United States Air and Radiation EPA420-R-98-008
Environmental Protection July 1998
Agency
SERA Tier 2
Report to Congress
^ Printed on Recycled Paper
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EPA420-R-98-008
Tier 2 Study
July 31,1998
FINAL
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I. EXECUTIVE SUMMARY
Purpose of the Tier 2 Study
This Tier 2 Study examines whether it is appropriate to require more stringent emission
standards for new passenger cars and light duty trucks, which make up the majority of motor
vehicles on the road today. As directed by Congress, the Environmental Protection Agency
(EPA) in this examination assesses the air quality need, technical feasibility, and cost
effectiveness of such technologies. This study is the first step in determining if more stringent
vehicle standards are needed to meet the National Ambient Air Quality Standards.
The Clean Air Act (CAA) directs the EPA to identify and set national ambient air quality
standards (NAAQS) for pollutants that cause adverse effects to public health and the
environment. EPA has set standards for six common air pollutants, known as "criteria
pollutants." They are ground-level ozone (an important component of smog), carbon monoxide,
lead, nitrogen dioxide, sulfur dioxide, and particulate matter (measured as PMI0 and PM25). For
each of these six pollutants, EPA set health-based or "primary" standards to protect public health
and welfare-based or "secondary" standards to protect the environment (crops, vegetation,
wildlife, buildings and national monuments, visibility, etc).
The CAA sets specific exhaust emission standards, beginning with the 1994 model year,
for light-duty vehicles (LDV), or passenger cars, and light-duty trucks (LDT), including sport
utility vehicles, minivans, and pick-up trucks. These are 'Tier 1" emission standards. The Act
requires the study of whether or not further reductions in emissions from these vehicles should be
required by setting more stringent 'Tier 2" emission standards. This assessment must address the
need for further reductions in motor vehicle emissions to attain and maintain the NAAQS,
including, at a minimum, three factors:
• the air quality need for more stringent standards,
• the availability of technology to implement more stringent standards, and
• the cost effectiveness of more stringent motor vehicle standards, as well as
alternative means to attain and maintain the NAAQS.
This 'Tier 2 Study" addresses these factors, as well as others relevant to the consideration
of whether to establish more stringent light-duty car and truck emission standards. For example,
the study incorporates in its analysis the National Low Emission Vehicle (National LEV or
NLEV) program, a voluntary agreement among automakers and Northeastern states to produce
cleaner cars nationally. The National LEV program ensures that, beginning in model year 1999
and fully phased in by model year 2001, vehicles will meet emission standards that are cleaner
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than Tier 1 standards by harmonizing with the more stringent exhaust emission standards
required by California.
The requirements for the Tier 2 Study and the manner by which the study was developed
are described in Chapter II. Introduction. As required by Congress, this study was released to
the public for comment on April 23, 1998. After the close of the public comment period, EPA
summarized the comments received, modified the draft study as necessary, and created this final
report for submission to Congress. The public comments and EPA's response, when
appropriate, are summarized in Appendices E and F. Overall, the comments resulted in minor
changes to the study and did not change any of the findings of the study.
This study does not include proposed new emission standards. Instead, it focuses on
addressing the three factors identified in the statute and raises and discusses broadly other related
issues. If it is determined that more stringent emission standards are necessary and viable, the
Agency will, through a rulemaking process, promulgate such standards by the end of 1999. The
issues discussed in this study would be more fully developed and analyzed as part of this
rulemaking.
Status of Air Quality in the United States
Air quality in the United States continues to improve. Nationally, the 1996 air quality
levels are the best on record for all six criteria pollutants. In fact, the 1990s show a steady trend
of improvement.
The improvements in air quality and economic prosperity that have occurred since EPA
initiated air pollution control programs in the early 1970s illustrate that economic growth and
environmental protection can be compatible. Since 1970, national total emissions of the six
criteria pollutants declined 32 percent, while U.S. population increased 29 percent and gross
domestic product increased 104 percent. Motor vehicle emissions have decreased 58% for
volatile organic compounds, 40% for carbon monoxide, and 3% for nitrogen oxides while
vehicle miles traveled have increased 121 percent.
Despite these continued improvements in air quality, however, approximately 46 million
people live in counties where air quality levels exceeded the level of the national air quality
standards for at least one of the six criteria pollutants that were in effect in 1996.
Even taking into consideration the trend toward improving air quality, many areas will
not be in attainment with the NAAQS in 2007, in spite of implementation of the National Low
Emission Vehicle (National LEV) program, programs to reduce regional transport of ozone
emissions, and other air pollution controls. Furthermore, many areas that are in attainment will
need ongoing programs to maintain their attainment, especially in light of continued economic
growth.
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Motor Vehicles' Contribution to Air Pollution
While current cars emit about 97% fewer pollutants than 1970 models, emissions from
motor vehicles still contribute a large portion of our air pollution. Nationwide, mobile sources
are estimated to contribute more than half of the nitrogen oxides (NOx) inventory; 42% of the
volatile organic compounds (VOC) inventory; one-quarter of the particulate matter-10 (PM-10)
inventory; and 80% of the carbon monoxide (CO) emissions.
In 1996, LDVs and LDTs contributed more than 25% of national VOC emissions. LDV
and LDTs contributed more than 53% of national CO and contributions to national NOx were
almost 22%.
American motorists traveled 2.5 trillion miles in 1997, with a nearly constant growth of
2% a year. In addition, sport utility vehicles, minivans and small pick-up trucks comprise almost
half of the passenger vehicles sold in the United States today, dramatically changing die overall
composition of motor vehicles on the road, as well as the emissions inventory.
Overview of the Tier 2 Study
Emissions from motor vehicles include volatile organic compounds, carbon monoxide,
nitrogen oxides, and particulate matter. VOC and NOx emissions combine to produce ozone, or
smog, in the atmosphere. Gaseous VOC and NOx emissions also help form PM in the
atmosphere. Elevated levels of ambient ozone, CO, and PM have been associated with increases
in both human morbidity and mortality. In addition, VOC emissions from motor vehicles
include known and probable human carcinogens. NOx emissions contribute to impaired
visibility and crop damage, as well as the acidification of lakes and estuaries.
Chapter III. Assessment of Air Quality Need describes and assesses the air quality need
for more stringent control of LDV and LDT emissions. The available evidence, discussed in this
chapter, supports the need for emission reductions beyond that provided by the Tier 1 standards,
the National LEV program and other control programs.
LDV and LDT emissions primarily affect the attainment of NAAQS for three pollutants:
ozone, particulate matter, and carbon monoxide. Motor vehicles' emission of these pollutants or
their precursors and the effects on NAAQS attainment is discussed. The atmospheric pathways
through which LDV and LDT emissions affect these NAAQS are identified, as well as health and
welfare impacts that are not directly addressed by the NAAQS.
This assessment finds that, in the time frame contemplated for Tier 2 standards, there will
be an air quality need for emission reductions to aid in meeting and maintaining the NAAQS for
both ozone and PM. Air quality projections of both ozone and PM-10 in the years 2007 to 2010
show continued nonattainment in a number of local areas, even after the implementation of
existing emission controls. The contribution of LDVs and LDTs to VOC and NOx emissions
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that form ozone is projected to be substantial. Further VOC and/or NOx emission reductions
beyond those provided by the Tier 1 light-duty motor vehicle standards, National LEV, and other
programs are still needed in order for all areas of the nation to attain the NAAQS for ozone.
These reductions would also provide needed assistance to additional areas in maintaining their
projected compliance with the ozone NAAQS.
Further reductions in emissions of PM and PM precursors beyond those provided by the
Clean Air Act are still needed in order for all areas of the nation to attain the NAAQS for PMI0.
These reductions would also provide needed assistance to additional areas in maintaining their
projected compliance with the PM,0 NAAQS.
While emissions of PM from LDVs are relatively small, the trend toward heavier vehicles
and the use of diesel fuel makes this an issue that must be analyzed. PM emissions from
gasoline-fueled vehicles are quite low, while PM emissions from diesel vehicles meeting the
Tier 1 PM standards are at least an order of magnitude greater. Widespread use of the diesel
engine in LDVs and LDTs without more stringent Tier 2 standards for particulate emissions
could significantly increase ambient levels of PM10, worsening compliance further.
In contrast with ozone and PM, EPA does not project significant numbers of CO
nonattainment areas in the future. Furthermore, any future exceedances will occur during
wintertime conditions. The air quality need for further CO emission reductions from motor
vehicles is being evaluated separately, in the context of the requirement to evaluate cold CO
emission reductions.
Chapter IV. Assessment of Technical Feasibility examines the technological feasibility of
controlling light-duty vehicle and light-duty truck emissions beyond the level of control provided
for by Tier 1 emission standards. The technological feasibility of more stringent LDV and LDT
emission standards is apparent. There is abundant evidence that technology exists to reduce
LDV and LDT emissions below Tier 1 levels.
The review of vehicle emission control technology begins with a discussion of the
emission performance of current Tier 1, National LEV, and California LEV technology vehicles.
The chapter then reviews the status and potential of a number of emission control technologies
which could be used to get emission control beyond Tier 1, and even beyond National LEV,
standards. Various technologies that could be used to reduce vehicle emissions below levels
currently incorporated in the National LEV and California LEV programs are described, ranging
from improvements to base engine designs to advancements in exhaust after-treatment systems.
The effect that gasoline sulfur may have on potential Tier 2 technologies is examined, as it has
become apparent that this is a critical factor to be considered.
The technologies discussed in this chapter are either currently in production on one or
more vehicle models or are in the final stages of development. Given the rapid pace of
technological advances made in the motor vehicle manufacturing industry in recent years, one
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can assume even greater opportunities available in 2004 and beyond. Automotive manufacturing
companies are already producing LDVs that meet National LEV standards, achieving much
lower emission levels than currently required. Some manufacturers have committed to market
LDTs that meet National LEV standards as soon as the 1999 model year.
An examination of the cost effectiveness of more stringent light-duty emissions standards
is found in Chapter V. Assessment of Cost and Cost Effectiveness, including a review of the cost
effectiveness of both mobile and stationary source controls for the primary pollutants of concern.
Information on costs and cost effectiveness for potential future emission control technologies is
presented in this chapter. This includes the cost effectiveness of LEV technologies, as well as
technologies that achieve emission reductions beyond LEV standards. The chapter estimates
cost effectiveness of certain emission reductions without making a determination of the specific
numerical values of potential regulatory standards.
Estimates of the cost of future technologies are highly uncertain and often inflated.
Frequently, engineers from the auto industry, as well as government regulators and outside
experts, predict future costs that eventually prove to be too high when the technology is actually
manufactured and installed on mass-produced vehicles. As stated previously, Tier 2 standards
cannot be effective until the 2004 model year at the earliest. Therefore, although the cost
estimates included in this study are EPA's best assessment of future technology, they may be
conservatively high.
EPA evaluates specific motor vehicle emission control technologies, including tighter air-
fuel controls and improved catalyst designs. EPA estimates that these technologies should be
able to reduce NMHC (non-methane hydrocarbons) by as much as 77% and NOx emissions by
80%, relative to Tier 1 vehicles on a per mile basis, at a cost well below $5000 per ton on an
annual basis. Comparing these reductions relative to National LEV yields a 7% reduction in
NMHC and 30% in NOx, at a cost also well below $5000 per ton. These emission reductions
would also be more than sufficient to meet the default Tier 2 standards listed in Table 3 of
section 202(i) of the CAA.
EPA evaluates the cost effectiveness of other current or potential control methods for
controlling emissions. The techniques for reducing LDV and LDT emissions appear to be
comparable to or more cost effective than many alternative methods of emission reduction. In
developing the National LEV regulations, EPA found that the National LEV standards provided
cost effective emission reductions from the Tier 1 standards relative to other emission control
programs (roughly $2000 per ton of NMHC and NOx controlled).
In addition to estimates of cost, this chapter also attempts to quantify the emission
reduction capabilities of these future technologies. In this way, the cost effectiveness, in units of
dollars per ton of emissions reduced, can be calculated and compared.
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Next Steps
Following submission of this Report to Congress, EPA will by rule, determine whether:
1) there is an air quality need for further emission reductions; 2) the technology for meeting more
stringent emissions standards will be available; and 3) obtaining further reductions in emissions
from light-duty vehicles and certain light-duty trucks will be needed and cost effective. If these
conditions exist, EPA will promulgate emission standards for such vehicles by December 1999,
providing significant and frequent opportunities for the involvement of interested parties
throughout the rulemaking process.
In its rulemaking, EPA will examine additional issues, as discussed in Chapter VI:
Regulatory Issues of this Tier 2 study. They will include the relative stringency of LDV and
LDT standards, the appropriateness of having separate standards for gasoline and diesel vehicles
versus having the same standards for such vehicles, and effects of sulfur in gasoline on catalyst
efficiency.
All LDVs have historically been required to meet the same numerical emission standards.
For example, large luxury cars and small sub-compacts both meet the same emission standards,
because both types of vehicles are used as personal transportation. In contrast, higher numerical
emission standards have historically been established for LDTs. As LDTs become a larger
portion of the passenger fleet, they have a disproportionate impact on in-use emissions. Options
for setting LDT emission standards given a particular set of LDV standards include: requiring
LDTs to meet the same numerical emission standards as LDVs; setting the LDT standards to
require use of the same emission control technology as the LDV standards; or setting different
standards based on vehicle use.
Another consideration is whether the same emission standards should be applied to
similar vehicles regardless of what fuel is utilized. Here, the primary fuel options for
conventional vehicles are gasoline and diesel fuel. The pollutants of most interest with regard to
applying the same standards to gasoline and diesel vehicles are NOx and PM exhaust emissions.
Both diesel and gasoline vehicles appear to be capable of meeting the range of possible Tier 2
NMHC and CO emission standards, so the issue of equivalent standards does not arise with
respect to these pollutants.
Sulfur in gasoline affects emissions of HC, CO and NOx by inhibiting the performance of
the catalyst. Recent information from test programs performed by the Coordinating Research
Council (CRC) and the auto industry suggests that not only do LEV and Tier 1 vehicles exhibit
decreased emissions performance due to fuel sulfur, but the more advanced the technology, the
more sensitive (on a percentage basis) the catalysts are to sulfur. The studies indicate that
increasing sulfur content could more than double NOx emissions and have a less severe, though
noticeable, effect on HC emissions. EPA addressed this issue in a recently released Staff Paper
on Gasoline Sulfur Issues (May 1998). EPA plans to consider issues related to sulfur levels in
gasoline, including geographic applicability and costs of controls, as part of the Tier 2
rulemaking.
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n. INTRODUCTION
In drafting the Clean Air Act, as amended in 1990, Congress envisioned that it may be
necessary to require additional emission reductions from new passenger vehicles in the beginning
of the 21st Century to provide needed protection of public health. Section 202 (i) of the CAA
outlines a process for assessing whether more stringent exhaust emission reductions from light-
duty vehicles and light-duty trucks should be required. Congress required the Environmental
Protection Agency to report the results of this assessment to Congress. Congress identified
specific standards1 that EPA must consider in making this assessment, but stated that the study
should also consider other possible standards. These standards, referred to as the 'Tier 2
standards" in this study, would be more stringent than the standards required for LDVs and LDTs
in the CAA beginning in model year 19942, but could not be implemented prior to the 2004
model year.
Specifically, Congress mandated that this study examine3:
1) the need for further reductions in emissions in order to attain or maintain the National
Ambient Air Quality Standards, taking into consideration the waiver provisions of section
209(b),
2) the availability of technology (including the costs thereof) in the case of light-duty
vehicles and light-duty trucks with a loaded vehicle weight of 3750 lbs or less, for
meeting more stringent emission standards than those provided in subsections (g) and (h)
for model years commencing not earlier than after January 1,2003, and not later than
model year 2006, including the lead time and safety and energy impacts of meeting more
stringent emission standards; and
1 Clean Air Act; Section 202 (i); Table 3: Pending Emission Standards for Gasoline and Diesel Fueled
Light-duty Vehicles and Light-duty Trucks 3,750 lbs LVW or Less.
Pollutant Emission Level in
grams per mile (g/mi)
NMHC 0.125 g/mi
NOx 0.2 g/mi
CO 1.7 g/mi
2 Section 202 (g) and (h).
3 Section 202 (i), Congress specified that, "The Administrator, with the participation of the Office of
Technology Assessment, shall..." However, the 104th Congress voted to cease funding the Office of Technology
Assessment after September 30, 1995, prior to the Agency developing plans for the Tier 2 study.
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3) the need for, and cost effectiveness of, obtaining further reductions in emissions from
such light-duty vehicles and light-duty trucks, taking into consideration alternative means
of attaining or maintaining the national primary ambient air quality standards pursuant to
state implementation plans and other requirement of this Act, including their feasibility
and cost effectiveness.
As the first draft of this study was being completed, an historic agreement between
automakers and the states, coordinated by EPA, established a voluntary National Low Emission
Vehicle program. This program requires that vehicles, sold in model year 1999 in the Northeast
and sold nationwide in model year 2001, meet more stringent emission standards than current
federal Tier 1 standards. The National LEV program also harmonizes, to the greatest practical
extent, federal requirements with the more stringent exhaust emission standards established by
the state of California.4 This program was prompted by the established air quality need in the
northeastern United States to assist states in meeting the National Ambient Air Quality
Standards. The National LEV program provides an additional feasibility and cost effectiveness
baseline for more stringent exhaust emission standards in the future compared to that identified
by Congress for the Tier 2 standards.
In conducting this study, EPA ensured that issues relevant to the study were explored
using a public process. The Agency published a Staff White Paper (See 62 FR 18346; April 15,
1997) and conducted a public workshop on April 23,1997. In addition, the Agency participated
in numerous meetings with states, environmental organizations and industry representatives.
As required by Congress, this study was released to the public for comment on April 23,
1998. After providing 45 days for public comment, EPA summarized the comments received
(see Appendices E and F), modified the draft study as necessary, and created this final report for
submission to Congress.
Based on the conclusions of this study, EPA now plans to determine, by rule, whether: 1)
there is a need for further emission reductions; 2) the technology for meeting more stringent
emissions standards will be available; and, 3) further reductions in emissions from light-duty
vehicles and certain light-duty trucks will be needed and cost effective, taking into consideration
other alternatives. If EPA determines that these conditions exist, then EPA shall promulgate
emission standards for such vehicles.
4 California has the authority under section 209(b) of the CAA to establish state specific vehicle and
engine emissions and testing programs.
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HI. ASSESSING THE AIR QUALITY NEED
The goal of this chapter is to assess the air quality need for additional control of motor
vehicle emissions that hinder areas of the country from attaining and/or maintaining National
Ambient Air Quality Standards, in particular those for ozone, particulate matter and carbon
monoxide.5 To understand the impact of these pollutants, and ozone precursors, this chapter
outlines their threat to public health and welfare and the manner in which they are formed and
transported in air. In assessing air quality need, EPA examined projections of future areas of
NAAQS nonattainment, as well as projections of areas needing to closely monitor maintenance
plans in the future. This chapter then assesses the contribution of light-duty vehicles (LDVs) and
light-duty trucks (LDTs) to the overall inventory for each pollutant and briefly explains other
benefits of LDV and LDT emission controls. Finally, this chapter reviews future projections of
air quality given all known and projected control strategies in the time frame contemplated for
potential Tier 2 controls. Evidence that additional motor vehicle controls should be considered
would include the fact that motor vehicles substantially contribute to total emission inventories in
nonattainment areas and in areas which affect nonattainment through transport, as well as areas
that may have difficulty maintaining their attainment status.
The available data indicate that in the time frame contemplated for Tier 2 standards there
will be an air quality need for emission reductions to aid in meeting the NAAQS for both ozone
and PM. EPA is continuing to evaluate the air quality need for further CO emission reductions
in the context of the requirement to evaluate cold CO emission reductions as discussed later in
this chapter. The available evidence also indicates that motor vehicle emissions will remain a
significant contributor to air pollution in a significant number of areas of the country.
A. Health and Welfare Effects of Ozone
Ground-level ozone is the prime ingredient of smog, the pollution that blankets many
areas during the summer.6 Short-term exposures (1-3 hours) to high ambient ozone
concentrations have been linked to increased hospital admissions and emergency room visits for
respiratory problems. Repeated exposures to ozone can exacerbate symptoms and the frequency
of episodes for people with respiratory diseases such as asthma. Other health effects attributed to
short term exposures include significant decreases in lung function and increased respiratory
symptoms such as chest pain and cough. These effects are generally associated with moderate or
heavy exercise or exertion. Those most at risk include children who are active outdoors during
the summer, outdoor workers, and people with pre-existing respiratory diseases like asthma. In
5 Hie Tier 2 standards would have no direct impact on the NAAQS for sulfur dioxide. However, gasoline
sulfur controls to enable tighter Her 2 standards, as discussed in Chapter VI, would reduce ambient levels of sulfur
dioxide.
6 Ozone also occurs naturally in the stratosphere and provides a protective layer high above the earth.
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addition, long-term exposures to ozone may cause irreversible changes in the lungs which can
lead to chronic aging of the lungs or chronic respiratory disease.
Ambient ozone also affects crop yield, forest growth, and the durability of materials.
Because ground-level ozone interferes with the ability of a plant to produce and store food, plants
become more susceptible to disease, insect attack, harsh weather and other environmental
stresses. Ozone chemically attacks elastomers (natural rubber and certain synthetic polymers),
textile fibers and dyes, and, to a lesser extent, paints. For example, elastomers become brittle
and crack, and dyes fade after exposure to ozone.
Ozone is not emitted directly into the atmosphere, but is formed by a reaction of VOC
and NOx in the presence of heat and sunlight. Ground-level ozone forms readily in the lower
atmosphere, usually during hot summer weather. VOCs are emitted from a variety of sources,
including motor vehicles, chemical plants, refineries, factories, consumer and commercial
products, and other industrial sources. VOCs are also emitted by natural sources such as
vegetation. NOx is emitted from motor vehicles, power plants and other source of combustion.
Changing weather patterns contribute to yearly differences in ozone concentrations and
differences from city to city. Ozone can also be transported into an area from pollution sources
found hundreds of miles upwind.
VOC emissions are not only important for their contribution to ambient ozone. Some
fraction of the VOCs emitted from motor vehicle are toxic compounds. At elevated
concentrations and exposures, human health effects from air toxics can range from respiratory
effects to cancer. Other health impacts include neurological, developmental and reproductive
effects.
NOx emissions produce a wide variety of health and welfare effects. Nitrogen dioxide
can irritate the lungs and lower resistance to respiratory infection (such as influenza). NOx
emissions are an important precursor to acid rain and may affect both terrestrial and aquatic
ecosystems. Atmospheric deposition of nitrogen leads to excess nutrient enrichment problems
("eutrophication") in the Chesapeake Bay and several other nationally important estuaries along
the East and Gulf Coasts. Eutrophication can produce multiple adverse effects on water quality
and the aquatic environment, including increased nuisance and toxic algal blooms, excessive
phytoplankton growth, low or no dissolved oxygen in bottom waters, and reduced sunlight
causing losses in submerged aquatic vegetation critical for healthy estuarine ecosystems.
Nitrogen dioxide and airborne nitrate also contribute to pollutant haze, which impairs visibility
and can reduce residential property values and revenues from tourism.
B. Role of VOC and NOx Emissions in Producing Atmospheric Ozone
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The production of ozone from VOC and NOx emissions7 involves a complex set of
chemical reactions, and different mixtures of VOCs and NOx can result in different ozone levels.
For example, large amounts of VOC and small amounts of NOx make ozone rapidly, but ozone
production is quickly limited by removal of the NOx. VOC reductions under these
circumstances show little effect on ozone while NOx reductions reduce ozone. (This condition is
referred to as NOx limited.)
Large amounts of NOx and small amounts of VOC result in the formation of inorganic
nitrates, but little ozone. In these cases, reduction of VOC emissions reduces ozone, but the
reduction of NOx emissions can actually increase ozone. (This condition is referred to as VOC
limited.) The highest levels of ozone are produced when both VOC and NOx emissions are
present in significant quantities.
The formation of ozone is further complicated by biogenic (natural) emissions,
meteorology and transport of ozone and ozone precursors. The contribution of VOC emissions
from biogenic sources to local ambient ozone concentrations can be significant and often
produces conditions which are NOx limited. Many of the above chemical reactions are sensitive
to temperature. When ambient temperatures remain high for several days and the air is relatively
stagnant, ozone and its precursors can actually build up and produce more ozone than typically
would occur on a single high temperature day. When air is moving, ozone and its precursors can
be transported downwind and contribute to elevated ozone levels outside of the area where the
NOx is emitted.
This study focuses on the response of ambient ozone to the reduction in either VOC or
NOx emissions, or both. In general, specific local areas are often described as being VOC or
NOx limited. Rural areas are almost always NOx limited, due to the relatively large amounts of
biogenic (from plants and trees) VOC emissions there. Urbanized areas can be either VOC or
NOx-limited, or a mixture of the two (moderate sensitivity to either pollutant, versus strong
sensitivity to one and little sensitivity to the other). In projecting future attainment of the revised
ozone NAAQS, EPA found that significant reductions in both VOC and NOx emissions would
be necessary.
C. Current Compliance with the Ozone NAAQS
As of October, 1997, EPA classified 59 ozone nonattainment areas with respect to the 1-
hour ozone standard, encompassing all or part of 249 counties. The population of these 59 areas,
based on the 1990 Census, is approximately 102 million, or 40 percent of the total U.S.
population. These areas are located in the 37 easternmost states, Arizona, New Mexico, and
California.
7 CO also participates in the production of ozone, much like a slowly reacting VOC.
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In July 1997, EPA established a new 8-hour ozone NAAQS to better protect against
longer exposure periods at lower concentrations than the current 1-hour standard. The 1-hour
NAAQS is still applicable in certain areas during the transition to the eight-hour standard (62 FR
38856, July 17, 1997). EPA reviewed ambient ozone monitoring data for the period 1993
through 1995 to determine which counties violated either the 1-hour or 8-hour NAAQS for ozone
during this time period.8'9 Eighty-four counties violated the 1-hour NAAQS during this 3-year
period, while 248 counties violated the 8-hour NAAQS. The 84 counties had a 1990 population
of 47 million, while the 248 counties had a 1990 population of 83 million. EPA is reviewing
more recent air quality data for 1996 and 1997. A preliminary assessment of 1994 through 1996
ozone monitoring data reveals only marginal changes in the number of counties experiencing a
nonattainment problem with the 8-hour NAAQS, and essentially no change in the population
levels impacted by nonattainment.
U.S Population (1990 Census) Living in Areas
Violating the Ozone NAAQS in 1993-1995
(Millions)
47
~ Attainment Areas
¦ Violating 1-Hour and 8-
Hour Ozone NAAQS
¦ Violating Only 8-Hour
Ozone NAAQS
D. Future Ambient Ozone Levels
The analysis of future ozone attainment provides a basis for assessment of the need for
additional emission reductions to achieve attainment and assure maintenance of the NAAQS.
EPA recently performed two projections of future ozone attainment status in the years 2007 to
2010. The first was part of EPA's 1997 ozone NAAQS rulemaking.
8 This use of the term "nonattainment" in reference to a specific area is not meant as an official designation
or future determination as to the attainment status of the area.
9 U.S. Environmental Protection Agency, Finding of Significant Contribution and Rulemaking for Certain
States in the Ozone Transport Assessment Group Region for Purposes of Reducing Regional Transport of Ozone;
Proposed Rule, 62 FR 60318 (November 7, 1997) ("OTAG SIP Call NPRM").
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The second was conducted for the EPA's recent notice of proposed rulemaking regarding
requirements for State Implementation Plans for 37 easternmost states. Through a two-year
effort known as the Ozone Transport Assessment Group (OTAG), EPA worked in partnership
with state and local government agencies in the 37 easternmost states, industry and academia to
address ozone transport. The work resulted in a proposed rule to reduce the regional transport of
ozone (OTAG SIP Call NPRM). The ozone projections supporting the OTAG SIP Call NPRM
used more advanced regional ozone modeling tools than those made in support of the revised
ozone NAAQS. However, the ozone NAAQS analysis covered the entire nation, while the
OTAG SIP Call NPRM only addressed ozone levels in the eastern U.S. Therefore, both are
discussed below. In developing a projection of future ozone nonattainment for the purpose of
this study, EPA combined the projections from the OTAG SIP Call NPRM for the 37-state
OTAG region with the projections from the Regulatory Impact Analysis (RIA) for the revised
ozone NAAQS for the remaining 11 states in the continental United States.
As part of the RIA for the revised ozone NAAQS, EPA projected future ambient ozone
levels in 2010 using a Regional Oxidant Model (ROM) extrapolation methodology. One of the
scenarios evaluated was a 2010 baseline, which included emission controls which have already
been implemented or mandated by the Clean Air Act, regional NOx emission control in the
eastern U.S. estimated to be associated with the then upcoming OTAG SIP Call NPRM, plus the
National Low Emission Vehicle program. This set of emission control strategies generally
represents all of the emissions reductions which may be expected from measures currently
adopted or planned by the states.
EPA used ROM air quality modeling, historical ozone air quality monitoring data and
emission inventory estimates to project baseline 2010 ozone levels for counties in the 48
contiguous states. For the purpose of this study, the standard and consolidated metropolitan
statistical areas (MSAs and CMSAs) containing these counties were identified. Nine areas with a
1990 population of approximately 49 million people were projected to be in nonattainment of the
1-hour ozone standard, 32 million people outside of California. Nineteen areas (with
approximately 79 million people as of 1990) were projected to be in nonattainment with the 8-
hour ozone NAAQS, 51 million people outside of California. The 51 million people living in the
projected nonattainment areas outside of California represent more than a fifth of the U.S.
population in 1990.10
The Tier 2 standards would primarily affect ozone outside of California due to the
applicability of California's traditionally more stringent motor vehicle standards to vehicles sold
in California. However, the Tier 2 standards would also indirectly, but significantly improve
ozone levels within California. This indirect benefit is due to the migration of non-California
vehicles into California when people move into that state. It is also due to the temporary
business and leisure travel of non-Californians into California. The California Air Resources
10 Populations in 1990 are presented in this study because of their ready availability and accuracy.
Populations in future NAAQS nonattainment and maintenance areas will generally be much higher.
13
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Board (ARB) recognized this benefit in the context of the NLEV program. The California ARB
used the benefits of the NLEV program to compensate for emission increases associated with a
delay in the implementation schedule for zero-emission vehicles.
Once an area attains a NAAQS, the CAA requires that it establish a plan for maintaining
this attainment. Otherwise, future economic and population growth can increase emissions to the
point where the area again violates the NAAQS. To estimate the number of areas that need to be
concerned about ozone NAAQS compliance in the future, EPA (for the Tier 2 study) also
identified metropolitan areas containing counties that were projected to be below the 8-hour
ozone NAAQS, but with a relatively small margin of safety (i.e., 15%). VOC and NOx emission
reductions associated with the Tier 2 standards would assist these areas in maintaining their
compliance.
In the ozone NAAQS RIA, EPA also projected that available local VOC and NOx
controls (at a cost of up to $10,000 per ton of VOC or NOx in 1990 dollars) could bring only two
of these 19 areas into attainment with the new 8-hour NAAQS. Seventeen (17) of the 19 areas
remained out of attainment after all available local controls. Overall, the available local controls
in the 19 areas only achieved 38% and 23% of the necessary VOC and NOx emission reductions
required. Clearly, these areas would need additional emission reductions in order to achieve the
new ozone NAAQS. As mentioned above, both the OTAG SIP Call and National LEV programs
were included in the baseline projections. Therefore, only motor vehicle controls beyond those
provided by Tier 1 and National LEV would qualify as additional control.
In the OTAG SIP Call NPRM, EPA proposed that 22 states and the District of Columbia
be required to submit revised SEPs demonstrating reductions in NOx emissions in order to reduce
the transport of ozone into ozone nonattainment areas. EPA relied upon the ambient ozone
modeling conducted during the OTAG process in developing the proposed emission reductions.
OTAG evaluated a wide variety of VOC and NOx emission controls for stationary, area and
mobile sources over a two year period. EPA reviewed OTAG ozone modeling which included
utility NOx emission reductions most closely resembling those being proposed, and controls for
other sources (stationary, areas and mobile) required by the CAA or which had already been
implemented. This modeling, like that conducted during the ozone NAAQS revisions process,
also assumed the implementation of a National LEV program. Complete details of the modeling
process can be found, in the OTAG SIP Call NPRM and associated documents. A list of the
specific emission control strategies assumed in this modeling is presented in Appendix A. Future
Ozone Nonattainment Projections.
For the purpose of the Tier 2 study, EPA reviewed the results of the OTAG SIP Call
NPRM analyses and found that 8 areas with a population of approximately 41 million people
were projected to be in nonattainment of the 1-hour ozone standard. Fifteen areas (with
approximately 63 million people) were projected to be in nonattainment with the 8-hour ozone
NAAQS.
14
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Combining the OTAG SIP Call NPRM projections for the OTAG region with those of
the ozone NAAQS RIA for the remainder of the country, EPA developed the following
projections of ozone nonattainment and maintenance areas in 2007 (OTAG region) and 2010
(remaining 11 states). The metropolitan areas projected to be in nonattainment are presented in
Appendix A.
Table 3.1 2007/2010 Ozone Nonattainment with CAA Conl
rols, OTAG SIP Call, & NLEV
OTAG
Region
(2007)
Non-CA, Non-
OTAG (2010)
California (2010)
Violating 1-Hour NAAQS
Number of Areas
8
0
4
1990 Population (millions)
41
0
18
Violating 8-Hour NAAQS
Number of Areas
15
1
6
1990 Population (millions)
63
2
28
Maintenance of the 8-Hour NAAQS (within 15% of NAAQS)
Number of Areas
85
11
7
1990 Population (millions)
118
11
9
For the purposes of this study, EPA also identified the Standard Metropolitan Statistical
Areas (SMSA) and CMSAs containing counties which were projected to be below the 8-hour
ozone NAAQS, but within 15% of the NAAQS. EPA found 103 areas (96 non-California areas)
to have projected ozone levels within 15% of the NAAQS, with a 1990 population of 136 million
(129 million outside of California). As already stated, additional emission reductions would
certainly assist such areas to maintain their attainment status and may actually be required, given
meteorological variability and uncertainties in emission and ozone modeling.
These projections of future ozone nonattainment provide evidence for the need for
additional VOC and NOx emission reductions beyond those considered in these studies. The
CAA provides states flexibility in selecting local emission control strategies to achieve the
NAAQS. EPA has augmented these local controls with cost effective national programs, some
mandated by the CAA and others using EPA's discretionary authority under the CAA. The
above analyses indicate that both local and national measures appear to be necessary for the
nation to achieve the ozone NAAQS. Tier 2 standards for LDVs and LDTs appear to be a
reasonable national control option for consideration. Because the above ozone projections of
future nonattainment already assumed and incorporated the permanent implementation of the
National LEV program, the focus for motor vehicle control programs should be on VOC and
NOx emission controls beyond the National LEV standards.
15
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E. Contribution of LDV/LDT Emissions to Total VOC and NOx Inventories
Since motor vehicles and their fuels were first regulated 25 to 30 years ago, their relative
contribution to ozone nonattainment problems has diminished, in spite of explosive growth in the
amount of travel. The relative cost of adopting further motor vehicle controls compared to other
reduction strategies depends in part on their future contribution to VOC and NOx emissions in
ozone nonattainment areas and areas contributing to ozone nonattainment through pollutant
transport. Auto industry comments received by EPA after publication of a preliminary white
paper on Tier 2 standards issues indicated that an updated assessment should be made of the
importance of LDVs and LDTs to the ozone nonattainment problem. Specifically, commenters
suggested that new information about the durability of emission control systems would alter the
projections of nonattainment made in the studies mentioned previously, perhaps to the extent that
no additional measures would be needed. In developing the study, EPA analyzed new mobile
source modeling data associated with a number of factors.
Emissions from motor vehicles are usually estimated by combining estimates of
emissions per mile (commonly called emission factors) with local estimates of vehicle miles
traveled. EPA developed a series of models to project in-use emission factors from on-road
motor vehicles. EPA is currently revising the MOBILE5 model. MOBILE6 will be issued in
1999.
While the analytical efforts involved in developing MOBILE6 are still underway, EPA
performed preliminary assessments of four key factors which could affect the need for Tier 2
standards.11 These factors are:
1) In-use emission deterioration rates for Tier 1 vehicles, LEVs, and late model Tier
0 vehicles;
2) The effect of "off-cycle" driving patterns and conditions on LDV and LDT
emissions, as well as the effect of off-cycle emission standards on these
emissions;12
3) The effect of fuel sulfur on emissions from low emitting vehicles, such as CA
LEVs and NLEVs; and
11 MOBILE6 is being developed through an extensive and open process which is continuing in parallel
with the Tier 2 standards process. The changes to MOBILE5b described herein should not be construed as pre-
judging the outcome of the MOBILE6 development process, but simply represent EPA's current best estimate of
some of the factors which are most relevant to the evaluation of the Tier 2 LDV/LDT standards.
12 "Off-cycle" emissions are those which occur during driving conditions not included in EPA's historical
certification driving cycle, the LA-4 cycle. The specific off-cycle driving conditions addressed here are aggressive
driving (high speeds and high accelerations) and driving with the air conditioner on.
16
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4) The characterization of the LDT fleet (i.e., relative LDV and LDT sales, and LDT
registrations and annual mileage versus age)
Regarding the first factor, recent testing of in-use vehicles produced since the late 1980s
shows much lower deterioration rates than were projected in 1993. As most of the in-use
emissions from LDVs and LDTs projected by MOBILE5 were due to deterioration in emission
control after a vehicle was first sold, reducing this deterioration decreases projected in-use
emissions dramatically.
In contrast, updated estimates of the other three factors all tend to increase in-use
emission projections. Emissions during driving conditions not represented in EPA's certification
driving cycle tend to be higher than those included in the test, since prior to implementation of
the Supplemental FTP there is little incentive for manufacturers to reduce these "off-cycle"
emissions. Higher levels of fuel sulfur have been shown to increase emissions by reducing
catalyst efficiency. In-use emissions increase whenever vehicles operate on fuel containing more
sulfur than certification fuel. Moreover, vehicles with very low emissions, such as LEVs, now
appear to be much more sensitive to sulfur than Tier 1 vehicles. Finally, LDTs tend to emit more
than LDVs as their emission standards have traditionally been numerically higher. The recent
dramatic trend toward the purchase of LDTs (e.g., sport utility vehicles) over LDVs was not
predicted in MOBILE5b. Increasing the fraction of in-use driving represented by LDTs increases
fleet-wide emission projections.
Overall, the four changes to MOBILE5b increase projected in-use emissions from LDVs
and LDTs (relative to MOBILE5b) in areas with enhanced Inspection and Maintenance (I/M)
programs. CO and NOx emissions also increase in areas without I/M. However, NMHC
emission projections decrease in areas without I/M. A more detailed discussion of this analysis
and the modifications made to MOBILE5b can be found in Appendix A.
EPA used the modified MOBILE5b model described above to estimate the contribution
of LDV and LDT emissions in four urban ozone nonattainment areas. The four areas were: New
York City, Chicago, Atlanta, and Charlotte. The first three areas represent the three greatest
ozone air quality challenges in the eastern U.S. according to the OTAG ozone modeling.
Charlotte represents a smaller, but growing area with a growing ozone problem.
The LDV/LDT and total motor vehicle contributions to total VOC and NOx emissions in
the four ozone areas are shown in the figures below. Light-duty vehicles and trucks contribute
14-20% of total VOC emissions and 22-32% of total NOx emissions based on the modified
MOBILE5b model. All of these percentage contributions are higher than would have been
predicted using MOBILE5b.
17
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2007 VOC Emissions - Contributions to Total Emissions
Modified MOBILE5b Model
100%
90%
80%
70%
60%
50%
40%
30% - —
20%
10%
Atlanta
Charlotte
Chicago
New York City
¦ Other Sources
~ Other Motor Vehicles
¦ Light-Duty Vehicles
and Trucks
18
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2007 NOx Emissions - Contributions to Total Emissions
Modified MOBILE5b Model
1 1
11
E j
1 1
1
1 1
Atlanta
Charlotte
Chicago
Nev York City
¦ Other
Sources
~ Other Motor
Vehicles
¦ Light-Duty
Vehicles and
Trucks
Given that the modified MOBILE5b model projects higher emissions than MOBILE5b,
the number of ozone nonattainment areas projected to exist in 2007 should be at least as high as
was described above. Thus, the new MOBILE6 model is unlikely to eliminate the need for
further VOC and NOx emission reductions in order for all areas to attain the ozone NAAQS.
The contribution of LDVs and LDTs to emission inventories in ozcne nonattainment areas is also
sufficiently large to be considered a reasonable target for further emission control.
F. Health and Welfare Effects of Particulate Matter
Particulate matter is the general term for the mixture of solid particles and liquid droplets
found in the air. Particulate matter includes dust, dirt, soot, smoke, and liquid droplets that are
directly emitted into the air from natural and manmade sources, such as windblown dust, motor
vehicles, construction sites, factories, and fires. Particles are also formed in the atmosphere by
condensation or the transformation of emitted gases such as sulfur dioxide, nitrogen oxides, and
volatile organic compounds.
Scientific studies suggest a likely causal role of ambient particulate matter in contributing
to a series of health effects. The key health effects categories associated with particulate matter
include premature mortality, aggravation of respiratory and cardiovascular disease (as indicated
by increased hospital admissions and emergency room visits, schoo_ absences, work loss days,
and restricted activity days), changes in lung function and increased respiratory symptoms,
19
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changes to lung tissues and structure, and altered respiratory defense mechanisms. PM also
causes damage to materials and soiling. It is a major cause of substantial visibility impairment in
many parts of the U.S.
Motor vehicle particle emissions and the particles formed by the transformation of motor
vehicle gaseous emissions tend to be in the fine particle range. Fine particles (those less than 2.5
micrometers in diameter) are of health concern because they easily reach the deepest recesses of
the lungs. Scientific studies have linked fine particles (alone or in combination with other air
pollutants), with a series of significant health problems, including premature death; respiratory
related hospital admissions and emergency room visits; aggravated asthma; acute respiratory
symptoms, including aggravated coughing and difficult or painful breathing; chronic bronchitis;
and decreased lung function that can be experienced as shortness of breath.
G. Current and Future Nonattainment Status
The first NAAQS for particulate matter regulated total suspended particulate in the
atmosphere. In 1987, EPA replaced that standard with one for inhalable PM (PM10 - particles
less than ten microns in size), because the smaller particles, due to their ability to reach the lower
regions of the respiratory tract, are more likely responsible for the adverse health effects. The
major source of PM10 is fugitive emissions from agricultural tilling, construction, fires, and
unpaved roads. Some revisions to the PM,0 standards were made in 1997. EPA has also
recently added new fine particle standards (PM25). Most of the particulate due to motor vehicles
falls in the fine particle category. These standards have both an annual and a daily component.
The annual component is set to protect against long-term exposures, while the daily component
protects against more extreme short-term events.
EPA recently projected ambient PM10 levels and the number of U.S. counties expected to
be in violation of the revised PM10 NAAQS in 2010.13 Forty-five CMS As, SMS As and
counties14 were projected to be in nonattainment of the original PM10 standards in 2010; Eleven
CMSAs, SMSAs and counties were projected to be in nonattainment of the revised PM10
standards. Using the same methodology, 102 CMSAs, SMSAs and counties were projected to
violate the new PM2 5 NAAQS. More information about this analysis may be found in Appendix
A.
It should be noted that an error was made in the figure in the Draft Tier 2 Study which
indicated the number of areas that would be in nonattainment of the PM standards ("Counties
13 Regulatory Impact Analyses for the Particulate Matter and Ozone National Ambient Air Quality
Standards and Proposed Regional Haze Rule, Innovative Strategies and Economics Group, Office of Air Quality
Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, N.C., July 16,1997.
14 Current definitions of PM10 nonattainment counties were used. These definitions sometimes include the
entire CMSA or SMSA and sometimes include only a county.
20
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Projected to violate NAAQS for PM in 2010," page 23). That figure showed 147 areas violating
the new NAAQS for PM2J. This error resulted from a double-counting of 45 of the counties
which are also projected to be in violation of the PM10 standard. The correct number is 102
counties, as shown in Table 3.2.
Table 3.2 Projected 2010 PM10/PM2.5 Nonattainment
22-State
OTAG
Region *
Non-CA, Non-
OTAG
California
Violating Original PM10 NAAQS
Number of Areas
8
25
12
1990 Population (millions)
8
3
7
Violating Revised PM10 NAAQS
Number of Areas
2
3
6
1990 Population (millions)
4
1
5
Violating New PM2.5 NAAQS
Number of Areas
59
33
10
1990 Population (millions)
34
8
13
* Plus ME, VT, NH, and future ozone nonattainment areas in TX and AZ
Based on the 1990 census, about 10 million people lived in the 11 counties projected to
be in nonattainment of the revised PM10 NAAQS, with about half living in the 22-state OTAG
region (plus areas with future ozone problems) and about half living in California. Ambient PM
reductions from more stringent motor vehicle standards would primarily affect areas outside of
California, because California has its own motor vehicle emission control program. California
areas would also benefit, however, through the temporary travel and permanent migration of out-
state vehicles into California. Of the nonattainment counties outside of California, two are
within urban areas (Dallas, Philadelphia). These urban areas contain the vast majority of the
non-California, nonattainment population.
In 1990, about 55 million people lived in the 102 counties projected to be in
nonattainment with the new PMW NAAQS, with about 60% living in the 22-state OTAG region
(plus areas with future ozone problems) and about 25% living in California.
Overall, a significant number of areas are projected to exceed the PM10 NAAQS in 2010
with existing emission controls, indicating that further particulate emission reductions appear to
be needed. Tier 2 particulate standards would reduce ambient levels of PM2 5, as well as PM10 (or
at least prevent increases), since the majority of particulate emissions from both gasoline and
diesel powered vehicles are smaller than 2.5 micrometers in diameter. As mentioned above, the
number of counties projected to violate the new PM2J NAAQS is much larger than that for the
21
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revised PM10 standards. Thus, Tier 2 particulate standards intended to assist attainment of the
PMI0 NAAQS could also benefit areas with elevated PM25 levels.
H. Particulate Emissions from Light-Duty Vehicles and Trucks
1. Direct Tailpipe Emissions
Congress set Tier 1 PM emission standards for LDVs and LDTs in the 1990 amendments
to the CAA. These standards are 0.10-0.12 g/mi at 100,000 miles. Tier 1 and LEV gasoline
LDVs and LDTs emit well below these Tier 1 PM standards (less than 0.010 g/mi). Diesel
vehicles meet the standards, but with very little compliance margin.
EPA projects that PM emissions from Tier 1 and LEV LDVs and LDTs average 0.01
g/mi at 20 mph and 0.02-0.03 g/mi at 35 mph (from PART5 model). In contrast, diesel vehicles
are projected to emit 0.10-0.11 g/mi PM. Thus, diesel PM emissions are 3.5-10 times higher
than those from gasoline vehicles. The greater PM emission level of light-duty diesels currently
has a limited impact on ambient PM levels, due to the small number of light-duty diesels being
sold. However, diesel engines are becoming a more popular option for larger LDTs and lighter
HDVs, particularly pick-ups and sport utility vehicles. PM emissions from the light-duty fleet
could increase dramatically if diesel sales increased without a change in the Tier 1 diesel PM
standard.
The following chart shows the relative contribution of vehicles versus other fine particle
emission sources (excluding fugitive dust emissions).
22
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U.S. 1990 PM-10 and PM-2.5 Emissions
1000 Tons per Year
3500
3000
2500
2000
1500
1000
500
0
® Other
Sources
¦ Fuel
Combustion
~ Non-road
Vehicles
¦ Highway
Vehicles
PM10
PM2.5
Secondary Formation of PM from Gaseous Emissions
In addition to their direct tailpipe PM emissions, gaseous emissions from LDVs and
LDTs can also affect ambient PM levels. In particular, gaseous emissions of SOx, NOx and
VOC form aerosols in the atmosphere through chemical transformation. These aerosols exist as
PM in the atmosphere.
The great majority of sulfur that enters the gasoline engine via the fuel is emitted in the
form of sulfur dioxide. A small fraction (1-2%) of the sulfur is emitted directly as sulfuric acid.
Sulfur dioxide reacts in the atmosphere to produce sulfur trioxide, which quickly combines with
water to form sulfuric acid. Sulfuric acid exists as a particulate matter in the atmosphere, due to
its low vapor pressure. Sulfuric acid can subsequently react with ammonia to form ammonium
bi-sulfate and ammonium sulfate, both of which also exist as PM in the atmosphere.
Most NOx emitted converts to gaseous nitric acid in the atmosphere. Nitric acid can react
with ammonia to form ammonium nitrate, which becomes PM in the atmosphere. However,
ammonia reacts preferentially with sulfuric acid over nitric acid. As there is generally an excess
of sulfuric acid in the atmosphere relative to ammonia, the presence of sulfuric acid suppresses
23
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the formation of ammonium nitrate and therefore the contribution of NOx emissions to fine
ambient PM. Implementation of control programs required by the CAA is leading to significant
reductions in sulfur dioxide emissions, which will reduce ambient levels of sulfuric acid.
Therefore, the conversion of NOx to nitrate PM could increase.
Organic aerosol can be formed in the atmosphere from gaseous VOC emissions. The
reactions that form secondary organic aerosol are generally more complex than those forming
sulfates and nitrates, primarily because of the great variety of specific organic molecules
comprising VOCs.15 Cyclic-olefins and aromatics produce the most secondary organic aerosol
per mass of VOC. Coniferous trees are the primary source of cyclic-olefins (pinene and
terpinene), while gasoline-fiieled vehicles are a primary source of ambient aromatics.
I. Health and Welfare Effects of Carbon Monoxide
Carbon monoxide (CO) is a tasteless, odorless, and colorless gas produced though the
incomplete combustion of carbon-based fuels. CO enters the bloodstream through the lungs and
reduces the delivery of oxygen to the body's organs and tissues. The health threat from CO is
most serious for those who suffer from cardiovascular disease, particularly those with angina or
peripheral vascular disease. Healthy individuals also are affected, but only at higher levels.
Exposure to elevated CO levels is associated with impairment of visual perception, work
capacity, manual dexterity, learning ability and performance of complex tasks.
1. Current and Future Nonattainment Status
Since 1979, the number of areas in the nation violating the NAAQS for CO16 has
decreased by a factor of almost ten, from 48 areas in 1979 to five areas in 1995 and 1996. For
the 1997 calendar year through the end of November 1997, only one area of the country had
experienced an exceedance of the standard.
In addition to the substantial decrease in the number of areas where the NAAQS is
exceeded, the severity of the exceedances has also decreased significantly. From 1979 to 1996,
the measured atmospheric concentrations of CO during an exceedance decreased from 20-25
ppm at the beginning of the period to 10-12 ppm at the end of the period. Expressed as a
multiple of the standard, atmospheric concentration of CO during an exceedance was two to
almost three times the standard in 1979. By 1996, the CO levels present during an exceedance
decreased to 10-30% over the 9 ppm standard.
15 A more detailed discussion of secondary organic aerosol can be found in Appendix 1.
16 The NAAQS for CO as defined in 40 CFR Part 50.8 is: "9 parts per million for an 8-hour average
concentration not to be exceeded more than once per year."
24
-------
Unlike the case with ozone and PM, EPA has not made any recent comprehensive
projections of future ambient CO levels and attainment and maintenance of the CO NAAQS.
However, similar to the Congressional requirement for this Tier 2 study, section 202(j) of the
CAA requires a separate study of the need for more stringent Cold CO standards. EPA is
currently conducting this study.
2. Contribution of LDYs/LDTs to Carbon Monoxide Emissions
At the national level, motor vehicle exhaust is estimated to contribute more than three-
fourths of all CO emissions; In cities, 95 percent of all CO emissions are produced by
automobiles. Other sources of CO include industrial processes within large factories, power
plants, and natural sources such as wild fires.
National Carbon Monoxide Emissions
(million short tons)
100000
80000
60000
40000
¦HHHi
:
fmgggmM
; ¦ : : ' - ¦¦¦ :¦: .-i.: , ,
1990 1993
1996
1999 2000 2002 2005 2007 2008 2010
Calendar Year
¦ Other
Sources
~ Non-Road
Vehicles
®On-Road
Vehicles
Exceedences of the CO NAAQS over the past three years tended to occur during winter
months of the year. This may indicate that further reductions in emission standards should be
directed towards emissions during cold weather ("cold CO standards," which apply at
temperatures of 15 to 25 degrees Fahrenheit), rather than warm weather (Tier 1 CO standards,
which apply at temperatures of 68-86 degrees Fahrenheit). However, as many of the CO
nonattainment areas are in the southern part of the U.S., more stringent "warm weather CO"
standards should not be ruled out at this time.
25
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J. Air Toxic Emissions from Motor Vehicles
The Clean Air Act lists 188 hazardous air pollutants (HAPs) or air toxics requiring EPA
evaluation and regulation (see CAA Section 112). The measurable health effects of exposure to
air toxics include not only cancer, but also non-cancer effects, such as immunological,
neurological, reproductive, developmental, and respiratory effects. Usually cancer incidence is
chosen to measure the problem since non-carcinogenic end points are much more difficult to
relate to specific toxic emissions.
EPA is developing an Integrated Urban Air Toxics Strategy, to be finalized by the end of
1998. The strategy will list certain area source categories of HAP emissions for later regulation
under section 112(d) and will reduce the incidence of cancer attributable to exposure to HAPs
emitted by stationary sources by not less than 75 percent. Another goal, per section 202(1) of the
Clean Air Act, is to develop cost-effective standards for motor vehicles and their fuels for at least
benzene and formaldehyde.
Mobile sources contribute significantly to only a small subset of the 188 HAPs. In 1993,
EPA published the Motor Vehicle-Related Air Toxics Study (MVRATS). This study
comprehensively summarized what was known about motor vehicle-related air toxics, focusing
on carcinogenic risk. Only qualitative discussion of non-cancer effects was included due to the
lack of sufficient health data to quantify these effects. The primary carcinogens examined were
benzene, formaldehyde, 1,3-butadiene, acetaldehyde and diesel particulate matter. Roughly 8-
9% of total VOC emissions from gasoline vehicles consist of benzene, formaldehyde, 1,3-
butadiene, or acetaldehyde. In general, emissions of air toxics from gasoline vehicle exhaust are
expected to decrease proportionately with reductions in VOC emissions. The primary diesel-
related air toxic addressed quantitatively by MVRATS is diesel particulate. The consideration of
Tier 2 particulate emission standards is addressed in more detail in Chapter VI.
26
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CHAPTER IV. ASSESSMENT OF TECHNICAL FEASIBILITY
The purpose of this chapter is to examine the technical feasibility of controlling light-duty
vehicle emissions beyond the level of control provided for by Tier 1 emission standards. This
chapter reviews and describes a variety of technologies capable of reducing emissions from Tier
1 levels. This chapter also estimates the emission reductions of selected technologies.
Automotive emission control technology has made remarkable advances in the past several years
and many of the technologies discussed in this chapter are technically feasible.
Some of the technologies discussed in this chapter, such as improvements to base engine
designs (to reduce engine-out emissions) and advancements in exhaust aftertreatment systems
(improved catalyst designs), are either in production on at least one or more vehicle models or
are in the final stages of development and will likely be introduced in model year (MY) 1999 or
MY2000 vehicles. Other technologies, such as fuel cells, are in earlier stages of development
and are potentially feasible by MY2004.
The next question to be addressed by this study is how cost effective these technologies
are. The cost-effectiveness discussion can be found in Chapter V. Assessment of Cost and Cost
Effectiveness. For illustrative purposes, this chapter will provide a brief discussion of potential
Tier 2 technologies. A more extensive discussion of the various technologies can be found in
Appendix B. Vehicle Technology.
In section 202(i), Table 3, of the CAA, Congress provided specific numerical values for
Tier 2 standards for EPA to consider in this study. Congress also instructed EPA to consider
standards that were different (either more or less stringent) than those specified in the CAA, as
long as such standards were more stringent than the Tier 1 standards. The emission reductions
associated with the selected emission control technologies discussed in this study will be
compared with those required to meet the standards shown in Table 3 of the CAA.
The review of vehicle emission control technology begins with a discussion of the
emission performance of technology found on current Tier 1, National LEV, and California Low
Emission Vehicle (LEV) technology vehicles. The first section also reviews the status and
potential of a number of emission control technologies which could be used to get emission
control beyond Tier 1 standards. The second section describes various technologies that could be
used to reduce vehicle emissions below levels currently incorporated in the National LEV and
California LEV programs. The third section provides a brief overview of the effect fuel sulfur
may have on potential Tier 2 technologies.
27
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A. Currently Feasible Vehicle Emission Control Technology
There have been considerable advances in emission control technology on conventional
vehicles over the past several years. Many of these advances occurred as a result of the standards
incorporated in the California LEV program which are more stringent than Tier 1 levels, i.e.,
Transitional Low Emission Vehicle (TLEV), LEV, and Ultra Low Emission Vehicle (ULEV).
These standards are included in the NLEV program, which will generally require the introduction
of vehicles meeting the LEV standards nationwide in MY2001. In fact, there are already many
vehicles in production, including some federal models, that meet TLEV and LEV standards, and
in some cases, ULEV standards.
Table 4.1 Tier 1, Default Tier 2, and LEV Emission Standards and Certification Levels
for Light Duty Vehicles (LDV)*
50,000 Mile (g/mi)
100,000 Mile (g/mi)
NMHC
CO
NOx
NMHC
CO
NOx
Standard
Tier 1
0.25
3.4
0.4
0.31
4.2
0.60
Tier 2**
-
-
—
0.125
1.7
0.20
LEV
0.075
3.4
0.2
0.09
4.2
0.30
Cert Levels
Tier 1
0.03-0.25
0.47-3.3
0.03-0.40
0.04-0.24
0.6-3.4
0.04-0.60
LEV
0.04-0.06
0.2-1.3
0.06-0.13
0.023-0.078
0.2-1.7
0.07-0.26
* Particulate standards: Tier 1 = 0.08 g/mi (50,000 miles), 0.10 g/mi (100,000 miles)
LEV = 0.08 g/mi (100,000 miles)
** Default Tier 2 standards in Table 3 of the CAA
Certification data in Table 4.1 derives from manufacturer certifications for 1998 LEV-
certified vehicles. As the data show, manufacturers are certifying LEVs with NMHC emissions
and NOx emissions at less than one-third the level of the 100,000 mile standards. Certification
to one-half or more of the standard is more typical. EPA recognizes that this additional margin
gives manufacturers the ability to ensure their LEVs comply with the standards even with in-use
variability and uncertainty of vehicle performance of the newer LEV vehicles, but it also
demonstrates that the technology is feasible to produce vehicles with emissions well below Tier 1
levels. It is quite clear, given current federal and California certification information, that the
technology exists for essentially all conventional vehicles to achieve lower emissions than are
required by Tier 1 standards.17
17 This study focuses on feasible technology that can achieve HC and NOx reductions. Even though
technology relating specifically to CO reductions is not discussed in detail, EPA notes that many of the technologies
used to reduce HC emissions also yield CO reductions as well.
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EPA also analyzed various individual technologies for their ability to provide further
emissions reductions. Improvement in emission controls requires reducing emissions levels
coming out of the engine ("engine-out" emissions) or increasing the efficiency of exhaust
aftertreatment systems. Typically, manufacturers use both approaches when trying to lower
emission levels. Emission reduction improvements for conventional vehicle technology (i.e.,
vehicles equipped with gasoline-fueled engines) come from four main technological areas. These
are improvements in base engine design, more precise air-fuel ratio control, better fuel delivery
and atomization, and continued advances in exhaust aftertreatment. The table below summarizes
technologies that can be used to reduce emissions from Tier 1 vehicles. It is important to point
out that the use of all of the following technologies is not required to further reduce emissions.
The choices and combinations of technologies will depend on several factors, such as cost,
current engine-out emission levels, effectiveness of existing emission control systems and
individual manufacturer preferences. As noted above, with the exception of a few technologies,
many of these technologies are used on at least a few Tier 1, TLEV, LEV and ULEV vehicles
already in production.
Table 4.2 Feasible Technologies for Emission Reductions (Reductions from Tier 1 Levels)
Technology
HC
NOx
Modifications to combustion chamber
3-10%
3-10%
Multiple valves with variable valve timing
30%
3-10%
Increased EGR (including electronic control)
0%
*10%
Improved A/F control (i.e., improved HEGO, improved power-train control
module microprocessor, faster fuel injectors, transient adaptive fuel control
algorithms, dual HEGO, and improved calibration)
10%
20%
UEGO
5%
23-35%
Air/fuel control in individual cylinders
22%
3%
Increased EGR (including electronic EGR)
0%
*10%
Air-assisted fuel injectors
3-10%
0%
Catalyst improvements (thermal stability, washcoat, cell densities)
10%
10%
Increased catalyst loading and volume
10%
20%
Advanced catalyst designs (tri-metal, multi-layered)
20-37%
30-57%
Close-coupled catalysts
50-70%
0-10%
Electrically-heated catalysts
*10%
5-10%
HC adsorbers
*10%
0%
NOTE: In general, these percentages cannot be simply summed to achieve a total emission reduction when more
than one emission control technology is being applied.
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Most of these technologies are either conventional technologies or extensions of
conventional technologies that have been in existence for some time now and have been proven
commercially, and are currently used on at least a few Tier 1, TLEV, LEV, or ULEV vehicles.
EPA is not aware of any potential safety concerns or energy impacts associated with their use.
Again, because these technologies are established technologies, EPA does not feel that any of
these technologies require unique lead time considerations. The primary lead time issue is
development of specific sets of control technology and engine calibrations for individual engine
families and vehicle models. This aspect of lead time will be considered during the Tier 2
rulemaking process.
The following discussion, focusing on technology needed for HC and NOx reductions, is
based on "Low-Emission Vehicle and Zero-Emission Vehicle Program Review", a staff report
published in November, 1996 by the California Air Resources Board (CARB) as part of its
biannual review of the California LEV program, information from the Manufacturers of
Emission Controls Association (MECA) and numerous vehicle manufacturers. EPA also
contracted Energy and Environmental Analysis, Inc. (EEA) to conduct a study evaluating the
potential availability of emission control technology to meet more stringent emission standards
for light-duty vehicles and light-duty trucks. The report is tided "Benefits and Cost of Potential
Tier 2 Emission Reduction Technologies." A detailed discussion of these technologies is
provided in Appendix B. Vehicle Technology.
1. Base Engine Improvements
There are several design techniques that can be used to reduce engine-out emissions,
especially for HC and NOx. The main causes of excessive engine-out emissions are unburned
fuel for HC and high combustion temperatures for NOx. Methods for reducing engine-out HC
emissions include the reducing of crevice volumes in the combustion chamber, reducing the
combustion of lubricating oil in the combustion chamber and developing leak-free exhaust
systems. Leak-free exhaust systems are listed under base engine improvements because any
modifications or changes made to the exhaust manifold can directly affect the design of the base
engine. Base engine control strategies for reducing NOx include the use of "fast burn"
combustion chamber designs with increased exhaust gas recirculation (EGR) and multiple valves
(intake and exhaust) with variable-valve timing.
2. Improvements in Air-Fuel Ratio Control
Modern three-way catalysts require the air-fuel ratio (A/F) to be as close to stoichiometric
operation (the amount of air and fuel just sufficient for nearly complete combustion) as possible.
This is because three-way catalysts simultaneously oxidize HC and CO, and reduce NOx. Since
HC and CO are oxidized during A/F operation slightly lean of stoichiometry, while NOx is
reduced during operation slightly rich of stoichiometry, there exists a very small A/F window of
operation around stoichiometry where catalyst conversion efficiency is maximized for all three
pollutants (less than 1% deviation in A/F or roughly ± 0.15). Thus, it is imperative to maintain
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the A/F ratio within this tight window of stoichiometric operation if emissions are to be further
reduced. In fact, the tighter the A/F ratio can be maintained, the higher the overall three-way
catalyst conversion efficiency that can generally be achieved, resulting in further reductions to
emissions. Therefore, technologies that enhance tighter A/F control can realize significant
reductions in HC, CO, and NOx emissions.
Contemporary vehicles have been able to maintain stoichiometric operation, or very close
to it, by using closed-loop feedback fuel control systems. At the heart of these systems is a single
heated exhaust gas oxygen (HEGO) sensor. The HEGO sensor continuously switches between
rich and lean readings. By attempting to maintain an equal number of rich readings with lean
readings over a given period, the fuel control system is able to maintain stoichiometric operation.
While this fuel control system is capable of maintaining the A/F ratio with the required accuracy
under steady-state operating conditions, the system accuracy is challenged during transient
operation where rapidly changing throttle conditions occur.
In addition to improved HEGO sensor designs, an additional post-catalyst HEGO sensor
can be used for additional fuel control refinements, resulting in a more robust and precise fuel
control system and reductions in HC and NOx. Another technology that can improve A/F control
is the use of an universal exhaust gas oxygen (UEGO) sensor, also known as a "linear oxygen
sensor," in lieu of a conventional HEGO sensor. UEGO sensors are capable of recognizing both
the direction and magnitude of A/F transients since the voltage output is "proportional" with
changing A/F ratio (each voltage value corresponds to a certain A/F), facilitating faster response
of the fuel feedback control system and tighter control of the A/F ratio.
Rich and lean A/F spikes that occur during transient operation can result in high
emissions. Therefore, any technologies that can help the fuel control system better anticipate
these A/F spikes can result in lower emissions. There are several technologies that can help
achieve this, such as controlling the A/F in each individual cylinder, rather than for the entire
engine, and the incorporation of transient adaptive fuel control algorithms that compensate for
component tolerances, component wear, varying environmental conditions, varying fuel
composition conditions, etc., that occur during transient operation. Finally, the use of electronic
throttle control in lieu of conventional mechanical systems, faster response fuel injectors, and a
quicker power-train control module microprocessor can help further tighten A/F control.
3. Improvements in Fuel Atomization
In addition to maintaining a stoichiometric A/F ratio, it is also important that a
homogeneous air-fuel mixture be delivered at the proper time and that the mixture is finely
atomized to provide the best combustion characteristics and lowest emissions. Poorly prepared
air-fuel mixtures, especially after a cold start and during the warm-up phase of the engine, result
in significantly higher emissions of unburned HC, since combustion of the mixture is less
complete. By providing better fuel atomization, more efficient combustion can be attained,
which should aid in improving fuel economy and reducing pollutants. Sequential multi-point
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fuel injection and air-assisted fuel injectors are examples of technologies available for improving
fuel atomization.
Typically, conventional multi-point fuel injection systems inject fuel into the intake
manifold by injector pairs. This means that rather than injecting fuel into each individual
cylinder, a pair of injectors (or even a whole bank of injectors) fires simultaneously into several
cylinders. Since only one of the cylinders is actually ready for fuel at the moment of injection,
the other cylinders) gets fuel at inappropriate times. With this less than optimum fuel injection
timing, fuel puddling and intake manifold wall wetting can occur, both of which can hinder
complete combustion. Sequential injection, on the other hand, delivers a more precise amount of
fuel to each cylinder at the appropriate time. Because of the emission reductions and other
performance benefits "timed" fuel injection offers, sequential fuel injection systems are very
common on today's vehicles and are expected to be incorporated in most, if not all, vehicles
soon.
Another method to further homogenize the air-fuel mixture is through the use of air-
assisted fuel injection. By injecting high pressure air into the fuel injector, and subsequently, the
fuel spray, greater atomization of the fuel droplets can occur. Since achieving good fuel
atomization is difficult when the air flow into the engine is low, air-assisted fuel injection can be
particularly beneficial in reducing emissions at low engine speeds. In addition, industry studies
show that the short burst of additional fuel needed for responsive, smooth transient maneuvers
can be reduced significantly with air-assisted fuel injection due to a decrease in wall wetting in
the intake manifold.
4. Improvements to Exhaust Aftertreatment Systems
Tremendous advancements in exhaust aftertreatment systems have emerged in the last
few years. The advancements in exhaust aftertreatment systems are probably the single most
important area of emission control development. Such advancements allow manufacturers to
more effectively reduce exhaust emissions, both during warmed-up operation as well as right
after a cold start, when the majority of emissions occur. Catalyst manufacturers are progressively
moving to palladium as the main precious metal in automotive catalyst applications.
Improvements to catalyst thermal stability and washcoat technologies allow manufacturers to
place catalysts closer to the engine, thereby increasing the catalyst's light-off time and thus
increasing its emission reduction capability. The design of higher cell densities and the use of
two-layer washcoat applications increases catalyst efficiency. There has also been much
development in HC and NOx absorber technology, which act to trap pollutants during cold starts
and release them after the catalyst is operating effectively. The use of secondary air injection
systems and insulated or dual wall exhaust pipes also contribute to the improvements in exhaust
aftertreatment and reduction in HC emissions. A detailed discussion of these technologies is
provided in Appendix B. Vehicle Technology.
5. Improvements in Engine Calibration Techniques
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One of the most important emission control strategies is not hardware-related. Rather, it
is the software and, more specifically, the algorithms and calibrations contained within the
software that are used in the power-train control module (PCM) which control how the various
engine and emission control components and systems operate. Advancements in software along
with refinements to existing algorithms and calibrations can have a major impact in reducing
emissions. As the PCM becomes more powerful with greater memory capability and speed,
algorithms can become more sophisticated. Advancements in computer processors, engine
control sensors and actuators and computer software, in conjunction with experience in
developing calibrations, allows manufacturers to improve and refine their calibration skills,
resulting in even lower emissions.
Manufacturers have suggested to EPA that perhaps the single most effective method for
controlling NOx emissions will be tighter A/F control which could be accomplished with
advancements in calibration techniques without necessarily having to use advanced technologies,
such as UEGO sensors. Manufacturers have found ways to improve calibration strategies such
that meeting federal cold CO requirements, as well as complying with LEV standards, have not
required the use of additional hardware, such as electrically heated catalysts (EHC) or adsorbers.
Since emission control calibrations are typically confidential, it is difficult to predict what
advancements will occur in the future. It is clear, however, that improved calibration techniques
and strategies are a very important and viable method for further reducing emissions.
6. Technology for Reduction of Particulate Emissions
Particulate emissions from gasoline-fueled vehicles consist of both carbon- and sulfur-
containing compounds. The carbonaceous particulate is produced from both the gasoline fuel and
engine lubricating oil. Available data indicate that particulate emissions are highest during cold
starts and lower during hot starts and warmed up operation. Technology aimed at reducing
gaseous NMHC emissions, such as improved air-fuel ratio control, tends to reduce carbonaceous
particulate emissions, as well. Carbonaceous particulate emission control from gasoline vehicles
will likely accompany required NMHC emission control. The predominant form of sulfur-
containing particulate from motor vehicles is sulfuric acid (commonly referred to as sulfate). This
sulfate is produced in both the engine and the exhaust system by the oxidation of sulfur dioxide.
However, the current approach of operating engines as close to stoichiometric as possible
coupled with advanced three-way catalysts appears to keep sulfate emissions at very low levels.
Therefore, the primary technique available for reducing sulfate emissions is to reduce gasoline
sulfur levels.
Diesel particulate emissions also consist of both carbonaceous and sulfate particulate.
Unlike gasoline emissions, carbonaceous particulate and NMHC emissions from a diesel engine
are not as directly related. Engine-related techniques for reducing particulate emissions include
higher fuel injection pressures, electronic engine control of injection timing, rate and duration
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and turbo charging/aftercooling. Exhaust aftertreatment techniques include the use of an
oxidation catalyst or a trap. The oxidation catalyst primarily reduces the heavy organic portion of
the carbonaceous particulate, which usually represents 30-50% of total carbonaceous particulate
emissions. Traps can reduce both organic and solid carbon particulate and are capable of
controlling 70-90% of carbonaceous particulate emissions.
Diesel-powered LDVs and LDTs produced in the late 1980s were capable of meeting
particulate emission standards in the range of 0.1-0.2 g/mi without the use of exhaust
aftertreatment. One manufacturer also produced some vehicles equipped with traps. A few light-
duty diesel models are being certified to the current Tier 1 standards of 0.1-0.12 g/mi without the
need for aftertreatment.
Sulfate emissions from a diesel engine form primarily in the engine and generally
represent 2% of the total sulfur in the fuel. The primary method to reduce sulfate emissions is to
reduce the sulfur content of diesel fuel. Under some conditions, the use of an oxidation catalyst
or a catalyst-containing trap can increase tailpipe out sulfate emissions.
B. Advanced Technologies
In addition to the technologies described above to reduce emissions from conventional
vehicles, technologies providing even greater reductions are being analyzed and developed.
These technologies are in various stages of development and some of them could be introduced
on ULEVs and zero emission vehicles (ZEV) to meet state and federal programs. Manufacturers
are also developing non-conventional vehicle technologies, in part as a response to the desire for
vehicles with lower emissions than those vehicles currently available or expected in the next few
model years. Many of these technologies could be utilized in the next generation of vehicles sold
nationwide.
California's emission control program has served as the impetus for development of
advanced emissions control technology, and technologies used to meet current stringent
standards in California could also be feasible for introduction nationwide.18 The California LEV
emission control program requires manufacturers to produce ULEV vehicles in order to meet the
18 California proposed more stringent emission control standards in December, 1997. The California LEV
2 program would reduce by 75% the current NOx standard for LEVs and ULEVs and introduce a new category of
standards, the super ULEV (SULEV: NMOG = 0.01 g/mi, CO = 1.0 g/mi, and NOx = 0.02 g/mi). The SULEV
standards are 120,000 mile standards. California is expected to make a final decision regarding the LEV 2 program
in November, 1998. EPA and California are trying to harmonize their programs when possible (e.g., National
LEV). EPA is closely monitoring California's actions regarding its LEV 2 proposal and will determine which parts
of the program, if any, are appropriate to address in the federal rulemaking.
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fleet average NMOG requirements.19 In many instances, manufacturers will use a combination of
the technologies described above to design and produce vehicles which comply with ULEV
standards. As California noted in its November, 1996 staff report, manufacturers may also need
to introduce EHCs on some vehicles where emissions control is more difficult, such as vehicles
with limited underhood space or larger displacement engines. Electrically-heated catalysts use an
auxiliary heating device to bring the catalyst up to its operating temperature more quickly than
typical heating by engine exhaust. One manufacturer announced it has developed a gasoline-
powered vehicle that utilizes advanced engine designs and catalysts to reduce emissions levels to
significantly below ULEV standards. Some manufacturers also chose to produce ULEVs using
engines that burn compressed natural gas. These engines give manufacturers additional
flexibility in designing and producing vehicles that meet the tighter ULEV standards. In general,
these engines are similar to gasoline-powered engines, but have modified fuel delivery and
storage systems. Compressed natural gas (CNG) powered vehicles also have lower evaporative
emissions than gasoline-powered vehicles.
California also requires manufacturers to develop ZEV technology, with widespread
introduction targeted for MY2003. Much of the development effort to date has focused on
electric vehicles, and many manufacturers have already made ZEVs available to consumers and
fleet purchasers. These vehicles use many newer technologies, such as advanced charging and
regenerating systems and vehicle structural design. Battery technology, which has been the
major technical limitation to date, has been and will be the focus of much developmental work.
Improved nickel-metal hydride, sodium nickel-chloride, lithium polymer, and lithium ion
batteries are some of the battery types being developed for use in electric vehicles produced in
the near future.
Manufacturers are also actively developing other non-conventional vehicle propulsion
systems which could emit pollutants at lower rates, possibly even significantly lower, than
current Tier 1 vehicles. While none of these systems are currently available in the United States,
they could be technologically feasible early in the next century. One system utilizes a hybrid
propulsion system, which combines a gasoline or diesel-powered engine with an electric motor
and is optimized to operate at maximum efficiency over changing driving conditions. These
designs can result in very high fuel efficiency and also very low emission levels (a manufacturer
estimates up to one tenth the current levels of HC, CO, and NOx).20
19 The National LEV program does not require ULEVs to be produced for a manufacturer to meet the fleet
average NMOG requirements. However, manufacturers are likely to produce and sell vehicles meeting ULEV
standards under the National LEV program, especially if a manufacturer needs to offset Tier 1 or TLEVs in its fleet
after MY2000 or if a manufacturer produces 50-state ULEV engine families and wants to generate fleet average
NMOG credits.
20 One manufacturer has introduced in Japan a hybrid vehicle which incorporates a gasoline engine and an
electric motor. Emissions are reduced in part by operating the engine under a constant load and thus minimizing
air-fuel ratio changes.
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This type of propulsion is also being developed as part of a joint venture between the
federal government and the domestic auto manufacturers. The Partnership for a New Generation
Vehicle (PNGV) has a design goal of producing production prototypes by 2004 that would
achieve up to 80 miles per gallon with very low emissions. Design work is focusing on hybrid
electric drives, powered by direct-injection drives or fuel cells, advanced batteries, advanced
combustion engines using renewable fuels and petroleum fuels, and increased use of lightweight
materials in vehicle construction. Technologies developed from this process, in addition to being
integrated into a PNGV vehicle, could be used to reduce emissions from vehicles meeting more
stringent standards.
Fuel cells are a promising propulsion system that is being developed for possible
introduction to consumers early in the next century. A fuel cell is an electrochemical device that
generates electricity from a chemical reaction between hydrogen and oxygen. The necessary
hydrogen can either be carried as a compressed gas or extracted from a fuel carried on the
vehicle, such as gasoline or methanol. The electricity produced from a fuel cell drives a traction
motor that in turn drives the wheels. Fuel cell use gives a vehicle long range, good performance,
rapid refueling and low or even zero emission levels.
C. Sulfur's Effect on Tier 2 Technology
The sulfur found in gasoline does not affect engine-out emissions of HC, CO, and NOx,
but it increases exhaust emissions of these pollutants by inhibiting the performance of the
three-way catalyst (TWC). The degree of sulfur inhibition to the catalyst has been shown to be
variable and depends upon both catalyst formulation and operating conditions. (Sulfur inhibition
is very sensitive to A/F ratio.) Sulfur strongly competes with pollutants for "space" on the active
catalyst surface. This limits the efficiency of catalyst systems to convert pollutants. Current
evidence, however, indicates that sulfur is not a permanent catalyst poison like lead (Pb). This
means that increases in emissions caused by high sulfur fuels may be at least partially reversed
once the high sulfur fuel is no longer used. Studies are underway to determine how quickly,
completely, and easily the sulfur will come off the catalyst when the vehicle is refueled with a
low sulfur fuel.
Recent information from the sulfur test programs performed by the Coordinating
Research Council (CRC) and the auto industry, suggests that not only do LEV and Tier 1
vehicles exhibit decreased emissions performance due to fuel sulfur, but the more advanced the
technology, the more sensitive (on a percentage basis) the catalysts are to sulfur. The studies
indicate that increasing sulfur content could more than double NOx emissions and have a less
severe, though noticeable, effect on HC emissions. In addition, vehicle manufacturers claim that
elevated fuel sulfur levels can interfere with the functioning of vehicle onboard diagnostic
systems by triggering the illumination of the vehicle's malfunction light. Any development of
Tier 2 standards will review the effect of sulfur on possible Tier 2 technologies, and possible
ways to reduce such effect. For example, some catalyst formulations show less sulfur sensitivity
than others; EPA will pursue this issue further in an effort to better understand why some
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catalysts respond differently to sulfur. EPA is aware that the American Petroleum Institute
(API), as well as some catalyst manufacturers, are further analyzing this issue. The Agency will
assess appropriate sulfur control programs for commercial fuel and appropriate certification fuel
specifications that are more representative of sulfur levels in commerce, as discussed in Chapter
VI.
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CHAPTER V. ASSESSMENT OF COST AND COST EFFECTIVENESS
The Clean Air Act requires EPA to examine "the need for, and cost effectiveness of,
obtaining further reductions in emissions from light-duty vehicles and light-duty trucks, taking
into consideration alternative means of attaining or maintaining the national primary ambient air
quality standards ..." (emphasis added). As discussed in the previous chapter, technology is
available today to reduce emissions from light duty vehicles well below Tier 1 levels. The
National LEV program assures that passenger cars and light trucks will be produced beginning in
the 1999 model year to LEV levels. The purpose of this chapter is to present information on
costs and cost effectiveness for potential emission control technologies beyond Tier 1
technologies. This includes the cost effectiveness of LEV technologies, as well as technologies
that achieve emission reductions beyond LEV standards. The chapter estimates cost
effectiveness of certain emission reductions without making a determination of the specific
numerical values of potential regulatory standards.
One lesson to be learned from the past 30 years of controlling motor vehicle pollution is
that the costs of future technologies are usually less than originally estimated. The auto industry,
as well as government regulators and outside experts, tend to over-predict future costs. The
actual costs are usually lower than predicted when the technology is manufactured and installed
on mass-produced vehicles. As stated previously, Tier 2 standards cannot be effective until the
2004 model year at the earliest. That is over five model years from the present. Therefore,
although the following cost estimates are EPA's best assessment of the technology discussed in
Chapter IV. Assessment of Technical Feasibility, they may prove to be over-predictions when
viewed several years into the future.
In addition to estimations of cost, this chapter also attempts to quantify the emission
reduction capabilities of these technologies. In this way, the cost effectiveness, in units of dollars
per ton of emissions reduced, can be calculated and compared.
The sources for the emissions reductions and costs of the various emission control
technologies were the EEA report, the CARB report, MECA, API, confidential information from
vehicle manufacturers and EPA technical assessments. Of these sources, only EEA, CARB and
several vehicle manufacturers supplied information on costs. Consequendy, these are the sources
that are primarily used for establishing cost effectiveness.
A. Cost Effectiveness of Low Emission Vehicle Technologies
It is not necessary to incorporate all of the technologies discussed in the previous chapter
in order to produce vehicles capable of emitting below Tier 1 levels. The choices and
combinations of technologies will depend on several factors, such as current engine-out emission
levels, effectiveness of current emission control technologies, and individual manufacturer
preferences.
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As discussed in Chapter IV. Assessment of Technical Feasibility, two of the most
promising emission control strategies for reducing emissions below Tier 1 levels are more
precise air/fuel (A/F) control and improved catalyst designs. One or the other or a combination
of these technologies are, in fact, what manufacturers have indicated they will utilize to achieve
LEV standards under the California or national LEV programs.
A vehicle designed to meet LEV standards will achieve the following emission
reductions relative to Tier 1 vehicles:
Table 5.1 Percent Reduction in Emissions of a LEV Vehicle Compared to Tier 1
Pollutant
Percent Emissions Reduction
NMHC
70%
NOx
50%
In the Regulatory Impact Analysis (RIA) prepared in support of the National LEV
rulemaking, EPA estimated the emission reduction benefits of National LEV vehicles in 49 states
(other than California). The costs in the RIA were based on California Air Resources Board
(CARB) estimates of California LEV (CALEV) program vehicle costs, revised in 1996. As
summarized in the table below, the total net present value HC emission reductions were
estimated to be 28.0 kilograms (kg), while the NOx emission reductions were estimated to be
25.3 kg. The net present value cost was estimated to be $115 per vehicle.
Table 5.2 Emissions Reduction, Cost and Cost
Effectiveness of a LEV Vehicle
Pollutant
Emissions Reduction
(kg/vehicle)
Cost/vehicle
($)
Cost Effectiveness
($/ton)
NMHC
28.0
57.5*
2054.
NOx
25.3
57.5*
2273.
NMHC+NOx
53.3
115.++
2158.
* Cost per vehicle assigned 50% each to NMHC and NOx.
++ After full phase in 2001 LEV cost is estimated to be $95 per vehicle.
As can be seen, the overall cost effectiveness of National LEV vehicles, based on a 1996
estimate, is $2158 per ton. Note that the above analysis uses gasoline-powered passenger cars
certified on California low sulfur gasoline and operated on higher-sulfur Federal gasoline, based
on information available at the time the program was developed and considers year round
emission reductions. EPA expects similar cost effectiveness results had the calculations been
performed for light trucks. In addition, EPA expects that these cost-effectiveness results are
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similar to those for the standards listed in Table 3 of section 202(i). The standards listed in that
table (and consequent emission reductions) are similar to LEV standards. The Table 3 NOx
standard is somewhat more stringent, the Table 3 NMHC standard is somewhat less stringent. In
addition, the technologies expected to be used to meet the Table 3 levels (and consequent costs)
are similar to the technologies expected to meet the LEV standards.
The automakers recently voluntarily agreed to produce LEV vehicles under the National
LEV regulatory framework. Some auto companies have also announced they would produce
certain light-duty trucks to meet LEV standards sooner than they would be required under the
National LEV program. In addition, some companies stated they will voluntarily reduce
emissions from light-duty trucks not included in the National LEV program. EPA's analysis of
the cost effectiveness of future light-duty vehicle emission standards focuses on standards more
stringent than LEV levels.
B. Cost Effectiveness of Technologies Beyond LEVs
The previous chapter presents information on the technical feasibility of achieving
emission levels beyond the LEV standards. A number of these technologies, such as ultra-
precise air-fuel ratio control, increases in catalyst loading or cell density, closer catalyst
proximity to the exhaust manifold, and variable valve timing, are available today. Others are
expected to be available to vehicle manufacturers before 2004. Although there does not exist a
large amount of specific data on the costs of such technologies, this section of the study will
summarize the available information. All of the following percentage emission reductions and
costs are incremental to Tier 1 technologies.
Estimates of emission reductions resulting from increases in catalyst loading and volume
were consistent among the various sources. EEA estimates a benefit of 10% for HC and 20% for
NOx. MECA and several vehicle manufacturers concurred with these estimates. For
improvements to catalyst formulations and substrate designs, the estimates were again a
consensus of 10% for HC and NOx. The benefit of using a close-coupled catalyst were estimated
by various vehicle manufacturers to range up to 70% for HC, and 10% for NOx. Information
from the American Petroleum Institute suggests that for catalysts utilizing tri-metal and multi-
layer designs, emission reductions ranging up to 37% can be achieved for HC and up to 57% for
NOx.
Estimates of emission reductions associated with ultra-precise A/F control vary.
Information from MECA and two vehicle manufacturers suggest that NOx emission benefits can
range up to 70%, while EEA estimated emission reductions of greater than 10% (no upper limit
was provided) for HC and NOx. For the purposes of this study, EPA estimates that the
combination of faster response fuel injectors, a faster PCM microprocessor, improved HEGO
sensor design (i.e., planar design) and the use of dual HEGO sensors and adaptive transient fuel
control would result in emission reductions at least up to 10% for NMHC and 20% for NOx. The
upper range of the estimates from MECA and the two manufacturers are actually higher than this
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estimate, because they believed that an important part of achieving tighter A/F control is the
continued development of more sophisticated calibration strategies used in conjunction with the
above mentioned technology.
Combining the emissions reduction potential of catalyst improvements and more precise
A/F control cited above, EPA estimates that NMHC tailpipe emissions of light-duty vehicles and
trucks produced in the 2004 model year time frame would be 77% less than Tier 1 vehicles. This
would equate to a NMHC emission standard of approximately 0.06 g/mi for LDV/LDT1 (LDT
below 3,450 pounds curb weight). As discussed below, EPA does not believe this is an upper
limit of the capability of future technology to reduce NMHC emissions.
In the case of NOx emissions, the above catalyst improvements and more precise A/F
control were combined with EPA's technical assessment of the potential for improvements in
EGR systems, such as electronically controlled EGR. This analysis shows that NOx emissions
from light-duty vehicles and trucks produced in the 2004 model year would be 80% less than
Tier 1 vehicles. This would equate to a NOx standard of approximately 0.08 g/mi for
LDV/LDT1.
Although the purpose of this study is not to propose Tier 2 emission standards, these
emission reductions can also be compared to those needed to achieve the default Tier 2
standards, listed above in Table 4.1. Applying the 77% and 80% NMHC and NOx reductions,
respectively, to the 100,000-mile Tier 1 standards (also listed in Table 4.1) yields 100,000-mile
emission levels of approximately 0.07 g/mi NMHC and 0.12 g/mi NOx. These levels are below
the default Tier 2 standards, suggesting that the default Tier 2 standards are technically feasible.
Emissions tests used to estimate the potential for catalyst-related technologies were
primarily performed at low sulfur levels (e.g., 30-100 ppm). Because the effectiveness of some
of the above catalyst-related technologies may be adversely affected by fuel sulfur content, the
above emission reductions potentials could be less if vehicles are operated on higher sulfur fuels.
Using these emission reduction factors, EPA estimated in-use emissions performance on
a per vehicle basis to represent a 77% and 80% reduction in NMHC and NOx emissions,
respectively. EPA performed a preliminary cost analysis of these technologies using the sources
cited above as well as EPA's own assessment. The results showed that the cost of additional
technology to achieve the emission reductions above for NMHC and NOx combined is $136 for
LDV/LDT1, and $161 for LDT2/LDT3/LDT4. (See Appendix C. Emission Reductions, Cost and
Cost Effectiveness for details of this analysis.)
With this information it was possible to calculate the cost effectiveness of the selected
technologies that achieve emission reductions beyond LEV levels. This was done using the
above cost factors and emission reduction effectiveness for LDVs and LDTs separately. The
results are shown below:
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Table 5.3 Emissions Reductions, Costs and Cost Effectiveness of Technologies Beyond
LEV and Incremental to Tier 1
Vehicle Class/
Pollutant
Nominal Emission
Level (g/mi)
Emissions
Reduction (g/mi)
Cost per Vehicle
($)
Annual
Cost Effectiveness
($/ton)
LDV/LDT1
NMHC
0.06
0.181
57.33 *
3151.
NOx
0.08
0.422
78.75*
1858.
NMHC+NOx
0.603
136.
2245.
LDT2.3.4
NMHC
0.07**
0.199
69.93*
3212.
NOx
0.14**
0.456
91.35*
1842.
NMHC+NOx
0.653
161.
2256.
* Cost per vehicle assigned 50% each to NMHC and NOx, after assigning EGR cost ($17) to NOx control.
** Standards shown represent LDT2/LDT3. Nominal standards for LDT4 could be 0.09 g/mi for NMHC and 0.22
for NOx.
EPA has also calculated the cost effectiveness of the package of technologies which
would achieve reductions beyond LEV levels as an incremental comparison to the National LEV
program. An "in-effect" finding for this voluntary program was published earlier this year, and
National LEV vehicles will be available nationwide beginning in the 2001 model year. While
EPA believes that the proper cost effectiveness analysis compares control measures against a
Tier 1 baseline, an analysis using a National LEV baseline is illustrative for the purposes of this
study. Using the same methodology as was presented above, the above package of technologies
reduce NMHC plus NOx emissions beyond those levels achieved by the NLEV standards at a
cost of $2400 per ton. This is only marginally higher than the cost effectiveness of these
technologies relative to the Tier 1 standards.
These estimates of the cost effectiveness of Tier 2 technologies do not include any cost
for reducing the sulfur level of commercial gasoline. Since the emission tests used to estimate
the potential for catalyst improvements were primarily performed at low sulfur levels (e.g., <100
ppm and nominally 40 ppm), these cost per ton estimates are most directly applicable when low
sulfur fuel is assumed to be used in both the Tier 1 and Tier 2 cases. The technologies described
above also reduce emissions when higher sulfur fuels are used. However, the potential for
catalyst-related technologies, including improved air-fuel ratio control, can be adversely affected
by fuel sulfur content. This is mitigated by the fact that the baseline Tier 1 emission levels would
be higher with high sulfur fuel and the overall emission reduction is a combination of the
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percentage emission reduction times the baseline emission level. Still, similar cost per ton
estimates assuming the use of high sulfur gasoline may be slightly higher. In the case where the
cost effectiveness of Tier 2 technologies is compared to the NLEV standards, the cost per ton
estimates should be approximately the same at either low or high sulfur fuels, since the effect of
high sulfur levels is affecting both NLEV and Tier 2 technology.
It is important to note that the presentation of these estimates does not imply that EPA
believes these levels of emission reductions are upper limits of future technology. As discussed
in the previous chapter, there are a number of emission control technologies that either have been
demonstrated to date or are expected to be available for use on production vehicles by 2004 that
can achieve emission reductions beyond those discussed above. For purposes of this study, EPA
selected certain technologies for which estimates of emissions performance and costs were
available. EPA expects that other, more effective, technology will be available prior to 2004.
Nonetheless, it appears the cost effectiveness of technology that exists today to reduce emissions
of light-duty vehicles and trucks beyond LEV levels is within the range of other available control
strategies.
C. Comparison to Other Control Strategies
This section discusses the cost effectiveness of other emission control strategies that may
provide alternative means of attaining or maintaining the NAAQS. EPA estimates the cost and
cost effectiveness of specific control measures as part of individual rulemaking. The estimates
are made available for public review and comment before final regulations are promulgated.
Numerous control measures have been put in place since the 1990 Clean Air Act amendments.
A review of national vehicle control measures mentioned in this report showed a range of
cost effectiveness estimates. Regarding motor vehicle controls, EPA estimates of the cost
effectiveness of recently promulgated programs are:
• Tier 1 standards for LDVs and LDTs: $6000 per ton of HC and $1380-1800 per ton of
NOx
• Supplemental FTP (SFTP) standards for aggressive driving: $457-$552 per ton of HC and
$150-$ 172 per ton of NOx
• SFTP standards for emissions with the air conditioning on: $2,050-$2,574 per ton of NOx
• On-board diagnostics (OBD) requirements: $1,974 per ton of HC, $1,974 per ton of
NOx, and $124 per ton of CO
Recent controls required on stationary point sources have been in the same general range.
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The question relevant to this study is, how do the cost effectiveness estimates for
technologies beyond Tier 1 compare with alternative control measures that have not yet been put
in place? The Regulatory Impact Analyses prepared for the recently revised NAAQS contains
the most comprehensive set of cost effectiveness estimates for potential emission control
measures. The RIA included measures for ozone precursors and particulate matter control
ranging from strategies that produce a cost savings up to and more than $10,000 per ton of
pollutant reduced.
The NAAQS analysis indicates that even after known and available control measures are
implemented, there will remain a substantial number of areas that are in need of additional
pollutant reductions in order to attain the new air quality standards. For these emission
reductions, which will need to come from a combination of mobile and stationary sources, the
NAAQS RIA incorporates a cost effectiveness threshold of $10,000 per ton of pollutant reduced.
The analysis documents many current technologies with control costs less than $10,000 per ton
and expects future and emerging technologies to produce similar cost effective control strategies.
The average control cost for measures included in the NAAQS ozone analysis is approximately
$2,600 per ton for NOx and $3,700 per ton for HC reductions.
The following are examples of potential control strategies and the cost per ton estimates
from the NAAQS RIA (incremental cost in 1990$):
• Industrial boilers conversion to natural gas: approximately $2,000 per ton of NOx
removed.
• Marine commercial engines: approximately $6,503 per ton of NOx removed.
• New heavy-duty vehicles powered by natural gas: approximately $2,400 per ton of
NOx avoided.
Based on this review of the NAAQS RIA, which is the best and most recent analyses of
cost effectiveness for a wide range of control measures, it appears that light-duty vehicle
emission standards that are more stringent than Tier 1 would be cost effective relative to the
control measures included in the NAAQS RIA. Further, it appears that technology is known
today that could reduce emission levels of HC and NOx from light-duty vehicles beyond LEV
levels in a cost effective manner. As shown above, it appears to EPA that technology is known
that has the potential to reduce HC emissions to levels at least 77% below Tier 1 levels at a cost
effectiveness of about $3300 per ton. Likewise, it appears that technology is known that has the
potential to reduce NOx emissions to levels at least 80% below Tier 1 levels at about $1800 per
ton, with a combined HC + NOx cost effectiveness of about $2,300 per ton. These cost
effectiveness estimates are well within the range of cost effectiveness of other, alternative control
measures that could be applied to both stationary and mobile sources in the future in order to
attain or maintain the NAAQS. In the above analysis the cost effectiveness on a per ton basis
examines both national control programs and local, regional or seasonal measures.
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As mentioned previously, the above estimates of potential emission reductions from Tier
1 levels (77% HC and 80% NOx) are not meant to imply limits of any future emission standards.
They were selected for analyses in this report to illustrate point estimates of emission reductions
that appear technically feasible and cost effective. EPA expects there are additional control
technologies that are or wiU soon be available that have potential to result in reductions that go
beyond the estimates analyzed here.
The discussion above addresses costs and cost effectiveness of HC and NOx reductions.
It does not include information on carbon monoxide or particulate matter reductions. As
mentioned earlier in this report, EPA is working on a study of the need for more stringent light-
duty vehicle CO standards that would apply at cold temperatures. That study is the appropriate
forum to address issues related to future CO emission requirements. It should be noted, however,
that most of the technology discussed in this report as reducing HC will also cause significant
reductions in CO emissions. The cost estimates presented above for HC-reducing technology
were calculated by assigning the costs to HC or HC + NOx control. If a portion of the costs had
been assigned to account for the expected CO reductions, the HC and NOx cost effectiveness
would appear more favorable.
No cost or cost effectiveness calculations were performed for additional future PM
controls, although Chapter IV. Assessment of Technical Feasibility discussed PM control
technology. The contribution of light-duty vehicles to the overall PM emissions inventory is
small. It may grow in the future, however. A number of auto and engine manufacturers recently
announced their intentions to consider the use of small diesel engines for the light-duty segment,
particularly light trucks and sport utility vehicles. For this reason it is appropriate for EPA to
consider the levels of future PM emission standards for light-duty vehicles as part of the
rulemaking that will be initiated following this study. If EPA decides to propose more stringent
PM standards for future vehicles, a full cost and cost effectiveness analysis will be performed as
part of proposed rulemaking.
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VI. REGULATORY ISSUES
In determining whether Tier 2 standards for LDVs and LDTs are appropriate, there are a
number of important issues that EPA will need to resolve that relate to the broader issues of air
quality, technical feasibility, and cost effectiveness. Seven issues are presented in this chapter:
A) Relative stringency of the Tier 2 LDV and LDT standards
B) Uniform versus separate standards for gasoline and diesel vehicles
C) Evaporative HC emission standards
D) Corporate average emission standards
E) Extended useful life and other ways to improve in-use emission performance
F) Test fuel specifications
G) Fuel sulfur and distillation properties
A. Relative Stringency of LDV and LDT Standards
All LDVs are required to meet the same numerical emission standards according to Clean
Air Act requirements. For example, large luxury cars and small sub-compacts, both used as for
personal transportation, meet the same emission standards. In contrast, EPA and CARB have
historically set higher numerical emission standards for LDTs than LDVs. While this was done in
part due to the larger size and mass of many LDTs, it was also due to their ability to haul cargo.
Higher loads produce higher exhaust temperatures, which require that catalysts be placed further
back from the engine, delaying light-off. Higher loads can also limit use of EGR for NOx
control. Today, mini-vans, small pick-ups, and sport-utility vehicles dominate LDT sales. Full
size pick-ups and vans (those vehicles most likely to be used in commercial applications)
represent less than 30% of total LDT sales. Also, over the past few years, improvements in the
temperature limits of automotive catalysts appear to have reduced the need to set less stringent
LDT emission standards as may have been true in the past.
In addition to the trend of designing LDTs explicitly for passenger transportation, total
LDT sales increased dramatically and now approach total car sales. Because of their numerically
higher emission standards, LDTs have a disproportionate impact on in-use emissions. Using the
modified MOBILE5b model described in Chapter III. Assessment of Air Quality Need, national
LDT emissions of HC and NOx will exceed LDV emissions by 83% and 66% respectively, in the
year 2007.
There are many options available for setting LDT emission standards given a particular
set of LDV standards. Three possible options are:
1) Require LDTs to meet the same numerical emission standards as LDVs, which
would mean setting standards regardless of vehicle use;
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2) Set the LDT performance standards based on use of the same emission control
technology most likely to be used to meet the LDV standards; or
3) Set different standards based on vehicle use.
Option 1 provides the greatest environmental benefit and could be justified based on the
belief that the great majority of LDT use is the same as that of LDVs. Under the current
California LEV standards, requiring LDTs to meet the same emission standards as LDVs would
provide the same emission benefits as reducing the LDV and LDT standards by 50%. (The
details of this analysis are presented in Appendix D.) This option would also most closely lead to
a determination of emission standards based on the expected use of the vehicle. It could,
however, result in higher emission control costs for some LDTs. This option might be
appropriate for those LDTs that were not used primarily for personal transportation.
The second option seeks to impose roughly equivalent emission control technology for
both LDTs and LDVs. LDVs and LDTs would still have marginally different emission standards
to account for the different vehicle weights and payloads, but the types of emission control
technologies found on each vehicle type would not differ as much as current LDVs and LDTs.
The third option may provide manufacturers with an incentive to produce LDTs in lieu of
LDVs if there is a significant difference in standards, though this choice is limited to an extent by
consumer demand. For example, more stringent LDV vehicle standards could be applied
proportionately to LDTs.
Another issue involved in setting LDT emission standards is the classification of LDTs
into weight categories, each potentially with its own set of emission standards. The current LDT
classifications are based on both curb weight and gross vehicle weight rating (GVWR) (see Table
6.1). The higher the curb weight or GVWR, the numerically higher the applicable emission
standards. While recognizing the increasingly more difficult task of meeting a given set of
emission standards with a heavier vehicle, this system also provides an incentive for
manufacturers to add weight to their vehicles in order to bump them up into a heavier
classification. There can also be a fuel consumption penalty associated with this action.
Table 6.1 Federal Light Truck Classifications
Classification
Gross Vehicle Weight
Rating (GVWR), pounds*
Curb Weight,
pounds*
Adjusted Loaded Vehicle
Weight, pounds*
LDT1
0-6000
0-3450
LDT2
0-6000
>3450
LDT3
6001-8500
<5750
LDT4
6001-8500
>5750
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* Curb weight is the weight of the vehicle sitting empty. GVWR is the measure of how much cargo a vehicle can
carry. Literally, GVWR is the maximum allowed weight of the vehicle when it is fully loaded. Adjusted loaded
vehicle weight is the numerical average of the curb weight and the GVWR.
CARB recently proposed a second phase of LEV emission standards for LDVs and LDTs.
As part of this proposal, CARB proposed to require LDVs and LDTs to meet essentially the same
emission standards and to redefine LDTs to include any truck at or below 7000 pounds curb
weight. If this approach were to be used by EPA for nationwide standards, it would move a
significant number of current HDVs into the LDT class. EPA's rulemaking will examine whether
the current divisions of LDTs based on curb weight and GVWR should be changed to use more
appropriate criteria.
B. Uniform Application of Emission Standards
Uniform standards refers to the application of the same emission standards to similar
vehicles regardless of what fuel is utilized. Here, the primary fuel options for conventional
engines are gasoline and diesel fuel. The pollutants of most interest in this section are NOx and
PM exhaust emissions. Both diesel and gasoline vehicles appear to be capable of meeting the
range of possible Tier 2 HC and CO emission standards, so the issue of equivalent standards does
not arise with respect to these pollutants. Therefore, NOx emission standards are discussed first
below, followed by PM emission standards.
1. NOx Standards
Section 202(g) of the CAA provides that light-duty diesels are required to meet less
stringent Tier 1 LDV/LDT NOx standards through model year 2003 than light-duty gasoline
vehicles. For example, diesel LDVs and LDT Is are only required to meet a 1.0 g/mi NOx
standard at 50,000 miles instead of the 0.4 g/mi NOx standard applicable to gasoline-fueled
vehicles. This does not apply in California or to National LEV vehicles certified to TLEV, LEV,
and ULEV standards. Should EPA decide not to promulgate Tier 2 standards, this difference in
standards would expire and both gasoline and diesel vehicles would be required to meet the same
Tier 1 emission standards. The CAA does not mention any continuation of this relaxation in the
context of the Tier 2 standards;. Further, the default Tier 2 emission standards21 apply to both
gasoline and diesel vehicles. While it is clear that Congress intended to ease the NOx standards
21 The default Her 2 emission standards would apply where EPA finds that there is a need for the Tier 2
standards and that such emission controls are feasible and cost effective, but does not promulgate any alternative
Tier 2 standard (see section 202(i)(3)(B) of the CAA). These default standards for LDVs are 0.125 g/mi NMHC,
1.7 g/mi CO and 0.20 g/mi NOx, at 100,000 miles.
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of diesel Tier 1 vehicles through 2003, it also appears that Congress intended this to be a
temporary measure.
Diesel engines are currently used in a small portion of the LDV and LDT fleets.
Therefore, they have little impact on fleet-wide emissions or fuel consumption. Diesels could,
however, comprise a greater fraction of sales in years to come. For example, the diesel engine
has been identified by the Partnership for a New Generation of Vehicles as the most promising
near term technology for high fuel efficiency vehicles. The U.S. government recently committed
significant research funds to promote the development of high-efficiency, low-emissions diesels
for future vehicles sold in the U.S. The target for the NOx emissions of the PNGV vehicle is 0.20
g/mi, or the current California LEV standard, for LDVs and LDTls. However, EPA has
projected in this study (see Chapter V) that emission levels for NOx below 0.20 g/mi are feasible
for gasoline engines. In order to meet such NOx levels, significant development work to diesel
engine and aftertreatment performance would be required.
The selection of the diesel as the near-term PNGV technology is due to its high fuel
efficiency, as compared to gasoline vehicles. When used in the same vehicle, the diesel engine is
more efficient than today's gasoline engine. There is a trend in the automotive marketplace,
however, toward larger, heavier vehicles that also sit higher off the road and are equipped with
4-wheel or all-wheel drive. These features decrease fuel economy. Thus, the diesel engine could
be used to increase the average size and weight of the vehicle fleet while still complying with the
Corporate Average Fuel Economy (CAF£) standards. In this case, fleet average fuel economy
would not increase. Another advantage of the diesel engine is that its fuel produces essentially no
evaporative emissions.
2. Tier 2 Particulate Standards
The CAA set Tier 1 particulate standards of 0.10-0.12 g/mi for LDVs and LDTs at
100,000 miles. These standards were based on the capabilities of diesel engine technology.
Gasoline vehicles can meet much more stringent PM standards (e.g., less than 0.01 g/mi). The
CAA does not include default Tier 2 PM standards, as it does for NMHC, CO and NOx
standards. It directs EPA to consider standards more stringent than the Tier 1 standards to meet
all NAAQS, which include the particulate NAAQS. It is appropriate to consider Tier 2 PM
standards along with those for the three gaseous pollutants.
Diesel LDVs and LDTs emit more PM emissions than gasoline-fueled vehicles, and the
small number of light-duty diesels currently sold makes their overall air quality impact small.
Diesels could become more prevalent in the future, however, and the public health impact of
their particulate emissions could be quite substantial. The primary technical issue is whether to
set Tier 2 particulate standards based on the capability of the gasoline engine and require diesels
to meet this standard in order to be sold or to set a more relaxed standard based on current and
projected diesel technology.
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EPA has not performed a detailed analysis of the capability of diesel engines to meet
stringent PM standards. California recently proposed a 0.01 g/mi PM standard for all LDVs and
LDTs, which would begin phasing in with the 2004 model year. The goals of the Partnership for
a New Generation of Vehicles include a 0.01 g/mi PM target.
In developing the proposed Tier 2 standards, EPA will perform assessments of the
environmental impacts of diesel PM emissions to facilitate resolution of this issue. One
assessment will estimate the ambient levels of PM10 and PM2 5 which would likely occur in urban
areas should substantial numbers of light-duty diesels be sold. This assessment will be
performed for possible Tier 2 PM standards ranging between 0.01 and 0.10 g/mi. EPA will also
assess the personal exposure to diesel PM emissions and project the resultant cancer impact of
this exposure.
In addition, EPA will assess the capability of future diesel engine designs to meet these
standards and whether the environmental impacts are severe enough to require PM standards
below the current capability of diesel engines. The diesel engine is not the only technology that
provides higher fuel efficiency than the current gasoline engine. Direct injection gasoline (GDI)
engines are being developed by a large number of automakers. These engines appear to provide
much of the fuel efficiency improvement available from a diesel engine. EPA will include these
engines in this assessment.
One last issue regarding Tier 2 PM emission standards is whether to establish such
standards only for operation over the traditional FTP driving cycle, or to also establish standards
for emissions during aggressive driving and air conditioner operation. EPA did not establish any
Tier 1 SFTP standards for PM emissions. EPA has not performed any assessments of the costs or
benefits of such standards, but will consider them in developing the proposed Tier 2 standards.
C. Evaporative HC Emission Standards
Evaporative HC emissions from Tier 1 and LEV vehicles exceed exhaust NMHC
emissions in-use. (Evaporative HC emissions as used herein include running losses, hot soak
emissions, diurnal emissions and resting losses.) It may be appropriate to consider tightening the
current evaporative HC emission standards in the process of considering tighter Tier 2 exhaust
emission standards.
CARB recently proposed a "zero evaporative emission" requirement which would
essentially require that evaporative HC emissions be below measurable levels. One manufacturer
recently announced the ability to produce a vehicle with "zero evaporative emissions" in-use.
CARB pointed to this vehicle, as well as to several other emission control technologies, as a
basis for the recently proposed zero-evap standards. These technologies included a second
charcoal canister to trap HC emissions not absorbed by the standard canister, bladder fuel tank
systems, pressurized fuel tanks, pressurized vapor reservoir systems, insulated fuel tanks and
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improved seals for the onboard vapor recovery systems (refueling emission controls). CARB also
pointed out that a number of current vehicles have certification levels of evaporative emissions
that equal less than one-fifth of the current emission standards.
EPA has not assessed the feasibility of tighter evaporative HC standards, nor their cost
and air quality benefit. These assessments will be performed prior to the proposal of the Tier 2
emission standards and will be used to determine whether more stringent evaporative HC
standards should be proposed along with more stringent exhaust emission standards. Should EPA
decide to include evaporative HC standards in its Tier 2 standards proposal, EPA will also
evaluate several new regulatory options for their control to provide the manufacturers greater
compliance flexibility.
D. Corporate Average Tier 2 Standards
The current Tier 1 emission standards apply to each LDV or LDT separately. There is no
flexibility to have some vehicles meet a more stringent and some vehicles meet a less stringent
standard and allow manufacturers to comply with standards based on a fleet average. EPA has,
however, established corporate average emissions standards in other contexts (e.g., heavy-duty
engine standards). The voluntary National LEV program uses a fleet average standard to help
determine manufacturer compliance with the requirements. Also, compliance with CARB's LEV
and proposed LEV-II standards is accomplished on a corporate average basis. CARB and the
National LEV program limit this flexibility somewhat, however, by specifying a limited number
of NMOG emission standards to which individual vehicle models may be certified. NOx
emission standards are directly tied to the specific NMOG emission standard selected for each
vehicle model (i.e., TLEV, LEV, ULEV).
The flexibility of a corporate average standard can encourage the design and production
of vehicles with advanced emission controls, as manufacturers can receive credit for the
additional emission reductions provided by vehicles certified to more stringent emission levels.
Such controls could include such vehicular concepts as gasoline-electric or diesel-electric hybrid
vehicles, electric vehicles and fuel-cell powered vehicles, as well as more optimal combinations
of emission control technologies. It can also facilitate the application of more stringent
standards, because the flexibility of averaging across a product line would allow manufacturers to
meet an overall corporate standard even when their highest emitting vehicles are less able to meet
a stringent standard (e.g., uniform standards for gasoline and diesel powered vehicles).
An additional advantage of averaging and trading systems generally is that they achieve
the target emission reductions at the lowest cost without EPA having to consider the incremental
cost-effectiveness of controls on a vehicle model basis. Without some form of averaging and
trading, it is possible that none of the three options for dealing with LDTs discussed above would
minimize the cost of the emission reductions that could be achieved.
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E. Extended Useful Life and Other Options to Improve In-Use Performance
Section 202(i) of the CAA, in directing EPA to perform this Tier 2 study, also directed
EPA to consider extending the useful lives of the LDV and LDT emission standards. EPA
believes that the purpose of this direction was to emphasize Congress' focus on the reduction of
emissions in-use and not simply by vehicle prototypes or by vehicles at low-mileage. Congress
extended the useful life of the LDV standards from 50,000 miles to 100,000 miles in the 1990
amendments to the CAA, but clearly believed that more might be needed to ensure appropriate
in-use emissions performance.
This focus on in-use emissions is consistent with EPA's focus on ensuring that its
emission standards produce emission reductions in the real world. Examples of this include the
onboard diagnostic (OBD) system requirements, the cold temperature CO standards and the
supplemental Federal Test Procedure (FTP) standards addressing off-cycle vehicle operation.
Extending the useful life of the emission standards is one possible approach to improving in-use
emissions performance. Such an extension would be consistent with marketplace trends toward
longer actual vehicle lives, as was mentioned in Chapter III. Assessment of Air Quality Need.
California has also proposed to extend the useful life of its Phase 2 LEV emission standards for
LDVs and LDTs to 120,000 miles from their current 100,000 miles. (EPA's useful life
requirements for its LDT standards is already 120,000-130,000 miles.)
EPA has not performed assessments of either the cost or in-use emission benefits of this
option. The in-use emission benefits will clearly depend on the baseline level of in-use emission
deterioration, which is being updated in MOBILE6. EPA plans to perform these economic and
environmental assessments to determine if this (or any related) options should be included in the
proposed Tier 2 standards.
F. Test Fuel Specifications
In order for EPA emission standards to produce emission reductions in the real world, the
test procedures used to determine compliance with these standards must be representative of real
world conditions. If test procedures are not representative, increases in emissions in use may not
be discovered in testing and thus mask substantially higher in-use emissions. That was EPA's
rationale behind the recent development of emission standards and test procedures for:
1) Aggressive driving patterns and air conditioning use;
2) Evaporative, running loss and resting loss emissions at high ambient temperatures
and during extended, multi-day soaks; and
3) CO emissions at low ambient temperatures.
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Regarding test fuels, while the current specifications for the certification gasoline are
sufficiently broad to include a wide range of gasoline, including average or typical gasolines, in
practice the composition of the fuel used for emission testing (commonly referred to as
Indolene) has not been representative of commercial gasoline. In particular, both the olefin and
sulfur contents of Indolene tend to be quite low relative to average commercial gasolines. For
example, Indolene tends to have a sulfur content of 100 ppm or less, while commercial gasoline
averages more than 300 ppm sulfur, with some commercial fuels containing 1000 ppm sulfur.
As mentioned above in Chapter III. Assessment of Air Quality Need and Chapter IV.
Assessment of Technical Feasibility, sulfur reduces catalyst efficiency significantly, particularly
for LEVs. Differences between sulfur levels in test and in-use fuels could have a significant
impact on the in-use emissions performance of motor vehicles. EPA believes that it is very
important that the fuel used for emission testing of Tier 2 vehicles be as representative as
possible of commercial gasoline. EPA will review its test procedures to consider more
representative fuel in testing. An issue with respect to sulfur would be whether the emission test
fuel sulfur level should be matched to that of the average commercial gasoline, the worst
commercial gasoline, or the average or worst gasoline sold in a smaller geographic area, such as
the worst ozone nonattainment areas.
G. Gasoline Sulfur
As discussed briefly in Chapter IV. Assessment of Technical Feasibility, the presence of
sulfur in gasoline has an impact on the performance of catalysts and thus on tailpipe emissions.
As catalyst technology has progressed, the sensitivity of catalyst efficiency to sulfur has appeared
to increase. Because the impact of gasoline sulfur on emissions is significant, EPA has started to
analyze the issues associated with a gasoline sulfur control program. This section discusses the
issues that must be considered when evaluating the cost and cost-effectiveness of reducing
gasoline sulfur. A more complete evaluation of these issues, including analyses of the data
available to date, is presented in a recently released Staff Paper on gasoline sulfur.22 This Staff
Paper is part of EPA* s commitment to undertake a parallel process, involving all interested
stakeholders, to determine appropriate measures to address the impact of sulfur on vehicle
performance.
22 "EPA Staff Paper on Gasoline Sulfur Issues," EPA-420-R-98-005, May 1998.
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Sulfur occurs naturally in crude oil and ends up in gasoline as a result of the refining
process. Currently, the sulfur content of both conventional and reformulated gasolines (RFG)
sold nationally average over 300 ppm. Maximum levels may get as high as 1000 ppm in
conventional gasoline and 500 ppm in reformulated gasoline (RFG). California gasoline
averages around 30 ppm, and is capped at a maximum 80 ppm. The oil industry estimates that
beginning in the year 2000, Federal Phase II RFG will average around 150 ppm sulfur, due to the
NOx reduction requirements for summertime RFG.
The amount of sulfur in the gasoline from any refinery depends on a number of factors,
including the amount of sulfur in the crude oil used and the extent and type of processing within
the refinery. Typically, sulfur in gasoline is reduced by hydrotreating certain hydrocarbon
streams. Hydrotreating requires hydrogen, which must be produced in the refinery or purchased
at substantial cost. The cost to the refining industry of reducing gasoline sulfur levels is
impacted by a number of variables and assumptions made when analyzing a control strategy,
including:
• Where would low sulfur gasoline be required? The size of the program (national,
regional, local) will have an impact on the net costs to the refining industry. This is due
to many factors, including the varied capabilities of refineries located in different parts of
the country to produce low sulfur gasoline.
• What level of sulfur reduction would be required? Reduction of sulfur in gasoline
requires the installation of capital equipment as well as increased operating expenses. The
greater the level of reduction, the greater cost per gallon.
• Is the inhibiting effect of sulfur on motor vehicle catalysts reversible? An irreversible
emissions impact could mean that motor vehicles that are fueled with a high sulfur
gasoline may have permanent catalyst damage, and thus higher emissions, even when
refueled on very low sulfur gasoline. This would be a reason for considering a national
sulfur reduction program. In contrast, if the effect were largely or wholly reversible upon
the use of low sulfur gasoline, sulfur reductions could be targeted to those areas most in
need of emission reductions.
• Does sulfur affect motor vehicle onboard diagnostic systems? If high sulfur levels are
found to cause substantial interference with OBD systems, causing illumination of the
malfunction indicator lights, it may be more appropriate to establish a national sulfur
program to avoid such illumination. However, if such illuminations are not substantial or
can be remedied through other means, than a national approach to sulfur control may not
be needed to appropriately address the problem.
There is great interest in determining whether changes can be made to catalyst designs
and fuel control strategies of those vehicles that prove to be highly sensitive to sulfur inhibition.
54
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Presently, there are no catalyst designs that are fully sulfur tolerant. Data from laboratory, engine
dynamometer testing and vehicle fleet studies show that all automotive catalyst designs have
some inhibition in performance resulting from sulfur. EPA will investigate the latest work being
done on the developing of sulfur resistant catalyst technology and attempt to determine the
feasibility, cost, and effectiveness of such technology.
There are many other factors that impact the final costs to the refining industry and
additional issues to be considered. For example, the availability of new technologies to reduce
gasoline sulfur at less cost than current technologies will make it more attractive and less
burdensome to the industry to reduce sulfur levels. However, some refiners, particularly small
refiners, may have difficulty in raising the capital necessary to invest in new equipment. All of
these issues and concerns will be addressed during the processes of evaluating Tier 2 standards
and sulfur control programs.
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Appendix A
FUTURE OZONE NONATTAINMENT PROJECTIONS
A. EPA Ozone NAAQS Analyses
In support of the revised ozone NAAQS, EPA projected future ambient ozone levels in
2010 to estimate the level of potential non-compliance with the revised standards. Baseline ozone
air quality concentrations in 2010 were estimated using a Regional Oxidant Model (ROM)
extrapolation methodology. Baseline in this context means that the only emission controls
presumed were those already implemented or mandated by the CAA, with two exceptions. These
two exceptions were that the projections also included the emission reductions from both the
anticipated regional NOx emission control in the eastern U.S., which is discussed in the next
section, and the National LEV program.
ROM air quality modeling information for 1990 and 2007 was used in combination with
1990 historical ozone air quality monitoring data to develop baseline 2007 ozone air quality for
the 37 Eastern U.S. states. For the Western U.S. states, EPA reviewed available urban scale
modeling. The 2007 predicted air quality was then adjusted to account for 2007/2010 emissions
inventory differences and additional ozone modeling and monitoring information (1993 - 1995
Aerometric Information Retrieval System (AIRS) monitoring data, ROM and Urban Air Shed
Modeling-V (UAM-V) air quality modeling data) to yield 2010 baseline ozone air quality data.
Because this future air quality is based on counties with monitoring data in 1990, the centroid
model was used to develop air quality for non-monitored counties through geographic
interpolation. Initial nonattainment areas for alternative ozone standards were identified based
on these modeled values for counties with ozone monitors in 1990. At the national level, nine
areas were predicted to be in initial nonattainment of the current one-hour ozone standard; an
additional 10 areas (19 total areas) were predicted to violate the 0.08 ppm NAAQS. These 19
areas encompassed a total of 203 counties with a total 1990 population of 78.6 million people.
B. OTAG SIP Call NPRM Analyses
EPA's proposed OTAG SIP Call relied in part upon ozone modeling performed as part of
the OTAG process. The OTAG process projected ozone levels in calendar year 2007. This year
reflects the ozone NAAQS attainment deadline for a number of the severe ozone nonattainment
areas within the OTAG region. OTAG performed baseline modeling which projected ozone
levels in 2007 based on estimates of emissions which would occur in 2007 under established
control programs. Included in the 2007 baseline are the net effects of growth and specific control
programs prescribed by the 1990 Clean Air Act Amendments. The control measures included in
the 2007 baseline are listed in Table A-l.
A-l
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Table A-l. OTAG 2007 Baseline Control Measures
Emission Source Category
Control Programs
UTILITY
Title IV Controls (phase 1 & 2 for all boiler types)
250 Ton PSD and NSPS
RACT & NSR in non-waived nonattainment areas (NAAs)
NON-UTILITY
POINT/OTHER AREA
RACT at major sources in non-waivered NAAs
250 Ton PSD and NSPS
CTG & Non-CTG RACT at major sources in NAAs & in Ozone Transport
Region
OTHER AREA
Two Phases of Consumer & Commercial Products & One Phase of Architectural
Coatings
State 1 & 2 Petroleum Distribution Controls in NAAs
Autobody, Degreasing & Dry Cleaning Controls in NAAs
NONROAD MOBILE
Federal Phase II Small Engine Standards
Federal Marine Engine Standards
Federal HDV (>= 50 hp) Standards - Phase I
Federal RFGII (statutory and opt-in areas)
9.0 RVP maximum elsewhere in OTAG
HIGHWAY MOBILE
Tier 1 LDV and HDV Standards
Federal RFG n (statutory and opt-in areas)
High Enhanced I/M (serious and above areas)
Low Enhanced I/M for rest of OTR
Basic I/M (mandated areas)
Clean Fuel Fleets (mandated areas)
9.0 RVP maximum elsewhere in OTAG
On-board Vapor Recovery
Overall, OTAG estimated that domain-wide emissions of NOx in the 2007 baseline are
approximately 12 percent lower than 1990 while emissions of VOC are approximately 20 percent
lower. The procedures for developing both 1990 and 2007 baseline inventories are described by
Pechan.1 The key findings from comparing the model predictions for the 2007 baseline to the
1990 base case scenario are:
• ozone levels are generally reduced across most of the region, including
nonattainment areas;
• some increases in ozone are predicted in areas where higher economic growth is
expected to occur, especially in the South;
• ozone levels aloft along regional "boundaries" are reduced, but average
concentrations above 100 ppb and peak concentrations above 120 ppb are still
predicted on several days; and
1 See OTAG Emission Inventory Final Technical Report.
A-2
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• ozone concentrations above the 1-hr and/or 8-hr NAAQS may still occur in the
future under similar meteorological conditions in many of the counties currently
violating either or both of these NAAQS.
The 2007 baseline emissions were reduced in an initial set of sensitivity modeling
performed to assess several broad strategy-relevant issues. All of these model runs involved
"across-the-board" emissions reductions (i.e., no source category-specific reductions). Based
upon the findings of the sensitivity runs, OTAG subsequently developed and simulated source-
specific region-wide control strategies in two rounds of modeling. These strategies were derived
from a range of control measures applied to individual source categories of VOC and NOx. The
controls were grouped into various levels of relative "stringency". The round-1 and round-2
modeling consisted of strategies that contained various combinations of controls from the least to
most stringent for each source category.
The round-1 modeling was a "bounding analysis" with runs that ranged from the lowest
level of control on all source categories (Run 1) to the highest level of control on all sources
(Run 2). Runs 3 and 4b were included to isolate the effects of the most stringent OTAG controls
on utilities only, versus this level of control on the other source categories. In the round-2
modeling, eight runs were simulated to examine the relative benefits of progressively increasing
the level of control on utilities, under two alternative levels of control applied to area, nonroad
and mobile sources.
The findings from the round-1 and round-2 OTAG strategy modeling that are particularly
relevant are:
• Clean Air Act programs will likely provide a reduction in ozone concentrations in
many nonattainment areas; however, some areas currently in nonattainment will
likely remain nonattainment in the future and new 8-hr nonattainment and/or
maintenance problem areas may develop as a result of economic growth in some
areas;
• NOx reductions from elevated and low-level sources are both beneficial when
considered on a regional basis; and,
• Further mitigation of the ozone problem will require regional NOx-oriented
control strategies in addition to local VOC and/or NOx controls necessary for
attainment in individual areas.
Because it models a regional control strategy for NOx similar to that proposed in the
Ozone SIP Call NPRM and because control strategies for other sources are generally kept at
Clean Air Act Amendment levels, Run 5 of the Round 2 modeling is a principal focus for both
the current OTAG analyses and the Tier 2 air quality assessment. The controls applied in Run 5
(shown in Table A-2) are believed to be the best current representation in the available modeling
A-3
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of the most likely scenario of control strategies to be in place in the time frame of potential Tier 2
emission standards.
Table A-2. OTAG Round 5 Control Strategies
Mandated CAA controls
Additional controls
UTILITY
* Acid Rain Controls (Phase 1 & 2 for all boiler types)
* RACT & NSR in nonattainment areas (NAAs)
without waivers
~ OTC NOx MOU (Phase II)
• 85 percent reduction from 1990 rate
or rate-base of 0.15 lb/mbtu for all
units, whichever is less stringent
NON-UTILITY
POINT SOURCES
* RACT at major sources in NAAs without waivers
* 250 Ton PSD and NSPS (not modeled)
* NSR in NAAs without waivers (not modeled)
* CTG & Non-CTG RACT at major sources in NAAs
& throughout OTC
* New Source LAER & Offsets for NAAs (not
modeled)
* "9 percent by 99" ROP Measures (VOC or NOx) for
serious and above areas
* NOx Controls based on cost per ton
of reduction (< $1,000 per ton) -
primarily low NOx burner technology
NONROAD
MOBILE
* Federal Phase II Small Engine Standards
* Federal Marine Engine Standards
* Federal HDV (>=50 hp) Standards-Phase 1
* Federal RFGII (statutory and opt-in areas)
* 9.0 RVP maximum elsewhere in OTAG
* "9 percent by 99" ROP Measures(VOC or NOx) for
serious and above areas
* Federal Locomotive Standards
(including rebuilds)
* HD Engine 4 g/bhp-hr Standard
HIGHWAY
MOBILE
* Tier 1 light-duty and heavy-duty Standards
* Federal reformulated gas (RFG II) (statutory and opt-
in areas)
* High Enhanced I/M (serious and above areas)
* Low Enhanced I/M for rest of OTR
* Basic I/M (mandated areas)
* Clean Fuel Fleets (mandated areas)
* 9.0 RVP maximum elsewhere in OTAG
* On board vapor recovery
* National LEV
* Heavy Duty Vehicle 2 g/bhp-hr
Standard
* Federal Test Procedure (FTP)
revisions
* "9 percent by 99" ROP Measures (if
substitute for VOC) in serious and
above areas
OTHER AREA
SOURCE
CONTROLS
* Two Phases of Consumer & Commercial Products &
One Phase of Architectural Coatings
* Stage 1 & 2 Petroleum Distribution Controls-NAAs
* Autobody, Degreasing & Dry Cleaning Controls in
NAAs
* "9 percent by 99" ROP Measures (VOC or
NOx)(serious and above areas)
None
In support of the proposed OTAG SIP Call, EPA developed procedures to project which
counties would exceed the 1-hour and 8-hour ozone standards in 2007 based on 1993-1995
ambient ozone data and the benefits of future emission controls included in the OTAG strategy
Run 5. This approach involved several steps that apply the ozone reductions predicted for Run 5
A-4
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to ambient data to estimate the expected impacts of this strategy on ozone concentrations. In
summary, the steps are:
(1) Calculate 1-hour and 8-hour ozone design values based on 1993-1995 monitoring
data for each county;
(2) Use 1990 and 2007 OTAG model predictions in a relative sense to estimate the
change in 1-hour and 8-hour ozone levels expected as a result of the controls in
Run 5;
(3) Apply the predicted percentage changes in 1-hour and 8-hour ozone to the 1993-
1995 ambient design values to adjust these values to reflect the effects of the
controls in Run 5; and
(4) Compare the adjusted design values to the level of the 1-hour or 8-hour NAAQS
(i.e., 0.12 and 0.08 ppm) to estimate whether the Run 5 controls would provide for
attainment.
This analysis projected that 12 counties in the OTAG area would be expected to remain in
nonattainment with the ozone 1-hour standard after the Run 5 emission controls were applied
described above. These nonattainment counties contribute, in whole or in part, to eight specific
Consolidated Metropolitan Statistical Areas (CMSA) or Metropolitan Statistical Areas (MSA).
For the purpose of this study, a list of metropolitan areas that contain counties projected to have
an 1-hour ozone nonattainment problem was developed and is presented in Table A-3, along with
the 1990 populations of the metropolitan areas. Clearly, while the Run 5 controls are projected
provide significant air quality benefits, the areas remaining in nonattainment and the populations
affected are significant.
A-5
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Table A-3. Areas and Populations Projected to Exceed 1-Hour and 8-Hour Ozone NAAQS after Run 5
Controls (1990 Census Populations)
Metropolitan Area
1-Hour
8-Hour
Atlanta, GA MSA
2,959,500
2,959,500
Baton Rouge, LA MSA
528,261
*
Charlotte-Gastonia-Rock Hill, NC-SC MSA
—
1,162,140
Chicago-Gary-Kenosha, IL-IN-WICMSA
—
8,239,820
Cincinnati-Hamilton, OH-KY-IN CMSA
—
1,817,569
Dallas-Fort Worth, TX CMSA
—
4,037,282
Houston-Galveston-Brazoria, TX CMSA
3,731,029
3,731,029
Manitowoc County, WI (not assigned to a metropolitan area)
82,507
82,507
Memphis, TN-AR-MS MSA
—
1,007,306
Milwaukee-Racine, WI CMSA
1,607,183
1,607,183
Nashville, TN MSA
—
985,026
New Haven-Bridgeport-Stamford-Waterbury-Danbury, CT NECMA
1,631,864
1,631,864
New York-No. New Jersey-Long Island, NY-NJ-CT-PA CMSA
17,830,586
17,830,586
Philadelphia-Wilmington-Atlantic City, PA-NJ-DE-MD CMSA
5,893,019
5,893,019
Pittsburgh, PA MSA
—
2,394,811
St. Louis, MO-IL MSA
—
2,492,348
Washington-Baltimore, DC-MD-VA-WV CMSA
6,726,395
6,726,395
Total Population
40.990.344
62.598.385
* Not projected to be in nonattainment with the NAAQS
EPA also projected that 39 counties in the OTAG area would be expected to remain in
nonattainment with the ozone 8-hour standard after the Run 5 emission controls were applied
described above . These nonattainment counties contribute, in whole or in part, to specific
Consolidated Metropolitan Statistical Areas or Metropolitan Statistical Areas. The resulting list
of metropolitan areas that contain counties projected to have an 8-hour ozone nonattainment
problem are presented in Table A-3, along with the population of the metropolitan area. As can
be seen, there are significantly more projected ozone nonattainment areas in 2007 under the 8-
hour ozone standard than under the 1-hour standard.
At least three caveats apply to these ozone projections. First, these projections are based
on air quality data from 1993-95. The data from this period will not be the basis for
nonattainment area designations for the 8-hour ozone standard. Those designations will be made
in the 2000 time frame and will be based on the most recent air quality data available at that time
(1997-1999). Therefore, while EPA expects that the vast majority of new counties will attain as
a result of the SIP Call regional NOx control strategy, the number of new counties may be more
or less than the number indicated above.
A-6
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Second, the estimate of which counties will attain the 8-hour standard is based on the
specific assumptions made by the OTAG Group in Run 5. Because the NOx controls proposed
by EPA in the OTAG NPRM are similar but not identical to those contained in Run 5, the
estimate may change when this rule is final and implemented. Therefore, the estimate of which
areas will attain the standards through the final regional NOx strategy may be higher or lower
than the number indicated above.
Third, the OTAG model only covers the eastern two-thirds of the nation. Specifically,
Arizona and California are not covered. Phoenix and numerous areas in California were
projected in the ozone NAAQS rule to exceed the 1-hour and 8-hour ozone standards in the
future. While the SIP Call analysis can be considered an update of the ozone NAAQS rule
analysis for the eastern portion of the nation, only the NAAQS rule addressed the western part of
the U.S. Therefore, the NAAQS rule projections for the west need to be added to those of the SIP
Call analysis in order to provide a complete projection of future ozone nonattainment in the U.S.
C. Future Particulate Matter Nonattainment Projections
EPA recently established new NAAQS for particulate matter (62 FR, July 18,1997). EPA
revised the existing NAAQS for inhalable PM (PM10) and established new NAAQS for fine PM
(PM2J). The existing NAAQS for PM10 were a 24-hour average of 150 ng/m3, with one
exceedance allowed per year, and an annual average of 50 pg/m3. The annual average standard
was left unchanged, as was the numerical level of the 24-hour standard. However, compliance
with the 24-hour standard was changed from allowing one exceedance per year to a 99th
percentile level (i.e., a statistical analysis of daily PM10 levels must show that the 99th percentile
is 150 |ig/m3 or less).
The new NAAQS for PM25 have a similar statistical form as the new NAAQS for PM10.
The differences are that the 24-hour standard is 50 ng/m3 (98% percentile level), while the annual
standard is 15 jig/m3.
In support of these new NAAQS, EPA projected future ambient PM levels in 2010 to
estimate the level of potential non-compliance with the new standards. Baseline 2010 emissions
were projected from 1990 by application of sector-specific growth factors (e.g., 1995 Bureau of
Economic Analysis estimates) and Clean Air Act-mandated controls to 1990 base year emissions.
Total 2010 emissions of VOC, NOx, S02 and secondary organic aerosols were estimated to
decrease from 1990 levels; however, emissions of primary PM10 and PM2J were estimated to
increase.
In addition to the 2010 projection just described, future ambient PM levels were also
estimated after implementation of a more stringent S02 emission cap on utilities. This emission
cap is 60% more stringent than the Phase 2 S02 cap under Title IV of the CAA. For the purpose
of the Tier 2 study, the most relevant projections are those prior to implementation of the SOz
A-7
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emission cap. The more stringent S02 emission cap on utilities has not yet been implemented,
and PM emission reductions from the Tier 2 standards could reduce the need for further PM
emission control envisioned in the S02 cap.
Baseline particulate matter air quality concentrations in 2010 were estimated using the
Phase U Climatological Regional Dispersion Model (CRDM). Initial nonattainment counties
(i.e., prior to application of the more stringent S02 emission cap on utilities) for each PM,0 and
PMjj standard were estimated based on these modeled air quality predictions for counties with
PM monitors during 1993 - 1995. At the national level, 45 counties were estimated to be in
nonattainment of the current PM10 standards (50/150- 1 expected exceedance) in 2010, while
only 11 counties were estimated to be in initial nonattainment of the revised PM,0 standards
(50/150- 99th percentile). Before applying the more stringent S02 emission cap, 102 counties
were estimated to violate the selected PM2 5 standard (15/65- 98th percentile) incremental to the
current PM10 standard in 2010.
For the purpose of the Tier 2 study, EPA developed the following list of counties
expected to exceed the revised PML0 NAAQS. Metropolitan areas are shown when the definition
of the current PMi„ nonattainment area consists of the entire CMSA or MSA. Only the county is
shown when the definition of the current PM10 nonattainment area only consists of a county.
Table A-4. Projected PM10 Nonattainment Areas in 2010 and their 1990 populations
State
N/A Area or County
1990 Population
California
Imperial Valley
109,303
Inyo County
18,281
Kings County
101,469
San Bernardino County
1,418,380
San Diego County
2,498.016
South Coast Air Basin
12,443,900
Iowa
Scott County
150,973
Montana
Park County
14,484
Pennsylvania
Pennsylvania County
1,585,577
Texas
Harris County
2,818,199
Washington
Walla Walla County
48,439
Total
22.899.442
A-8
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D. Revisions to MOBILE5b
This section describes the four types of modifications which were made to MOBILE5b. A
more detailed description of the modifications made to MOBILE5b can be found in a separate
EPA report.2
1. In-use Emission Deterioration Rates
Vehicle emissions in-use tend to increase with vehicle age and mileage. This is referred to
as emission deterioration and is often a significant factor in determining the in-use emissions
performance of real-world vehicles.
When MOBILE5 was developed, the latest model vehicles in-use were certified to the
Tier 0 emission standards. The projections of in-use emission deterioration in MOBILE5 for
these vehicles were based on the testing of in-use Tier 0 vehicles which hd not yet been through
an inspection and maintenance (I/M) program. The rate of emission deterioration for Tier 1
vehicles and LEVs had to be projected from emission data on Tier 0 vehicles.
In the process of developing MOBILE6, EPA is reviewing in-use emission data from both
later Tier 0 vehicles and Tier 1 vehicles. EPA believes that the in-use emission deterioration rates
proposed for these vehicles (and LEVs) in MOBILE6 will be significantly lower than those in
MOBILES. However, the proposed MOBHJE6 estimates were not available at the time of this
analysis. In lieu of the MOBILE6 estimates, rates, basic emission rates (zero-mile emissions plus
emission deterioration rates) from California's CALIMFAC model were substituted into
MOBILE5. The CALIMFAC basic emission rates are much lower than those in MOBILE5 and
are consistent directionally with the basic emission rates expected to be used in MOBILE6.
The basic emission rates from CALIMFAC without I/M are plotted versus mileage in
Figures A-l through A-3, along with those from MOBILE5.
2 "Methodology for Modifying MOBILE5b in the Tier 2 Study", EPA Technical Report,
April, 1998.
A-9
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Figure A-l. LDV NMHC Emissioiis: MOBILES vs. T2AT, No I/M
- - M5 Tier 0
- - M5 Tier 1
- -a- - M5 LEV
—T2ATTierO
—B—T2ATTler 1
—a—T2AT LEV
40 60
Thousand Miles
Note: "T2AT" means 'Tier 2 Analysis Tool."
A-10
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Figure A-2. LDV CO Emissions: MOBILES vs. T2AT, No I/M
Thousand Miles
—*—M5 Tier 0
Tier 1
LEV
—9—T2AT Tier 0
—b—T2ATTier 1
—6—72AT LEV
Note: "T2AT' means "Tier 2 Analysis Tool."
A-ll
-------
Figure A-3. LDV NOx Emissioiis: MOBILES vs. T2AT, No I/M
2
0
1
E
w
- - M5 "Tier 0
__b__M5 Tier 1
__a__M5 LEV
o T2AT Tier 0
—b—T2AT Tier 1
—6—T2AT LEV
20
40 60
Thousand Mies
80
100
Note: "T2AT' means 'Tier 2 Analysis Tool."
As can be seen, the CALIMFAC rates for all three types of vehicles are much lower than
those from MOBILE5. The emission factors with I/M are not shown. With I/M, however, the
CALIMFAC emission factors for Tier 0 and 1 vehicles are still much lower than those from
MOBILE5. With enhanced I/M, the CALIMFAC and MOBILES emission estimates for LEVs
are much more similar.
2. Off-cycle Emission Effects and Their Control
"Off-cycle" emissions are those that occur during driving conditions not included in
EPA's historical certification driving cycle, the LA-4 cycle. EPA promulgated emission standards
for two specific off-cycle driving conditions in 1996, which will be effective starting with the
2000 model year. These two conditions are aggressive driving (high speeds and high
accelerations) and driving with the air conditioner on. California implemented similar standards
for vehicles meeting its LEV standards.
MOBILE5 does not include estimates of these off-cycle emissions, nor the effectiveness
of off-cycle emission standards. MOBILE6 will contain such factors. However, as was the case
for emission deterioration, the MOBILE6 off-cycle emission factors are not yet available. For
A-12
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this study, EPA developed estimates of these off-cycle emissions both before and after the
implementation of off-cycle emission standards. These factors are based on EPA emission data
obtained for the development of MOBILES, as well as EPA and CARB analyses associated with
their respective off-cycle emission rules. These off-cycle factors are in the form of multiplicative
factors which are applied to the basic emission rates in MOBILE5b, which are based on emission
measurements over the LA-4 cycle.
The off-cycle factors for a typical high ozone day are shown in Table A-5.
Table A-5. Off-Cycle Adjustment Factors
I HC 1 CO 1 NOx
Prior to O ff-Cycle Emission Control
tier OLDV/LDT1
1.24
2.24
1.70
Tier 0 LDT2/LDT3/LDT4
1.21
2.10
1.68
Tier 1 & LEV LDV/LDT1
1.78
2.90
1.75
tier 1 & LEV LDT2/LDT3/LDT4
1.73
2.73
1.74
After Off-Cycle Emission Control
Tier 1 LDV/LDT1
1.07
1.39
1.22
Her 1 LDT2/LDT3/LDT4
1.08
1.46
1.20
_EV LDV/LDT1
1.03
1.46
1.11
F V T nT7/I TVH/1 .TYTd
10d
1 AH
1 in
As can be seen, the off-cycle emission factors for all types of vehicles prior to off-cycle
emission control are quite substantial for all three pollutants. The implementation of off-cycle
emission controls dramatically reduces the impact of these off-cycle conditions on in-use
emissions. The EPA off-cycle standards eliminate roughly 70-90% of the off-cycle emission
impact for Tier 1 vehicles. The CARB off-cycle standards eliminate roughly 80-95% of the off-
cycle emission impact for LEVs.
3. Effect of Fuel Sulfur on Emissions
In the Draft Study, EPA presented an estimate of the effect of sulfur on emissions from
LEVs based on data gathered from MOBILE5b and the CALIMFAC model. The analysis has
subsequently been revised, and was included in EPA's Staff Paper on Gasoline Sulfur Issues.
For completeness, a summary of that analysis is presented here.
Two test programs evaluating the impact of sulfur on emissions from LEVs and ULEVs
were recently completed by the Coordinating Research Council (CRC) and the auto industry.3
The CRC program consisted of twelve 1997 LEV passenger cars, representing six different
3 CRC is a research organization sponsored by automobile manufacturers and oil
companies.
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models from five different vehicle manufacturers. The vehicles were tested with fuel sulfur
levels of 40 (the baseline level to represent California certification and in-use fuel sulfur levels),
100,150,330, and 600 ppm. The remaining properties of the fuel represented national averages.
The vehicles were first tested in an "as received" condition (average vehicle mileage of 10,000
miles) and with the catalysts bench-aged to simulate 100,000 miles of operation (although the
oxygen sensors were original, low mileage sensors).
The auto industry testing was performed by members of the American Automobile
Manufacturers Association (AAMA) and the Association of International Automobile
Manufacturers (AIAM). The AAMA/AIAM program consisted of 13 production and
production-intent LEV and ULEV LDVs and eight LEV and ULEV light-duty trucks (LDTs). A
total of ten vehicle manufacturers participated in the program. The vehicles were tested at the
same sulfur levels as the CRC program. The other fuel properties were those of California Phase
II certification fuel. All vehicles were equipped with aged components to simulate 100,000
miles.
The results of the CRC and AAMA/AIAM programs have been combined.'1 Table A.6
shows the percent increase in emissions associated with increasing the fuel sulfur level from 40
ppm to 150 ppm and 330 ppm, respectively, for both LDVs and LDTs designed to meet the LEV
and ULEV standards. Only the 100,000-mile data are presented. For comparison, the sulfur
impact on Tier 0 and Tier 1 vehicles, obtained from data generated by the Auto/Oil Air Quality
Improvement Research Program ("Auto/Oil") is also presented in the table.
4 The test results from each pair of LEVs in the CRC test program were averaged and
assumed to represent a single vehicle. The results for vehicles from die same model line and
certified set of emission standards which were tested in both the CRC and AAMA/AIAM test
programs were also averaged and assumed to represent a single vehicle.
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Table A.6 Increase in Emissions with Fuel Sulfur Increases from Baseline (40 ppm) for LEVs and ULEVs
(LDVs and LDTs) and Older Vehicles
[Source: CRC and AAMA/AIAM Test Programs]
Pollutant
NMHC
CO
NOx
Sulfur, ppm
ISO ppm
330 ppm
ISO ppm
330 ppm
150 ppm
330 ppm
LEV and ULEV, LDVs and LDTs
All LDV/LDT1
26.7%
43.0%
58.0%
75.8%
65.7%
136%
All LDT2/LDT3
23.0%
26.4%
12.5%
31.2%
33.7%
65.5%
Tier 1 LDVs
Normal Emitters
—
20.9%
—
21.1%
—
13.6%
Tier 0 LDVs and LDTs
Normal Emitters
5.9%
16.3%
5.7%
15.8%
6.4%
13.8%
High Emitters
-0.6%
-1.6%
4.7%
12.9%
2.8%
7.6%
These results indicate that emission control technologies being utilized on current LEV
and ULEV LDVs are, on average, much more sensitive to sulfur than Tier 0 or Tier 1 technology.
For example, the percentage increases in NOx emissions for LEV and ULEV LDVs are roughly
10 times greater than those for Tier 0 and 1 vehicles. Emissions from the LEV and ULEV LDTs
are also more sensitive than the Tier 0 and Tier 1 vehicles tested earlier, but to a much lesser
extent. The LDTs had a higher level of base emissions on 40 ppm sulfur fuel, which may
indicate that their technology differs less dramatically from the Tier 1 LDVs tested earlier.
4. Characterization of the LDT Fleet
Sales of LDTs have risen steadily over the past several years, significantly increasing
market share and VMT relative to LDVs. As a result, the default VMT mix in MOBILES under-
predicts the LDT share of both the in-use vehicle fleet and VMT. EPA is updating these factors
in MOBILE6, but the updated estimates are not yet available. Therefore, an update of the
contribution of LDTs to the in-use vehicle fleet and VMT was developed for the purpose of this
study.
The basis for the updated LDT registration and mileage distributions, as well as the LDT
fraction of LDV and LDT VMT, was a recently developed EPA model characterizing the growth
in LDT sales and usage (hereafter referred to as the VMT model).5 The LDT VMT fraction was
5 German, John., "VMT and Emission Implications of Growth in Light Truck Sales",
EPA Report.
A-15
-------
further sub-divided between LDTl/LDT2s and LDT3/LDT4's using data from R.L. Polk.6 As the
VMT model also produced a revised registration distribution for LDVs, this was included in the
modified MOBILEE5b model, as well.
The resultant VMT fractions for LDVs and LDTs are shown in Table A-7 below.
Table A-7.
Light Duty VMT Fractions
Year
LDV
LDT1
72
LDT3/4
MOBILE5b
T2AT
MOBILE5b
T2AT
MOBILE5b
T2AT
2000
0.614
0.503
0.191
0.257
0.086
0.122
2005
0.600
0.450
0.197
0.293
0.087
0.139
2007
0.595
0.435
0.199
0.303
0.087
0.144
2010
0.589
0.415
0.201
0.317
0.088
0.150
2015
0.581
0.398
0.204
0.328
0.089
0.156
0S7S
PT"
mm
nm
nn«o
n i5«
As can be seen, the fraction of LDV VMT in the modified MOBILE5b model is much
lower than was projected in MOBILE5b. (The emission factors from the modified MOBILE5b
model are labeled "T2AT" in the chart, which is an acronym for Tier 2 Analysis Tool.) For
example, by 2020, LDVs will represent less than 40% of combined LDV/LDT driving, while
MOBILE5b projected nearly 60%. Most of the growth is in the LDT1 and LDT2 group, which
includes small pick-ups, minivans and smaller sport utility vehicles. (MOBILE5b refers to this
group as LDT1, while MOBILE5b refers to the LDT3/LDT4 group as LDT2. This is a carryover
from the Tier 0 standards, where there were only two categories of LDTs.)
Directionally, the changes in VMT mix and age distribution serve to increase overall
emission inventory estimates relative to MOBILE5b. Since trucks have higher emission rates
than vehicles and older trucks are dirtier than newer trucks, an increase in truck VMT and a
flattened age distribution will increase the relative contribution of older trucks to overall
inventory.
3. LDV/LDT Emissions in Urban Areas
The above modifications to MOB IT ,F,5b affect the projected emission factors of in-use
light-duty vehicles. While the ultimate goal of this section is to project future motor vehicle
emission inventories and ozone impacts, it is first useful to compare the gram per mile emission
estimates from MOBILE5b with and without the above four modifications. Once these emission
factors have been determined, they can be combined with local estimates of VMT for the various
6 Accurex Environmental Corporation, "Update of Fleet Characterization Data for Use in
MOBILE6", Report for EPA, May 1997.
A-16
-------
vehicle classes to develop local emission inventories. From there, airshed models can be used to
assess ozone impacts.
To do this; EPA used MOBILE5b with and without the above mentioned modifications to
estimate motor vehicle emission factors for three sets of local vehicle-related control strategies.
These three control strategies generally represent the range of controls projected to be
implemented in future ozone nonattainment areas in the OTAG and EPA regional ozone
modeling described above. The three strategies are:
1) Federal Phase 2 RFG, National LEV program in 1997 and high enhanced I/M
(applies to 2007 ozone nonattainment areas in the Northeast, such as New York
City, Philadelphia, Washington, D.C. and Baltimore)
2) Federal Phase 2 RFG, National LEV program in 2001 and high enhanced I/M
(applies to 2007 ozone nonattainment areas such as Houston, Chicago, Phoenix,
Milwaukee, and Dallas)
3) Conventional gasoline, National LEV program in 2001 and high enhanced I/M
(applies to 2007 ozone nonattainment areas, such as Atlanta, St. Louis, Charlotte,
Nashville, Pittsburgh, and Cincinnati)
In addition to these three control scenarios, EPA evaluated a fourth scenario indicative of
an area that is both in attainment with the ozone NAAQS and outside of any ozone transport
region. Such an area would not have an I/M program, nor require RFG. However, they would be
part of the National LEV program, as this program applies in all states outside of California
which have not adopted the California LEV program.
MOBILE5b was run for calendar year 2007 for each of these four scenarios to
approximate the emission factors which were used in the regional ozone modeling. Vehicle speed
was assumed to be 24.7 miles per hour (the approximate average in-use speed) and the ambient
temperature range was assumed to be 72-96 °F.
These emission factors only approximate those used in the regional ozone modeling. In
the regional ozone modeling, separate MOBILE5 runs were made for each hour of a several day
ozone transport period. Each run had different ambient temperatures and may have used varying
vehicle speeds and VMT distributions across vehicle classes. Duplicating this methodology was
beyond the scope of this study and, in any event, should not have affected the overall outcome of
the comparison being made herein. The modifications to MOBILE5b described in the previous
section apply at all vehicle speeds and ambient temperatures. Therefore, the relationship between
the MOBILE5b and modified MOBILE5b exhaust emission factors should not be sensitive to the
vehicle speed or ambient temperatures used in the model. The specific inputs used here were
selected to be representative of average in-use vehicle speeds in urban areas and temperatures
occurring on high ozone days.
A-17
-------
Both MOBILE5b and the modified MOBILE5b were run for a range of calendar years
(2000,2005,2007,2010,2015 and 2020) in order to indicate the change in emissions over time,
as well as a direct comparison against MOBILE5b in 2007. Figures A-5 through A-7 present the
NOx, NMHC, and CO emission factors for MOBILE5b with and without the modifications for
the Northeast emission control scenario for all vehicles. The curves shown in the figures are
simple least-square polynomial regressions. The MOBILE5b/Modified MOBILE5b comparison
is very similar for the other two control scenarios which include high enhanced I/M.
A-18
-------
Figure A-5. Fleet-wide NMHC Emissions
OTR NLEV with RFG and I/M
Calendar Year
« Modified
MOBILE5b
A MOBILBb
Roty.
(Modified
MOBQ_E5b)
Roly.
(MOBILBb)
Figure A-6. Fleet-wide CO Emissions
OTR NLEV with RFG and I/M
16.0
14.0
12.0
S
w
10.0
S
©
•mm
J
8.0
F
6.0
a
0
u
4.0
2.0
0.0
« Modified
MOBILBb
A MOBILBb
PDly.
(Modified
MOBILE5b)
¦Ftoty.
(MOBILBb)
2000
2005
2010
Calendar Year
2015
2020
A-19
-------
Figure A-7. Fleet-wide NOx Emissions
OTR NLEV with RFG and I/M
Calendar Year
~ Modified
MOBHE5b
A MOBILE5b
(Modified
MOBILESb)
R)ly.
(MOBILBb)
As can be seen, the modified MOBILE5b model projects that NOx, NMHC, and CO
emissions in 2007 will be roughly 18-15%, 61% and 30% higher, respectively, than as projected
by MOBILE5b. This indicates that the effects of adding off-cycle emissions, an increased sulfur
sensitivity for LEVs and updated LDT usage is greater than the effect of lower in-use
deterioration rates.
Figures A-8 through A-10 present the emission factors for typical ozone attainment areas
outside of ozone transport regions using both the modified and unmodified MOBILE5b models.
In this case, the modified MOBILE5b model projects higher CO and NOx emission factors and
lower NMHC emission factors in 2007 than MOBILE5b. NOx emissions with the modified
MOBILE5b model fall below those of MOBILE5b after roughly 2008. The primary reason for
the differences between this case and the Northeast ozone nonattainment case is the absence of
high enhanced I/M in this case. The MOBILE5b projections for LEV emissions are very
sensitive to the presence of high enhanced I/M. With high enhanced I/M, LEVs essentially meet
their emission standards in-use. Without this degree of I/M, LEVs emit substantially above their
standards.
A-20
-------
Figure A-8. Fleet-wide NMHC Emissions
Non-OTR NLEV without RFG or I/M
2000
« Modified
MOBLE5b
~ MOBLBb
— R>|y.
(Modified
MOBILE5b)
Paly.
(MOBILSb
)
2005
2010
Calendar Year
2015
2020
Figure A-9. Fleet-wide CO Emissions
Non-OTR NLEV without RFG or I/M
Calendar Year
* Modified
MOBLBb
A MOBIL E5b
Poly.
(Modified
MOBIL E5b)
Poly.
(MOBLE5b)
A-21
-------
Figure A-10. Fleet-wide NOx Emissions
Non-OTR NLEV vtithout RFG orl/M
3.0
2.5
OS
0.0 —
2000
« Modified
MOBLBb
A MOBLBb
— My.
(NtodJied
MOBLBb)
— Baly.
(MOBLBb)
2005
2010
Calendar Year
2015
2020
With the lower in-use emission deterioration rates included in the modified MOBILE5b
model, LEVs emit very close to their emission standards even without I/M. Therefore, there is
very little difference in projected LEV emissions between the modified and unmodified
MOBILESb models when high enhanced I/M is present. In this case, the off-cycle, sulfur and
truck-related effects dominate and emissions are higher with the modified model. However,
without high enhanced I/M, the modified model projects much lower in-use emission
deterioration rates for LEVs. These lower deterioration rates dominate the other factors and the
modified model projects lower in-use emissions.
Thus, the modified MOBILE5b model projects higher emissions in ozone nonattainment
areas which were projected to have high enhanced I/M in the OTAG modeling and sometimes
lower, sometimes higher emissions elsewhere. One of the findings of OTAG was that a given
amount of emissions occurring in or near the ozone nonattainment area had a greater ozone
impact than emissions further upwind. The impact of upwind emissions was found to be
significant, just not as significant as local emissions on a ton for ton basis. Given that emissions
in the local ozone nonattainment areas are projected to be much higher with the modified model,
the projected ozone levels in these areas are also likely to be higher, despite the possibility of
lower emissions upwind.
An important factor in determining the impact of Tier 2 emission standards on ambient
ozone is the relative contribution of LDV and LDT emissions in urban ozone nonattainment
A-22
-------
areas. The LDV/LDT inventory contribution will be estimated here for four such areas: New
York City, Chicago, Atlanta, and Charlotte. The first three areas represent the three greatest
ozone air quality challenges in the eastern U.S. according to the OTAG ozone modeling.
Charlotte represents a smaller, but growing area with a growing ozone problem.
VOC and NOX emission inventories for high ozone days were developed as part of the
OTAG modeling. Total emission inventories are available, as well as those for all on-road motor
vehicles. However, separate emission inventories for light and heavy-duty vehicles were not
made available. Because the VMT distributions by vehicle class used in the ozone modeling may
have differed from the MOBILE5b default assumptions used in the previous section, separating
the emissions from the two basic types of vehicles is not straightforward.
EPA estimated separate light and heavy-duty emissions in each of the four areas using a
five step process.
1) A fleet-wide NOX emission factor applicable to the OTAG modeling of each
specific area was determined by dividing the motor vehicle emission inventory by
the total VMT used in developing the OTAG inventory.
2) The split between light and heavy-duty VMT was estimated by adjusting this ratio
until the fleet-wide NOX emission factor from the unmodified MOBILESb run
described above matched that determined in step 1. In performing this match-up,
the distribution of light-duty VMT between LDVs, LDTls, and LDT2s was held
constant, as was the distribution of heavy-duty VMT between gasoline and diesel
vehicles.
3) Updated fleet-wide NMHC and NOX emission factors were estimated using the
vehicle-class specific emission factors from the modified MOBILE5b runs and the
VMT distributions determined in step 2.
4) Updated motor vehicle emission inventories were estimated by multiplying the
OTAG inventories by the ratio of the fleet-wide emission factors determined in
step 3 to the original OTAG emission factor estimated in step 1.
5) The LDV/LDT emission inventories were derived from the total motor vehicle
inventories using the vehicle-class specific emission factors from the modified
MOBILE5b model and the VMT distributions by vehicle class from step 2.
The results of this analysis for the four cities are shown in Tables A-8 through A-10.
Emission inventories are shown for both light-duty and all motor vehicles. These are shown
based on MOBILE5b both with and without modification. Also shown are total VOC, CO and
NOX emission inventories from all sources. The non-motor vehicle emissions were taken
directly from the OTAG Round 2 Run 5 emission inventories. As the non-motor vehicle CO
emission inventories were not available from OTAG, these are not shown below.
A-23
-------
Table A-8. VOC EMISSIONS - OTAG RUN 5 (tons/day)
Metropolitan Area
Emission Model
Motor Vehicles
All
Light-Duty
Total
Sources
\tlanta, GA MSA
MOBILE5b
65
92
389
Modified MOBILE5b
81
109
406
Dharlotte-Gastonia-Rock Hill, NC-SC MSA
MOBILE5b
33
58
235
Modified M0BHE5b
42
67
243
Zhicago-Gary-Kenosha, IL-IN-WICMSA
MOBILESb
107
146
908
Modified MOBILESb
137
176
938
"few York-N. New Jersey-Long Island, NY-NJ-CT-PA CMSA
|MOBILE5b
170
225
1,361
LfnHifipH Mnnn F.Sh
710
971
1 din
Table A-9. CO EMISSIONS - OTAG RUN 5 (tons/day)
Metropolitan Area
Emission Model
Motor Vehicles
All
Sources
Light-Duty
Total
Atlanta, GA MSA
MOBILE5b
591
815
-
Modified MOBILESb
1,160
1,384
-
Zharlotte-Gastonia-Rock Hill, NC-SC MSA
MOBILE5b
204
340
-
Modified MOBILESb
399
535
-
Hhicago-Gary-Kenosha, IL-IN-WI CMSA
MOBILE5b
946
1,220
-
Modified MOBILESb
1,781
2,054
-
"•Jew York-N. New Jersey-Long Island, NY-NJ-CT-
PA CMSA
|MOBILE5b
1,742
2,164
-
MORTT FSh
-
A-24
-------
Table A-10. NOX EMISSIONS • OTAG RUN 5 (tons/day)
Metropolitan Area
Emission Model
Motor Vehicles
All
Sources
Light-Duty
Total
Atlanta, GA MSA
MOBILESb
78
165
394
Modified MOBILE5b
131
218
447
Zharlotte-Gastonia-Rock Hill, NC-SC MSA
MOBILE5b
27
81
185
Modified MOBILE5b
45
100
203
Zhicago-Gary-Kenosha, IL-IN-WICMSA
MOBILE5b
144
263
877
Modified MOBILESb
243
362
977
^ew York-N. New Jersey-Long Island, NY-NJ-CT-1
JA CMSA
[MOBILE5b
257
437
1,204
MORnPSh
H fr",
1 T77
The next two tables show the light-duty motor vehicle contribution to total emissions and
the total motor vehicle contribution to total emissions for VOC and NOX.
Table A-ll. VOC EMISSIONS - CONTRIBUTION TO TOTAL EMISSIONS (%)
Metropolitan Area
Emission Model
Motor Vehicles
Light-Duty
All
Atlanta, GA MSA
MOBILE5b
17%
24%
Modified MOBILE5b
20%
27%
Hharlotte-Gastonia-Rock Hill, NC-SC MSA
|MOBILE5b
14%
25%
(Modified MOBILE5b
17%
27%
-hicago-Gary-Kenosha, IL-IN-WI CMSA
|MOBILE5b
12%
16%
[Modified MOBILE5b
15%
19%
•tew York-N. New Jersey-Long Island, NY--NJ-CT-PA CMSA
|MOBILE5b
12%
17%
l
10®,
A-25
-------
Table A-12. NOX EMISSIONS - CONTRIBUTION TO TOTAL EMISSIONS (%)
Metropolitan Area
Emission Model
Motor Vehicles
Light-Duty | All
\tlanta, GA MSA
MOBILE5b
20%
42%
Modified MOBILE5b
29%
49%
Iharlotte-Gastonia-Rock Hill, NC-SC MSA
tMOBILESb
15%
44%
(Modified MOBILE5b
22%
49%
Ihicago-Gary-Kenosha, IL-EN-WICMSA
MOBILESb
16%
30%
Modified MOBILESb
24%
37%
"Jew York-N. New Jersey-Long Island, NY--NJ-CT-PA CMSA
MOBILE5b
21%
36%
MoHifipH MfYRTT RSh
11%
M%
As can be seen, based on MOBILE5bt the light-duty contribution to total emissions
ranges from 12-17% for VOC and 15-21% for NOx. The light-duty contribution to total
emissions increases to 15-20% for VOC and 22-31% for NOx based on the modified MOBILE5b
model. The contribution of all motor vehicles is roughly 4-11% higher for VOC and 14-29%
higher for NOx. The contribution of LDVs and LDTs to these emission inventories is substantial
and merits further control, to the degree that it is cost effective.
A-26
-------
Appendix B
VEHICLE TECHNOLOGY
The purpose of this appendix is to further expand upon the technical discussion that was
presented in Chapter IV. Assessment of Technical Feasibility. For the purpose of continuity,
some of same text from Chapter IV is included in this appendix.
Vehicle exhaust emissions can be reduced by a number of technologies, but the most
potential for improvement exists in reductions to base engine-out emissions, improvement in air-
fuel ratio control, better fuel delivery and atomization, and continued advances in exhaust
aftertreatment.
The following descriptions provide an overview of the latest technologies capable of
reducing exhaust emissions. The descriptions will also discuss the state of development and
current production usage of the various technologies. It is important to point out that the use of
all of the following technologies is not required to further reduce emissions. The choices and
combinations of technologies will depend on several factors, such as current engine-out emission
levels, effectiveness of existing emission control systems, and individual manufacturer
preferences. As noted above, with the exception of a few technologies, many of these
technologies are used in some Tier 1, TLEV, LEV and ULEV vehicles already in production.
In order to have a more complete understanding of the latest technologies, including the
state of development and current production usage of the various technologies, EPA contracted
Energy and Environmental Analysis, Inc. (EEA), to conduct a study evaluating the potential
availability of emission control technology to meet more stringent emission standards for light-
duty vehicles and light-duty trucks. The report is titled "Benefits and Cost of Potential Tier 2
Emission Reduction Technologies." EPA also used as references, the staff report on "Low-
Emission Vehicle and Zero-Emission Vehicle Program Review," published in November 1996
by the State of California Air Resources Board (CARB), and information from the Manufacturers
of Emission Controls Association (MECA) and numerous vehicle manufacturers.
A. Base Engine Improvements
There are several design techniques that can be used for reducing engine-out emissions,
especially for HC and NOx. The main causes of excessive engine-out emissions are unburned
HCs and high combustion temperatures for NOx. Methods for reducing engine-out HC
emissions include the reduction of crevice volumes in the combustion chamber, reducing the
combustion of lubricating oil in the combustion chamber and developing leak-free exhaust
systems. Leak-free exhaust systems are listed under base engine improvements because any
modifications or changes made to the exhaust manifold can directly affect the design of the base
engine. Base engine control strategies for reducing NOx include the use of "fast burn"
combustion chamber designs, multiple valves with variable-valve timing, and exhaust gas
recirculation.
B-l
-------
1. Combustion Chamber Design
Unbumed fuel can be Crapped momentarily in crevice volumes (the space between the
piston and cylinder wall) before being subsequently released. Since trapped and re-released fuel
can increase engine-out HC, the reduction of crevice volumes is beneficial to emission
performance. One way to reduce crevice volumes is to design pistons with reduced top "land
heights" (distance between the top of the piston and the first piston ring). The reduction of
crevice volume is especially preferable for vehicles with larger displacement engines, since they
typically produce greater levels of engine-out HC than smaller displacement engines. EEA
estimates the emission reduction of reducing crevice volumes in the combustion chamber to 3%-
10% for NMHC, with negligible effects for NOx.
Another cause of excess engine-out HC emissions is the combustion of lubricating oil .
that leaks into the combustion chamber, since heavier hydrocarbons in oil do not oxidize as
readily as those in gasoline. Oil in the combustion chamber can also trap gaseous HC from the
fuel and release it later unburned. In addition, some components in lubricating oil can poison the
catalyst and reduce its effectiveness. To reduce oil consumption, vehicle manufacturers will
tighten tolerances and improve surface finishes for cylinders and pistons, improve piston ring
design and material, and improve exhaust valve stem seals to prevent excessive leakage of
lubricating oil into the combustion chamber. According to CARB and EEA, virtually all
vehicles meeting LEV and ULEV standards, will have to incorporate features to reduce oil
consumption.
As discussed above, engine-out NOx emissions result from high combustion
temperatures. Therefore, the main control strategies for reducing engine-out NOx are designed
to lower combustion temperature. The most promising techniques for reducing combustion
temperatures, and thus engine-out NOx emissions, are the combination of increasing the rate of
combustion, reducing spark advance, and adding a diluent to the air-fuel mixture, typically via
exhaust gas recirculation. The rate of combustion can be increased by using "fast burn"
combustion chamber designs. A fast burn combustion rate provides improved thermal efficiency
and a greater tolerance for dilution from EGR resulting in better fuel economy and lower NOx
emissions. There are numerous ways to design a fast burn combustion chamber. However, the
most common approach is to induce turbulence into the combustion chamber which increases the
surface area of the flame front and thereby increases the rate of combustion, and to locate the
spark plug in the center of the combustion chamber. Locating the spark plug in the center of the
combustion chamber promotes more thorough combustion and allows the ignition timing to be
retarded, decreasing the dwell time of hot gases in the combustion chamber and reducing NOx
formation. According to CARB and EEA, most vehicle manufacturers induce turbulence into the
combustion chamber by increasing the velocity of the incoming air-fuel mixture and having it
enter the chamber in a swirling motion (known as "swirl").
2. Improved EGR Design
B-2
-------
One of the most effective means of reducing engine-out NOx emissions is exhaust gas
recirculation. By recirculating spent exhaust gases into the combustion chamber, the overall air-
fuel mixture is diluted, lowering peak combustion temperatures and reducing NOx. As
discussed above, the use of high swirl, high turbulence combustion chambers can allow the
amount of EGR to be increased from current levels of 15 to 17 percent to levels possibly as high
as 20 to 257 percent, resulting in a IS to 20 percent reduction in engine-out NOx emissions.
Many EGR systems in today's vehicles utilize a control valve that requires vacuum from
the intake manifold to regulate EGR flow. Under part-throttle operation where EGR is needed,
engine vacuum is sufficient to open the valve. However, during throttle applications near or at
wide-open throttle, engine vacuum is too low to open the EGR valve. While EGR operation only
during part-throttle driving conditions has been sufficient to control NOx emissions for most
vehicles in the past, more stringent NOx standards and emphasis on controlling off-cycle
emission levels may require more precise EGR control and additional EGR during heavy throttle
operation to reduce NOx emissions. Many manufacturers now use electronic EGR in place of
mechanical back-pressure designs. By using electronic solenoids to open and close the EGR
valve, the flow of EGR can be more precisely controlled.
CARB projects that all LEV and ULEV vehicles will utilize electronic EGR systems in
lieu of mechanical systems. While most manufacturers agree that electronic EGR gives more
precise control of EGR flow rate, not all manufacturers are using it. Numerous LEV vehicles
certified for the 1998 model year still use mechanical EGR systems, and in some cases, no EGR
at all. Nonetheless, the use of EGR remains a very important tool in reducing engine-out NOx
emissions, whether mechanical or electronic.
3. Multiple Valves and Variable-Valve Timing
Conventional engines have two valves per cylinder, one for intake of the air-fuel mixture
and the other for exhaust of the combusted mixture. The duration and lift (distance the valve
head is pushed away from its seat) of valve openings is constant regardless of engine speed. As
engine speed increases, the aerodynamic resistance to pumping air in and out of the cylinder for
intake and exhaust also increases. By doubling the number of intake and exhaust valves,
pumping losses are reduced, improving the volumetric efficiency and useful power output.
In addition to gains in breathing, the multiple-valve (typically 4-valve) design allows the
spark plug to be positioned closer to the center of the combustion chamber (as discussed above)
which decreases the distance the flame must travel inside the chamber. In addition, the two
streams of incoming gas can be used to achieve greater mixing of air and fuel, further increasing
combustion efficiency which lowers engine-out HC emissions.
7 Some manufacturers have stated that EGR impacts the ability to control net air-fuel ratios tightly due to
dynamic changes in exhaust back pressure and temperature, and that the advantages of increasing EGR flow rates
are lost partly in losses in air-fuel ratio control even with electronic control of EGR. Higher EGR flow rates can be
tolerated by modern engines with more advanced combustion chambers, but EGR cooling may be necessary to
achieve higher EGR flow rates within acceptable detonation limits without significant loss of air-fuel control.
B-3
-------
Even greater improvements to combustion efficiency can be realized by using valve
timing and lift control to take advantage of the 4-valve configuration. Conventional engines
utilize fixed-valve timing and lift across all engine speeds. Typically the valve timing is set at a
level that is a compromise between low speed torque and high engine speed horsepower. At light
engine loads it would be desirable to close the intake valve earlier to reduce pumping losses.
Variable valve timing can enhance both low speed torque and high speed horsepower with no
necessary compromise between the two. Variable valve timing can allow for increased swirl and
intake charge velocity, especially during low load operating conditions where sufficient swirl and
turbulence tend to be lacking. By providing a strong swirl formation in the combustion chamber,
the air-fuel mixture can mix sufficiently, resulting in a faster, more complete combustion, even
under lean air-fuel conditions, thereby reducing emissions. Variable valve technology by itself
may have somewhat limited effect on reducing emissions. Several vehicle manufacturers
estimate emission reductions of 3%-10% for both, NMHC and NOX, but reductions could be
increased when variable valve timing is combined with optimized spark plug location and
additional EGR.
Multi-valve engines already exist in numerous federal and California certified vehicles
and are projected by CARB to become even more common. CARB also projects that in order to
meet LEV and ULEV standards, more vehicles will have to make improvements to the induction
system, including the use of variable valve timing.
4. Leak-Free Exhaust System
Leaks in the exhaust system can result in increased emissions, but not necessarily from
emissions escaping from the exhaust leak to the atmosphere. With an exhaust system leak,
ambient air is typically sucked into the exhaust system by the pressure difference created by the
flowing exhaust gases inside the exhaust pipe. The air that is sucked into the exhaust system is
unmetered and, therefore, unaccounted for in the fuel system's closed-loop feedback control,
resulting in erratic and/or overly rich fuel control. This results in increased emission levels and
potentially poor driveability. In addition, an air leak can cause an oxidation environment to exist
in a three-way catalyst at low speeds that would hamper reduction of NOX and lead to increased
NOX emissions.
Some vehicles currently use leak-free exhaust systems today. These systems consist of an
improved exhaust manifold/exhaust pipe interface plus a corrosion-free flexible coupling inserted
between the exhaust manifold flange and the catalyst to reduce stress and the tendency for
leakage to occur at the joint. In addition, improvements to the welding process for catalytic
converter canning could ensure less air leakage into the converter and provide reduced emissions.
CARB and EEA project that vehicle manufacturers will continue to incorporate leak-free exhaust
systems as emission standards become more stringent.
B. Improvements in Air-Fuel Ratio Control
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Modern three-way catalysts require the air-fuel ratio (A/F) to be as close to stoichiometric
operation (the amount of air and fuel just sufficient for nearly complete combustion) as possible.
This is because three-way catalysts simultaneously oxidize HC and CO, and reduce NOx. Since
HC and CO are oxidized during A/F operation slightly lean of stoichiometry, while NOx is
reduced during operation slightly rich of stoichiometry, there exists a very small A/F window of
operation around stoichiometry where catalyst conversion efficiency is maximized for all three
pollutants (i.e., less than 1% deviation in A/F or roughly ± 0.15). Contemporary vehicles have
been able to maintain stoichiometric, or very close to it, operation by using closed-loop feedback
fuel control systems. At the heart of these systems has been a single heated exhaust gas oxygen
(HEGO) sensor. The HEGO sensor continuously switches between rich and lean readings. By
maintaining an equal number of rich readings with lean readings over a given period, the fuel
control system is able to maintain stoichiometry. While this fuel control system is capable of
maintaining the A/F with the required accuracy under steady-state operating conditions, the
system accuracy is challenged during transient operation where rapidly changing throttle
conditions occur. Also, as the sensor ages, its accuracy decreases.
1. Dual Oxygen Sensors
Many vehicle manufacturers have placed a second HEGO sensor(s) downstream of one or
more catalysts in the exhaust system as a method for monitoring the catalyst effectiveness of the
federally and California mandated on-board diagnostic (OBDII) system. In addition to
monitoring the effectiveness of the catalyst, the downstream sensors can also be used to monitor
the primary control sensor and adjust for deterioration, thereby maintaining precise A/F control
at higher mileages. Should the front primary HEGO sensor, which operates in a higher
temperature environment, begin to exhibit slow response or drift from its calibration point, the
secondary downstream sensor can be relied upon for modifying the fuel system controls to
compensate for the aging effects. By placing the second sensor further downstream from the hot
engine exhaust, where it is also less susceptible to poisoning, the rear sensor is less susceptible to
aging over the life of the vehicle. As a result, the use of a dual oxygen sensor fuel control system
can ensure more robust and precise fuel control, resulting in lower emissions.
Currently, all vehicle manufacturers use a dual oxygen sensor system for monitoring the
catalyst as part of the OBD II system. As discussed above, most manufacturers also utilize the
secondary HEGO sensor for trim (i.e., adjustments to) of the fuel control system. It is anticipated
that all manufacturers will soon use the secondary sensor for fuel trim.
2. Universal Oxygen Sensors
The universal exhaust gas oxygen (UEGO) sensor, also called a "linear oxygen sensor",
could replace conventional HEGO sensors. Conventional HEGO sensors only determine if an
engine's A/F is richer or leaner than stoichiometric, providing no indication of what the
magnitude of the A/F actually is. In contrast, UEGO's are capable of recognizing both the
direction and magnitude of A/F transients since the voltage output of the UEGO is "proportional"
with changing A/F (i.e., each voltage value corresponds to a certain A/F). Therefore,
proportional A/F control is possible with the use of UEGO sensors, facilitating faster response of
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the fuel feedback control system and tighter control of A/F. Some vehicle manufacturers have
estimated emission reductions attributed to the use of a UEGO sensor to be 5% for NMHC and
23%-35% for NOx. EPA feels that the estimate for NMHC seems low.
Although some manufacturers are currently using UEGO sensors, EEA claims that some
manufacturers are of mixed opinion as to the future applicability of UEGO sensors. Because of
their high cost, manufacturers claim that it may be cheaper to improve HEGO technology rather
than utilize UEGO sensors. An example of this is the use of a "planar" design for HEGO
sensors. Planar HEGO sensors have a thimble design that is considerably lighter than
conventional designs. The main benefits are faster heat-up time and sensor response.
3. Individual Cylinder A/F Control
Another method for tightening fuel control is to control the A/F in each individual
cylinder. Current fuel control systems control the A/F for the entire engine or a bank of
cylinders. By controlling A/F for the entire engine or a bank of cylinders, any necessary
adjustments made to fuel delivery for the engine are applied to all cylinders simultaneously,
regardless of whether all cylinders need the that amount of fuel delivered. For example, there is
usually some deviation in A/F between cylinders. If a particular cylinder is rich, but the "bulk"
A/F indication for the engine is lean, the fuel control system will simultaneously increase the
amount of fuel delivered to all of the cylinders, including the rich cylinder. Thus, the rich
cylinder becomes even richer having a potentially negative effect on the net A/F.
Individual cylinder A/F control helps diminish variation among individual cylinders.
This is accomplished by modeling the behavior of the exhaust gases in the exhaust manifold and
using sophisticated software algorithms to predict individual cylinder A/F. Individual cylinder
A/F control requires use of an UEGO sensor in lieu of the traditional HEGO sensor, and requires
a more powerful engine control computer. Some vehicle manufacturers have estimated the
potential emission reductions for individual cylinder A/F control to 22% for NMHC and 3% for
NOx, but EPA feels that based on conversations with other manufacturers, that the estimate for
NOx reduction is too low.
4. Adaptive Fuel Control Systems
The fuel control systems of virtually all current vehicles incorporate a feature known as
"adaptive memory" or "adaptive block learn." Adaptive fuel control systems automatically
adjust the amount of fuel delivered to compensate for component tolerances, component wear,
varying environmental conditions, varying fuel compositions, etc., to more closely maintain
proper fuel control under various operating conditions.
For most fuel control systems in use today, the adaption process affects only steady-state
operation conditions (i.e., constant or slowly changing throttle conditions). Because transient
operating conditions have always provided a challenge to maintaining precise fuel control, the
use of adaptive fuel control for transient operation would be extremely valuable. Accurate fuel
control during transient driving conditions has traditionally been difficult because of inaccuracies
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in predicting the air and fuel flow under rapidly changing throttle conditions. Air and fuel
dynamics within the intake manifold (fuel evaporation and air flow behavior), and the time delay
between measurement of air flow and the injection of the calculated fuel mass, result in
temporarily lean A/F during transient operation. Variation in fuel properties, particularly
distillation characteristics, also increases the difficulty in predicting A/F during transients. These
can all lead to poor drive ability and an increase in NOx emissions.
Adaptive transient fuel control is already being utilized by some manufacturers across
their entire product line. CARB expects the use of adaptive transient fuel control to be
incorporated in virtually all LEVs and ULEVs.
5. Electronic Throttle Control Systems
As mentioned above, the time delay between the air mass measurement and the calculated
fuel delivery presents one of the primary difficulties in maintaining accurate fuel control and
good drive ability during transient driving conditions. With the conventional mechanical throttle
system (a metal linkage connected from the accelerator pedal to the throttle blade in the throttle
body), quick throttle openings can result in a lean A/F spike in the combustion chamber.
Although algorithms can be developed to model air and fuel flow dynamics to compensate for
these time delay effects, the use of an electronic throttle control system, known as "drive-by-
wire" or "throttle-by-wire," may better synchronize the air and fuel flow to achieve proper
fueling during transients (e.g., the driver moves the throttle, but the fuel delivery is momentarily
delayed to match the inertial lag of the increased airflow).
While this technology is currently used in several vehicle models, it is considered
expensive and those vehicles equipped with the feature are expensive higher end vehicles.
Because of its high cost, it is not anticipated that drive-by-wire technology will become
commonplace in the near future.
C. Improvements in Fuel Atomization
In addition to maintaining a stoichiometric A/F ratio, it is also important that a
homogeneous air-fuel mixture be delivered at the proper time and that the mixture is finely
atomized to provide the best combustion characteristics and lowest emissions. Poorly prepared
air-fuel mixtures, especially after a cold start and during the warm-up phase of the engine, result
in significantly higher emissions of unburned HC since combustion of the mixture is less
complete. By providing better fuel atomization, more efficient combustion can be attained,
which should aid in improving fuel economy and reducing emissions. Sequential multi-point
fuel injection and air-assisted fuel injectors are examples of the most promising technologies
available for improving fuel atomization.
1. Sequential Multi-Point
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Typically, conventional multi-point fuel injection systems inject fuel into the intake
manifold by injector pairs. This means that rather than injecting fuel into each individual
cylinder, a pair of injectors (or even a whole bank of injectors) fires simultaneously into several
cylinders. Since only one of the cylinders is actually ready for fuel at the moment of injection,
the other cylinders) gets too much or too little fuel. With this less than optimum fuel injection
timing, fuel puddling and intake manifold wall wetting can occur, both of which can hinder
complete combustion. Sequential injection, on the other hand, delivers a more precise amount of
fuel that is required by each cylinder to each cylinder at the appropriate time. Because of the
emission reductions and other performance benefits "timed" fuel injection offers, sequential fuel
injection systems are very common on today's vehicles and are expected to be incorporated in all
vehicles soon.
2. Air-Assisted Fuel Injectors
Another method to further homogenize the air-fuel mixture is through the use of air-
assisted fuel injection. By injecting high pressure air into the fuel injector, and subsequently, the
fuel spray, greater atomization of the fuel droplets can occur. Since achieving good fuel
atomization is difficult when the air flow into the engine is low, air-assisted fuel injection can be
particularly beneficial in reducing emissions at low engine speeds. In addition, industry studies
have shown that the short burst of additional fuel needed for responsive, smooth transient
maneuvers can be reduced significantly with air-assisted fuel injection due to a decrease in wall
wetting in the intake manifold. EEA estimates a reduction in NMHC emissions of 3%-10% for
air-assisted fuel injection. At least three manufacturers are currently using air-assisted injection
in some of their models.
D. Improvements to Exhaust Aftertreatment Systems
Over the last five years or so, there have been tremendous advancements in exhaust
aftertreatment systems. Catalyst manufacturers are progressively moving to palladium (Pd) as
the main precious metal in automotive catalyst applications. Improvements to catalyst thermal
stability and washcoat technologies, the design of higher cell densities, and the use of two-layer
washcoat applications are just some of the advancements made to catalyst technology. There has
also been much development in HC and NOx absorber technology. The advancements to
exhaust aftertreatment systems are probably the single most important area of emission control
development.
1. Catalysts
As previously mentioned, significant changes in catalyst formulation, size and design
have been made in recent years and additional advances in these areas are still possible.
Palladium is likely to continue as the noble metal of choice for close-coupled applications and
will start to see more use in underfloor applications. Palladium catalysts, however, are less
resistant to poisoning by oil-and fuel-based additives than conventional platinum/rhodium
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(Pt/Rh) catalysts. Based on current certification trends and information from EEA, it is expected
that Pd catalysts will be used in the close-coupled locations while conventional or tri-metal
(Pd/Pt/Rh) catalysts will continue to be used in underfloor applications. Some manufacturers
have suggested that they will use Pd/Rh in lieu of tri-metal or conventional Pt/Rh catalysts for
underfloor applications. As palladium technology continues to improve, it may be possible for a
single close-coupled catalyst to replace both catalysts. If fact, at least one vehicle manufacturer
currently uses a single Pd-only catalyst for one of their models. According to EEA, new Pd-only
catalysts are now capable of withstanding exposure to temperatures as high as 1050°C and, as a
result, can be moved very close to the exhaust manifold to enhance catalyst light-off
performance.
In addition to reliance on Pd and tri-metal applications, catalyst and vehicle
manufacturers have developed "layered" catalysts. Typically, conventional catalysts have a
single washcoat layer applied to the catalyst substrate. The washcoat is the material that contains
the noble metals and numerous other substances such as base metals, stabilizers, etc. By
applying the washcoat in layers (one layer on top of another) and using slightly different
washcoat and noble metal formulations for the various layers, manufacturers have found that
emissions can be further reduced from single layer applications and, in some cases, reduced
significantly.
Manufacturers are developing catalysts with substrates that utilize thinner walls in order
to design higher cell density, low thermal mass catalysts for close-coupled applications
(improves mass transfer at high engine loads and increase catalyst surface area). The cells are
coated with washcoat which contain the noble metals which perform the catalysis on the exhaust
pollutants. The greater the number of cells, the more surface area with washcoat that exists,
meaning there is more of the catalyst available to convert emissions (or that the same catalyst
surface area can be put into a smaller volume). Cell densities of 600 cells per square inch (cpsi)
have already been commercialized, and research on 900 cpsi catalysts has been progressing.
Typical cell densities for conventional catalysts are 400 cpsi.
The largest source for HC continues to be from cold start operation where the
combination of rich A/F operation and the ineffectiveness of a still relatively cool catalyst result
in excess HC emissions. One of the most effective strategies for controlling cold start HC
emissions is to reduce the time it takes to increase the operating temperature of the catalyst
immediately following engine start-up. The effectiveness or efficiency of the catalyst increases
as the catalyst temperature increases. One common strategy is to move the catalyst closer to the
exhaust manifold where the exhaust temperature is greater (a close-coupled catalyst). Another
strategy is to use an electrically-heated catalyst. The EHC consists of a small electrically heated
catalyst placed directly in front of a conventional catalyst. Both substrates are located in a single
can or container. The EHC is powered by the alternator, or solely from the vehicle's battery, or
from a combination of the alternator and battery. The EHC is capable of heating up almost
immediately, assisting the catalyst that directly follows it to also heat up and obtain light-off
temperature (the catalyst temperature where catalyst efficiency is 50%) quickly. Manufacturers
indicate that EHCs will probably only be necessary for a limited number of LEV/ULEV engine
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families, mostly larger displacement V-8s where cold start emissions are difficult to control.
According to EE A, EHCs can reduce NMHC emissions by k 10% and NOx emissions by 5%-
10%, and with continuing improvements in conventional catalyst light-off time, thermal
durability, and overall activity, EHCs will become unnecessary for any vehicle to meet the
LEV/ULJEV standards the next few years.
2. Adsorbers/Traps
Other potential exhaust aftertreatment systems that are used in conjunction with a catalyst
or catalysts, are the HC and NOX adsorbers/traps. Hydrocarbon adsorbers are designed to trap
HC while the catalyst is cold and unable to sufficiently convert the HC. They accomplish this by
utilizing an adsorbing material that holds onto the HC. Once the catalyst is warmed up, the
trapped HC are released from the adsorption material and directed to the fully functioning
downstream three-way catalyst. There are three principal methods for incorporating the adsorber
into the exhaust system. The first is to coat the adsorber directly on the catalyst substrate. The
advantage is that there are no changes to the exhaust system required, but the desorption process
cannot be easily controlled and usually occurs before the catalyst has reached light-off
temperature. The second method locates the adsorber in another exhaust pipe parallel with the
main exhaust pipe, but in front of the catalyst and includes a series of valves that route the
exhaust through the adsorber in the first few seconds after cold start, switching exhaust flow
through the catalyst thereafter. Under this system, mechanisms to purge the trap are also
required. The third method places the trap at the end of the exhaust system, in another exhaust
pipe parallel to the muffler, because of the low thermal tolerance of adsorber material. Again, a
purging mechanism is required to purge the adsorbed HC back into the catalyst, but adsorber
overheating is avoided. Several vehicle manufacturers estimate reductions in HC of greater than
10%.
NOX adsorbers have been researched, but, according to EEA, are generally recognized as
a control for NOx resulting from reduced EGR. They are typically used for lean-burn
applications and are not applicable to engines that attempt to maintain stoichiometiy all the time.
3. Secondary Air Injection
Secondary injection of air into exhaust ports after cold start when the engine is operating
rich, coupled with spark retard, can promote combustion of unburned HC and CO in the exhaust
manifold and increase the warm-up rate of the catalyst. This is one of the oldest and most
established emission control technologies in use, yet over the past 5 to 10 years it has
disappeared from most vehicles, except for those with the largest displacement engines. With
LEV and ULEV requirements, however, secondary air is again becoming a valuable emission
control technology, especially in conjunction with EHCs and adsorbers.
4. Insulated or Dual Wall Exhaust System
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Insulating the exhaust system is another method of furnishing heat to the catalyst to
decrease light-off time. Similar to close-coupled catalysts, the principle behind insulating the
exhaust system is to conserve heat generated in the engine for aiding the catalyst warm-up.
Through the use of laminated thin-wall exhaust pipes, less heat will be lost in the exhaust system,
enabling quicker catalyst light-off. CARB projects that all LEV and ULEV vehicles will utilize
insulted exhaust systems, however, EEA claims that as catalyst technology advances and the
catalyst is moved closer to the engine, the benefits of insulated exhaust systems diminish rapidly.
E. Improvements in Engine Calibration Techniques
Of all the technologies discussed above, one of the most important emission control
strategies is not hardware-related. Rather, it's the software and, more specifically, the algorithms
and calibrations contained within the software that are used in the power-train control module
(PCM) which control how the various engine and emission control components and systems
operate. Advancements in software along with refinements to existing algorithms and
calibrations can have a major impact in reducing emissions. Confidential discussions between
manufacturers and EPA suggest that manufacturers believe emissions can be further reduced by
improving and updating their calibration techniques. As computer technology and software
continues to advance, so does the ability of the automotive engineer to use these advancements in
ways to better optimize the emission control systems. For example, as processors become faster,
it is possible to perform calculations quicker, thus allowing for faster response times for things
such as fuel and spark control. As the PCM becomes more powerful with greater memory
capability, algorithms can become more sophisticated. Manufacturers have found that as
computer processors, engine control sensors and actuators, and computer software become more
advanced, and, in conjunction with their growing experience with developing calibrations, as
time passes, their calibration skills will continue to become more refined and robust, resulting in
even lower emissions.
Manufacturers have suggested to EPA that perhaps the single most effective method for
controlling NOx emissions will be tighter A/F control which could be accomplished with
advancements in calibration techniques without necessarily having to use advanced technologies,
such as UEGO sensors. Manufacturers have found ways to improve calibration strategies such
that meeting federal cold CO requirements as well as complying with LEV standards, have not
required the use of advanced hardware, such as EHCs or adsorbers.
Since emission control calibrations are typically confidential, it is difficult to predict what
advancements will occur in the future, but it is clear that improved calibration techniques and
strategies are a very important and viable method for further reducing emissions.
F. Particulate Emissions
Particulate emissions from gasoline-fueled vehicles consists of both carbon- and sulfur-
containing compounds. The carbonaceous particulate is produced from both the gasoline fuel and
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engine lubricating oil. Available data indicate that particulate emissions are highest during cold
starts, and lower during hot starts and warmed up operation.
Technology aimed at reducing gaseous NMHC emissions tends to reduce carbonaceous
particulate emissions, as well. Examples are modifications to pistons and rings to reduce oil
consumption, close-coupled catalysts to reduce cold start emissions, advanced catalyst
technology and improved air-fuel ratio control. EPA is not aware of any particulate emission
control techniques for gasoline vehicles that is not also being considered for NMHC emission
control. As indicated in the previous chapter, the need to reduce NMHC emissions from gasoline
vehicles appears to be greater than the need to reduce carbonaceous particulate emissions.
Therefore, carbonaceous particulate emission control from gasoline vehicles will likely
accompany required NMHC emission control.
The predominant form of sulfur-containing particulate from motor vehicles is sulfuric
acid (commonly referred to as sulfate). This sulfate is produced in both the engine and the
exhaust system by the oxidation of sulfur dioxide. The amount of sulfate emissions is generally
directly proportional to the amount of sulfur in the fuel, though more than 98% of the fuel sulfur
is emitted as sulfur dioxide. Sulfate emissions can also be affected by the air-fuel ratio of the
engine and the type of catalyst employed. The addition of excess air into an oxidation catalyst
can especially increase sulfate emissions. However, the current approach of operating engines as
close to stoichiometric as possible coupled with advanced three-way catalysts appears to keep
sulfate emissions at very low levels. Therefore, the primary technique available for reducing
sulfate emissions is to reduce gasoline sulfur levels.
Diesel particulate emissions also consist of both carbonaceous and sulfate particulate.
Unlike gasoline emissions, carbonaceous particulate and NMHC emissions from a diesel engine
are not as directly related. Engine-related techniques for reducing particulate emissions include
higher fuel injection pressures, electronic engine control of injection timing, rate and duration,
and turbo charging/aftercooling. Exhaust aftertreatment techniques include the use of an
oxidation catalyst or a trap. The oxidation catalyst primarily reduces the heavy organic portion of
the carbonaceous particulate, which usually represents 30-50% of total carbonaceous particulate
emissions. Traps can reduce both organic and solid carbon particulate and are capable of
controlling 70-90% of carbonaceous particulate emissions.
Diesel-powered LDVs and LDTs produced in the late 1980s were capable of meeting
particulate emission standards in the range of 0.1-0.2 g/mi without the use of exhaust
aftertreatment. One manufacturer also produced some vehicles equipped with traps. A few light-
duty diesel models are currently being certified to the current Tier 1 standards of 0.1-0.12 g/mi
without the need for aftertreatment.
Sulfate emissions from a diesel engine form primarily in the engine and generally
represent 2% of the total sulfur in the fuel. The primary method to reduce sulfate emissions is to
reduce the sulfur content of diesel fuel. The use of an oxidation catalyst or a catalyst-containing
trap can increase sulfate emissions.
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G. Advanced Technology
Thus far, the technology assessment performed in this study focused on conventional
emission control technology for vehicles with gasoline-powered spark ignition engines. There
are a number of advanced technologies in the near horizon that may be capable even further
reductions in emissions. Examples of such technologies are fuel cells, electric vehicles, and
hybrid vehicles.
Fuel cell technology converts such fuels as methanol, natural gas, and gasoline into
electrical energy without generating the pollutants associated with internal-combustion engines.
A fuel cell is made of a thin plastic film sandwiched between two plates. Hydrogen fuel and
oxygen from the air are electrically combined in the fuel cell to produce electricity. Typically,
the only by-products are heat and water vapor. A fuel cell coupled with an electrically powered
drive-train is essentially a quiet, zero-emissions vehicle.
Electric vehicles use electric motors to power the wheels. The electric motors are
powered by packs of batteries stored underneath the vehicle. These vehicles use many newer
technologies, such as advanced charging and regenerating systems as well as vehicle structural
design. Battery technology, which has been the major technical limitation to date, has been and
will be the focus of much developmental work. Improved nickel-metal hydride and lithium ion
batteries are two of the battery types being analyzed for use in electric vehicles produced in the
near future.
Hybrid vehicles are typically powered by a combination of two powertrain systems.
There is usually a low or zero-emitting main powertrain system (e.g., battery-powered electric
motors) that powers the vehicle during steady-state operation, when power demands are low.
When more power is required to accelerate or drive up a hill, an axillary powertrain, usually a
small displacement internal combustion engine, is used. The engine may be diesel-powered, or
some derivative thereof, or an alternative-fuel powered spark ignition engine that is low emitting
Because the engine used is small and low polluting, and the majority of operation uses the non-
engine powertrain, hybrid vehicles have the potential to be very low emitting vehicles.
Appendix C
EMISSION REDUCTIONS, COSTS AND COST EFFECTIVENESS
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The discussion in Appendix B. Vehicle Technology demonstrates that there are numerous
emission control technologies currently available, and, in many cases in use, capable of reducing
emissions below Tier 1 standards. The purpose of this appendix is to expand upon the discussion
in Chapter V. Assessment of Cost and Cost Effectiveness on estimating the emission benefits and
costs associated with emission control technologies capable of reducing emissions below Tier 1
standards.
As discussed earlier, the sources for the benefits and costs of the various emission control
technologies were the EEA report, the CARB report, MECA, API and confidential information
from vehicle manufacturers. Of these sources, only EEA, CARB and several vehicle
manufacturers supplied information on costs. Consequently, these are the sources that are
primarily used for establishing cost effectiveness.
It was also stated earlier that it was not necessary to incorporate all of the technologies
discussed above in order to produce vehicles capable of emitting below Tier 1 levels. The
choices and combinations of technologies will depend on several factors, such as current engine-
out emission levels, effectiveness of current emission control technologies, and individual
manufacturer preferences. It was noted that there are four technological areas that have the
greatest potential for further reducing emissions. For the purposes of this study, EPA will
present estimates for emission benefits and costs using six technological approaches.
• Improved A/F control
• Increased catalyst volume and loading
• Improved catalyst washcoat/substrate designs
• Close-coupled catalyst
• Advanced catalyst design
• Increased EGR rates
These technologies are the main technologies being used by vehicle manufacturers to
meet LEV, and soon, National LEV standards. Although there are currently only a few vehicles
certified to ULEV standards (one of which is a compressed natural gas vehicle), it is anticipated
that these same technologies will be used to meet ULEV requirements as well. The LEV
standards represent a reduction (from Tier 1 standards) of 70% for NMHC and 50% for NOx.
The default Tier 2 standards represent a 50% reduction for NMHC and NOx, respectively, while
the ULEV standards represent a 84% reduction in NMHC and a 50% reduction in NOx. The
emission reduction estimates used in the study, and based on the above six technologies, results
in emission reductions of up to 77% for NMHC and up to 80% for NOx.
For the purposes of this study, EPA projects that tighter A/F ratio control can be achieved
by using a combination of faster response fuel injectors, a faster PCM microprocessor, improved
HEGO sensor design (planar design), the use of dual HEGO sensors and adaptive transient fuel
control, and improved calibration strategies. The estimates of emission benefits for tighter A/F
control through the use of the technologies/strategies vary. Information from MECA and two
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vehicle manufacturers suggest that NOx emission benefits can range from 20% to 70%, while
EE A estimated emission reductions of greater than 10% (no upper limit was provided) for HC
and NOx. They stressed, however, that the upper range of the estimates could only be achieved
through more sophisticated calibration strategies used in conjunction with the above mentioned
technology, and that these strategies were not yet available. Based on this information, EPA
projects that the emission benefits resulting from tighter A/F control to be 10% for NMHC and
20% for NOx.
Estimates for emission benefits of modest increases in catalyst loading and volume were
consistent among the various sources. EEA estimates a benefit of 10% for HC and 10% or
greater for NOx. MECA and several vehicle manufacturers concurred with these estimates.
Thus, EPA projected a benefit of 10% for NMHC and 20% for NOx. For improvements to
catalyst formulations and substrate designs, the estimates were a consensus of 10% for HC and
NOx. Therefore, EPA projected benefits of 10% for both NMHC and NOx. The benefits of
using a close-coupled catalyst were estimated by various vehicle manufacturers to range from
50% to 70% for HC, while estimates for NOx were lower at approximately 10%. EPA projected
the emission benefits for close-coupled catalysts at 50% for NMHC and 10% for NOx. Finally,
information from the American Petroleum Institute suggested that for catalysts utilizing
advanced (tri-metal and multi-layer) designs, emission reductions ranging from 20% to 37% can
be achieved for HC and 30% to 50% for NOx. EPA projected advanced catalyst design emission
benefits of 37% for NMHC and 50% for NOx.
EEA estimated the emission benefit for increased EGR rates (most likely occurring from
the use of electronic EGR) to be 10% or greater for NOx (EGR does not reduce NMHC or CO).
Several vehicle manufacturers also indicated that increased EGR could result in reductions of
10% or greater. Based on this information, EPA has projected NOx emission benefit resulting
from increased EGR rates to be 20%.
The total emission benefits estimated by EPA for tighter A/F control, improvements to
catalyst designs, and increased EGR rates, as mentioned earlier, are up to 77% for NMHC and up
to 80% for NOx. Table C. 1 lists the projected Tier 2 technologies used in the study and their
associated emission reductions.
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Table C.l List of Potential Tier 2 Technologies and Associated Emission Reductions
Technology
Percent Emission Reduction
NMHC
NOx
Improved A/F Control
10%
20%
Increased Catalyst Volume and
Loading
10%
20%
Improved Catalyst
Washcoat/Substrate
10%
10%
Close-Coupled Catalyst
50%
10%
Advanced Catalyst Design
37%
50%
Increased EGR
0%
20%
Total
77%
80%
These estimates were determined by combining the percent emission reduction for the
respective technologies in a multiplicative fashion as seen below.
NMHC = 100% - (100%-10%)*(100%-10%)*(100%-10%)*(100%-50%)*(100%-37%)*(100%-
0%) = 77%
NOx = 100% - (100%-20%)*(100%-20%)*(100%-10%)*(100%-10%)*(100%-50%)*(100%-
20%) = 80%
Table C.2 lists the estimated costs for the respective technologies. Cost estimates are
presented for NMHC, NOx, and NMHC+NOx for LDV and LDT. The costs associated with
each technology are estimates of the manufacturing costs. In assessing the cost to consumers of
emission control equipment, EPA uses a "markup" approach to estimate the retail price
equivalent (RPE) for an emission control component from an estimate of the component's direct
manufacturing cost. Given this methodology, the difference between the RPE and the direct
manufacturing cost includes allocated overhead costs, profit margins, and other indirect cost
estimates at several stages in the production and marketing process. The current RPE factor
being used by EPA is 1.26. The last row of table C.2 is the total estimated retail price equivalent
cost (i.e., total manufacturing cost x RPE factor (1.26)).
C-3
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Table C.2 Estimated Costs for Respective Technologies
Cost per vehicle ($)
LDV/LDT1
LDT 2/3/4
Technology
NMHC
NOx
NMHC+N
Ox
NMHC
NOx
NMHC+N
Ox
Improved A/F Control
$2.65
$2.65
$5.30
$3.05
$3.05
$6.10
Increased Catalyst Volume and
Loading
$6.50
$6.50
$13.00
$7.60
$7.60
$15.20
Improved Catalyst
Washcoat/Substrate
$6.20
$6.20
$12.40
$7.20
$7.20
$14.40
Close-Coupled Catalyst
$10.15
$10.15
$20.30
$10.15
$10.15
$20.30
Advanced Catalyst Design
$20.00
$20.00
$40.00
$27.50
$27.50
$55.00
Increased EGR
$0.00
$17.00
$17.00
$0.00
$17.00
$17.00
Total
$45.50
$62.50
$108.00
$55.50
$72.50
$128.00
Total x RPE (1.26)
$57.33
$78.75
$136.05
$69.93
$91.35
$161.28
All cost estimates for different engine sizes are based on information supplied by EEA,
CARB, MECA, and various vehicle manufacturers. For all of the technologies except increased
EGR, cost estimates are dependant upon engine size. As engine size increases, so do costs.
Engine size was defined as 4-cylinder, 6-cylinder, and 8-cylinder. A single cost estimate for each
technology was developed by weighting the three individual costs by 1996 sales. Because costs
for 4-cylinder technologies is lower, combined with the fact that LDVs have a higher percentage
of 4-cylinder engines, LDVs have lower costs than LDTs. Conversely, because larger engines
have higher costs, and LDTs have a higher percentage of large engines, LDTs have higher costs
than LDVs.
EEA estimated the cost of improved A/F control to be $10.60 for LDV and $12.20 for
LDT, while CARB estimated this action could be done at little or no additional cost, because
they argued that improvements to A/F would only constitute software changes only with no
additional hardware cost. EPA believes that some vehicles would only require software changes
while others will require hardware modifications. Therefore, EPA estimated the cost of A/F
control to be the average of the EEA and CARB estimates, or $5.30 for LDV and $6.10 for LDT.
Note that CARB has estimated that a portion of their ULEV fleet would utilize improved fuel
preparation, such as air-assisted injection, at a cost of $8-12 for such vehicle.
The cost estimates for increased catalyst volume and loading, as well as improvements to
catalyst washcoat and substrate, were taken directly from EEA estimates and were $13.00 for
LDVs and $15.20 for LDTs and $12.40 for LDVs and $15.20 for LDTs, respectively.
C-4
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The cost estimates of $40.00 for LDVs and $55.00 for LDTs for advanced catalyst design
were taken from proprietary information supplied by several vehicle manufacturers.
Cost estimates for close-coupled catalysts came from CARB. They estimated the cost to
be the same for all engine sizes, however, they estimated that a number of Tier 1 vehicles
equipped with 4-cylinder engines already use close-coupled catalysts. Therefore, the incremental
cost for 4-cylinder engines is less than for the larger engines.
Estimates for increased EGR rates came directly from EEA. However, as stated above,
costs for EGR were the same for all engine sizes and were not sales weighted.
Cost Effectiveness Calculation
EPA estimated the lifetime costs and emissions benefits on a per vehicle basis. Cost
effectiveness is represented as the dollar cost per ton of emissions reduced ($/ton). The cost
component, the numerator, is taken directly from the above discussion of vehicle costs, using
$136 per vehicle for LDVs and $161 for LDTs.
Conceptually, the benefit calculation is derived by taking an estimate of in-use emissions
for Tier 1 vehicles and applying the percent reduction estimates of 77% for NMHC and 80% for
NOx. The resulting benefit is thus the difference between the Tier 1 level and the 'Tier 2
control" level.
The Tier 1 in-use level is based on the modified version of MOB1LE5 discussed in
Appendix A. The CALIMFAC zero mile emission factor and average in-use deterioration factor8
were adjusted for the effect of off-cycle driving patterns on emissions (Step 1). The resulting
Tier 1 in-use emission rate is then multiplied by the percent emission reductions estimated for
Tier 2 controls, 77% for NMHC and 80% for NOx. The emission benefit is the difference
between the Tier 1 level and Tier 2 control level (Step 2).
The next step is to convert the gram per mile emission benefit into a per vehicle lifetime
emission benefit. This is achieved by multiplying the gram per mile emission benefit by average
lifetime miles. The lifetime miles are discounted using a standard discount rate of seven percent
in order to discount the emission benefits by the number of years in the future in which they are
realized.9 The last step is to convert the grams into tons (Step 3). Dividing the per vehicle cost
by the per vehicle emission benefits yields the dollar per ton cost effectiveness estimate (Step 4).
mileage applied to the deterioration factor is the average in-use mileage weighted by the fleet travel
fraction to account for higher usage rate for new vehicles. The average for LDVs and LDTls is 68,000 miles, while
LDT2 is 81,000 miles, and LDT3 and LDT4 was 100,000 miles.
'For LDVs the lifetime mileage used is 132,000 miles discounted to 90,000 miles. The lifetime mileage
used for LDTs is 154,000 discounted to 97,000 miles.
C-5
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Step 1: (Zero mile emission rate + (deterioration rate * average mileage))*(off-cycle
effect) = in-use emission rate
Step 2: Tier 1 in-use emission rate * (percent reduction) = Tier 2 emission benefit (g/mi)
Step 3: (Tier 2 emission benefit (g/mi))*(discounted life time mileage)/(grams per ton
conversion factor)= per vehicle Tier 2 emission benefit (tons)
Step 4: Per vehicle cost ($)/ per vehicle emission benefit (tons)= Cost effectiveness
estimate ($/ton)
The tables below provide the specific values used in carrying out the four steps discussed above.
C-6
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Table C.3. Tier 1NMHC Emission Rates and Per Mile Benefits
LDV/LDT1
LDT2
LDT3/LDT4
Zero Mile HC Emissions (g/mi)
0.1569
0.1440
0.1402
HC Emission Deterioration Rate (g/mi
per 1,000 miles)
0.00142
0.00161
0.0016
Average In-Use Mileage
68,000
81,000
100,000
HC Emissions @ Average Mileage
(g/mi)
0.2535
0.2744
0.3002
NMHC Fraction of HC Emissions
0.868
0.868
0.868
Off-Cycle Emission Adjustment Factor
1.07
1.07
1.07
Average In-Use NMHC Emissions
(g/mi)
0.2354
0.2549
0.2788
Emission Control (%)
0.77
0.77
0.77
Average In-Use NMHC Emission
Reduction (g/mi)
0.1813
0.1962
0.2147
C-7
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Table C.4. Tier 1 NOx Emission Rates and Per Mile Benefits
LDV/LDT1
LDT2
LDT3/LDT4
Zero Mile Emissions (g/mi)
0.3091
0.3009
0.2976
Emission Deterioration Rate (g/mi per
1,000 miles)
0.00188
0.00205
0.00202
Average In-Use Mileage
68,000
81,000
100,000
Emissions @ Average Mileage (g/mi)
0.4369
0.4670
0.4996
Off-Cycle Emission Adjustment Factor
1.208
1.208
1.208
Average In-Use Emissions (g/mi)
0.5278
0.5641
0.6035
Emission Control (%)
0.80
0.80
0.80
Average In-Use Emission Reduction
(g/mi)
0.4223
0.4513
0.4828
C-8
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Table C.5. Cost Effectiveness of NMHC Emission Control
LDV
LDT1
LDT2
LDT3/LDT4
In-Use Emission
Reduction (g/mi)
0.1813
0.1813
0.1962
0.2147
Lifetime VMT (miles)
132,000
154,000
154,000
154,000
Lifetime Emission
Reduction (tons)
0.0264
0.0307
0.0333
0.0364
Discounted Lifetime
VMT (miles)
90,000
97,000
97,000
97,000
Discounted Lifetime
Emission Reduction
(tons)
0.0180
0.0194
0.0210
0.0229
Cost ($ per vehicle)
$57.33
$57.73
$69.93
$69.93
Cost Effectiveness ($
per ton)
$3,191
$2,981
$3,336
$3,049
Cost Effectiveness for
LDV/LDT1 and
LDT2/3/4 ($ per ton)
$3,151
$3,212
C-9
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Table C.6. Cost Effectiveness of NOx Emission Control
LDV
LDT1
LDT2
LDT3/LDT4
In-Use Emission
Reduction
(g/mi)
0.4223
0.4223
0.4513
0.4828
Lifetime VMT
(miles)
132,000
154,000
154,000
154,000
Lifetime
Emission
Reduction (tons)
0.0614
0.0716
0.0765
0.0819
Discounted
Lifetime VMT
(miles)
90,000
97,000
97,000
97,000
Discounted
Lifetime
Emission
Reduction (tons)
0.0419
0.0451
0.0482
0.0516
Cost ($ per
vehicle)
$78.75
$78.75
$91.35
$91.35
Cost
Effectiveness ($
per ton)
$1,882
$1,746
$1,895
$1,771
Cost
Effectiveness for
LDV/LDT1 and
LDT 2/3/4 ($
per ton)
$1,858
$1,842
C-10
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Table C.7. Cost Effectiveness of NMHC+NOx Emission Control
LDV
LDT1
LDT2
LDT3/LDT4
In-Use Emission
Reduction
(g/mi)
0.6035
0.6035
0.6475
0.6975
Lifetime VMT
(miles)
132,000
154,000
154,000
154,000
Lifetime
Emission
Reduction (tons)
0.0877
0.1024
0.1098
0.1183
Discounted
Lifetime VMT
(miles)
90,000
97,000
97,000
97,000
Discounted
Lifetime
Emission
Reduction (tons)
0.0598
0.0645
0.0692
0.0745
Cost ($ per
vehicle)
$136.00
$136.00
$161.00
$161.00
Cost
Effectiveness ($
per ton)
$2,273
$2,109
$2,328
$2,161
Cost
Effectiveness for
LDV/LDT1 and
LDT 2/3/4 ($
per ton)
$2,245
$2,256
C-ll
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Appendix D
CLASSIFICATION OF LDTs
In the Clean Air Act Amendments of 1990, Congress required that the smallest LDTs
(LDTls)10 meet the same emission standards as LDVs. However, the emission standards for
LDT2s, LDT3s and LDT4s remained less stringent than the LDV/LDT1 standards. The primary
distinction between these LDT sub-categories and between the LDT and heavy-duty vehicle
(HDV) categories is GVWR. Figure D-l describes the definition of the four LDT sub-classes and
HDVs.
Figure D-l:
Federal Light Truck Classifications
Curb Weight
Because of this incentive, many LDT models have migrated to heavier categories with
higher numerical emission standards. For example, 57% of all LDTs certified in 1987 would
10 LDTs with a curb weight of 3450 pounds or less and a gross vehicle weight rating
(GVWR) of less than 8500 pounds.
D-l
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have fallen into the lightest current LDT sub-category (LDT1). This would have included the
Chrysler minivans, the Jeep Cherokee and Wrangler and most Bronco II and Blazer models. By
1996, only 16% of all LDTs certified were LDTls. Essentially all minivans are now LDT2s, as
are all compact sport utility vehicles.
Also, a number of previous LDTs now have GVWRs which exceed 8500 pounds, which
moves them into the HDV category. Examples are many Ford F250 and all F350 pick-ups, the
GMC 3500 full-sized van and the GMC Suburban 2500.
Table D.l shows the current 100,000-mile, California LEV standards for LDVs and LDTs
(vehicle categories as defined by EPA). Also shown are the fleet-wide average standards using
the in-use VMT fractions developed in Chapter DL As can be seen, the fleet-average NMHC and
NOx standards are nearly 50% higher than the LEV standards for LDVs.
Table D.l LEV Emission Standards (g/mi @ 100,000 miles)
NMHC"
NOx
NMHC+NOx
LDV
0.09
0.3
0.39
LDT1
0.09
0.3
0.39
LDT2
0.13
0.5
0.63
LDT3 (MDV2)
0.23
0.6
0.83
LDT4 (MDV3)
0.28
0.9
1.18
WftiffhtftH Avftrapfl
nn«
fI4T7
n<7S
Table D.2 compares the emission reduction potential of equating the LDV and LDT
standards at the LDV LEV level with that resulting from a 50% reduction in all of the current
LEV standards (e.g., 0.045 and 0.10 g/mi NMHC and NOx for LDVs, respectively). As can be
seen, the two strategies yield almost equivalent reductions in in-use emissions. This highlights
the need to address the relationship between the LDV and LDT standards in the process of
considering tighter emission standards for both vehicle classes.
Table D.2 Emission Reductions Associated with Various LDV/LDT Control Strategies (g/mi)
NMHC
NOx
NMHC+NOx
Baseline
LDTs Meet LDV Standards
0.048
0.137
0.185
50% Reduction fmm I.F.V Standards
nnas
n isn
n 1QS
11 The California standards are actually in terms of non-methane organic gases, or
NMOG, which is nearly equivalent to NMHC.
D-2
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Appendix E
SUMMARY AND RESPONSE TO COMMENTS ON DRAFT STUDY
The Agency received numerous comments on the Draft Tier 2 Study, released for public
comment on April 23,1998. The comments enabled EPA to better define and understand the
various issues. The vast majority of comments pertained to Tier 2 rulemaking issues rather than
to the analyses and conclusions of the Draft Study. For example, many of the comments
addressed regulatory issues raised in the Draft Study to help the Agency better outline a potential
Tier 2 emission standards rulemaking. EPA also received many comments on the topic of
gasoline sulfur control. While this topic was raised in the Draft Study, gasoline sulfur control
was the primary topic of a separate staff paper issued shortly after the Draft Tier 2 Study. EPA
has summarized these comments on regulatory issues in Appendix F, including those on gasoline
sulfur control. EPA will address these comments as it develops the proposed Tier 2 and gasoline
sulfur rulemaking, as their resolution is outside of the scope and purpose of the Tier 2 Study.
The following sections summarize and respond to those comments directly related to the analyses
and conclusions of the Draft Study.
The majority of the comments on the Draft Study were supportive and none of the
comments provided a substantive challenge to the three primary questions of need, feasibility,
and cost effectiveness addressed in the Study. All of the comments are summarized in the
following section, categorized by chapter, then topic. EPA's response to the comments
immediately follows the summary of each comment. Although the Agency is only required by
the CAA to summarize the comments, EPA feels that it is appropriate to respond as well to
comments directly related to the study. Overall, the comments resulted in only minor changes to
the Draft Study.
ASSESSING THE AIR QUALITY NEED
Response to Comments on Air Quality Issues
General Comments
Overall, most commenters agreed with the conclusions of the air quality assessment, at
least for ozone: that additional emission reductions from motor vehicles are required to assist in
attainment of the NAAQS. Supporting this position were import auto manufacturers (AIAM,
Toyota, and Nissan), the oil industry (API, NPRA, Exxon, Sunoco, Sinclair), state organizations
and individual states, and environmental groups. AAMA disagreed with this point, however,
stating that EPA had not met the requirement laid out in the Clean Air Act to demonstrate an air
quality need for ozone reductions.
E-l
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Beyond this fundamental issue, the various groups were divided. Commenters from the
oil industry stressed that the need for nationwide ozone control was not demonstrated, as well as
the need for control of PM, CO and toxics. Conversely, state and environmental groups stressed
that PM, CO, toxics and considerations such as greenhouse gas emissions and visibility should
receive elevated treatment from the Agency. The detailed comments primarily addressed the
version of the Agency's inventory model used in the study, known as Modified MOBILE5b, the
use and application of the OTAG and NAAQS air quality modeling in the study, regulatory
issues related to air quality, and the issues mentioned above. Each are discussed in the following
sections.
Modified MOBILE5b model: Overview
In support of the draft study, the Modified MOBDJE5b model was developed to improve
the emission projections of MOBILE5b. Modifications were made where adequate data had
become available since the development of MOBILE5b and which were relevant to the
estimation of exhaust emissions from LDVs and LDTs. Modified MOBILE5b incorporates
lower vehicle deterioration, off-cycle emissions and their control, fuel sulfur effects on LEVs,
and increases in light-duty truck VMT and survival rate. Comments were received on detailed
elements of this model from STAPPA/ALAPCO, Toyota, AAMA and API.
Fuel Sulfur Adjustments
Comments: ST APP A/ALAPCO commented that the factors used to account for the impacts of
fuel sulfur on LEV emissions reflected smaller emission impacts than those presented in EPA's
Gasoline Sulfur Paper.
Response: The factors used to reflect the impact of sulfur on NOx emission from LEVs in
Modified MOBILE5b were much smaller than those presented in the Gasoline Sulfur Paper. The
statistical procedure used to develop the Modified MOBILE5b factors was found to
underestimate such impacts when the effect is large (i.e., greater than 30%). The impact of sulfur
on LEV emissions for future versions of the Modified MOBILE5b model will be estimated using
methods similar to those employed in the Gasoline Sulfur paper. This correction was not made
for the final study, however, as qualitatively it will increase out-year emission projections,
serving to more strongly reinforce the conclusions made in the draft study. This modification
will be reflected in the emission projections made to support any proposed Tier 2 and gasoline
sulfur standards.
High Emitter Treatment
Comments: API had two comments related to the treatment of high emitters: 1) the Agency
should perform a more rigorous analysis on the impacts of lower vehicle standards on high
emitters, rather than relying on CALIMFAC's assumptions, and 2) the off-cycle correction
factors were developed based on normal emitters only, but applied to high emitters as well.
E-2
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Toyota echoed the latter point, and commented that in general high emitters should be accounted
for correctly in MOB1LE6 before assessments can be made for future regulations
Response: EPA is continuing to evaluate available emission data in order to more accurately
estimate in-use emissions from both normal and high emitting vehicles. However, EPA still
believes that the CALIMFAC emission factors are closer to those likely to arise from this
evaluation for 1988 and later model year vehicles than those contained in MOBILE5b currendy.
Likewise, EPA is continuing to evaluate off-cycle correction factors and their application to both
normal and high emitters. Unfortunately, emission data on high emitting vehicles certified to
lower standards (Tier 1 and later) are extremely scarce, making the estimation of off-cycle
emissions from these vehicles highly uncertain. However, the applicability of Inspection and
Maintenance programs in areas with significant ozone problems minimizes the influence of high
emitters in the emission projections. Therefore, whether the off-cycle correction factors are
applied to all vehicles or just normal emitters would have little impact on the total emissions
projected in these areas and would not change the basic conclusions of the study.
Emission Trends
Comments: AAMA commented that the Agency's conclusion that vehicle emissions would
increase after the turn of the century as a result of VMT growth is not consistent with the results
of the modified model.
Response: The Modified MOBILE5b model used in the study projects that reductions in
gram per mile emissions from the in-use vehicle fleet will continue through 2020 due to the
turnover of the fleet to vehicles certified to tighter emission standards. These reductions appear
to be sufficient to counter the impact of moderate levels of VMT growth (e.g., 2%) through at
least 2015-2020. However, as discussed above, this model underestimates the impact of sulfur
on NOx emissions from LEVs. Higher LEV sulfur sensitivity will increase future emissions
more than current emissions, as the fleet becomes more dominated with LEVs. Thus, the
fleetwide emission reductions occurring over time will decrease. EPA estimates that with the
higher LEV emission sulfur sensitivity, VMT growth would begin to counter reductions in per
mile light-duty emissions in the 2015 timeframe. More importantly, emissions from the light-
duty fleet will continue to be a significant source of emissions in ozone nonattainment areas for
the foreseeable future even after the implementation of LEV and SFTP standards.
Other Issues
API made several comments on details of the Modified MOBILE5b model, addressed
below:
Comment: Non-sulfur fuel corrections on LEVs should be reconsidered, since the MOBILE5-
based corrections are based on 1990 and earlier vehicles, and sulfur corrections on pre-LEVs
should be reconsidered
E-3
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Response: Both are valid issues, but would have only a minor impact on Modified
MOBILE5b results because existing MOBILE5b estimates for both issues are not expected to
change significantly in MOBILE6. Addressing these issues would not impact the conclusions of
the study; however, they will be considered for future versions of the model.
Comment: MOBILE6's proposed start/running separation will impact the sulfur correction
factors, since sulfur effects are likely different on each mode.
Response: The sulfur corrections applied in Modified MOBILE5b are based on FTP
emissions, so a representative weighting of start and running emissions are inherent to the
correction factors. As mentioned above, EPA is still in the process of developing revised basic
emission rates for late model year vehicles, including separate emission estimates for starts and
warmed up operation. Once these emission rates are available, separate sulfur correction factors
could be developed for the two types of vehicle operation. However, as long as the breakdown
of start and warmed up operation in-use is near that of the FTP, there should be no net change to
the impact of sulfur on emission.
Comment: Changes planned for MOBILE6 to evaporative emission estimates may increase
overall evaporative inventory; these changes are not reflected in Modified MOBILE5b, which
may lead to inaccurate representation of Tier 2 benefits and overall emission inventories.
Response: Updated estimates of in-use evaporative emissions are still under development. It
is uncertain how projections of evaporative emissions will change. Therefore, it is not clear
whether the projected evaporative emission inventory in the future will increase or decrease
relative to MOBILE5b. However, changes to the evaporative estimates should not impact the
conclusions of the study, which primarily apply to exhaust emissions. Changes in projected
evaporative emissions will only modestly affect the base ozone levels. EPA will include any
available revised projections of in-use evaporative emissions in its Tier 2 related analyses as they
become available.
Comment: Modified MOBILE5b predicts that light truck sales will continue to increase,
when in fact they are likely to stabilize in the near future.
Response: Modified MOBILE5b predicts that light-duty truck vehicle miles traveled (VMT)
will continue to increase, not sales. This projection assumes a stabilization of LDT sales in 2002
at roughly 50% of overall LDV and LDT sales. LDT VMT continues to increase beyond this
point, however, due to fleet turnover (LDT fraction of light-duty VMT would eventually
stabilize, but beyond 2020).
Comment: In using the CALIMFAC basic emission rates, Modified MOBILE5b should
account for differences in ARB and EPA standards.
E-4
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Response: As mentioned in Appendix A, the CALIMFAC rates were used as a general
approximation for the revised basic emission rates (zero-mile emissions plus emission
deterioration rates) that EPA expects to use in MOBILE6. This is true despite slight differences
in California and Federal emission standards. Because of the uncertainty in these future rates,
altering the CALIMFAC rates to match the Federal standards wasn't considered critical.
However, if this modification were made it would primarily increase NOx emissions for Tier 0
vehicles. This would increase the overall emission projections of the model and further support
the conclusions drawn in the Draft Study. As mentioned above, EPA is in the process of
developing revised basic emission rates using recent in-use emission data and will incorporate
these revised rates into Modified MOBILE5b as soon as they are available.
Application of OTAG/NAAOS Ozone Modeling: Overview
The air quality assessment presented in the study relies primarily on modeling performed
by the Ozone Transport Assessment Group (OTAG). OTAG's projections of the number of
areas (and population within those areas) in nonattainment of the Ozone NAAQS (assessed
separately for the 1-hour and 8-hour standards) in 2007 with existing controls were used in the
study as the basis for determining the need for additional control. A set of control scenarios
evaluated as part of the OTAG process known as Run 5 of Round 2 was used to estimate the
emission controls most likely to exist at the time which the Tier 2 standards would be
implemented (i.e., 2004). OTAG used a modified version of MOBELE5a for on-highway
emission projections which reflected most, if not all of the modifications subsequently included
in MOBILE5b. (The differences between MOBILE5a and MOBILE5b are not significant for the
purposes of this analysis, in any event.)
In the Tier 2 Study, Modified MOBILE5b was used to provide a more accurate estimate
of future on-highway emissions in four ozone nonattainment areas relative to MOBILE5b. The
OTAG ozone modeling runs were not re-run with Modified MOBILE5b. Modified MOBILE5b
projected higher emissions relative to MOBILE5b in the year 2007, the year of the OTAG ozone
projections. This should increase the level of ozone projected in the future and increase the
number of projected ozone nonattainment areas. As such, it would only serve to strengthen the
evidence of the need for further VOC and NOx emission reductions.
Several comments were received, primarily from the auto manufacturers, regarding the
applicability of the OTAG work to the determination of need for lower vehicle emission
standards.
Consideration of Existing Motor Vehicle Control Programs
Comments: AAMA, NADA, AIAM and Toyota all commented to the effect that reliance on
Round 2 Run 5 of the OTAG work did not account for the benefits of existing motor vehicle
control programs such as On-Board Diagnostics (OBD), I/M, enhanced evaporative test
procedures, SFTP and the effects of improved durability. Toyota added that a comprehensive
E-5
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assessment of air quality requires the corroboration of the real world impacts of these regulations
prior to consideration of additional regulation.
Response: As mentioned above, the OTAG modeling used a modified version of
MOBILE5a, which was roughly equivalent to MOBILE5b. Contrary to the comments received,
this model accounted for most of the motor vehicle control programs mentioned in the above
comments, such as enhanced evaporative control, OBD, NLEV and I/M. SFTP controls are not
accounted for in either MOBILE5a or MOBILE5b, but off-cycle emissions, which the SFTP
standards seek to reduce, are also not included. The much greater sensitivity of LEVs to sulfur is
also not accounted for by these models. MOBILE5a's and MOBILE5b's in-use emission
deterioration rates for late model year vehicles reflect the data available in the early 1990's.
These rates now appear to be lower.
Many of these changes tend to balance one another. The inclusion of off-cycle emissions
increases emission estimates from pre-2000 model year vehicles, while the sensitivity of LEV
emissions to sulfur tends to increase emissions from post-2000 model year vehicles. Greater
LDT sales and usage (relative to LDVs) tend to increase emissions, while lower basic in-use
emission deterioration rates tend to decrease emissions from all vehicles. The net result of these
differences are therefore smaller than might be expected by a simple examination of the
individual effects.
As mentioned above in the overview of this section, Modified MOBILE5b projected
higher emissions relative to MOBILE5b in the year 2007, the year of the OTAG ozone
projections. This should increase the level of ozone projected in the future and increase the
number of projected ozone nonattainment areas. As such, changing the modeling would only
serve to strengthen the evidence of the need for further VOC and NOx emission reductions.
Regarding Toyota's comment on the need for real world assessment, a full assessment of
motor vehicle-based requirements such as enhanced evaporative control, SFTP and OBD would
require evaluation of in-use emissions for several years after the implementation of each rule.
EPA is currently evaluating all the available exhaust and evaporative emission data available in
order to develop improved estimates of fleetwide in-use emissions. These improved estimates
will be incorporated into Modified MOBILE5b as they are available.
Impact of Modified MOBILE5b on OTAG Ozone Projections
Comments: AAMA commented that Modified MOBILE5b should have been utilized to
determine the change in air quality need relative to that projected in the OTAG work. They
contend that Modified MOBILE5b would predict a larger decrease in emissions between 1990
and 2010 than MOBILE5b (AAMA reported reductions of 86% for VOC and 57% for NOx for
Modified MOBILE5b, compared to 77% and 38% using MOBILE5b).
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Response: The degree of emission reduction between 1990 and 2007 is relevant to the
projection of future ozone levels, as performed in support of EPA's proposed OTAG SIP Call.
However, the modifications included in Modified MOBILE5b were oriented towards future
vehicles. That is why EPA only presented emission projections for 2000 and beyond. To
illustrate this point, basic emission rates in Modified MOBILE5b were only reduced to reflect
lower deterioration back to 1988; if reductions in basic emission rates prior to 1988 were made,
estimates of 1990 emission levels would decrease. Given this and the underestimation of the
impact of sulfur on LEV emissions, the difference in 1990-2010 emission reductions between
MOBILE5b and Modified MOBILE5b cited by AAMA are likely overestimated. Thus, it is
inappropriate to use Modified MOBILE5b to estimate emissions in 1990, or to use this model to
estimate the change in emissions between 1990 and some future year. As improved estimates of
in-use emissions are available for all relevant model year vehicles, EPA will incorporate any
changes into its MOBILE model. At this time, EPA does not believe that any such changes are
likely to be substantial.
Consideration of Local Sources
Comments: AAMA, AIAM, and Toyota commented that the impact of other existing control
measures, in particular local control measures, should be taken into consideration before
determining the need for tighter vehicle emission standards. Specifically, AAMA and AIAM
commented that controls which will be in place under the 1-hour ozone and PM10 SIPs were not
included in Round 2 Run 5 of the OTAG work, as well as additional controls listed in the 8-hour
ozone and PM2J NAAQS RIA as potential approaches for meeting these standards. The OTC
commented, however, that despite the implementation of several additional local controls by
member states, attainment of the ozone NAAQS will not be achieved. This latter point was also
made by New York, who stated that additional reductions will be necessary beyond the wide
range of local controls already imposed.
Response: The ozone projections developed under Round 2 Run 5 included the benefits of
local emission control measures mandated by the Clean Air Act, and any additional local controls
which had been established by the time of these analyses (roughly 1996-1997). In a few cases,
states are implementing further local controls as part of their 1-hour ozone SDPs. Directionally,
these controls will decrease the number of future ozone nonattainment areas. However, as
indicated by the ozone NAAQS RIA, implementation of all local controls costing $10,000 per
ton of VOC or NOx had a very small impact on the number of projected nonattainment areas.
Therefore, the absence of these additional planned local controls in the OTAG projections should
not substantially affect the projected number of ozone nonattainment areas. Comments by the
Ozone Transport Commission and the State of New York support this conclusion, indicating that
even with the imposition of a multitude of local controls, further reductions in motor vehicle
emissions are necessary to achieve attainment with the NAAQS.
With regard to the comments on local emission controls needed to attain the 8-hour ozone
and PM2J NAAQS, the potential control measures suggested for attainment with these standards
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have to be considered on equal footing with potential Tier 2 standards, as such measures have not
yet been adopted. This being the case, it is not appropriate to account for the impact of these
potential "future" control measures prior to assessing the air quality need for Tier 2 standards.
Population Statistics
Comments: AAMA commented that the population statistics quoted in the study may be
misleading, since they reflect the number of people who live in a nonattainment area, and are
thus exposed to unhealthy levels of air pollution less frequently than would be presumed by some
unfamiliar with the subject. Sinclair commented that some quotations of the populations
statistics included population in California, which should be excluded from the totals quoted in
the study.
Response: The population statistics cited in the Draft Study reflect the number of people who
may be exposed to unhealthy levels of ambient ozone and particulate matter, as defined under the
implementation provisions of the ambient air quality standards. This is the proper figure to be
considering in assessing whether further reductions need to be made to these harmful pollutants.
The definitions of nonattainment areas for specific pollutants consider the general extent of each
pollutant's elevated levels, as well as other factors.
For example, ozone nonattainment areas are generally defined as the metropolitan or
consolidated metropolitan statistical area due to the regional nature of high ozone levels. PM10
nonattainment areas, on the other hand, are generally counties, as the geographical extent of
elevated PM10 levels is generally more limited.
Regarding Sinclair's comment, the majority of the benefit from Tier 2 standards will
undoubtably fall outside of California. However, there will be some benefit within California
due to the migration and travel of Federal vehicles into California. The study does break out the
California population where appropriate.
Fuel Control Considerations
Comments: AAMA commented that air quality need should first take into account nationwide
fuel sulfur control (then local controls, as previously discussed) before determining the need for
additional vehicle control. Sunoco and NPRA commented that OTAG found the benefits of fuel
control to be small, adding that OTAG did not include fuel controls in its final recommendations.
Response: The purpose of the Tier 2 Study as outlined by Congress is to assess the need for
further emission reductions from LDVs and LDTs via Tier 2 standards. The Study also identified
gasoline sulfur levels as an important factor in setting any Tier 2 standards. EPA's Gasoline
Sulfur Paper went further in assessing the potential emission benefits and costs of reducing
gasoline sulfur levels in-use. EPA recognizes the interaction between fuel quality and vehicle
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emission controls. As EPA proceeds with the Tier 2 rulemaking, it will review any potential Tier
2 standards in conjunction with potential changes in gasoline sulfur requirements. In fact, the
relative cost and effectiveness of fuel and/or vehicle controls will be a critical factor in the
development of the Tier 2 rulemaking.
Regarding Sunoco's and NPRA's comments, the OTAG work did not incorporate the
recently established effects of sulfur on LEV emissions. Thus, OTAG's past projections of the
benefits for fuel control would necessarily be much smaller than those developed now. Thus,
any past OTAG conclusions regarding the benefit of fuel control are no longer considered
accurate.
Other Issues
Comments: AAMA and NAD A commented on two more general issues related to the OTAG
work. First, the OTAG modeling is meant to assess transport rather than nonattainment. Second,
that OTAG (and hence the draft study) does not adequately deal with the issue of "NOx
disbenefit," the phenomena in which reduced NOx levels can actually increase ambient ozone
levels. Toyota commented on the latter issue in a more general way, saying that a comprehensive
ozone reduction strategy is needed, rather than simply pursuing reductions in both VOC and
NOx. Related to this issue, the OTC commented that their review of OTAG's work concluded
that reductions in VOC and NOx provide additional reductions in ozone, with NOx reductions
being more effective. Massachusetts commented that their own modeling indicates that
reductions in "low level" NOx (for which vehicles are the primary contributor) are effective in
reducing ambient ozone levels.
Response: The OTAG ozone modeling did find that reductions in NOx emissions sometimes
resulted in increased, rather than decreased ozone levels. However, the geographic extent of
these increases were orders of magnitude less than the area showing decreased ozone. Also, the
ozone increases only occurred on selected days of the ozone episodes evaluated and generally
were not on the days when ozone was the highest. Evaluated from the opposite perspective,
increasing NOx emissions is clearly not an effective ozone reduction strategy. Reductions in
NOx emissions are clearly effective in reducing ozone over wide geographical areas and clearly
comprise a critical part of the nation's overall ozone control strategy. In fact, as NOx emissions
are further controlled, the degree and extent of any NOx disbenefit diminishes and eventually
disappears. The key role of NOx control is corroborated by the comments from the OTC and
Massachusetts.
Areas which reflect such NOx disbenefits are also generally very sensitive to VOC
emission reductions (i.e., reductions in VOC emissions are very effective in reducing ozone).
Any reductions in VOC emissions from potential Tier 2 standards would mitigate and possibly
eliminate any limited NOx disbenefit which might occur.
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The focus of OTAG and its ozone models was clearly on transport rather than on the
demonstration of ozone nonattainment in any particular local area. The grid sizes used in the
OTAG ozone model are much larger than that used in SIP-level ozone modeling. The ozone
episodes used by OTAG represented atmospheric conditions conducive to ozone transport and
not necessarily the highest absolute ozone levels in any particular area. However, the OTAG
ozone models are useful in projecting the ozone impacts of VOC and NOx emission controls
implemented over broad regions of the country. When coupled with historic ozone
measurements, as was done in support of EPA's proposed OTAG SIP Call, the model can be
used to project the general degree of ozone nonattainment existing across the nation in the future.
This projection does not have the same degree of confidence as is needed to demonstrate
attainment in a SIP. However, SIP level assessments are not normally conducted to justify
national vehicle nor fuel standards. The combination of historic ozone data and the OTAG ozone
modeling represent a much more sophisticated tool compared to previous mobile source
assessments.
Need for Nationwide Ozone Control
Comments: Comments from the oil industry, represented by API and several individual oil
companies, stated in general that the Agency had not demonstrated the need for nationwide
reductions in ozone. In particular, API commented that the need for control in "15%" ozone
areas (i.e. those areas within 15% under the NAAQS) was questionable, due to the large amount
of VOC and NOx increase needed to push these areas into nonattainment, and the uncertainty of
health effects associated with lower ambient ozone levels.
Response: Given steady economic and VMT growth, reductions in base emission rates are
required for areas close to nonattainment to ensure that they remain in attainment. Regarding
health effects, the NAAQS dictate the level at which exposure to ozone is unhealthy. Reduced
VOC and NOx levels are needed to ensure compliance with the NAAQS for areas currently in
attainment. EPA will further evaluate these issues and the relative merits of national and
regional programs in the context of the rulemaking process.
API did not provide any technical support for their claim that large increases in VOC and
NOx emissions would be needed to cause ozone levels to increase 15%. If the only emission
source assumed to increase was motor vehicles, then the percentage increase required would
likely be large. However, economic growth can cause upwind emissions to increase, so
background ozone can increase over time. Economic growth can also cause local emission from
sources other than motor vehicles to increase, as well. SIPs place absolute emission caps on
some sources, but not all. Therefore, 15% is not large compared to economic and VMT growth
of 2-3% per year.
In addition to providing room for continued economic growth, nationwide emission
controls provide valuable environmental benefits not related to ozone. Tier 2 standards would
reduce ambient levels of nitrate PM and air toxics. PM10 nonattainment areas are scattered
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throughout the U.S. (including the West), and people are exposed to toxics and their associated
cancer risk wherever vehicles are driven.
Need for Diesel Control
Comments: EMA commented that the Agency did not adequately assess the need for control
of diesel LDTs. With regard to air quality issues, they commented that Modified MOBILE5b
was not used to assess the air quality impact of diesel penetration, and that the Agency should
perform a thorough inventory analysis to determine the impact of diesel LDTs before
determining whether Tier 2 standards are required.
Response: The inventory estimates presented in the study from Modified MOBILE5b include
the impacts of diesel LDVs and LDTs. The intent of the study's air quality assessment is to
establish the need for further control from LDVs and LDTs as a whole. However, as gasoline
vehicles dominate the light-duty fleet, the air quality assessment was, practically, an assessment
of the impact of gasoline-fueled LDVs and LDTs. Because of their current low market share,
light-duty diesels have a relatively small contribution to total motor vehicle emissions. However,
in the heavier vehicle classes, where the penetration of diesels is substantial or dominant, the
contribution of diesels to the overall emission inventory is significant.
If a need exists to reduce emissions from the gasoline-dominated light-duty fleet in order
to achieve the NAAQS for ozone or PM10, then there is similarly a need to prevent any increases
in emissions resulting from a further dieselization of the light-duty fleet. The technical feasibility
and cost of diesels achieving Tier 2 emission standards and equity considerations are other
important factors in any determination that Tier 2 standards for diesels are appropriate. These
issues were discussed in a broad fashion in the section of the Draft Study on regulatory issues
and will be addressed in detail as any Tier 2 standards are developed and proposed.
PM. CO. Toxics and other considerations
Comments: The oil industry in general commented that the need for Tier 2 standards should
focus on ozone reduction, and that need for control of PM, CO and toxics had not been
established. With regard to PM, API commented that the number of people living in PM
nonattainment areas and the contribution of motor vehicles to PM inventory was small. In
addition, API commented that the assessment of secondary PM (caused by formation of
particulates from gaseous emissions) is complex and requires further testing and modeling by
EPA to better understand the issue. These points were generally echoed by Sunoco. Regarding
CO, Sunoco commented that there was no need for further control since attainment goals had
been achieved, and will continue with fleet turnover. Sunoco and API commented that toxics
should not be considered in determining the need for Tier 2 standards, due to cost
ineffectiveness. Sinclair added that visibility should not be a consideration in determining air
quality need, since the Agency's charge from Congress was to base need on attainment of the
NAAQS.
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By contrast, state and local organizations, as well as individual states, called for EPA to
increase the relative importance of PM, CO and toxics in determining air quality need.
STAPPA/ALAPCO commented that the Agency should place equivalent emphasis on PM
emissions, including secondary PM, and consider the impact of motor vehicle emissions on other
issues such as acid rain, visibility and greenhouse emissions They also commented that EPA
should focus more on the need for CO control, given the delay in assessing Cold CO Phase II
standards and CO problems in warm weather climates. Alaska and Washington reiterated these
points, particularly with regard to PM and CO.
Response: The ozone impacts of LDV and LDT emissions will continue to be a central
consideration in the development of the Tier 2 rulemaking. However, the Agency is not
constrained to look only at criteria pollutants in determining appropriate motor vehicle standards.
The need for reductions to meet and maintain NAAQS levels is only a "part of the study" that
EPA must undertake under section 202(i) regarding "whether or not further reductions in
emissions from [LDVs and LDTs] should be required." Moreover, EPA has independent
authority under section 202 (in particular subsections (a) and (1)) to regulate pollution beyond
that specified in section 202 (i).
Thus, the Agency considers PM, CO and toxics (as well as other issues raised by
commenters) to be very relevant in the consideration of Tier 2 standards. Health and welfare
concerns are associated with each of the pollutants; the need for (and benefits of) controlling
each of these pollutants will be considered in the development of the Tier 2 rulemaking.
Regulatory Issues
Modeling for the Tier 2 Rulemaking
Comments: AIAM encouraged the Agency to conduct airshed modeling to determine adequate
Tier 2 standards in the OTC region. Sunoco made a similar comment, recommending that air
quality modeling be performed to quantify vehicle-fuel system impacts. AIAM also commented
that it is imperative for MOBILE6 to be complete in time for the final Tier 2 rule.
Response: The Agency does not intend to duplicate the extensive air quality modeling work
done as part of the NAAQS or OTAG processes for the Tier 2 rulemaking. This work, as laid out
in the study, clearly shows the need for ozone control in nonattainment areas. With regard to
ozone, Tier 2 standards will be based on the cost effectiveness of precursor control, given the
need to address the existing ozone problem.
As the Agency moves forward in the Tier 2 rulemaking, it intends to utilize the best
available estimates of in-use light-duty motor vehicle emission. As such, EPA will continue to
update the Modified MOBILESb model as additional data and analyses become available.
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ASSESSMENT OF TECHNICAL FEASIBILITY
Chapter IV of the Tier 2 Draft Study examined the technical feasibility of controlling
light-duty emissions beyond the level of control provided by Tier 1 emission standards. The
Study reviewed and described a variety of technologies capable of reducing emissions from Tier
1 levels. The Study also estimated the emission reductions of selected technologies and
concluded that many of the technologies discussed in the Study are technically feasible. The
Study discussed currently feasible vehicle emission control technologies, as well as advanced
technologies.
EPA received a number of comments on the Agency's assessment of technical feasibility.
The vast majority of the comments centered around the methodology and associated assumptions
used by EPA to determine emission reduction estimates for individual technologies and for an
overall vehicle. It should be noted, however, that the Agency did not receive any comments that
challenged the Draft Study's conclusion that it is technically feasible to reduce emissions from
Tier 1 or LEV levels. In fact, EPA received numerous comments from state, environmental and
oil industry commenters agreeing that such reductions were feasible.
All of the comments received are summarized in the following section. Response to
comments are included where appropriate.
Emission Reduction Benefits
Comments: There were several comments critical of the way EPA estimated emission
reduction benefits. All of these comments were from members of the automotive industry. The
American Automobile Manufacturers Association (AAMA) stated that the Draft Study did not
adequately assess the technological feasibility of obtaining further reductions in emissions from
LDVs and LDTs because EPA used unsubstantiated emission reduction benefits of individual
technologies, and the benefits were derived with an overly simplistic, unexplained calculation.
AAMA argued that the only valid method for determining the true reduction potential of
technologies is to perform emission testing of actual hardware on a representative sample of
vehicles. They were also critical of the fact that EPA used the percent emission reductions for
individual technologies and projected a system emission benefit with what they deemed an
"unsubstantiated" multiplicative formula. Toyota also expressed concern over EPA assessing
technologies in an add-on fashion, rather than as an integrated and complete emission control
system. AAMA stated that the interactive effects of individual emission control technologies are
complex and analysis requires extensive testing and research. AAMA felt that EPA's approach
did not account for product variation.
Finally, Toyota and AIAM commented that EPA's inclusion of increasing palladium (Pd)
content in the catalyst raises questions about future supply and price of the precious metal. The
use of Pd in vehicles is predicted to increase dramatically in the future and the stockpiles will be
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depleted, possibly resulting in a severe shortage of Pd in the future. Toyota stated that EPA
needs to take this factor into consideration prior to setting stringent emission standards,
especially stringent NMHC standards that can only be met with electrically-heated catalysts or
close-coupled Pd catalysts.
Response: AAMA argues that the only valid method for determining emission reduction
potential of various technologies is through emission testing of actual hardware. The emission
reductions presented in the Draft Study are all tied to actual emission testing results. The sources
for emission reduction estimates used in the Study by EPA were CARB, MECA, API, several
vehicle manufacturers, and the EEA report. All of the information presented to EPA from these
sources were either directly derived from emission testing, or in the case of the EEA report, from
correspondence with auto manufacturers, which is also based on emission test results.
EPA does not agree the Study used an overly simplistic and "unsubstantiated"
multiplicative formula for determining overall vehicle emission reduction estimation. First, the
multiplicative method used by EPA recognizes the fact that once a specific technique has been
applied to reduce emissions, there are fewer emissions left to reduce further. Using this method,
two techniques which are both capable of reducing emissions by 50% are projected to together
reduce emissions by 75% (50% for the first, plus 25% (50% of the remaining 50%) for the
second), rather than by 100%, which would be the simply sum of the two control efficiencies.
The only remaining question is whether the second and subsequent techniques are still effective
after the previous techniques have been applied. This is clearly the case for combining controls
which address engine out emissions and those which address emissions in the tailpipe. When a
number of engine-out emission control techniques or a number of tailpipe emission control
techniques were being combined, EPA developed estimates which represented the incremental
emission control available after implementation of the other techniques.
EPA agrees that there can be the potential for over- or under-estimating emission
reduction potential when combining a number of individual control technologies on a single
vehicle. Emission reductions achieved can also differ between manufacturers and between
various models. Because of the difficulty in predicting variances in hardware design and the
synergistic effect of combining multiple control technologies, EPA used engineering judgement
in selecting emission reduction estimates. In some cases where the available projections varied
widely, EPA selected reduction levels that were in the middle or lower end of the range of
available estimates to be conservative.
Toyota and AIAM raised concern about the potential for Tier 2 emission standards to
result in a shortage of Pd. As Toyota pointed out, vehicle catalysts are already the single largest
use of Pd worldwide and much of the supply is coming from limited worldwide stockpiles. The
demand for Pd has been steadily increasing with the advent of California's LEV program and is
anticipated to increase even more with NLEV, LEV n, and Tier 2 requirements in the U.S. and
more stringent emission standards being implemented in Europe. This is an important issue that
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EPA is currently investigating. EPA will consider the results of this investigation in the Tier 2
rulemaking.
Diesel Technology
Comment: The Engine Manufacturers Association (EMA) felt that the study neglected to
prove feasibility of diesel technology to meet tighter emission standards. EPA performed an
analysis for gasoline-powered vehicles, but not for diesel-powered vehicles, which have unique
combustion characteristics and emission control technologies. EPA based its case for technical
feasibility for diesels on gasoline vehicles. The State of Washington also commented that EPA
should perform a detailed analysis of the capability of diesel engines to meet more stringent PM
standards based upon projected diesel technology.
Response: The LDV and LDT new and in-use fleets are overwhelmingly dominated by the
gasoline engine. Therefore, EPA focused the technical feasibility and cost effectiveness portions
of the Tier 2 study on gasoline-fueled vehicles. The conclusions of the Tier 2 Study
correspondingly flow from the analysis of gasoline vehicles.
EPA devoted a section of the study to the issue of the relationship between the potential
Tier 2 emission standards for gasoline and diesel vehicles and presented various options for
setting Tier 2 standards for diesels. The role of the diesel engine and its future air quality impact
are uncertain at this time. However, this issue, including any concerns regarding technological
feasibility of controls for diesel engines, will be fully addressed when EPA reviews potential Tier
2 standards for both vehicle types.
Truck Technology
Comment: AAMA and the National Automobile Dealers Association (NADA) argued that
the functional capabilities of trucks must be considered when evaluating technological feasibility.
They felt that the Draft Study focused on a fixed percentage reduction for all vehicles without
regard for their functional capabilities. They stated that truck standards should be set based on
feasibility demonstrated using similar emission control technologies as cars. They also
commented that trucks are designed to meet customer demands for increased functionality.
Trucks have heavier structures, larger tires, axles, brakes, vehicle inertias, and experience greater
drive train losses. Trucks also experience greater aerodynamic drag forces because of larger
frontal areas and higher ground clearances. These differences increase the amount of work
required of trucks, which increases the vehicle's exhaust volume and emissions.
Response: EPA recognizes that there are some aspects of the design of LDVs and LDTs
which are inherently different. Some of these aspects, like weight and frontal area, inherently
increase fuel consumption and can increase emission. However, the Tier 1 standards for most
LDTs are numerically higher than those for LDVs. Therefore, EPA judged that was appropriate
to project that specific emission control technologies could achieve the same emission
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reductions, in percentage terms, for LDVs and LDTs relative to the Tier 1 standards. This
implies that the resulting emission levels for LDTs are still numerically higher than those for
LDVs. EPA is not aware of any information which indicates that the technologies it identified in
the Draft Tier 2 Study cannot be applied to LDTs.
Further, evidence exists that the current gap between LDV and LDT emissions should be
able to be narrowed considerably, again assuming the use of the same technology on both types
of vehicles. The Manufacturers of Emission Controls Association (MECA) commented that
LDTs currently have looser air-to-fuel (A/F) ratio control, less use of close-coupled catalysts,
proportionally lower catalyst volumes and precious metal loadings, and less sophisticated catalyst
substrates than LDVs. Historically, one of the biggest problems in reducing LDT emissions to
LDV emission levels has been the potential for thermal damage to the catalyst if it was placed as
close to the engine as typically occurs with LDVs. Because trucks are heavier, have larger
displacement engines, and, at times, necessarily operate under high load conditions (e.g., when
carrying a load or hauling a trailer), catalyst operating temperatures can reach high, potentially
damaging levels. MECA commented that the thermal durability of three-way catalysts has
greatly expanded in the past five years from 900 °C to nearly 1100 °C. Thus the higher
temperatures that might have been seen with some LDT operating conditions is no longer a
barrier.
As stated above, EPA feels that there is minimal to no difference between the technology
available and its associated emission reduction performance for LDVs and LDTs. The only
inherent differences that continue to exist are related to basic vehicle design, such as size and
weight, which can still affect engine load and emissions. EPA will consider these differences in
assessing the technical feasibility and cost as it develops its proposal for the Tier 2 rulemaking.
Assumptions Regarding Technological Capabilities and Advanced Technologies
Comment: There was a strong division among the commenters regarding the assumptions
that the Agency should be making about the capability of vehicle and truck manufacturers to
mass produce advanced emission control technologies that can reduce emissions substantially
below Tier 1 levels. For instance, API and several individual refiners indicated that the Agency
should be relying on the best technologies which are currently available and are already in
commercial use. These vehicle technologies, they argue, are capable of reducing emissions
below Tier 1 levels, and their sole consideration avoids the problems associated with setting
vehicle standards based on unproven technology. In contrast, several state organizations,
environmental and public advocacy groups indicated that Tier 2 emission standards must take
into account new and emerging technologies that are expected to be available by the time the Tier
2 standards go into effect (nominally 2004) and that the Tier 2 study should have reflected in
greater detail these technologies.
Response: Congress mandated that EPA assess in the Tier 2 study whether technology would
be available which would meet, no earlier than the 2004 model year, more stringent standards
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than those listed in section 202 (g) and (h) of the Act. In answering this question, EPA focused
on technologies and systems that are generally currently available. As the study shows, these
technologies can be utilized in a manner which achieves significant emissions reductions. The
study discussion on technologies that might be utilized for Tier 2 vehicles was not meant to be an
exclusive list of technologies, but instead showed a variety of technologies that manufacturers
might incorporate in their vehicles. The Tier 2 rulemaking will analyze more fully the costs and
benefits of technologies discussed in the study, including advanced technologies like fuel cells
and hybrid vehicles, as part of EPA's determination on the appropriate level of potential Tier 2
emissions standards.
Comment: AIAM felt that the Draft Study should mention gasoline direct injection (GDI)
engines in the discussion of advanced technologies. These engines can offer a 15-20% decrease
in C02 emissions and should be considered by EPA.
Response: The advanced technologies discussion in the study was included to highlight the
fact that there is significant research and development as well as production work being done on
vehicle technologies, including technologies for alternatively-fueled vehicles, that could lead to
significant emission reductions. This discussion was not intended to be an exclusive list of such
technologies and EPA will continue to analyze these technologies, or others that are identified, as
part of the Tier 2 rulemaking.
Cost Estimates of Technology
Comments: The commenters seemed to be split as to their opinion of the cost estimates used
in the Draft Study for the respective emission control technologies. The National Park Service
(Department of the Interior), the State of Alaska, and STAPPA/ALAPCO all agreed with the
conclusions on cost estimates presented by EPA in the Draft Study and also agreed that history
has proven that past cost estimates have been too high. The National Automobile Dealers
Association (NADA) and AAMA, while not disagreeing with EPA's cost estimates, felt that the
Study's cost estimates were much lower than those presented in the EEA report, which was done
specifically for EPA. NADA said that EPA's cost estimates were 2-3 times lower than the EEA
report, and the study appears to ignore the estimates provided by EEA and any costs associated
with 8-cylinder engines. AAMA also was concerned that EPA did not provide any justification
for the methodology used to estimate the non-hardware costs of vehicle production (e.g.,
engineering and design, development, validation, manufacturing, and overhead costs). Toyota
echoed similar concerns saying that EPA did not appear to estimate costs for software,
maintenance, etc.
Response: In developing cost estimates for the Draft Study, EPA used several sources. EPA
had cost information available from some vehicle manufacturers, CARB, and a report done for
the Agency by Energy and Environmental Analysis, Inc. (EEA) titled "Benefits and Cost of
Potential Tier 2 Emission Reduction Technologies." As EPA developed cost estimates for the
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various emission control technologies projected for lowering emission levels beyond Tier 1
levels, engineering judgement was used to determine which pieces of cost information were the
most appropriate. This meant reviewing information from all of the sources and making a
determination as to what costs seemed the most realistic. In doing so, EPA was not obligated to
only use cost information supplied by EEA. For example, EEA estimated a cost of $10.60 for
improving A/F control for LDVs which included the use of fast response fuel injectors, planar
oxygen sensors, and a faster microprocessor. CARB, on the other hand, estimated this action
could be done at little or no cost, because improvements to A/F would only constitute software
changes with no additional hardware costs. EPA felt that some level of hardware would be
necessary, but also agreed with CARB that significant improvements to A/F control would result
from improvements to fuel control calibrations. Thus, EPA choose to take the average of EEA's
and CARB's estimates. In the case of cost estimates for increased catalyst volume and loading,
as well as improvements to catalyst washcoat and substrate, the study used EEA's estimates
directly. The technologies EPA included in its estimate are all currently available and EPA does
not expect any additional costs associated with maintenance of these technologies.
Comments: AAMA and NADA also expressed some concern that the study did not consider
the cost estimates for 8-cylinder engines.
Response: The Study considered cost estimates as a function of engine size; 4-cylinder, 6-
cylinder, and 8-cylinder engines were all considered. A single cost estimate for each technology
was developed by weighting the three individual costs by 1996 sales. EPA used data from
MECA, CARB, and discussions with auto manufacturers in making its projections for 8-cylinder
engines.
Comments: AAMA and Toyota suggested that EPA did not provide any justification for the
methodology used to estimate the non-hardware costs of vehicle production (e.g., engineering
and design, development, validation, manufacturing, and overhead costs).
Response: The methodology used by EPA to estimate the non-hardware costs of vehicle
production is referred to as the "retail price equivalent" (RPE). RPE is often utilized by the auto-
industry as an indicator of the average price impact to consumers. The estimation of RPE
requires a detailed knowledge of the economics of the auto industry, and a number of
approaches have been developed to best characterize the various cost elements that go into an
RPE estimate. Typically, RPE attempts to estimate the factory overhead and general overhead
for administration, sales, marketing, and research and development. The Study used an RPE of
26% or a factor of 1.26. This is the current factor being used by the Agency for regulations.
Safety, Lead-Time, and Energy Impacts
Comments: The oil industry and AAMA pointed out that the study neglected to address the
issues of safety, lead-time, and energy impacts with respect to technological feasibility.
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Response: The issues of safety, lead-time, and energy impacts on technological feasibility
were not explicitly addressed in the draft study. No commenters mentioned any safety or energy
impacts associated with the specific emission control technologies identified in the study.
Likewise, EPA has no information that would indicate any such impacts. All of the technologies
are currently used on at least one vehicle model already in production. These issues are
addressed in the final study (see chapter IV) and will continue to be considered and addressed in
any proposal the Agency develops for the Tier 2 rulemaking. Leadtime issues are also discussed
in chapter IV of the final study.
COST EFFECTIVENESS
EPA's Overall Approach to Cost-Effectiveness
Comments: While not necessarily disagreeing with the study's conclusions, a number of
commenters criticized the nature of the study's approach to cost-effectiveness as being simplistic
and listed several neglected issues. For instance, AAMA and several refiners commented that
the vehicle and the fuel must be considered together when the cost-effectiveness of a Tier 2
program is being evaluated because of the link between vehicle-related and fuel-related
emissions and controls. EMA, on the other hand, pointed to the exclusion of a separate cost-
effectiveness analysis for diesel light-duty vehicles and trucks, decrying the EPA's assertion that
the cost-effectiveness calculations based on light-duty gasoline vehicles would also apply to light
trucks. Finally, Sunoco recommended that the EPA define the enforcement provisions that
would accompany Tier 2 and any associated gasoline sulfur regulations, and incorporate the
enforcement-related costs into the cost-effectiveness assessment. Other comments on specific
aspects of the study's cost-effectiveness analysis are discussed separately below.
Response: The study made use of a nationwide, annual, per vehicle approach to cost-
effectiveness, which is consistent with many past analyses of motor vehicle control programs.
This approach was deemed to be particularly appropriate in the Tier 2 study, because the purpose
of the study was only to determine if "Tier 2" standards (i.e., standards more stringent than Tier
1) were cost effective. The purpose of the study was not to develop and evaluate specific Tier 2
standards, nor to evaluate specific regulatory frameworks for a Tier 2 program. The study only
evaluated the potential for advanced technologies to provide cost-effective reductions in
emissions of criteria pollutants. See chapter VI for a more complete discussion of the regulatory
issues associated with the Tier 2 rulemaking.
As regards the inclusion of potential fuel changes in the evaluation of cost-effectiveness,
the study focused on vehicle technology because the Clean Air Act's requirements for the study
focused on vehicle standards. EPA addressed the impact of gasoline sulfur on post-Tier 1
vehicles in a separate staff paper. The emissions associated with the selection of vehicle
technologies which were used in the study's cost-effectiveness analysis are representative of
operation on low sulfur gasoline, consistent with the low sulfur content of current certification
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fuel (currently 30 - 100 ppm). Thus, the cost effectiveness estimates presented in the study are
most representative of a scenario in which in-use sulfur levels have been reduced to the levels of
federal certification fuels (30-100 ppm). EPA expects that the application of these vehicle
technologies would also produce substantial emission reductions at higher sulfur levels. EPA
will fully integrate fuel and vehicle emission controls in its evaluation of cost-effectiveness in the
NPRM planned for later this year.
With regard to gasoline-fueled LDTs, the study projected that the same technology which
could be applied to LDVs could be applied to LDTs, with generally the same percentage
effectiveness. The study also found evidence that improvements in emission control technology
had eliminated many of the historically inherent differences between LDV and LDT emissions.
No data was received from any commenter refuting these findings.
The Agency did not specifically assess the cost effectiveness of Tier 2 standards for diesel
vehicles or trucks. The new and in-use LDV and LDT fleets are currently dominated by the
gasoline engine. Therefore, EPA focused the technical feasibility and cost effectiveness portions
of the Tier 2 study on gasoline-fueled vehicles. This approach was sufficient to fulfill the Clean
Air Act mandate that EPA assess whether Tier 2 standards were technically feasible and cost
effective.
EPA devoted a section of the study to the issue of the relationship between the potential
Tier 2 emission standards for gasoline and diesel vehicles and presented various options for
setting Tier 2 standards for diesels. This issue will be fully addressed when EPA proposes
specific Tier 2 standards for both vehicle types.
Many of the comments highlighting shortcomings in the study's cost-effectiveness
calculations appear to arise from a misunderstanding of the per-vehicle approach taken by the
Agency. There are generally two approaches to calculating the costs and benefits of a control
program. The calendar year approach adds up all the costs and benefits projected to occur over a
specific time frame. This time frame is usually fairly long (e.g., 33 years), so that startup costs
are included, but do not dominate the result. Another approach is the per vehicle or per engine
approach. This approach has been commonly used by the Agency in analyses of national motor
vehicle and engine controls where the bulk of the costs and benefits can be associated with a
particular vehicle or engine throughout or at specific times in its life. The two approaches yield
approximately the same result when common cost and benefit inputs are used. The per vehicle
approach is simpler to conduct, when it can be applied. It also ensures that the costs and benefits
of the program are properly accounted for by considering all the benefits accrued over the
lifetime of the vehicle as well as the control costs which usually occur once at the time of vehicle
or engine purchase.
The annual accounting of benefits is consistent with the approach used in other programs
in accounting for NOx and VOC benefits. Although some commenters, such as API, NPRA, and
several individual refiners, indicated that NOx and VOC benefits should only be accounted for in
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the summer when ozone is an issue, the accounting of benefits on an annual basis allows for a
direct comparison of the cost-effectiveness of Tier 2 vehicles to the cost-effectiveness of other
programs. While ozone benefits generally occur primarily in the summer months, there are in
fact other environmental benefits, such as ambient PM and toxic reductions, which occur year-
round. The Agency restricted its comparison of the cost effectiveness of potential Tier 2
standards to other programs which had also been assessed on a year round basis to ensure
consistency.
Cost-Effectiveness Showing
Comments: There was a strong division among the commenters regarding whether the study's
cost-effectiveness analysis provided a reasonable basis for concluding that Tier 2 vehicles can be
cost-effective. The Department of the Interior's National Park Service, several environmental
commenters, the States of Massachusetts and Alaska, and MECA all agreed with the study's
conclusion that Tier 2 vehicles can be cost-effective. In contrast, a number of other commenters,
including both API and AAMA, indicated that the study falls short in assessing the potential
cost-effectiveness of Tier 2 vehicles because it does not provide sufficient comparisons to other
programs. AAMA also provided its own estimate of the cost-effectiveness of potential Tier 2
standards at $12,000 - $16,000 per ton NOx + VOC, stating that these values fall far above the
maximum criteria for a cost-effective program.
Response: The study did in fact compare the cost-effectiveness of Tier 2 vehicles to the cost-
effectiveness of other control programs. For instance, the study included a range of cost-
effectiveness values (in terms of $/ton) for single pollutants for other control measures
implemented since passage of the Clean Air Act Amendments of 1990, including those for
stationary sources. In comparing the cost-effectiveness of Tier 2 vehicles with the cost-
effectiveness of those previous programs, it appears that Tier 2 vehicles would in fact be cost-
effective. The study also made comparisons to other potential control measures which had not
yet been implemented. The cost-effectiveness of these latter programs was evaluated in detail in
the Regulatory Impact Analysis (RIA) associated with the revised NAAQS for ozone. Again the
Agency concluded that, in comparison to these other potential control measures, Tier 2 vehicles
could be cost-effective since the $/ton values estimated for Tier 2 vehicles was comparable to the
$/ton values estimated for those other control programs.
EPA determined AAMA used cost' estimates of $232 for a four cylinder engine and $306
for six cylinder engines (incremental to the Tier 1 standards) based on information AAMA found
in the EEA report. AAMA also projected a VOC+NOx reduction of 0.0189 tons per vehicle,
derived from emission rates which AAMA believes may be used in EPA's upcoming MOBILE6
model. Dividing $232 by 0.0189 tons yields $12,275/ton and dividing $306 by 0.0189 tons
yields $16,190/ton, yielding the cost effectiveness range cited by AAMA in their comments.
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In estimating vehicle costs, AAMA did not assume use of the same technologies as EPA
cited in the draft study. The primary difference between the technologies selected by AAMA and
EPA is that AAMA included an electric air pump system at a cost of $125 for four cyclinder
engines and $160 for six cylinder engines. However, AAMA did not modify the projected
emission reductions based on the use of this additional technology. Specifically, electric air
pumps are designed to speed up catalyst light-off, which primarily reduces HC emissions. EPA
projected the use of some technologies not used on current LEVs, but not electric air pumps, in
calculating the 77% VOC reduction identified in the study.
If EPA had included the cost of an electric air pump system, the costs for LDVs and
LDTs would have increased by $179 and $197, respectively. These costs include sales weighting
the above costs by the fraction of 4,6 and 8 cylinder engines in the two vehicle classes, and
multiplying by the Retail Price Equivalent (RPE) factor of 1.26. Total costs would thus have
increased to $315 for LDVs and $358 for LDTs. These cost estimates are even higher than those
estimated by AAMA, due to the inclusion of the RPE factor and other smaller differences in the
technologies selected by EPA and AAMA. EPA acknowledges that there are many different
combinations of technology that can be used to lower emissions, and the list of technologies
presented in the Tier 2 study may be expanded once Tier 2 standards have been developed.
However, EPA chose to include technologies it believes would provide cost effective emission
control, based on currendy available information.
AAMA's estimated per-vehicle VOC+NOx benefit of 0.019 tons is a factor of three lower
than the benefit of 0.06 tons estimated for LDVs by EPA in the study. EPA's analysis was based
on in-use emission rates from California's CALIMFAC model, used in the Modified MOBILE5b
model to estimate planned changes in the MOBILE6 basic emission rates. Emission rates for
MOBILE6 are currently under development, and thus have not been proposed; as such, the
CALIMFAC rates are still EPA's most current estimate of how MOBILE6 will project in-use
emission levels. AAMA's estimates are presumably based on emission rates which were merely
under deliberative consideration for MOBILE6. The rates used by AAMA have not been
proposed for use in MOBILE6, and as such cannot be considered updated MOBELE6 (or
Modified MOBILE5b) emission rates. An additional likely reason for AAMA's lower benefit
estimate is that they did not appear to consider benefits from off-cycle driving, which are
included in EPA's analysis.
Thus, EPA does not believe a change to the cost effectiveness estimates made in the study
is appropriate.
Comment: Some commenters suggested that other factors be taken into account in evaluating
cost-effectiveness in addition to, or in lieu of, comparisons to other programs. For instance, the
International Center for Technology Assessment suggested that any control program costing
$10,000 per ton or less ought to be considered "cost-effective."
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Response: For the purposes of the study, the Agency has determined that comparative
assessments of cost-effectiveness are the most appropriate means for evaluating potential Tier 2
standards, rather than assessments measured with respect to a fixed $/ton limit. The Agency has
determined that the evaluated options for Tier 2 are cost-effective when compared to other
programs.
Comment: A few commenters, including the State of Alaska and the Department of the
Interior's National Park Service, reiterated the study's recognition that past cost estimates have
often proven to be too high once the program was actually underway. These commenters
suggested that the Agency accept higher $/ton estimates in the study as a result.
Response: Comparative assessments of cost-effectiveness as generally based on pre-
implementation cost estimates, such that lower in-use costs are not accounted for. Thus the
comparative cost-effectiveness assessments summarized in the study provide the best means for
determining whether to establish Tier 2 standards.
Point of Comparison for Cost-Effectiveness Calculations
Comment: Marathon Oil suggested that cost-effectiveness should be measured with respect
to LEVs rather than Tier 1 vehicles, since LEVs will already be commercially available by the
time Tier 2 vehicles go into effect. The technology has already been developed for LEVs, so no
new costs will be imposed on them from any Tier 2 standards, and the emission benefits
attributable to LEVs will already be accruing by the time Tier 2 standards would go into effect.
Response: The Clean Air Act envisioned that the Tier 2 standards would be compared to the
Tier 1 standards, which were to be the existing standards prior to the promulgation of the Tier 2
standards. The Act did not envision a voluntary NLEV program. Recognizing this, the study
focused on the cost effectiveness of emission controls beyond Tier 1, but also provided cost
effectiveness estimates for control beyond NLEV. The Agency determined that Tier 2 standards
can be cost-effective with respect to either baseline.
Comment: Several commenters highlighted the fact that the study estimates the costs and
benefits associated with a conglomerate of emerging emission control technologies, questioning
whether this was appropriate. API and Marathon Oil, for instance, suggested that cost-
effectiveness be determined on an incremental basis that allows a $/ton value to be determined in
stepwise fashion for each new type of technology that is added to a Tier 1 vehicle. The Ozone
Transport Commission, on the other hand, suggested that, instead of making its own judgements
regarding which technologies are most likely to be used in Tier 2 vehicles and the benefits
associated with those technologies, the EPA should instead use either the default Tier 2 standards
in the Clean Air Act or California's LEV-II standards as the basis for estimating the benefits of
Tier 2 vehicles.
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Response: The study included an incremental cost effectiveness analysis. The study's
"conglomerate" approach, in which a selection of technologies was chosen as a means towards
estimating the potential benefits of Tier 2 vehicles, was intended to provide an initial estimate of
the types of emission controls which are technologically feasible and cost effective. In order to
most accurately estimate the additional costs and emission benefits of Tier 2 vehicles, it is
necessary to first investigate what is technologically feasible. Beginning with a set of emission
standards and then estimating the set of technologies that can attain those standards is analogous
to putting the cart before the horse. Additionally, synergisms exist between a number of the
control technologies and it is more realistic to evaluate these technologies together than
separately. For example, many of these technologies are found together on current California
LEV and ULEV vehicles. The purpose of this portion of the study was to evaluate whether
emission control beyond the Tier 1 standards was cost effective. The study was not designed to
select the level of Tier 2 emission control which was most cost effective, or marginally cost
effective relative to other programs. The technology necessary to achieve the California LEV-II
standards has not yet been clearly quantified. In addition, the Agency deemed it inappropriate to
use the default Tier 2 standards from the Clean Air Act as the basis for the cost-effectiveness
calculations, since the NMOG standards applicable to existing LEVs are already more stringent
than the default Tier 2 NMHC standard. Thus the "conglomerate" approach provides a better
description of potential Tier 2 standards than either the Clean Air Act's default Tier 2 standards
or California's LEV-II standards.
The study did not include an incremental cost effectiveness analysis for each technology.
Such analysis will be addressed fully in the proposed Tier 2 rulemaking.
Accounting of Costs and Benefits
Comment: API, NPRA, and several individual refiners commented that the benefits
associated with Tier 2 vehicles should not be summed annually and nationally. Instead, they
indicated that benefits should only be accounted for during times and in places where they
actually have an impact on air quality. Thus NOx and VOC benefits should only be accounted
for during the summer in ozone nonattainment areas and ozone transport regions.
Response: As discussed above, the study made use of a per-vehicle approach to cost-
effectiveness that necessarily results in $/ton values which represent an annual accounting of
benefits. The annual accounting of NOx and VOC benefits is consistent with the approach used
in other programs, and thus the study's approach provides for a direct comparison of the cost-
effectiveness of Tier 2 vehicles to the cost-effectiveness of other programs. The study's per-
vehicle approach to cost-effectiveness also means that the $/ton values represent the cost-
effectiveness of a single Tier 2 vehicle operating in an area where low sulfur standards apply,
which is generally where NOx and VOC benefits are deemed beneficial to air quality. Whether
low sulfur standards will apply regionally or nationally is a regulatory issue that will be
addressed in the NPRM.
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Comments: Many commenters provided suggestions for which benefits should be accounted
for in the cost-effectiveness calculations, and how. Beyond NOx and VOC emissions, several
commenters suggested that reductions in CO, particulate matter, and toxic pollutants also be
taken into account, though most commenters did not specify whether this should be
accomplished through a simple mass sum of all reductions, or through an alternative means such
as crediting the costs of implementing Tier 2 vehicles. Other commenters, such as
STAPPA/ALAPCO and the International Center for Technology Assessment, suggested that the
study also take credit for such incidental benefits as reductions in acid rain, better visibility, and
fewer greenhouse gas emissions in its cost-effectiveness calculations. Sinclair Refining, on the
other hand, specifically identified visibility as an example of a benefit that should not be taken
into account because it is unrelated to attaining or maintaining any NAAQS. In similar fashion,
Sunoco Oil questioned whether any benefits of Tier 2 vehicles beyond NOx and VOC should be
taken into account in the cost-effectiveness analysis.
Response: The Clean Air Act identifies attainment and maintenance of the NAAQS as "a
part of' the Tier 2 study regarding "whether or not further reductions in emissions from [LDVs
and LDTs) should be required." It is also appropriate to review other economic and
environmental benefits associated with the Tier 2 standards. For instance, if fuel economy were
projected to increase or decrease because of the standards, it would be appropriate to include the
added cost and/or benefit. Likewise, if the incidence of cancer is projected to increase or
decrease, the value of these health impacts should also be included. The same is true for
visibility, acid precipitation, etc. In addition, the inclusion of benefits associated with reductions
in other criteria pollutants would be consistent with the Act's charge. The cost effectiveness
analysis included in the study did not quantitatively include these other benefits, as the Tier 2
controls evaluated appear to be cost-effective without their consideration. EPA plans to include
appropriate public health and environmental benefits in evaluating the Tier 2 standards in the
NPRM.
Comment: In the context of assessing the NOx and VOC benefits for Tier 2 vehicles, several
commenters disagreed with the study's approach of using a mass sum of the two pollutant
categories. For instance, API indicated that the overall cost-effectiveness should be based on
ozone reduction benefits estimated through air quality modeling rather than relying on the mass
of ozone precursors reduced. Alternatively, API suggested that NOx be weighed more heavily
than VOC, since NOx appears to be the more important pollutant to control for mobile source
impacts on ozone. Marathon Oil went further, suggesting that VOC benefits be ignored
altogether in calculating the cost-effectiveness of Tier 2 vehicles.
Response: The relative effects of NOx and VOC on the formation of ozone can vary
substantially from region to region and even from hour to hour within a given region. As a
result, it is very difficult to establish a single ratio of NOx to VOC that is representative of the
impact of these two pollutants on ozone in all areas at all times. Calculating the cost
effectiveness of the Tier 2 standards in terms of ozone impact would require photochemical grid
modeling, which is beyond the scope of the study. The study calculates separate $/ton values for
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NOx, VOC, and NOx+VOC to allow the most appropriate comparison to other programs, some
of which evaluated the cost effectiveness of only one ozone precursor, while others evaluated the
cost-effectiveness of both NOx and VOC.
Comment: There was disagreement concerning the study's allocation of costs to the separate
$/ton values for NOx and VOC. AIAM agreed with the study's approach of splitting costs, but
suggested that the separate costs for NOx control and VOC control be made proportional to the
mass of NOx and VOC benefits produced. API, on the other hand, disagreed with any allocation
of costs between NOx and VOC.
Response: EPA generally assigns costs to either NOx or VOC control depending on the
purpose of that particular emission control technique. When both VOC and NOx emissions are
controlled substantially and simultaneously, then the costs are split between the two pollutants
evenly. In the study, when calculating separate cost effectiveness estimates for NOx and VOC
control, the Agency deemed it inappropriate to include all costs in each case, since the total costs
would have been lower had only one of the two pollutants been controlled. AIAM's suggested
approach of allocating costs to NOx and VOC in a proportional manner to the mass of each
pollutant reduced would have the effect of producing identical $/ton values for NOx, VOC, and
NOx+VOC. Thus, the value of applying this technique is unclear given that the cost
effectiveness of VOC+NOx control has already been calculated.
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Appendix F
SUMMARY OF COMMENTS ON REGULATORY ISSUES
In Chapter VI, EPA raises a number of important issues that the Agency will need to
resolve in developing Tier 2 standards for LDVs and LDTs, ranging from the relative stringency
of the Tier 2 LDV and LDT standards to test fuel specifications and the appropriate level of
sulfur in commercial gasoline. These issues were also outlined in the Draft Study, and EPA
received a number of comments on these issues. This Appendix summarizes the comments
received, grouped by topic. Since the Agency raised these issues only to gather information for
future rulemaking, and since these issues do not directly impact the analysis and conclusions of
the Study, EPA is not responding directly to these comments at this time. Rather, these
comments will be considered fully during the development of the proposed Tier 2 standards and
gasoline sulfur requirements. A complete list of commenters is provided at the end of this
Appendix for the reader's information.
I. Relative Stringency of the Tier 2 LDV and LDT Standards
EPA outlined three possible options for setting LDV and LDT standards. The three
possible options were:
1) Require LDTs to meet the same numerical emission standards as LDVs;
2) Set the LDT standards to require use of the same emission control technology as the LDV
standards; or
3) Set different standards based on vehicle use.
EPA received comments supporting all three options. However, the majority of the
comments supported option 1, requiring LDTs to meet the same numerical emission standards as
LDVs. Those supporting option 1 were individual states, regional state affiliations,
environmental groups, health organizations, and several oil companies.
Auto manufacturers suggested a combination of options 2 & 3. AAMA suggested that
the current truck classification system should retained, while AIAM felt that EPA should explore
new definitions for LDT classes that recognize vehicles that are designed and used for similar
purposes and set standards appropriate for each class. Both groups felt that equivalent emission
control technologies should be required on trucks as on cars, but the truck standards should be
numerically higher.
API stated that LDT standards should be based on a cost effectiveness level equal to the
cost effectiveness for LDV standards. EMA noted that EPA must take into account the
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functional requirements of trucks and felt that diesel powered LDTs should have separate and
numerically higher emission standards than LDVs.
Several states, state organizations, and environmental groups felt that in addition to LDVs
and LDTs having the same numerical emission standards, EPA should also adopt California's
proposed LEV II emission program, while AIAM argued that EPA should refrain from adopting
standards as stringent as California's.
Finally, several oil industry groups suggested that Tier 2 emission standards should
include trucks over 6,000 lb GVWR, and several state and environmental commenters felt EPA
should include trucks up to and over 8,500 lb GVWR.
II. Uniform Application of Emission Standards
In the Tier 2 Study, EPA referred to uniform standards as the application of the same
emission standards to similar vehicles regardless of what fuel is utilized. The primary fuel
options for conventional engines are gasoline and diesel fuel.
EPA received comments from a wide spectrum of groups, including states, environmental
groups, the oil industry, and auto manufacturers. All but one of the commenters agreed that
future Tier 2 emission standards should be the same for gasoline and diesel fuel. Only one
commenter, EMA, felt that there should be separate standards. EMA felt EPA did not justify the
need for additional regulation for LDTs, and in particular, for LDTs powered by diesel engines.
Therefore, EMA did not see any reason to have fuel neutral emission standards.
The American Lung Association (ALA) encouraged EPA to require diesel LDVs and
LDTs to meet the same SFTP emission standards as those required for gasoline LDVs and LDTs.
III. Evaporative VOC Emission Standards
EPA suggested that it may be appropriate to consider tightening the current evaporative
VOC emission standards in the process of considering tighter Tier 2 exhaust emission standards.
It also mentioned that CARB has recently proposed a "zero evaporative emission" which would
essentially require that evaporative VOC emissions be below measurable levels.
Several commenters, including states, oil industry commenters, and auto manufacturers,
agreed that EPA should consider tighter evaporative VOC emission standards. Several even
suggested that EPA should consider "inherently zero evaporative emission" requirements, similar
to California. There was also the suggestion that EPA should determine the stringency of
evaporative VOC standards based on cost effectiveness.
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Toyota argued that before EPA considers tightening evaporative standards, further
discussion needs to take place on how to appropriately incorporate the evaporative emission
effects into EPA's in-use emission modeling to determine whether there is any need to tighten
evaporative VOC emission standards.
IV. Corporate Average Tier 2 Standards
The Study stated that EPA is considering establishing corporate average emissions
standards for Tier 2, similar to the fleet average standards that will be used by the voluntary
National LEV program and currently exist for California's LEV program.
There were no comments opposed to the concept of corporate averaging for Tier 2
emission standards. Several commenters from states and the auto industry stated that EPA
should consider corporate averaging of Tier 2 emission standards. New York and AIAM
suggested that EPA should give consideration to a corporate averaging program that includes
both hydrogen and nitrogen oxide emissions. AIAM also felt that EPA should consider other
concepts for vehicle manufacturers to gain emission credits against any average standard, such as
1) voluntarily certifying to longer useful life, 2) voluntarily electing to conduct in-use
enforcement without screening vehicles for proper maintenance and use, and 3) voluntarily
electing to certify to the same standard for useful life as for 50,000 miles.
V. Extended Useful Life and Other Options to Improve In-Use Performance
Section 202(i) of the CAA directed EPA to consider in the Tier 2 Study extending the
useful lives of the LDV and LDT emission standards. Therefore, the Study stated that EPA was
considering extending the useful lives for LDVs and LDTs to 120,000 miles from their current
100,000 miles, similar to what California had recently proposed in their Phase 2 LEV emission
program (i.e., LEV II).
EPA received several comments from states, health organizations, and the oil industry
suggesting that useful life requirements be increased from the current 100,000 mile requirement.
All of the comments suggested that useful life should, at a minimum, be raised to 120,000 miles,
while the International Center for Technology Assessment (CTA) stated that it should be raised
to as high as 160,000 miles.
AIAM disagreed with the other commenters and argued that the useful life requirement
should not change. They stated that changes to useful life should not be considered until data is
available on the effectiveness of the current useful life requirements.
VI. Test Fuel Specifications
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In the Study, EPA stated that in an attempt to further develop test procedures that are
representative of real world conditions, the Agency is considering requiring test fuel to be the
same as, or "representative " of commercial in-use fuel. In the study, EPA only commented on
gasoline, not diesel fuel.
EPA received comments from several states and several members of the oil industry. All
agreed that Tier 2 emission standards should require certification and in-use fuel to be the same.
The commenters from the oil industry felt that this should only apply to sulfur content, while the
various state commenters suggested that all fuel specifications should be the same. CTA
commented that EPA should use the "worst" commercial fuel for testing. Toyota stated that a
changes in the test fuel should result in a change in standards to compensate.
VII. Gasoline Sulfur
Among the regulatory issues raised in the Draft Study was the question of the need to
control commercial gasoline sulfur levels to reduce the negative emissions impact that sulfur has
on the performance of automotive catalysts. In response to the various issues raised in that
discussion (Section G of Chapter VI), a number of comments were received. These comments
are summarized in the following sections, grouped by topic.
In addition to the short discussion in the Draft Study, EPA has released a more detailed
analysis of the issues surrounding control of gasoline sulfur in a Staff Paper released in May
1998.1 EPA is in the process of receiving comments on the Staff Paper and thus is not
responding to comments on the Staff Paper in this document. However, the Agency will
consider the comments received on the Staff Paper during the development of the rulemaking.
A. Appropriate Sulfur Level for Commercial Gasoline
In the Draft Study, EPA indicated that the level of sulfur control would be determined on
the basis of cost and emissions reductions, as well as technology enablement. A number of
parties commented that sulfur should be reduced to California gasoline sulfur levels - nominally
30 ppm on average, with a maximum of 80 ppm. Nissan noted that it is doubtful that Tier 2
standards could be feasible without reducing gasoline sulfur levels to at least 40 ppm. The
automotive industry was joined by the Manufacturers of Emission Controls Association (MECA)
in calling for this level. In addition, STAPPA/ALAPCO, the OTC, the ALA, and various
individual states also supported this level. Massachusetts supported even lower levels to enable
more advanced technologies, such as fuel cells. Generally, maximized emissions reductions and
enablement of even cleaner technologies in the future were cited as arguments for reducing
'Office of Mobile Sources, EPA, "Staff Paper on Gasoline Sulfur Issues," EPA 420-R-
98-005, May 1998.
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gasoline sulfur to these levels. AAMA also cited the need to have consistent fuel standards
worldwide given the move to harmonize emissions standards worldwide.
Other parties argued for more limited sulfur control. In most cases, the sulfur level
suggested by the API/NPRA proposal -150 ppm on average - was cited as an acceptable level for
the region defined to get low sulfur fuel, with an average level of 300 ppm for the rest of the
country. API argued that some vehicles available today can meet Tier 2-type emissions standards
with gasoline sulfur levels of 150 ppm, and thus lower levels were not needed. In addition, to
representatives of the oil industry, several states supported this level. Florida indicated that 150
ppm would be an acceptable temporary level of sulfur control, although the state clearly indicated
the need to go even lower in the long term. Oklahoma expressed the opinion that states should
have the right to determine what level of sulfur they want (or how quickly they want lower sulfur
fuel) to meet their own needs.
B. Geographic Extent of Sulfur Control Program
As noted in Chapter VI, the geographic extent of a sulfur control program - whether it
applies nationally or to a more limited region - has implications for the costs and the emissions
benefits to be gained from sulfur control. Comments were received in support of both options.
The oil industry, represented by the American Petroleum Institute (API) and the National
Petrochemical & Refiners Association (NPRA), as well as individual oil companies, supported a
regional sulfur program in lieu of a national program. API and NPRA have jointly proposed a
regional program that would provide lower sulfur fuel to the 22 states covered by the NOx SIP
call. Specific arguments in favor of a regional program included the belief that other areas had
limited air quality needs for control or would benefit little from additional mobile source
controls, citing the work of the Ozone Transport Assessment Group. Others stated that a
regional fuel program could help to restrict the growth of individual state "designer" or
"boutique" fuels designed to address air quality problems in a limited area. Several individual
states also expressed interest in a regional program. For example, Florida, not included among
the 22 states, expressed interest in a regional program provided they would be included in the
region. Other states supported a regional program due to the belief that not all areas need or want
sulfur control. Idaho specifically suggested that states outside of the control region be given the
opportunity to opt-in to the more stringent sulfur level if they want more control. API stated that
the impact of sulfur on catalysts was reversible, negating the need for a national program.
Other parties gave strong support to a national sulfur control program. Automakers,
represented by the American Automobile Manufacturers Association (AAMA) and the
Association of International Automotive Manufacturers (AIAM), expressed support for a
national sulfur program and even petitioned the Agency to implement a national, low sulfur
gasoline program in the near future. STAPPA/ALAPCO and the Ozone Transport Commission
(OTC) have made similar resolutions, and many individual states commented in support of a
national program. Environmental organizations, such as the American Lung Association and the
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American Council for an Energy Efficient Economy, also favor a national sulfur control program.
Arguments supporting the need for a national program, beyond the general emissions benefits
and vehicle technology enabling explanations, included the fact that most of the international
community, including Europe, Japan, Canada, and other countries are moving towards low
gasoline sulfur requirements for the early 2000s, as well as concerns regarding reversibility and
illumination of onboard diagnostics lights.
C. Sulfur's Impact on Catalysts and the Reversibility of this Impact
EPA has estimated the impact of sulfur on emissions based on test data demonstrating the
effect sulfur has on catalysts. EPA also raised the question about whether future automotive
catalysts could be designed to be less sensitive to sulfur than those available today. In response,
API suggested that there were various technical solutions to reducing the impact of sulfur on
emissions and designing cleaner vehicles, such as reducing engine-out emissions, improving
control of air-fuel ratios, and others, that indicated very low sulfur levels were not needed.
Sinclair noted that LEVs and ULEVs are cleaner than Tier 1 vehicles regardless of sulfur level.
In contrast, the auto industry commenters and MECA all commented that sulfur control is critical
to enable emission control hardware to perform at the levels necessary to meet likely Tier 2
standards. These commenters noted that not only does sulfur impact current vehicle emissions,
but as vehicles are required to be cleaner (and thus their emission control systems more efficient),
sulfur inhibits their performance.
EPA also noted that a key question was how reversible the sulfur effect is an issue that
would help to determine both the maximum acceptable sulfur level and the geographic extent of
a sulfur control program. Several parties, including the auto industry, STAPPA/ALAPCO,
MECA, and a group of 22 environmental organizations, commented that reversibility is a
concern and the variability in data on reversibility argues for sulfur control. Individual
commenters referenced work done by a catalyst manufacturer, Johnson Matthey, which suggests
that long term exposure to high sulfur fuel leads to less reversible catalyst damage than short
term exposure. Many comments also argued that some of the techniques needed to reduce the
sulfur impact on catalysts, such as high temperatures and/or rich (low oxygen) operation, would
not be possible in the future as catalysts were required to be increasingly durable and new
standards controlling "off-cycle" emissions under the supplemental federal test procedure
(SFTP). Commenters from the oil industry presented data which they interpret to demonstrate
that the catalyst degradation due to sulfur levels up to 300 ppm can be completely reversed. The
oil industry comments also presented data which was cited to demonstrate that vehicles exist
today which can meet SFTP emissions standards when operated on sulfur levels up to 300 ppm.
D. Sulfur Control Costs and Refinery Considerations
Although EPA provided no estimates of sulfur control costs or other refining industry
impacts of sulfur control in the Draft Study, there was a discussion of the need to consider costs
and other issues when developing a sulfur control program. (EPA presented a more detailed
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evaluation of costs and related issues in the Staff Paper.) Several comments submitted on the
Draft Study addressed these types of issues.
Many comments addressed what refining technologies should be considered in evaluating
the feasibility and cost of sulfur control. Several states, as well as STAPPA/ALAPCO,
encouraged that emerging sulfur removal technologies, such as a new process being developed by
CDTECH, be considered. These commenters further suggested that standards should be set to
push improvements in refining technology. In contrast, Sunoco specified that only commercially
proven technologies be considered as the basis for justifying sulfur reductions. Ford suggested
that the Agency investigate current and future refining technologies in the U.S. to understand
why 10% of refineries are already making low sulfur gasoline with no apparent marketplace
disadvantages.
Other comments addressed the factors that should be considered when evaluating sulfur
control. Cost was mentioned by many commenters as a key consideration. Sinclair suggested
that costs be evaluated for different parts of the country, and that the Agency consider that the
costs to consumers will vary as rural consumers tend to use more gasoline than urban dwellers.
Sunoco noted the cost of enforcement for refiners. Other oil industry representatives suggested
that in addition to cost per gallon of gasoline, the Agency should consider overall costs, lead
time, and energy impacts in deciding the appropriate level of sulfur control. Specific attention
was called to the anticipated growth in demand for refined products, and the commenters
suggested that the ability of the industry to meet this demand as well as additional environmental
requirements be considered in the Agency's evaluation. MECA encouraged EPA to give
adequate lead time to refiners, as well as to provide implementation flexibility. Nissan, however,
stated that API's own cost estimates indicated that the cost of controlling fuel sulfur to
AAMA/AIAM recommended levels was cost-effective. Ford indicated that EPA's cost estimates
(presented in the Staff Paper on gasoline sulfur) were too high.
E. Other Comments
Many comments were received on technical issues related to gasoline sulfur that were not
explicitly raised in the Draft Tier 2 Study. Some of these issues were discussed in the Staff Paper
on Gasoline Sulfur Issues, and several parties appeared to be addressing both documents when
submitting their comments. For completeness, the comments received on other sulfur-related
issues are summarized here.
1. Sulfur's Effect on Advanced Technologies
Several commenters addressed the effect that sulfur is likely to have on more advanced
technologies, such as gasoline direct injection engines using lean-NOx catalysts, or gasoline-
powered fuel cells. STAPPA/ALAPCO expressed the opinion that the enabling of such
technologies is of even greater concern than the resolution of the reversibility of the sulfur effect
on today's catalysts. API expressed the opinion that lean-NOx catalysts will not require low
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sulfur gasoline, citing test data from a Mitsubishi vehicle. Furthermore, oil industry commenters
argued that the needs of advanced technologies should not enter into the current debate over
gasoline sulfur levels since such vehicles will not be introduced into the U.S. market any time
soon.
Automotive industry commenters and catalyst manufacturers suggested that sulfur control
is necessary to enable future technologies, because advanced technology catalysts would be
permanently damaged (irreversibly) by sulfur. One comment encouraged the Agency to consider
going to even lower sulfur levels (below 40 ppm) for the benefit of these technologies. The C02
reductions to be achieved through the use of these advanced technologies was cited as
justification for reducing sulfur to enable these technologies.
The National Conference of State Legislatures took the arguments for advanced
technologies a step further. They encouraged EPA (and Congress) to fund increased research and
development of alternative fuels (alternatives to gasoline) and alternative-fueled vehicles.
2. Air Quality Concerns and Benefits of Sulfur Control
Many commenters, in supporting their positions on the need for sulfur control, made
recommendations about what air quality concerns should be considered in evaluating the need for
sulfur reductions. The National Conference of State Legislatures (NCSL) and AIAM both
suggested that toxics should be factored into the evaluation; the NCSL encouraged EPA to focus
specifically on toxics. AIAM also encouraged consideration of other benefits of sulfur control,
including reductions in the formation of secondary particulate matter (PM) in the form of sulfates
and nitrates, reduced acid deposition due to S02 reductions, and improved visibility.
Commenters from the oil industry, by contrast, suggested that the Agency only consider what is
needed to achieve the NAAQS for ozone, PM, and carbon monoxide (CO).
The environmental community encouraged a broader consideration of the benefits of
sulfur control. Twenty-two environmental groups joined together to encourage year-round
control of sulfur based on the belief that the public health benefits to be achieved occur year-
round. Other environmental groups suggested that the public health benefits outweigh the costs,
and thus argued for national, year-round control to the lowest levels.
3. Need to Control Other Gasoline Properties
A number of comments addressed the need to control gasoline properties in addition to
sulfur to enable vehicles to meet expected Tier 2 standards. The automotive industry suggested
that the Agency control the distillation properties of gasoline by restricting the "driveability
index" (DI) of the fuel. They claimed that fuels with driveability indices too high have an impact
on their ability to control the ratio of air to fuel in the engine, and thus impact emissions. One
commenter also suggested that, since high DI fuels are expected to cause performance problems
in addition to higher emissions, high DI fuels could sour customers on some of the newer,
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cleaner technologies if DI were not controlled. Comments from Exxon argued against the need
to control gasoline distillation properties, arguing that technological improvements such as using
air assisted injection to improve fuel vaporization before combustion would be preferred.
At least one automotive industry comment also suggested that the Agency control
combustion chamber deposits (CCD), arguing that control of CCD was needed to permit vehicles
to meet the very clean emissions levels expected for Tier 2.
4. Need to Control Diesel Fuel Properties
Since diesel vehicles (both cars and light trucks) may be required to meet the same Tier 2
standards as gasoline vehicles, a number of comments addressed the question of whether diesel
fuel changes were necessary to enable these vehicles to meet the standards. Sunoco encouraged
EPA to consider diesel fuel changes only upon review of the needs of heavy-duty engines in
addition to the needs of light duty diesel cars and trucks. The automotive industry
representatives and most of the commenters from the environmental community suggested that
diesel fuel sulfur levels must be controlled to no more than 50 ppm if diesel engines will be able
to meet Tier 2 standards. Some of these commenters stated that low sulfur diesel would enable
certain catalysts and/or the use of exhaust gas recirculation to control emissions. The benefits of
reducing diesel sulfur levels were noted to include reductions in particulate formation via a
reduction in sulfates, and reductions in S02 emissions. The Engine Manufacturers Association
suggested that, in addition to sulfur levels, cetane, aromatics, and density of diesel fuel also
needed to be controlled to enable the cleanest diesel engine technologies.
Some commenters, such as MECA, suggested that diesel sulfur control be pursued
concurrently with gasoline sulfur controls to enable refiners to make appropriate capital
investments. Sunoco commented that, contrary to expectations, control of diesel sulfur levels
concurrent with gasoline sulfur control would not necessarily result in economies of scale due to
the number of variables that must be considered, including the sulfur levels required in the two
fuels, the location of the refinery, the technologies available to desulfurize these fuels, etc. Even
if the feed to the fluidized catalytic cracker unit (FCC) were desulfurized (the expectation if both
diesel and gasoline sulfur levels are controlled), Sunoco argued that additional desulfurization
may be required if one or both fuels are pushed to the lowest sulfur levels.
VHI. Miscellaneous
EPA received several comments on regulatory issues that were not raised in the Draft
Study. These comments are summarized below.
AIAM and Nissan suggested that EPA adopt a phase-in of the Tier 2 standards over a
three to four year period to allow vehicle manufacturers to incorporate emission control system
revisions along with model changeover. AIAM stated that a similar strategy was followed by
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EPA in the Tier 1 standards and by CARB in its LEV standards and in most other regulatory
actions that have been promulgated in the past decade. Nissan also favored streamlining of
certification.
AIAM and COSVAM both argued that EPA should provide for the needs of small
volume manufacturers (SVMs). AIAM stated that if a phase-in approach were adopted, then
SVMs should not have to comply with the new Tier 2 requirements until the final year of the
phase-in, i.e., when all other manufacturers achieve 100 percent compliance. COSVAM
commented that the air quality impact of vehicles sold by SVMs is small, and the proportionally
higher burden emission requirements place on SVMs necessitates additional flexibility.
The Northeast Alternative Vehicle Consortium (NAVC) wanted EPA to recognize the
fact that advanced transportation technologies (i.e., hybrid electric vehicles and fuel cells) are
advancing at an extremely rapid pace and that it is important for the Tier 2 regulations to
recognize the rapid technology advancements and their co-benefits of reducing criteria pollutants
and greenhouse gas emissions. They therefore suggested that EPA incorporate two year
technology reviews with the regulations so that goals are not set in stone for too long.
A commenter from environmental groups recommended labeling of emission levels on
new vehicles and setting a PM standard for the supplemental federal test procedure (SFTP) and
eliminating diesel testing waivers.
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LIST OF COMMENTERS
Docket ID #
Commenting Party
* n-D-oi to -
36
These documents received before draft Tier 2 study issued for public comment
n-D-37
David T. Saunders (private citizen)
n-D-38
Shawn R. Cowls (private citizen)
n-D-39
Robert Brooks (private citizen)
n-D-40
H.M. Gilbreath (private citizen)
n-D-41
Nancy Kerby (private citizen)
U-DA2
Christopher Jesse Imbach (private citizen)
n-D-43
Coalition Of Small Volume Automobile Manufacturers, Inc. (COSVAM)
H-D-44
Manufacturers of Emission Controls Association (MECA)
H-D-45
Wisconsin Department Of Transportation (DOT)
n-D-46
Oklahoma Department of Environmental Quality (DEQ)
H-D-47
Northeast Alternative Vehicle Consortium (NAVC)
n-D^8
Misc. Environmental Organizations (Amer. Council for Energy Efficient Economy, etc.)
n-D-49
State and Territorial Air Pollution Program Administrators/Association of Local Air Pollution
Control Officials (STAPPA/ALAPCO)
n-D-50
Alaska Department of Environmental Conservation (DEC)
II-D-51
American Petroleum Institute (API)
n-D-52
Ozone Transport Commission (OTC)
n-D-53
New York State - Department of Environmental Conservation (DEC)
n-D-54
National Association of Automotive Dealers (NADA)
n-D-55
Nissan North America Inc
n-D-56
National Petroleum Refiners Association (NPRA)
n-D-57
22 Environmental Groups, Including: Alaska Center for the Environment,...
n-D-58
National Park Service/US Dept of Interior
n-D-59
American Lung Assn (Blake Early)
n-D-60
Exxon
n-D-6i
The International Center for Technology Assessment/The Campaign on Auto Pollution (Blake
Ethridge)
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n-D-62
Association of International Automobile Manufacturers (AIAM)
n-D-63
Massachusetts (Executive Office of Environmental Affairs)
n-D-64
Washington - Dept of Ecology
n-D-66
Environmental Advocates
n-D-67
Idaho - Governor
n-D-68
National Conference of State Legislatures
n-D-70
Sinclair
n-D-71
American Automobile Manufacturers Association (AAMA)
n-G-01 to -03
moved to II-D category
n-G-04
Toyota
n-G-05
Engine Manufacturers Association (EMA)
n-G-06
Sunoco
n-G-07
Duplicate of II-G-05
n-G-08
M. Thomas, American Council for Energy Efficient Economy (ACEEE); J. Hathaway, Natural
Resources Defense Council (NRDC); R. Hwang, Union of Concerned Scientists (UCS)
n-G-09
J. Colucci, Automotive Fuels Consulting, Inc.
II-G-10 to -64
Internet mail from private citizens in support of more stringent Tier 2 standards and sulfur
controls
n-G-65
Florida Department of Environmental Protection (DEP)
n-G-68
Ford - Kelly Brown (comments on sulfur paper)
n-G-66
Marathon Ashland Petroleum
n-G-67
Virginia (Governor)
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