(Abridged Version by Ildefonso J. Rubrico)
07 September 1999
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Topics: ----------------------------------------------------------------------- ENVIRONMENTAL PROTECTION AGENCY 40 CFR Parts 80 and 86 [AMS-FRL-6337-4]
RIN 2060-AI32 Control
of Diesel Fuel Quality
AGENCY: Environmental Protection Agency. ACTION: Advance
notice of proposed rulemaking. SUMMARY: Diesel engines used in motor vehicles and nonroad equipment are a major source of nitrogen oxides and particulate matter, both of which contribute to serious health problems n the United States. We are considering setting new quality requirements for fuel used in diesel engines, in order to bring about large environmental benefits through the enabling of a new generation of diesel emission control technologies. Because the pursuit of diesel fuel quality changes would be a major undertaking for the Agency and affected industries, and because of the many unre-solved issues involved, we are publishing this advance notice to summarize the issues, with the goal of helping you to better inform us as we consider how to proceed. To aid this process, we have grouped key questions under issue to-pic headings that are numbered sequentially throughout this notice. Although this advance notice solicits comment on all potentially beneficial diesel fuel quality changes, we believe that the most promising change would be fuel esulfurization for the purpo- se of enabling new engine and aftertreatment technologies that, although highly effective, are sensitive to sulfur. FOR FURTHER INFORMATION CONTACT: Carol Connell, U.S. EPA, National Vehicle and Fuels Emission Laboratory, 2000 Traverwood, Ann Arbor, MI 48105; Telephone (734) 214-4349, FAX (734) 214-4050, E-mail connell.carol@epa.gov. ---------------------------------------------------------------------------------------------------------------------- I. Why Is EPA
Considering Diesel Fuel Changes? Diesel
engines contribute greatly to a number of serious air pollution
problems, especially the health and welfare effects of ozone and
particulate matter (PM). Millions of Ame-ricans live in areas that
exceed the national air quality standards for ozone or PM. As
discussed in detail in the follo-wing section, diesel emissions account
for a large portion of the country's PM and nitrogen oxides, a key precursor
to ozone formation. By 2010, we estimate that diesel engines will
account for more than one-half of mobile source emis-sions, and
nearly 70% of mobile source PM emissions (not taking into account
emission reductions from proposed Tier 2 emission standards for
light-duty vehicles and trucks, discussed below). \1\ In this notice, the term ``diesel engine'' generally refers
to diesel-fueled engines, rather than to engines operating on the
diesel combustion cycle, some of which use alternative fuels, such
as methanol or natural gas, instead of diesel fuel. Diesel emissions in this country come mostly from heavy-duty trucks and nonroad equipment, but a potentially large additional source may grow out of auto manufacturers' plans to greatly increase the sales of diesel-powered light-duty vehicles (LDVs) and especially of light-duty trucks (LDTs), a category that includes the fast-selling sport-utility vehicles, minivans, and pickup trucks. These plans will be greatly affected by our own plans to adopt stringent new emission standards for these light-duty highway vehicles (referred to as ``Tier 2'' standards) that we have proposed to phase in between 2004 and 2009. A key approach taken in developing the Tier 2 standards has been ``fuel-neutrality''-- applying standards equally to diesel- and gasoline-powered vehicles. As a result, the proposed Tier 2 and PM standards are far more challenging for diesel engine designers than the most stringent heavy-duty engine standards promulgated to date. We have proposed Tier 2 standards concurrent with a proposal to reduce the sulfur content of gasoline, in part because gasoline sulfur reduction will enable advanced catalyst technolo- gies needed to achieve the new standards. With this advance notice, we are seeking comment on the merits of improving the quality of diesel fuel as well, as an enabler of advanced technolo- gies for diesel emission control, without which diesel vehicles may not be able to meet Tier 2 standards. These advanced sulfur-sensitive technologies have the potential to reduce diesel engine NO emissions by up to 75% and PM emissions by 80% or more. Thus this potential action on diesel fuel is, like gasoline sulfur control, closely tied to our Tier 2 standard-setting activity. Decisions on diesel fuel quality need to be made quickly so that the Tier 2 program may be implemented in the most coordinated and cost-effective manner. We therefore plan to pursue this action on an accelerated schedule. If, following this advance notice, we decide that a proposal is warranted, we plan to publish a notice of proposed rulema- king later this year, and a final rule as soon as possible after that. Although the impetus for near-term action on diesel fuel quality comes from our efforts to set fuel-neutral Tier 2 standards for the ight-duty market, any emissions control technologies that prove effective in light-duty diesel applications are likely to be effective with heavy- duty highway engines as well. Thus higher quality diesel fuel for heavy-duty applications, combined with more stringent heavy-duty engine emission standards that effectively introduce the new technologies, could provide large environmental benefits, though perhaps on a different implementation schedule than that required for the light-duty program. This might take the form of a phased in program, involving a regulated grade of premium fuel that is initially focused on servicing the light-duty diesel fleet, but that gradually widens its market penetration to fulfill the expanding need created by sales of new heavy-duty vehicles that also employ the ad- vanced technologies. Various possibilities and issues associated with such an approach are dis- cussed in detail below in this notice. In addition to enabling new control technologies, the use of higher quality diesel fuel is likely to improve the emissions performance of the existing fleet of diesel engines as well, as explained below. Eventually these advanced technologies could also find application in nonroad equipment, although implementation timing would have to consider a number of special challenges in control- ling nonroad engine emissions, including the fact that current nonroad diesel fuel is unregula- ted and has much higher sulfur levels than highway fuel. It may also be necessary to regulate nonroad diesel fuel in an earlier time frame, to a quality level similar to that of current highway fuel (which has sulfur levels capped at 500 parts per million (ppm)), in order to pro- vide for the transfer of advanced highway engine technologies already under development for use with that fuel. This technology transfer is expected to play an important role in the implementation of the recently promulgated Tier 3 nonroad diesel engine emission standards, and of the stringent PM standards planned for promulgation in 2001. (The 2001 rulemaking will also review the feasi- bility of the recently promulgated Tier 3 standards, and may amend them if appropriate.) II. Diesel Engines and Air Quality The diesel engine is increasingly becoming a vital workhorse in the United States, moving much of the nation's freight, and carrying out much of its farm, construction, and other labor. Every year, about a million new diesel engines are put to work in the U.S., and as their utili- ty continues to grow, so too does their annual fuel consumption, now over 40 billion gallons. However, the societal benefits provided by the diesel engine have come at a price--diesels emit millions of tons of harmful exhaust pollutants annually. Compounding our concerns over emissions from applications in which diesels are currently prevalent, we are aware that manufacturers are considering the introduction of a new generation of diesel engines for use in light-duty highway vehicles. Even at modest projected sales ramp- up rates, this introduction could greatly increase the number of diesel engines in operation over the next several years. Although in the past much of our attention in addressing the diesel pollution problem has focused on engine design, the role of fuel formulation has been recognized from the beginning. A number of fuel properties and constituents can be varied in the refinery process with varying effects on emissions. Furthermore, some advanced emission control technologies may be degraded by constituents in diesel fuel, even to the extent of precluding the use of these technologies. Diesel engines are large contributors to a number of serious air pollution problems, parti- cularly the health and welfare effects caused by ozone and particulate matter. The particulate from diesel exhaust also is thought to pose a potential cancer risk. These concerns for cancer risk and other adverse health effects are discussed in detail below, followed by a discussion of diesel contributions to emissions inventories. A. Ozone and Particulate Matter Ground-level ozone, the main ingredient in smog, is formed when volatile organic compounds (VOC) and NO react in the presence of sunlight, usually during hot summer weather. Motor vehicles are significant sources of both VOC and NO. Diesel engines, in part- icular, are significant sources of NO emissions. Power plants and other combustion sources also are large emitters of NO. VOCs are emitted from a variety of sources, including chemical plants, refineries and other industries, consumer and commercial products, and natural sources such as vegetation. Particulate matter is the term for a mixture of solid particles and liquid droplets found in the air. Particulate matter is distinguished between ``coarse'' particles (larger than 2.5 microns) and ``fine'' particles (smaller than 2.5 microns). Coarse particles generally come from vehicles driven on unpaved roads, materials handling, windblown dust, and crushing and grinding operations. Fine particles result from sources such as fuel combustion (from motor vehicles, power plants and industrial facilities), wood stoves and fireplaces. Fine particles also are formed in the atmosphere from gases such as sulfur dioxide, NO and VOC. Particles directly emitted from motor vehicles, including diesel engines, and those formed by motor vehicle gaseous emissions, are in the fine particle range. Ozone can cause acute respiratory problems, aggravate asthma, cause inflammation in lung tissue, and impair the body's immune system defenses. Particulate matter, especially fine parti- cles, has been linked with a series of significant health problems, including premature death, aggravated asthma, acute respiratory symptoms, chronic bronchitis, and shortness of breath. Furthermore, the particulate matter from diesel engines is thought to pose a potential cancer risk, as discussed in the next section. Fine particles can easily reach the deepest recesses of the lungs. Inhalation of ozone and particulate matter has been associated with increased hospi- tal admissions and emergency room visits. With both ozone and particulate matter, those most at risk are children and people with preexisting health problems, especially asthmatics. Because children's respiratory systems are still developing, they are more susceptible to environmental threats than healthy adults. The elderly also are more at risk from exposure to fine particles, especially those already suffering from heart or lung disease. In addition to serious public health problems,
ozone and particulate matter cause a number of environmental and
welfare effects. Fine particles are a major cause of visibility
impairment in many of our most treasured national parks and wilderness
areas, and many urban areas. Parti- culate matter also can damage
plants and materials such as monuments and statues. Ozone adverse-
ly affects crop yield, vegetation and forest growth, and the durability
of materials. By weake- ning sensitive vegetation, ozone makes
plants more susceptible to disease, insect attack, harsh weather
and other environmental stresses. NOx itself, one of the key precursors
to ozone, contributes to fish kills and algae blooms in the Chesapeake
Bay and other sensitive watersheds. \3\ See 63 FR 57356, October 27, 1998, ``Finding
of Significant Contribution and Rulemaking for Certain States
in the Ozone Transport Assessment Group Region for Purposes of
Reducing Regional Transport of Ozone''. This action is known as
the ``NO SIP Call'. \4\ For a full description
of this analysis, see ``Draft Regulatory Impact Analysis--Control
of Air Pollution from New Motor Vehicles: Tier 2 Motor Vehicle
Emission Standards and Gasoline Sulfur Control Requirements;''
Chapter III.B.; (EPA420-R-99-002); hereafter referred to as ``Tier
2/Gasoline Sulfur Draft RIA'' (EPA Docket A-97-10). In addition to widespread ozone nonattainment, particulate
matter continues to be a signi- ficant air quality problem. In
1997, 8 million Americans lived in 13 counties that exceeded the
air quality standard for particulate matter less than 10 microns
in size (PM10). We project that by 2010, 11 counties, with a combined
population of about 10 million people, will be in nonattainment
for the revised PM10 standard. We also have established a new air
quality standard for fine particles (PM2.5). Monitoring data to
determine nonattainment of the new PM2.5 standard is not yet available.
However, we project that by 2010, 102 counties, with a combined
population of 55 million people, will violate the PM2.5 air quality
standard. B. Air Toxics Diesel exhaust PM typically consists of a solid core, composed mainly of elemental carbon, which has a coating of various organic and inorganic compounds. The diameter of diesel particles is very small with typically 75-95 percent of the particle mass having a diameter smaller than 1.0 micron. The characteristically small particle size increases the likelihood that the particles and the attached compounds will reach and lodge in the deepest and more sensitive areas of the human lung. Both the diesel particle and the attached compounds may be influential in contributing to a potential for human health hazard from long term exposure. EPA's draft Diesel Health Assessment identifies lung cancer as well as several other adverse respiratory health effects, including respiratory tract irritation, immunological changes, and changes in lung function, as possible concerns for long term exposure to diesel exhaust. The evidence in both cases comes from the studies involving occupational exposures and/or high exposure animal studies; the Health Assessment, when completed, will recommend how the data should be interpreted for lower environmental levels of exposure. The draft Health Assessment is currently being revised to address comments from a peer review panel of the Clean Air Science Advisory Committee. The California Air Resources Board has identified
diesel exhaust PM as a ``toxic air contaminant'' under the state's
air toxics program, based on the information available on cancer
and non-cancer health effects. California is in the process of
determining the need for, and appropriate degree of, control measures
for diesel exhaust PM. Note that California limited its finding
to diesel PM, as opposed to diesel exhaust. EPA's assessment activities
of diesel exhaust PM are coincident with, but independent from,
California's evaluation. The concerns for cancer risk and other adverse health effects from exposure to diesel PM are heightened by the potential expansion of diesels in the light-duty vehicle fleet. Diesel engines are used in a relatively small number of cars and light-duty trucks today. By far, heavy-duty highway and nonroad diesel engines are the larger sources of diesel PM. However, vehicle and engine manufacturers project that diesel engines likely will be used in an increasing share of the light- duty fleet, particularly light-duty trucks. If these projections prove accurate, the potential health risks from diesel PM could increase substantially. EPA's proposed emission standard for PM under the Tier 2 program would limit any increase in potential cancer risks associated with the potential increase in light-duty diesel sales. C. Diesel Contribution to Emission Inventories The diesel engine pollutants of most concern are NOx and PM. Nitrogen and oxygen in the engine's intake air react together in the combustion chamber at high temperatures to form NOx. Particulate emissions result from incomplete evaporation and burning of the fine fuel droplets which are injected into the combustion chamber, as well as small amounts of lubricating oil that enter the combustion chamber. The VOC emissions from diesel engines are inherently low, because the fuel burns in the presence of excess oxygen which tends to completely burn hydrocarbons. Evaporative emissions also are insignificant due to the low evaporative rate of diesel fuel. --------------------------------------------------------------------------- \8\ Motor vehicles' contribution to the VOC inventory typically consists of unburned fuel hydrocarbons in the exhaust and evaporative emissions from vehicle fuel systems. --------------------------------------------------------------------------- Diesel engines make up a significant portion of
the NOx and PM from mobile sources. Moreover, the contribution
of diesel engines to air pollutant emission inventories is expected
to grow as more light-duty diesel vehicles and trucks enter the
market. The emission inventory discussed below is the same as
the ``base case'' prepared for the Tier 2 pro-posed rulemaking.
This inventory accounts for emission standards that have been
promulgated already for each of the vehicle categories (e.g.,
light-duty, heavy-duty highway and nonroad), but does not include
the impact of pro-posed light-duty Tier 2 standards. The Tier
2 standards would tend to decrease the relative contribution of
light-duty emissions in the inventory, and thus increase the heavy-duty
and nonroad relative contributions. On the other hand, substantial
growth in light-duty diesel sales would tend to substantially
increase the light-duty vehicle PM inventory, because diesels
emit more PM than the gasoline vehicles they replace. Although
the fuel-neutral Tier 2 standards would tend to mitigate
this impact, growth in diesel sales, especially before and during
the phase-in years of the pro-posed Tier 2 program, would still
tend to increase the light- duty PM inventories. These considerations
are important in assessing how the focus for diesel fuel control
may shift in the future, beyond the 2007-2010 base case view.
The inventory is reported in the 2007- 2010 time frame because
those dates are important for State Implementation Plan purposes
in attaining the ozone and PM NAAQS. Mobile source emissions account
for almost one-half of all NOx emissions nationwide. By 2010,
mobile source NOx emissions will total more than 7.8 million tons.
As shown in Figure 1, by 2010, we project that all diesel engines
combined will account for 53% (4.1 million tons) of mobile source
NOx emissions. Heavy-duty diesels account for 15% of the mobile
source contribution, and nonroad diesels account for 38%. Light-duty
vehicles and trucks account for 40% of mobile source NOx emissions.
Currently, almost all of the light-duty fleet is fueled by gasoline,
and less than 1% of the NOx emissions come from light-duty diesels.
In the 2007 inventory, the proportion of NOx emissions from these
various vehicle categories is similar. Mobile sources account for 20% of direct PM10 emission inventories (excluding natural sources and fugitive dust). By 2010, mobile source direct PM10 emissions will total almost 621,000 tons. As shown in Figure 2, by 2010, we project that diesel engines will account for nearly 70% (434,000 tons) of all mobile source PM10 emissions. Heavy-duty diesels account for 9% of the mobile source PM10 contribution, and nonroad diesels account for 60%. Light-duty vehicles and trucks account for 16% of mobile source PM10 emissions. Currently, almost all of the light- duty fleet is fueled by gasoline. However, as more diesels enter the light-duty market, light-duty diesels could become a significant portion of mobile source PM emissions, as discussed above. The proportion of PM10 emissions from these various vehicle categories in the 2007 inventory is similar. It is also important to note that mobile source
emissions generally make up a larger fraction of the emission
inven-tory for urban areas, where human population and light-duty
vehicle travel is more concentrated than in rural areas. We recently
conducted a study to compare the level and sources of emissions
in four U.S. cities (Atlanta, New York, Chicago, and Charlotte)
versus the nationwide inventory. For example, in Atlanta by 2010,
mobile sources are ex-pected to account for 81% of all NOx emissions,
while nationally they account for 44%. Similarly, in Atlanta by
2010, mobile sources will account for nearly 60% of all direct
PM10 emissions , while nationally they account
for 20%. Highway emissions of NOx, PM10 and PM2.5 in Atlanta are
more than double the national inventory. Nonroad PM10 and
PM2.5 emissions in Atlanta also are more than double the national
inventory. In the other cities studied, mobile source NOx and
PM10 emissions also were generally considerably higher than the
national inventory. \13\ This is the portion of the PM10 inventory that
excludes natural sources and fugitive dust. At this stage, we have not yet evaluated the emission reductions that could be achieved by introducing higher quality diesel fuel and the technologies it may enable, since the effectiveness of these technologies remains uncertain. Howe-ver, as discussed in Section VI.A., some people involved in the development of these technologies project per vehicle emission reductions of up to 75% for NOx and over 80% for PM, and so large inventory reductions may be possible. III. Diesel Emissions Control: Progress and Prospects Since the 1970's, highway diesel engine designers have employed numerous strategies to meet the challenge pre-sented by our emissions standards, beginning with smoke controls, and focusing in this decade on increasingly strin-gent NOx, hydrocarbon, and PM standards. More recently, standards for various categories of nonroad diesel en-gines, such as those used in farm and construction machines, locomotives, and marine vessels, have also been pursued by the Agency. Our most recent round of standard setting for heavy-duty highway diesels occurred in 1997 (62 FR 54693, October 21, 1997), effective with the 2004 model year. This action, combined with previous standard- setting actions, will result in engines that emit only a fraction of the NOx, hydrocarbons, and PM produced by their higher- emitting counterparts manufactured just a decade ago. Nevertheless, certain characteristics inherent
in the way diesel fuel combustion occurs have prevented achievement
of emission levels comparable to today's gasoline-fueled vehicles.
While diesel engines provide advantages in terms of fuel efficiency,
durability, and evaporative emissions, controlling NOx emissions
is a greater challenge for diesel en- Considering the air quality impacts of diesel engines and the plans of manufacturers to increase the market pene-tration of light-duty diesel vehicles, it is imperative that progress in diesel emissions control continue. Fortunately, encouraging progress is now being made in the design of exhaust aftertreatment devices for diesel applications. Aftertreatment devices, such as catalytic converters, which have been employed successfully on gasoline engines for decades, have had only limited use with diesel engines. This is primarily due to the difficulty of making such devices perform well in the diesel's oxygen-rich exhaust stream, and to the great success that diesel engine designers have had up to now in meeting challenging emission standards without aftertreatment. The combination of encouraging progress in effective aftertreatment design and the challenge presented by the proposed stringent Tier 2 standards is changing this situation. As discussed in detail below, promising new technologies may allow a step change in diesel emissions control, of a magnitude comparable to that ushered in by the automotive catalytic converter in the 1970's. However, it appears that changes in diesel fuel quality may be needed to bring this step change about. IV. What Fuel Changes Might Help? Debate and research on changing diesel fuel to lower emissions has focused on several fuel specifications: cetane level, aromatics content, fuel density, distillation characteristics (T90 and T95), oxygenates content, and sulfur con-tent. Control of these parameters may have the potential to provide direct benefits by incrementally lowering emis-sions when the fuel is burned, although the benefit may vary depending on the sophistication of the engine technology involved. Much of the available data on the effects of fuel
parameter changes is for heavy-duty engines. In preparation for
the 1999 technology review to assess the ability of heavy-duty
diesel engines to meet the combined NOx and nonme-thane hydrocarbon
(NMHC) standard in 2004, an industry/EPA workgroup was tasked
with evaluating the incre-mental impact of changes in diesel fuel
properties on NOx and hydrocarbon emissions. This study employed
advan-ced technology heavy-duty diesel engines expected to be
used to meet the 2004 standard. These engines depend on exhaust
gas recirculation (EGR) and optimization of engine design, but
not on advanced aftertreatment. The study focused
on separately identifying the emissions impacts of changes in
fuel density, aromatics content (both total and polycyclic aromatics),
and cetane number (both natural and additive-enhanced) The results of this study showed that state-of-the-art heavy-duty engines are mostly insensitive to changes in these parameters. Changes in diesel fuel density and aromatics were found to have the greatest beneficial effect on emis-sions. Yet large concurrent changes in these fuel parameters reduced NOx emissions by only 10%. Of the total effect, approximately 5% was attributed to the reduction in fuel density, and 5% to the reduction in aromatics content. Inc-reasing the cetane number was found to have no observable emissions benefit, although previous studies on older-technology engines showed a benefit. Changing other fuel parameters was also found to have either no effect, or only a small effect on emissions. Effects on PM emissions were not included in this study. Another study, documented as the ``EPEFE Report'',
examined the effects of fuel parameter changes on NOx,
PM, hydrocarbon, and carbon monoxide emissions in both light-
and heavy-duty diesel engines. This study also found only small
effects on NOx emissions from changes in density, polycyclic aromatics
content, cetane, and T95 (less than 5% for any one parameter change,
less than 10% overall). Although the magnitude and even the direction
of the emis-sions changes were different for light- and heavy-duty
vehicles, the small magnitude of the impacts was consistent. The
largest impacts on PM emissions were from lowering T95
(7% in light-duty testing, no effect in heavy-duty testing) and
density (19% in light-duty, 2% in heavy-duty), although the benefit
of the density change was determined to be confounded by a physical
effect--lower density fuel decreased the fueling rate and engine
power which in turn affected emissions. Thus the need for additional
data on how fuel changes affect PM emissions appears to be especially
pron-ounced, especially considering the possible need for diesel
PM reductions in the existing fleet to address potential air toxics
concerns. A lack of emissions sensitivity to
changes in diesel fuel cetane and aromatics content was observed
in another recently-published paper, which reported on testing
conducted with an advanced technology heavy- duty engine
(designed to achieve a 2.5 grams/horsepower-hour (g/hp-hr) NOx
emissions level). A recent literature review of diesel emissions
studies sought to decouple the incremental impact on emissions
of changes in one fuel parameter Reducing the sulfur content of diesel fuel has the potential to provide large indirect technology-enabling benefits in addition to some amount of direct emission benefits. In fact, sulfur reduction appears to be the only fuel change with potential to enable new technologies needed to meet Tier 2 light-duty or anticipated future heavy-duty standards. Therefore, although other specifications changes are under consideration, at this point we believe that sulfur control is the most likely means of achieving cost-effective diesel fuel emission reductions, as discussed in detail in the remainder of this notice. Because we have more complete information on the effects that diesel fuel changes have on emissions from heavy-duty engines than from light-duty engines, we believe that any preliminary conclusions one might draw regarding changes other than sulfur are more tentative for light-duty applications. We welcome any information that would help us to assess the potential benefits and costs of changes other than sulfur in light-duty diesel fuel. Such information may become especially relevant if we pursue an implementation plan that treats this fuel separately, as discussed in Section XI. Issue 1: Fuel Changes Other Than Sulfur.-- Should EPA pursue diesel fuel changes other than sulfur control? What costs and emission reductions would be involved? Are there additional data on emissions impacts of fuel changes, especially for light-duty applications? Should a diesel fuel quality program be structured to encourage gas-to-liquid or other non-petroleum blends? V. Diesel Fuel Quality in the U.S. and Other Countries A. Current Diesel Fuel Requirements in the U.S. EPA set standards for diesel fuel quality in 1990
(55 FR 34120, August 21, 1990). These standards,
effective since 1993, apply only to fuel used in highway diesel
engines. The standards limit the sulfur concentration in fuel
to a maximum of 500 ppm, compared to a pre- regulation average of 2500
ppm. They also protect against a rise in the fuel's aromatics
level from the then-existing levels by setting a minimum cetane
index of 40 (or, alternatively, a maxi-mum aromatics level of
35%). Aromatics tend to increase the emissions of harmful pollutants.
These regulations were established in response to a joint proposal
from members of the diesel engine manufacturing and petroleum
refining industries to reduce emissions and enable the use of catalysts
and particulate traps in meeting EPA's PM standards for diesel engines.
As a result of our diesel fuel regulation, highway
diesel fuel sulfur levels average about 340 ppm outside of California.
Alaska has an exemption from our existing 500
ppm limitation (permanent in some areas, temporary in others)
and is currently seeking a permanent exemption for all areas of
the state, because of special difficulties in supplying lower
sulfur diesel fuel for that market (63 FR 49459, September 16,
1998). Similarly, Am-erican Samoa and Guam also have permanent
exemptions from our existing 500 ppm limitation (July 20, 1992,
57 FR 32010 and September 21, 1993, 58 FR 48968). We currently do
not regulate diesel fuels that are not intended for use in highway
engines. Diesel fuel sold for use in most nonroad applications such
as construction and farm equip-ment has sulfur levels on the order
of 3300 ppm. \19\ ``A Review of Current and Historical Nonroad
Diesel Fuel Sulfur Levels'', Memorandum from David J. Korotney,
Fuels and Energy Division, March 3, 1998, EPA Air Docket A-97-10,
Docket Item II-B- 01. California set more stringent standards in 1988 for motor vehicle diesel fuels for the South Coast air basin. These standards took effect statewide in 1993. They apply to both highway and nonroad fuels (excluding marine and lo-comotive use), and limit sulfur levels to 500 ppm and aromatics levels to 10%, with some flexibility provisions to ac-commodate small refiners and alternative formulations. B. Diesel Sulfur Changes in Other Countries Progress toward diesel fuel with very low sulfur
levels has advanced rapidly in some parts of the world. The Eu-ropean
Union's ``Auto Oil Package'' was adopted recently in an effort
to improve air quality, by establishing an in-tegrated approach
to setting requirements for fuels in such a way that vehicles
can produce their best environmental performance. As part of the
Auto Oil Package, the European Union adopted new fuel specifica-tions
for diesel fuel. These specifications contain a diesel fuel sulfur
limit of 50 ppm by 2005, with an interim limit of 350 ppm by 2000. The
Member States will be required to monitor fuel quality to ensure
compliance with the specifications. \21\ European Union Directive 98/69/EC published
on December 28, 1998 (OJ L350, Volume 41, page 1). In the United Kingdom, the entire diesel fuel supply
soon will be at sulfur levels of 50 ppm, based on recent an-nouncements
by major refiners. The United Kingdom currently offers a two-penny
tax break for diesel fuel. Finland and Sweden also have tax incentives
encouraging low sulfur diesel fuel. Finland's tax incentive applies
to diesel with sulfur levels below 50 ppm, which accounts for
90% of the Finnish market. Sweden's tax incentive applies to diesel
with sulfur levels below 10 ppm. \23\ ``International Activities Directed at Reducing Sulphur in Gasoline and Diesel, A Discussion Paper,'' Dr. Mark Tushingham, Environment Canada, 1997. \24\ CONCAWE, Report No. 6/97, ``Motor Vehicle Emission Regulations and Fuel Specifications--Part 2--Detailed Information and Historic Review (1970-1996).'' --------------------------------------------------------------------------- Japan recently proposed to limit sulfur in diesel fuel to 50 ppm. The proposal allows a phase-in of about 10 years, to give refineries time to invest in new facilities. Japan's Environment Agency is expected to decide on the new diesel sulfur limit after holding hearings and consulting with the Central Environment Council, an advisory panel to the prime minister. --------------------------------------------------------------------------- \25\ ``Sulfur Limit for Diesel Fuel May Be Lowered'', Japan Times Online, June 2, 1998. --------------------------------------------------------------------------- In North America, Mexico and Canada have regulated diesel sulfur levels to a maximum of 500 ppm, as in the U.S. Canada recently announced a proposal to lower gasoline sulfur, but the proposal does not address diesel fuel at this time. However, Canada recognized that a lower diesel sulfur level may be necessary to protect public health and to support future diesel engine technologies. The Canadian Government Working Group recommended that emissions from on-road diesel fuels be examined further to determine their impact on public health. \26\ ``Final Report of the Government Working Group on Sulphur in Gasoline and Diesel Fuel--Setting a Level for Sulphur in Gasoline and Diesel Fuel,'' July 14, 1998. --------------------------------------------------------------------------- Issue 2: Experience Outside the U.S.--What lessons can we learn from the experience of other countries in planning for and producing low sulfur diesel fuel? VI. Potential Benefits of Reducing Sulfur We believe that diesel fuel desulfurization should be evaluated primarily for its potential to enable new engine and aftertreatment technologies with large air quality benefits. How-ever, there may be other effects as well, as discussed further below. A. Technology Enablement Sulfur-sensitive technology enablements can be further grouped into two categories: those that can be achieved with some success using current fuel but which have significantly improved emissions performance with low sulfur fuel, and those that must have low sulfur fuel. The following discussion provides our current understanding of prospective technologies in both categories, built from a review of the technical literature and from numerous discussions with the people who are developing these concepts. Note that we believe the viability and sulfur-sensitivity of these technologies are, to varying degrees, still open issues; also, there may be other promising technologies not included here. A major goal of this advance notice is to establish the degree of confidence warranted in claims that robust, cost-effective emission control technologies will be made viable or greatly enhanced by fuel desulfurization. Another major goal is to ascertain what sulfur levels may be needed. Manufacturers have suggested that sulfur should be capped at 30 ppm, although the need for even lower levels has also been discussed. Even for those technologies that require low-sulfur fuel to function, there may be a range of operation in which the technologies may be able to tolerate higher sulfur levels but emissions performance may be further enhanced by additional reductions in fuel sulfur. We are interested in information that will help us understand both the range of sulfur levels over which operation of the relevant control technologies is possible, and the relationship between emissions performance and fuel sulfur levels within this range. Issue 3: Sulfur-Tolerant Technologies.--What full useful life NOx and PM emission levels may be achievable for diesel passenger cars and light-duty trucks, and for heavy-duty engines, without a change in diesel fuel? At what costs? When could these levels be achieved in production vehicles and engines? Issue 4: Sulfur-Sensitive Technologies.--How feasible are the sulfur-sensitive technologies (discussed below) for light-duty and heavy-duty applications? Are there others? What full useful life PM and NOx emission levels could they achieve and when? What sulfur levels do they require? Are any of them substantially enhanced by additional sulfur reductions beyond the sulfur levels required just for proper functioning? What is the relationship between fuel sulfur levels and emissions performance associated with these technologies? How durable are they? What mainte-nance is required? What is the potential that they could eventually be made sulfur-tolerant? What are the cost imp-lications? What is their fuel economy impact, if any? What problems might occur due to sulfur derived from lube oil being introduced into the combustion chamber, either through intentional mixing of used oil with fuel or from vap-orization off of the cylinder wall? Issue 5: In-Use Emissions.--How well will sulfur-sensitive emission control technologies perform over the complete range of operating cycles and environmental conditions encountered by vehicles in use? For example, will there be functional problems or high emissions during periods of sustained high loads or idling, or at extremes of ambient temperature and humidity? 1. Technologies Improved By Sulfur Reduction Technologies that may derive benefit from diesel fuel desulfurization include cooled EGR, lean-NOx catalysts, PM filters, oxidation catalysts, and selective catalytic reduction (SCR). None of these technologies appear to have a threshold low sulfur level, above which the technology is simply not viable. Rather, every degree of sulfur reduction would provide correspondingly greater latitude for engine or aftertreatment designers to target their designs for aggressive emission reductions. Thus, we need to be able to quantify the expected emission reductions in order to assess the effectiveness, including incremental cost-effective-ness analysis where appropriate, of various levels of control. The application of electronically controlled EGR
to diesel engines is an effective means of controlling NOx emissions.
Cooling the recirculated exhaust gas before it reenters the combustion
chamber can greatly increase EGR efficiency. NOx emissions
reductions of up to 90% are believed possible with cooled EGR systems
for heavy-duty diesel applications. However, manufacturers have
claimed that one of the primary limiters on how extensively cooled
EGR can be used is the potential for condensation of sulfuric acid and
associated corrosion-related durability prob-lems. We have not yet
received any durability data to support these claims using realistic
in-use operating conditions and corrosion-resistant materials. Acid
aerosol formation may also increase the frequency of oil changes due
to inc-reased acidification of engine lubricating oil. It is not
clear at this time that removing sulfur from fuel is the only
solution to these problems, if they indeed exist. Any actual oil
acidification problem may be addressable by increasing alkaline
oil additives, and corrosion- resistant materials are available for
durable EGR cooler construction. Various types of lean-NOx catalysts are either in production or under investigation for reduction of NO emissions in lean exhaust environments such as those present in diesel exhaust. These catalysts include two types: (1) Active catalysts require a post-combustion fuel injection event and (2) passive catalysts require no post-injection. Although some active catalyst systems have higher NOx removal efficiencies than similar passive catalyst systems, NOx removal efficiencies are still only in the range of 15 to 35% on average. It is more likely that these systems will be used for incremental NOx reduction for light-duty applications in combination with other technologies, such as cooled EGR. Lean-NOx catalysts are prone to long-term efficiency loss due to sulfur-induced deactivation or ``poi-soning''. They may also produce unwanted sulfate PM. Both of these problems can be mitigated by reducing fuel sulfur, though higher sulfur fuel can be accommodated by using less effective catalyst formulations. One method of exhaust aftertreatment for controlling diesel PM emissions is to pass diesel exhaust through a ce-ramic or metallic filter (sometimes called a ``soot filter'' or ``PM trap'') to collect the PM, and to use some means of burning the collected PM so that the filter can be either periodically or continuously regenerated. Filter designs have used catalyzed coatings, catalytic fuel additives, electrical heating, and fuel burners to assist trap regeneration. Failure to consistently regenerate the filter can lead to plugging, excessive exhaust back-pressure, and eventually overheating and permanent damage to the filter. Inconsistent regeneration due to the low frequency of adequately high tempe-rature exhaust transients has been a particular problem in applying PM filters to light-duty diesel vehicles. Although PM filters have been used with current fuels, some designs, especially those that use catalyst materials susceptible to sulfate generation, can be made more effective with lower sulfur fuel. In addition, some PM filter system concepts may require low sulfur fuel, as discussed below. Oxidation catalysts are a proven technology already in widespread use on diesel engines. They reduce exhaust PM by removing volatile organics, some of which are adsorbed onto soot particles. They also reduce emissions of gas-eous hydrocarbons. Oxidation catalysts have utility not only for direct reduction of PM and hydrocarbons, but also as a potential clean-up device to preclude hydrocarbon slip downstream of NOx catalysts or PM filters that inject diesel fuel. In the relatively low-temperature environments characteristic of diesel engine exhaust streams, catalyst formula-tions containing precious metals such as platinum are particularly useful, because they function at fairly low tempera-tures. Unfortunately, these metals also promote the conversion of SOx to sulfate PM, thus potentially increasing PM emissions, so oxidation catalyst designers must work a careful balance to succeed with current fuel. Sulfur reduction can obviously mitigate this problem and enable more aggressive oxidation catalyst formulations. SCR for NOx control is currently used on stationary diesel engines, and has been proposed for mobile applications. SCR uses ammonia as a NOx reducing agent. The ammonia is typically supplied by introducing a urea/water mixture into the exhaust upstream of the catalyst. The urea/water mixture is stored in a separate tank that must be periodically replenished. These systems can be very effective, with NOx reductions of 70 to 90%, and appear to be tolerant of current U.S. on-highway diesel fuel sulfur levels. However, there is concern that applying current SCR technology to highway vehicles will require use of catalyst formulations that are sensitive to sulfur, such as those employing platinum, to deal with the broad range of operating temperatures typical of highway diesel engines in use. There is also potential for formation of ammonia sulfate, which is undesirable because it is a component of fine PM.28 In addition, SCR systems bring some unique concerns. First, precise control of the quantity of urea injection into the exhaust, particu-larly during transient operation, is very critical. Injection of too large of a quantity of urea leads to a condition of ``am-monia slip'', whereby excess ammonia formation can lead to both direct ammonia emissions (with accompanying health and odor concerns) and oxidation of ammonia to produce (rather than reduce) NOx. Second, there are potential hurdles to overcome with respect to the need for frequent replenishment of the urea supply. This raises issues related to supply infrastructure, tampering, and the possibility of operating with the urea tank dry. Third, there may be modes of engine operation
with substantial NOx generation in which SCR does not function
well. Finally, there is concern that SCR systems may produce N2O,
a gas that has been associated with greenhouse- effect emissions. Issue 6: Selective Catalytic Reduction--How could the discussed difficulties with SCR ammonia slip, infrastructure, reductant maintenance, robustness, and N2O production be resolved? 2. Technologies Likely To Require Low Sulfur Fuel Technologies that are not currently considered feasible with current fuel, but which might become feasible if the sulfur content of diesel fuel were lowered, include NOx storage catalyst systems and continuously regenerable PM filter systems. Although still in early stages of development,
NOx storage catalyst technology shows promise for NOx reductions
of 50 to 75% in use. Some projections of ultimate efficiency range as
high as 90%.> However, these catalysts are also very prone to
sulfur poisoning due to sulfate buildup. Diesel engines employing
NOx storage catalyst systems will probably be limited to the use
of diesel fuels with less than 30 to 50 ppm sulfur. Even at such
fairly low sulfur levels, frequent sulfate purging cycles may be needed
to restore catalyst function. Alternatively, even lower fuel sulfur
levels, on the order of 5 to 10 ppm, may be needed to manage the
frequency of purging cycles. Manufacturers have sugges-ted that further
development of NOx catalyst systems could eventually enable diesel
engines to reach the fuel-neutral Tier 2 fleet average NOx standard
of 0.07 grams/mile (see discussion below on Diesel Sulfur Control
and Tier 2). The recently developed continuously regenerating
PM filter has shown considerable promise for light-duty diesel
applications due to its ability to regenerate even at fairly low
exhaust temperatures. This filter technology is capable of a large
step change in PM emissions, with typical PM reductions exceeding
80%. However, these systems are also fairly intolerant of fuel
sulfur, and are effectively limited to use with diesel fuel with
sulfur levels below 50 ppm. Given that these filter designs appear
to have similar efficiencies to less sulfur-sensitive PM filter
concepts, it is important for us to better understand potential
advantages and disadvantages of the various trap concepts in determining
whether or not low sulfur fuel is needed for effective PM control. B. Other Effects In addition to the primary benefits associated with the enablement or improved utilization of technologies discussed above, desulfurization could have other effects that should be assessed as well. Desulfurization will reduce the direct emissions of sulfate PM and SOx, both of which are harmful pollutants. Sulfate PM emissions contribute to the overall inventory of PM10 and PM2.5, both pollutants for which EPA has set National Ambient Air Quality Standards. SOx (one component of SOx) is also a criteria pollutant, and some portion of emitted SOx is chemically transformed in the atmosphere to sulfate PM, and is therefore considered a secondary PM source. Although we do not directly regulate the emissions of SOx from diesel engines, because the overwhelming majority of these emissions are from stationary sources like powerplants, diesel SOx reductions would nevertheless be of some benefit to the environment. The introduction of desulfurized highway diesel fuel would provide immediate SOx and PM emission reductions from the large and growing population of heavy-duty diesel engines in the United States. These emission reductions would even extend to some portion of the nonroad equipment fleet because some significant, though undetermined, portion of this fleet is fueled with highway diesel fuel rather than the generally less expensive nonroad diesel fuel, for reasons of convenience. In contrast to technology-enabling benefits, these direct emission reductions derive added air quality value from the fact that they are realized immediately as existing vehicles are refueled with the new fuel, rather than gradually over many years as new technology vehicles replace older models in the fleet. On the other hand, although this secondary benefit from sulfate and SOx reductions in the existing fleet would result whether or not we set new engine emission standards, it would not be expected to carry over to engines built after new sulfur controls take effect. This is because testing of these engines to verify compliance with motor vehicle emis-sion standards would be expected to be conducted using a low sulfur test fuel, reflective of the in-use fuel. A low sul-fur test fuel, with no change in emission standards, allows the engine manufacturer to back off on emissions controls to optimize engine cost, performance, or fuel economy. Thus earlier model year engines designed for higher sulfur fuel could actually run cleaner than later engines designed to the same standards, once sulfur controls take effect. Issue 7: Direct Benefits of Sulfur Reduction--How much direct incremental environmental benefit can be achieved by diesel fuel sulfur reduction? Manufacturers have claimed that lower sulfur fuel will improve the durability of engines and emissions controls, and will reduce the need for maintenance, including oil changes. These benefits would produce a cost savings to vehicle owners. They may also produce an indirect emissions benefit because, although manufacturers must take steps to ensure durable emissions controls (such as providing warranties and assuming liability over a set useful life), many engines may have high emissions because they last well beyond the regulatory useful life or because they are poorly maintained. Therefore, provisions that inherently extend emission controls' life or reduce the need for emissions-affecting maintenance can be beneficial. Some manufacturers have claimed that this is especially relevant for engines employing an extensive degree of cooled EGR, although this is yet to be proven. As discussed above, we have not yet received any durability data to support these claims using realistic in-use operating conditions and corrosive resistant materials. On the other hand, because reduced sulfur appears to enhance the durability of the engines, and not just that of the emission controls, environmental disbenefits may result from diesel fuel sulfur reduction, due to the potential that higher- quality fuel will make older, higher-emitting engines last longer in the field. Furthermore, fuel changes may inadvertently and detrimentally alter fuel system components such as o-ring seals, and may also reduce the helpful lubricating effect that some sulfur compounds have on fuel system components, although it also appears that steps can be taken to preclude these effects, such as the use of lubricity additives. Issue 8: Durability and Maintenance Impacts--Are there quantifiable environmental benefits or disbenefits from such secondary effects as more durable controls, reduced maintenance needs, or longer-lived high- emitting trucks? What steps, if any, need to be taken to ensure that fuel changes would not degrade fuel system components in the existing fleet? Would lubricity additives be required to restore any loss in fuel lubricity characteristics compared to current fuel? If so, what would the environmental and cost impacts of these additives be? VII. Diesel Sulfur Control and Tier 2 Although almost all highway diesel engines used
in the United States today are in heavy-duty trucks and buses,
the impetus for near- term action on diesel fuel quality arises from
our efforts to set stringent new Tier 2 emission stand-ards for
passenger cars and light trucks. These standards will apply to
vehicles powered by any fuel-- including both gasoline and diesel. As
part of the Tier 2 rulemaking, we also are proposing to lower
gasoline sulfur levels, in part to enable the use of advanced
catalytic converters. Manufacturers of diesel engines and vehicles
have argued that setting Tier 2 standards without concurrent diesel
fuel changes will be unfair to diesels, because diesel fuel quality
would be worse than gasoline fuel quality. Some argue that, beyond
fuel-neutrality considerations, diesel fuel quality improve-ment
is needed to combat global warming because it will facilitate
the marketing of more diesel vehicles and, in their opinion, thereby
reduce emissions of global warming gases. Others counter that
diesel vehicles should be discouraged because diesel exhaust is a
serious health hazard that improvements in diesel fuel quality will
do little to mitigate. Some also believe that any fuel economy
improvements from diesels will be offset by manufacturers' sale of more
large vehicles, resulting in no net improvement in fleetwide fuel
economy, and thus no net reduction in global warming emissions. --------------------------------------------------------------------------- In establishing the Tier 1 light-duty vehicle standards currently in place, the Clean Air Act made special, explicit provision for diesel vehicles. However, the framework it provided us for the setting of Tier 2 standards made no special reference to diesel engines. In our July 1998 Tier 2 Report to Congress, we therefore concluded that Congress did not intend special treatment for diesel engines after 2003. Under the Tier 2 proposal's fuel-neutral approach, there are not separate emission standards for diesels. However, the proposed Tier 2 program allows manufacturers to sell some engines with higher emissions--in the range achieva-ble by both gasoline and diesel vehicles with current fuel quality--during the early phase-in years of the program. Table 1 summarizes the proposed Tier 2 emission standards. Manufacturers would have to meet a corporate average NOx standard for the entire fleet of vehicles sold, but would have the flexibility to certify different vehicle models to different sets of emission standards (referred to as ``bins''). Some bins have a NOx emission standard that is higher, and some lower, than the corporate average NOx standard. The proposed Tier 2 standards would be phased in over time, allowing a portion of a manufacturer's vehicle sales to meet the less stringent ``interim'' standards. During the phase-in years, the program would establish separate interim standards for the following vehicle categories: -LDVs and light light-duty trucks (LLDTs), less than 6000 pounds GVWR. -Heavy light-duty trucks (HLDTs), 6000 pounds GVWR or greater. Table 2 shows when the interim and Tier 2 standards would be phased in, by indicating the percentage of manufacturers' vehicle sales required to meet the respective standards each year. Even when the Tier 2 standards are fully phased in, manufacturers still would be able to certify vehicles in the higher-emitting bins. However, sales of vehicles in the higher-emitting bins would be limited by a manufacturer's ability to comply with the proposed corporate average NOx standard. Table 1.--Proposed
Tier 2 Exhaust Emission Standards
Highest-emitting
NOx PM LDV/LLDT ------------------------------------------------------------------------ Interim...................... 0.30 0.60 0.06 Tier 2....................... 0.07 0.20 0.02 HLDT ------------------------------------------------------------------------ Interim...................... 0.20 0.60 0.06 Tier 2....................... 0.07 0.20 0.02 ------------------------------------------------------------------------
Table 2.--Proposed Phase-In for Tier 2 Standards
2004
2005 2006
2007 2008 2009
& later Tier 2............................ ........... ...........
........... ........... 50
100 *0.60 grams/mile NOx cap applies to balance of these vehicles during the 2004-2006 phase-in years As shown in Tables 1 and
2, some diesel and gasoline LDV/LLDTs could be certified to emission
standards of 0.60 grams/mile NOx and 0.06 grams/mile PM through
the 2006 model year. HLDTs, where diesels are most likely to find
a large market, could be certified to these same emission standards
through 2008. We expect that
these ``highest bin'' emission standards, although challenging, could
be met by diesel vehicles without fuel changes. In model year 2007 and
beyond for LDV/LLDTs, and in model year 2009 and beyond for HLDTs, the
highest emission stan-dards available for vehicle certification would
be 0.20 grams/mile for NOx and 0.02 grams/mile for PM. It is
likely that diesel fuel sulfur control would be needed to enable
diesels to achieve these more stringent emission standards. Furthermore, even though some HLDTs can be marketed in the highest bin (0.60 NOx/0.06 PM) through model year 2008, by model year 2007, or perhaps even 2006, the phase-in percentage of the more stringent interim corp-orate average NOx standard (0.20 grams/mile) becomes great enough that it may start to curtail sales of vehicles in the highest bin. Thus, diesel fuel changes may be critical for continued sales of diesel-powered HLDTs in these earlier model years. In summary, it appears most likely that the need for diesel vehicles to employ technologies dependent on low sulfur diesel fuel under the Tier 2 program will occur by the 2006 or 2007 model year, implying that low sulfur fuel should be available for these vehicles sometime in 2005 or 2006. This presumes of course that the development of robust, sulfur-sensitive diesel technologies achieving the Tier 2 emission levels will be successful. There may also be merit in providing for an early introduction of the low sulfur fuel, at least perhaps on a limited basis, to allow proveout of tech-nologies that require this fuel. Issue 9: Diesels In Tier 2--If diesel fuel changes were not adopted, when and to what extent would the anticipated diesel market growth be curtailed under the proposed phased in approach to Tier 2? What is the likelihood that diesels will not be able to meet proposed Tier 2 standards even with fuel changes? What is the likelihood that ad-vances in sulfur-tolerant control technologies would negate the need for low sulfur fuel after a few years? Would an early introduction phase of low sulfur fuel to demonstrate technologies be of value? How soon and on what scale might this be implemented? VIII. Heavy-Duty Highway Engines The sulfur-sensitive technologies discussed above show promise in a wide range of diesel applications, including light- and heavy-duty vehicles and nonroad equipment. Heavy-duty engines typically have different operating cha-racteristics than light-duty engines, most notably more frequent occurrences of higher temperature exhaust stream flows that can facilitate catalysis. These differences may affect design decisions, such as what catalyst formulations and devices to use, but do not appear to be so great as to rule out technology- enabling sulfur control for any class of die-sel applications. Particularly if sulfur-sensitive technologies work well on light-duty vehicles, we would expect them also to find application with heavy-duty engines. Engine designers are now developing engines to meet the 2004 heavy- duty highway engine NOx + NMHC emission standard that we set in 1997. We are currently conducting a technology review, to be completed later this year, to re-evaluate the appropriateness of this standard. Although low-sulfur fuel would add to the control options available for engines designed for this standard, we do not expect it to provide corresponding new-engine emissions benefits without changes in the engine emissions standards. Manufacturers would be likely to design engines to emit at roughly the same NOx levels either way--low enough to meet the standards with some compliance margin--and take advantage of the higher quality fuel to improve fuel economy or other performance parameters. Engine changes that improve fuel economy, such as timing advance, may incidentally decrease PM emissions as well, but the degree to which this would happen without a change in standards is uncertain. Although we have not yet performed an assessment of the feasibility of more stringent NOx and PM standards for heavy-duty highway engines in model years after 2004, the technologies discussed above show great promise for large further reductions in these emissions. The concurrent need for diesel fuel changes to enable these technologies would, of course, be an important part of any Agency activity directed toward setting more stringent standards, as would an evaluation of the air quality need for further diesel engine emission reductions and of the need for adequate leadtime for engine manufacturers to implement new standards. The earliest that EPA could implement more stringent than current NOx standards that might be en-abled by low sulfur diesel fuel is the 2007 model year. More stringent PM standards based on such fuel could be ev-aluated for implementation as early as model year 2004. The Agency would address these issues further in a separate regulatory action. Issue 10: Future Heavy-Duty Highway Engine Standards--How do emission control challenges and solutions differ for light-and heavy- duty diesel engines? How might these differences affect fuel quality requirements? What heavy-duty NOx and PM emission standards may be feasible with low sulfur fuel? When could they be implemented? What would be the cost of such heavy-duty emission standards? Low sulfur fuel may also bring about a potentially very large environmental benefit in the existing fleet of diesel engines. There are programs under consideration by some states through which older diesel engines would be ret-rofitted with emission-reducing technologies. Some of the sulfur-sensitive technologies discussed above may be useful for this purpose. Aftertreatment devices have proven especially adaptable to retrofit situations, although some of the more sophisticated systems that require careful control of engine parameters may not be as suitable. Thus sulfur re-duction could potentially enable not just incremental emission reductions from the existing fleet, but large, step-change reductions in PM and NOx as well, in areas where incentives for retrofitting are provided. Note that this benefit could be extended to nonroad diesel engines, provided the retrofit program ensures fueling with low sulfur fuel as well. Issue 11: Retrofit Potential--Can the sulfur-sensitive emission control technologies be retrofit to existing engines? At what cost? What environmental benefits might be achieved? Over the past year or so, various interested groups have expressed their positions on sulfur levels in diesel fuel. Here, we summarize only those positions that have been communicated formally (either to EPA or other govern-mental entities). One goal of this notice is to generate discussion that will help us better understand the positions of these and other stakeholders. Together, the (then existing) American Automobile
Manufacturers Association, the European Automobile Manufacturers
Association, and the Japan Automobile Manufacturers Association
proposed a World-Wide Fuel Charter in June 1998. The goal of this
global fuels harmonization effort is to develop common, worldwide
recom-mendations for ``quality fuels'', considering customer requirements
and vehicle emissions technologies. Three cate-gories of fuel
quality are proposed for diesel fuel, based on the extent of emission
control requirements. Category 3 fuel quality is for markets with
advanced requirements for emission controls (such as California
Low and Ultra-Low Emission Vehicles). The sulfur content recommended
for Category 3 diesel is 30 ppm. The Ford Motor Company, Chrysler Corporation (now
DaimlerChrysler) and General Motors Corporation further urged
the Administration to make significant progress in bringing about
low sulfur diesel and gasoline fuels. These companies stressed
the importance of low sulfur diesel and gasoline fuels in reducing
vehicle emissions and enabling the successful introduction of
advanced engine and emission control technologies. The State and Territorial Air Pollution Program
Administrators (STAPPA) and the Association of Local Air Pollution
Control Officials (ALAPCO) adopted a resolution urging us to pursue
the most stringent highway and nonroad diesel fuel sulfur standards
that are technologically and economically feasible. These
associations believe that stringent national standards for diesel
sulfur, combined with stringent standards for low sulfur gasoline and
vehicle emissions, are essential to address the full range of the
country's air pollution problems-- including ozone, particulate matter,
regional haze and toxics. STAPPA/ALAPCO recommended that such diesel
sulfur standards take effect by 2003. They urged us to announce our
intention to adopt such standards as soon as possible, so that
petroleum refiners could consider the least-cost ways of complying
with both gasoline and diesel sulfur controls. They also urged
us to consider nonroad diesel fuel changes and to adopt the most
stringent sulfur standards feasible to enable emerging control
technologies. The Engine Manufacturers Association (EMA) also
urged us to reduce the sulfur content of diesel fuel. EMA cited
the need for low sulfur diesel fuel to enable the introduction
of new catalytic aftertreatment devices, reduce fine pa-rticulate
emissions, and improve engine emissions durability. EMA is involved
in a number of activities with other organizations to support
low sulfur diesel fuel requirements. EMA offered to share the
data from each of these projects with us as they become available.
These activities include: -Examining the impact of fuel sulfur on engine life, particularly the corrosive effects. -Analyzing the environmental impact of reduced sulfate conversion and effects on the particulate matter emissions inventory from diesel engines. -Preparing an economic analysis of the refining
costs associated with lowering diesel sulfur levels, considering
proposed changes to gasoline sulfur and potential synergies from
reducing sulfur in the input stream rather than individual distillate
streams. Dated: May 1, 1999. Carol M. Browner, Administrator. [FR Doc. 99-11383 Filed 5-6-99; 11:03 am] BILLING CODE 6560-50-P [Federal Register: May 13, 1999 (Volume 64, Number 92)]
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