Rethinking the Ozone Problem in Urban and Regional Air Pollution (1991) / Chapter Skim
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12 Alternative Fuels
12 Alternative Fuels
Pages 379-412
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From page 379... ...
The central role of VOCs in the formation of tropospheric ozone suggests that changing fuels could be effective by reducing the reactivity of the VOC emissions, the total mass emitted, or both. Gasoline and the exhaust from conventionally fueled vehicles are highly reactive in the atmosphere because 379
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From page 380... ...
. 985 1994 1999 2004 Year FIGURE 12-1 Estimated nationwide VOC emissions by source category, by year.
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From page 381... ...
For example, reducing the reactivity of VOCs can reduce ozone in NOx-rich urban centers, such as downtown Los Angeles and New York, but would likely provide little help in regions with high VOC-to-NOx ratios, such as Houston and Atlanta. The degree to which the different alternative fuels could improve air quality is discussed below.
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From page 382... ...
382 Mobile sources Organic solvent evaporation Surface coating Petroleum industry Gas marketing Treatment, storage & disposal facilities Other industries Chemical manufacturers Solid waste disposal Nonresidential fuel _ combustion Miscellaneous RETHINKING THE OZONE PROBLEM Source size El Small · Large 0Yo 10% 20% 30% Total VOC emissions 40% 50% FIGURE 12-2 VOC emissions in nonattainment cities, by source category, 1985. Stationary sources that emit more than 50 tons per year of VOCs are included in the "Large" category.
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From page 383... ...
In the middle term (5-20 years) , likely candidates to replace gasoline- and diesel-powered vehicles are similar vehicles powered by internal combustion engines that run on methanol, natural gas, or reformulated gasoline.
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From page 384... ...
Other fuels, in particular hydrogen and electricity, are more attractive from an environmental standpoint. Advances in battery technology could make electric vehicles an attractive alternative to vehicles with internal combustion engines.
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From page 385... ...
Still, some general conclusions can be developed, and these are discussed at the end of the chapter. ATTRIBUTES OF ALTERNATIVE FUELS Reformulated Gasoline As the name implies, reformulated gasoline is a refined petroleum product whose composition is similar to gasoline.
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From page 386... ...
VOC emissions from NGVs mimic the fuel, and are largely methane (Table 12-1~. Given its very low atmospheric reactivity, methane has great potential for reducing ozone formation.
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From page 388... ...
Pure methanol is a colorless, toxic liquid with low vapor pressure and high heat of vaporization. Although the latter two attributes can lower emissions when an engine is warm, they also make it difficult to start a vehicle running on pure methanol when cold, and high cold start emissions ensue.
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From page 389... ...
It is not clear whether methanol use would lead to lower NOX emissions. Limited tests on flexibly fueled vehicles show some NOX reductions, but a dedicated MFV would use a higher compression ratio, which could lead to higher NOX emissions.
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From page 390... ...
It is also possible that the mass emissions rate would be lower. To minimize evaporative emissions, the RVP of gasoline in California and in the northeastern United States is mandated to be less than 9.0 psi.
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From page 391... ...
The increased evaporative emissions and increased concentrations of ethanol and acetaldehyde in the atmosphere would lead to increases in such pollutants as PAN (Tanner et al., 1988~. Ethanol is more reactive than methanol and other blending agents such as MTBE (Carter, l990b, 1991; Japar et al., 1990)
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From page 392... ...
Net CO and VOC emissions would be reduced by 95-99% (Krupnick et al., 1990; Sperling and DeLuchi, 1989~. Alternative Fuels For Heavy-Duty Vehicles Most of the current discussion of alternative vehicles centers on light-duty vehicles (cars and small trucks)
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From page 393... ...
Accordingly, ozone has been the focus of most studies, and accompanying effects are sometimes given. Because ozone formation is the result of a complex interaction of photochemistry, transport, and emissions, the primary tools for testing the effects of alternative fuels are photochemical air-quality models; box, trajectory, and grid-based models have been used.
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From page 394... ...
Ozone reductions varied widely, from zero to 80%, depending on the HCHO content and amounts of VOC emissions. Differences between smog chambers and the atmosphere make it difficult to use smog chamber results directly for predicting urban and regional airquality changes that would result from methanol use.
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From page 395... ...
(1990) found peak ozone reductions of 9-17~o in 2000, depending on the fuel type simulated, and of about 45rO in 2010.
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From page 396... ...
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From page 397... ...
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From page 399... ...
are predicted to see more substantial ozone reductions. Total removal of light-duty VOC emissions led to only a 7% ozone reduction in the cities studied.
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From page 400... ...
Ultimately the AQIRP provide extensive information about the air-quality impacts of reformulated gasoline and methanol blends, but only limited information is available at this time. In particular, only the predicted impacts of a limited variation in gasoline composition are available as used in 1989-model-year vehicles (Auto/Oil Air Quality Improvement Research Program, 1991; Hochhauser et al., 1991~.
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From page 401... ...
NOX and CO also decreased by 26% each. Air-Qualit~r Benefits of Other Fuels There have been few detailed studies of the likely air-quality benefits of alternative fuels other than methanol and reformulated gasoline.
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From page 402... ...
Given the minor reactivity reduction of ethanol compared with gasoline, the increased evaporative emissions would negate much of the ozone reduction, and actually could lead to increased ozone production. This is similar to the effect resulting from use of low methanol blends in flexibly fueled vehicles (Figure 12-3~.
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From page 403... ...
. Peak ozone reductions of as much as 4.1% were found.
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From page 404... ...
In essence, this is the local sensitivity of ozone formation to emissions of specific organic gases, and it is given as the maximum number of moles of ozone formed by a one-mole increase of carbon in VOCs. A summary of their calculation results is given in Table 12-3 for some species typically emitted from alternate and conventional vehicles.
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From page 405... ...
REGULATORY IMPLEMENTATION OF ALTERNATIVE FUEL USE Because of the considerable contribution of mobile source emissions to
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From page 406... ...
a Peak Exposure Carter (1989) CO 1 1 1 Aldehydes >C2 64 64 93b ALkanes 16 11 9.5c Alkenes 67 83 516 Aromatics 51 82 53e Ethene 71 67 78 Formaldehyde 119 148 180 Toluene 15 24 25 Methanol 17 14 17 aAirshed model results were combined with the population distribution to find the sensitivities of both the peak ozone and ozone exposure as VOC emission rates are increased.
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From page 407... ...
(1989) are used for a flexibly fueled vehicle fueled on M85 and M100.
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From page 408... ...
A regulatory problem that has plagued alternative fuels and reformulated gasoline has been how to treat all fuels equally, without apparent bias that is unwarranted on an air-quality basis. One strategy to account for the lower ozone-forming potential of alternative fuels, yet allow for all fuels and technologies to compete on an equal regulatory basis, is to use a "reactivity-adjusted" emission standard.
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From page 409... ...
SUMMARY Alternative fuels have the potential to improve air quality, especially in
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From page 410... ...
Also, it must be stressed that the use of alternative fuels other than electricity and natural gas may have little effect on the increase in emissions that occurs over time with in-use vehicles, particularly its "super-emitters." It is this emissions deterioration that is the most central aspect of the motor vehicle emissions problem (Chapter 9~. Alternatively fueled vehicles could reduce mass emissions of volatile organic compounds (VOCs)
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From page 411... ...
Although the degree to which alternatively fueled vehicles can improve air quality is not known, the use of alternative fuels can become part of an effective ozone control strategy. Certain applications now exist where these fuels can be used effectively.
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