using fuel A)
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From page 185... ...
In fact, for each emissions category, lower RVP is associated with higher diurnal or hot-soak emissions in at least one of the three fuel pairs considered here. In the case of hot-soak emissions, a lower RVP fuel produced a higher reactivity that was significant at the 93% confidence level.
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From page 186... ...
-7 0.1 0.8 0.2 No significant and consistent effect apparent. Effect of Oxygenates Using MTBE Inspection of Table 7-1 indicates that there are three fuel pairs that can be used to assess the effect of adding MTBE to gasoline, two from AQIRP Phase ~ and one from AQIRP Phase IT.
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From page 187... ...
TO EVA! UA HE /MPACTS OF RUGS TABLE 7-4 Effect of RVP on Diurnal Emissions from Three AQIRP Fuel Pairs 187 Fuel Pair % Decrease in .
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From page 188... ...
A comparison of the exhaust, diurnal, and hot-soak emissions of these fuel pairs, and the statistical significance of the differences are presented in Tables 7-6, 7-7, and 7-S, respectively. As in the previous comparisons, there is little evidence here to suggest a statistically significant effect of MTBE.
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From page 189... ...
TO EVA! UATE IMPACTS OF RUGS TABLE 7-6 Effect of MTBE on Exhaust Emissions from Three AQIRP Fuel Pairs _ _ 189 % Decrease in Emissions Attributable Fuel Pair to MTBEi pValue2 Summary A
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From page 190... ...
oxygen content as that of the MTBE-blended fuel and thus less volume percent oxygenate (see Table 5-21. A comparison of ethanol and MTBEblended fuels with similar volume percent oxygenate, but different oxygen content, is provided by the data from the California Ethanol Test Program discussed in the next section.
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From page 191... ...
TO EVA! UATE IMPACTS OFRFGS TABLE 7-8 Effect of MTBE on Hot-Soak Emissions from Three AQIRP Fuel Pairs 191 % Decrease .
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From page 192... ...
MTBE on Diurnal Emissions from Two AQIRP Fuel Pairs Fuel Pair % Decrease in Emissions Attributable to Ethanols pValue2 Summary A Effect on mass of VOC emissions {g/mi)
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From page 193... ...
. Negative value indicates an emissions or reactivity increase with the addition of ethanol.
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From page 195... ...
Fortunately, the California Ethanol Testing Program produced a considerably more-detailed database on this issue. During the program, multiple tests were made to characterize the emissions from LDVs using a fuel with MTBE (fuel 63)
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From page 196... ...
As a result, the reactivity of the combined exhaust and evaporative emissions using the ethanol-blended fuel was estimated by CARB to be about 17% larger than those using the MTBE-blended RFG. The committee analyzed data obtained from the California Ethanol Testing Program before publication of CARB's (1998)
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From page 197... ...
that the mass of evaporative emissions from AQIRP fuels with ethanol are greater than those from fuels with MTBE. However, for one of the fuel pairs considered, the difference is cut by more than a factor of 2 when measured on the basis of reactivity; in the case of the other fuel pair, the reactivity from the ethanol-containing fuel is actually found to be less than that of the MTBE-containing fuel.
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From page 198... ...
ANALYSIS USING THE COMPLEX AND PREDICTIVE MODELS The analyses presented in the preceding two sections could perhaps be criticized for being based on test results from a limited number of fuels, and thus not representative of a fleet-wide response to changes in fuel composition. Indeed, in the case of the AQIRP study the smallness of the sample size limited the ability to unequivocally conclude that oxygenates had, or did not have, an impact.
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From page 199... ...
The resulting exhaust and evaporative emissions predicted by the Complex Model are given in Table 7-14 and the percentage decrease in exhaust emissions predicted by the Predictive Model, relative to the reference fuel, are listed in Table 7-15.5 Because neither the Complex nor the Predictive Models estimate the composition of the emissions, these models cannot be used to predict changes in the reactivity of the · ~ emissions. TABLE 7-14 VOC and NOx Emissions for Various Fuels Predicted by EPA's Complex Modela Emissions (mg/mi)
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From page 200... ...
On the other hand, the small and borderline significant increases in NOx exhaust emissions and evaporative VOC emissions, as suggested in the AQIRP data, associated with the addition of MTBE are not reflected in the results of the Complex Model. Like the Complex Mode!
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From page 201... ...
Data from the California Ethanol Testing Program indicate that the exhaust emissions from vehicles using ethanol-containing fuels are about 10% lower than those arising from vehicles using fuels with MTBE. There is also some indication that oxygenates in fuels lead to somewhat higher emissions of NOx-an effect that could have undesired impacts on air quality in rural areas and on regional scales.
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From page 202... ...
Recall from the committee's earlier analyses that the overall effect of RFGs might be an approximate 20% reduction in the reactivity of LDV emissions and a few partsper-billion reduction in peak ozone concentrations. After combining exhaust and evaporative emissions, the use of ethanol, as opposed to MTBE, as an oxygenate would lead to a decrease in the effectiveness of RFGs but not a total cancellation.
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