Ozone-Forming Potential of Reformulated Gasoline (1999) / Chapter Skim
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6 The Effects of Reformulated Gasoline on Ozone and Its Precursors
6 The Effects of Reformulated Gasoline on Ozone and Its Precursors
Pages 131-174
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From page 131... ...
As a prelude to Chapter 7, in which an attempt is made to quantify and compare the ozone-forming potential of eight different RFG blends, this chapter assesses available information on the overall impact of the RFG program on ozone and its precursors as deduced from measurements. The steps taken in the approach to make that determination are illustrated in the "Decision Tree" depicted in Figure 6-~.
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From page 132... ...
~3 FIGURE 6-1 The Decision Tree illustrates the steps taken in an effort to quantify and compare the ozone-forming potential of various RFG blends. The figure indicates the types of findings at each step that resulted from the committee's considerations of the currently available observations that are pertinent to the reduction of ozone concentrations and other air-quality issues.
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From page 133... ...
WHAT CHANG ES I N MOTOR-VEH ICLE EXHAUST EM ISSIONS OF VOCs, NOx, CO, OR AIR TOXICS ARE OBSERVED IN LABORATORY TESTS WHEN RFGs ARE USED? Probably the most extensive single data set on the emissions of motor vehicles using RFG blends is that compiled from the Auto/Oi} Air Quality Improvement Research Program (AQIRP)
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From page 134... ...
The comparison is made for the older fleet, the current fleet, federal Tier ~ vehicles, and vehicles with "advanced technology." With the exception of formaldehyde,2 the RFG blends showed significantly lower toxic emissions for every class of vehicle when compared to emissions resulting from the industry-average gasoline. 2Many RFG blends appear to result in an increase in fo~aldehyde exhaust emissions.
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From page 135... ...
135 .O en .m o a_ Cal ~5 ILL Cal ._ au t,7 a)
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From page 137... ...
In viewing these figures, it should also be borne in mind that the ozone-forming potential of VOC emissions is determined by the total mass of the emissions as well as the reactivity of the species that are emitted. The relative contribution of each of these factors can be inferred by comparing the specific and total reactivities of the emissions because the specific reactivity is a measure of the amount of ozone
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From page 138... ...
In this case, composite, specific reactivities were calculated for each fuel using the AQIRP measurements of exhaust emissions (weighted for all cycles of operation) , evaporative emissions, running losses, resting losses, and refueling losses from LDVs using the EMFAC-7E emissions model and the measured vapor pressures of the fuels.
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From page 140... ...
~ ~ ~ ~ a: Fuel Composition FIGURE 6-4 Comparison of the specific reactivity (potential g 03/g VOc for the total VOC emissions) with the contribution of using industry-average fuel A and various RFGS.
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From page 141... ...
Exhaust Emissions of NQ The AQIRP data suggest that the effect of RFG on exhaust emissions of NOX will vary depending upon the specific properties of the blend. For example, NOX emissions were lowered by 6 + 1.9%4 by reducing olefin content from 20 to 5%, while reducing T90 from 390°F to 280°F increased NOX emissions by 5 + 2.4%, and the impact of lowering aromatic VOC content did not have a statistically significant effect (i.e., NOX emissions were lowered by 2.
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From page 142... ...
Overall, lower RVP appears to be the major contributor to lowered VOC emissions resulting from the use of RFG. It is important to note that before implementation of the RFG program, reductions in RVP were mandated and likely led to a significant decrease in VOC emissions.
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From page 143... ...
for HCs, CO, and NOx from current-fleet vehicles fueled with various RFGS that have very similar hydrocarbon compositions but contain different amounts of sulfur compounds (fuels Y4 to Y8 in Table ~1~. In contrast, the engine-out emissions show very little effect of the sulfur content of the fuel, consistent with the importance of sulfur-catalyst interactions that lower the effectiveness of the catalyst.
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From page 144... ...
In its second level of investigation, the committee focuses on whether the effects of RFG blends seen in these laboratory tests are also found in the emissions of motor vehicles operating under actual driving conditions. Emissions studies of this nature are typically carried out in two ways: (~)
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From page 145... ...
The vehicle fleet, ambient conditions, driving conditions through the tunnel, the tunnel, and the ambient air quality are described in detail in Kirchstetter et al.~1999a)
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From page 146... ...
was measured during the Colorado oxygenated fuels program (Bishop and Stedman 19901. NOx emissions showed no change during the two sampling periods.
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From page 147... ...
, die} not change significantly from the low-oxygenate to the high-oxygenate period. The 1994-1997 Stucties During the five sampling periods of this study, California gasoline changed composition from the 1994 summer and fall values indicated in Table 6-2 to California Phase 2 RFG.
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From page 148... ...
148 cr.
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From page 149... ...
Combining that result with those for exhaust emissions indicated that the ozone-forming potential (measured as total reactivity by the MIR scale) of all on-road emissions decreased by S% or less as a result of RFG blends.
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From page 150... ...
The measurement and analysis, which is based on the amount of light absorbed by the compounds contained in the exhaust, have been shown to quantitatively determine CO emissions in the exhausts to within +5% and VOC emissions to within +15% (Lawson et al. 1990; Stephens and CadIe 1991; Ashbaugh et al.
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From page 151... ...
They reported a 16 _ 3% decrease in CO emissions from the use of oxygenated fuel at 2.0% oxygen. A followup study using this technique was carried out in Denver to determine the effectiveness of the 1991-1992 winter Colorado oxygenated fuels program (PRC 19921.
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From page 152... ...
/NE a- . MODEL ~ MODEL YEAR MODEL YEAR FIGURE 6-7 Location-specific data from the Denver area using remote sensing.
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From page 153... ...
They found that 7% of the vehicles accounted for more than 50% of CO emissions and 10% of the vehicles accounted for more than 50% of the VOC emissions. This group probably involves I~DVs that were not well maintained or have otherwise improperly functioning emissions control systems.
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From page 154... ...
ARE THERE DATA TO SUPPORT MEANINGFUL ANALYSIS OF ATMOSPH ERIC DATA TO DETERM IN E THE EFFECT OF RFGS? The tunnel studies and remote-sensing measurements discussed in the previous section have provided useful information concerning the effects of RFG blends on the emissions of a variety of ozone precursors, including CO from LDVs.
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From page 156... ...
LDV emissions of benzene are derived directly from benzene and from higher aromatics in the fuel. The RFG programs, with their prescribed reductions in benzene and other aromatics (see Table 5-3)
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From page 157... ...
However, in the committee's view, the studies are not conclusive. The Oxygenated Fuels Program was initiated in the midst of other control programs and technological improvements designed to lower CO emissions.
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From page 159... ...
159 _ ~ g ~ a., ~ , ~ C~ o of Go cn ~n Cal An In a)
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From page 161... ...
161 Cal Go ~ ~ Go Go · LO ~ ~ ~ ~ ~ (D C~ o ~ C~ o ~oo ~ ~ _' ~ o ~ CNi ~t ~ ~_ ~{Y)
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From page 162... ...
The presence of strong downward trends in CO throughout the time series in the post-1987 period complicates evaluation of mid-series changes to regulatory policy. Examination of CO concentrations before and after implementation of the oxygenated fuels program might very well indicate a decrease in CO, but this decrease may be indicative of the overall downward trend that began well prior to the implementation of the program as opposed to the program itself.
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From page 163... ...
. Examination of the ~ and 2o values in Table 6-5 reveals varied results for the sites.s Most sites had positive ~ values (indicative of a benefit from the oxygenated fuels program)
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From page 164... ...
To address this problem, Larsen and Brisby assumed that the contribution of the cleaner-burning fuels program to the overall ozone decrease was proportional to the estimated percent reduction in the precursor emission inventory resulting from the program. Thus, even though the Larsen and Brisby study was based on ambient ozone concentrations, the attribution of a portion of the observed ozone decrease to the use of cleaner-burning gasoline was derived from an emission inventory and does not constitute empirical verification of program effectiveness.
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From page 165... ...
Ozone then increased slightly in 1994, and then decreased again in 1995. Whereas the oxygenated fuels program was implemented in California in 1992, the RFG program was implemented in 1996.
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From page 166... ...
. r T T ~ 8t 83 85 87 89 91 93 95 YEAR D FIGURE 6-11 Daily maxima of ozone concentrations at Riverside, CA, from 1980 to 1997 (A)
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From page 167... ...
However as discussed above, it is unlikely that such a signal in ambient ozone concentrations could be discernible given the relatively large variability in ozone, the myriad factors that affect ozone concentrations, and the rather small overall impact RFG is projected to have on ozone.) The three questions recommended here for consideration are briefly discussed below.
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From page 168... ...
Although measurements of LDV emissions in a laboratory setting are informative, they do not necessarily represent the emissions of LDVs in operation under actual driving conditions. Confirmation that laboratory-measured emission reductions also occur on the road can be obtained through tunnel studies and remote sensing of tailpipe emissions.
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From page 169... ...
The most dramatic effects on ozone-precursor exhaust emissions seen in the various gasoline compositional matrices studied were those due to lowering the fuel's RVP and the amount of sulfur-containing compounds. Only slight reductions, less than 10%, in the CO and VOC emissions can be ascribed to the addition of either MTBE or ethanol.
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From page 170... ...
However, discerning a statistically significant effect of RFGs on ambient ozone concentrations has thus far proven to be quite difficult. This is most likely because ambient ozone concentrations tend to be quite variable from year to year and the RFG program is but one of a multitude of ozone-mitigation programs underway in the nation whose impact on ozone is of a similar or larger magnitude.
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From page 172... ...
As discussed in the next chapter, such a reduction size limits the ability to document the benefits of RFGs and to reliably distinguish between the ozone-forming potentials of different RFG blends.
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From page 173... ...
-0.2 + 0.3 2010 -0.1 + 0.2 -0.3 + 0.2* 0.0 + 0.2 aThe predicted effects may not be reflective of the greatest change in gasoline composition such as changes from the late 1980s to when California Phase 2 RFG began to be used.
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From page 174... ...
' ::, :~: "":'''~$.:''~2$. = ~.~8 Cif 'a W le ~,, .~ or FIGURE 6-12 The areas where the RFG program was implemented during 1995.
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