Counties whose 2030 control case is within 10 percent of the      ..............  ..............           -0.09
 annual PM2.5 standard, population-weighted.....................
----------------------------------------------------------------------------------------------------------------
\a\ Averages are over counties with 2005 modeled design values.
\b\ Population numbers based on Woods & Poole data. Woods & Poole Economics, Inc. 2001. Population by Single
  Year of Age CD.
\c\ This analysis assumed emissions reductions from Tier 3 vehicle standards would occur in all states and did
  not account for emission reductions associated with LEV III vehicle standards in California and other states
  that have subsequently adopted it. The analysis for the final rule will account for LEV III vehicle standards.
\d\ Eight of these counties are in California, see Table 7-35 in the DRIA.

                Table III-11--Average Change in Projected 24-hour PM2.5 Design Values in 2030 \c\
----------------------------------------------------------------------------------------------------------------
                                                                                Change in 2030
                           Average \a\                            Number of U.S.       2030        design value
                                                                     counties     Population \b\   ([mu]g/m\3\)
----------------------------------------------------------------------------------------------------------------
All.............................................................             569     245,111,480           -0.16
All, population-weighted........................................  ..............  ..............           -0.20
Counties whose 2005 base year is violating the 2006 24-hour                  108      91,474,036           -0.29
 PM2.5 standard.................................................
Counties whose 2005 base year is violating the 2006 24-hour       ..............  ..............           -0.27
 PM2.5 standard, population-weighted............................
Counties whose 2005 base year is within 10 percent of the 2006               140      53,990,060           -0.18
 24-hour PM2.5 standard.........................................
Counties whose 2005 base year is within 10 percent of the 2006    ..............  ..............           -0.21
 24-hour PM2.5 standard, population-weighted....................
Counties whose 2030 control case is violating the 2006 24-hour                21      31,002,272           -0.50
 PM2.5 standard \d\.............................................
Counties whose 2030 control case is violating the 2006 24-hour    ..............  ..............           -0.32
 PM2.5 standard, population-weighted \d\........................
Counties whose 2030 control case is within 10 percent of the                   7       4,212,913           -0.37
 2006 24-hour PM2.5 standard....................................
Counties whose 2030 control case is within 10 percent of the      ..............  ..............           -0.50
 2006 24-hour PM2.5 standard, population-weighted...............
----------------------------------------------------------------------------------------------------------------
\a\ Averages are over counties with 2005 modeled design values.
\b\ Population numbers based on Woods & Poole data. Woods & Poole Economics, Inc. 2001. Population by Single
  Year of Age CD.
\c\ This analysis assumed emissions reductions from Tier 3 vehicle standards would occur in all states and did
  not account for emission reductions associated with LEV III vehicle standards in California and other states
  that have subsequently adopted it. The analysis for the final rule will account for LEV III vehicle standards.
\d\ Eleven of these counties are in California, see Table 7-37 in the DRIA.

3. Nitrogen Dioxide
    Although our modeling indicates that by 2030 the majority of the
country will experience decreases of less than 0.1 ppb in their annual
NO2 concentrations due to this proposal, annual
NO2 concentrations are projected to decrease by more than
0.3 ppb in most urban areas. These emissions reductions would also
likely decrease 1-hour NO2 concentrations and help any
potential nonattainment areas to attain and maintain the standard.
Additional information on the emissions reductions that are projected
with this proposal is available in Section 7.2.1 of the draft RIA.
4. Air Toxics
    Our modeling indicates that the impacts of proposed Tier 3
standards include generally small decreases in ambient concentrations
of air toxics, especially in urban areas, with notable nationwide
reductions in benzene. Although reductions are greater in 2030 (when
Tier 3 cars and trucks would contribute nearly 90 percent of fleet-wide
vehicle miles travelled) than in 2017 (the first year of the proposed
program), our modeling projects there would be small immediate
reductions in ambient concentrations of air toxics due to the proposed
sulfur controls in 2017. Furthermore, the full reduction of the vehicle
program would be realized after 2030, when the fleet has fully turned
over to Tier 3 vehicles. Air toxics pollutants dominated by primary
emissions (or a decay product of a directly emitted pollutant) have the
largest impacts, rather than air toxics that primarily result from
photochemical transformation. Specifically, in 2030, our modeling
projects that the proposal would decrease ambient benzene
concentrations across much of the country on the order of 1 to 5
percent, with reductions ranging from 10 to 25 percent in some urban
areas. Our modeling also shows reductions of 1,3-butadiene and acrolein
concentrations in 2030 ranging between 1 and 25 percent, with 1,3-
butadiene decreases of at least 0.005 [mu]g/m\3\ in urban areas. These
toxics are national risk drivers and the reductions in ambient

concentrations from this proposed rule would result in reductions in
risks from cancer and noncancer health effects. In some parts of the
country (mainly urban areas), ethanol and formaldehyde concentrations
are projected to decrease on the order of 1 to 5 percent in 2030 as a
result of the proposal. Decreases in ethanol concentrations are
expected due to reductions in VOC as a result of the proposed
standards. Changes in ambient acetaldehyde concentrations are generally
less than 1 percent across the U.S., although the proposal may decrease
acetaldehyde concentrations in some urban areas by 1 to 2.5 percent in
2030.
    Although the reductions in ambient air toxics concentrations
expected from the proposed Tier 3 standards are generally small, they
are projected to benefit the majority of the U.S. population. As shown
in Table III-12, over 80 percent of the total U.S. population is
projected to experience a decrease in ambient benzene and acrolein
concentrations of at least 2.5 percent, with more than 90 percent of
the populations projected to experience 1,3-butadiene concentrations of
similar magnitude. Over 80 percent of the U.S population is projected
to experience at least a 1 percent decrease in ambient ethanol
concentrations, and over 60 percent would experience a similar decrease
in ambient formaldehyde concentrations with the proposed standards.

 Table III-12--Percent of Total Population Experiencing Changes in Annual Ambient Concentrations of Toxic Pollutants in 2030 as a Result of the Proposed
                                                                      Standards \a\
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                              Benzene        Acrolein      1,3-Butadiene   Formaldehyde       Ethanol      Acetaldehyde
                     Percent change                          (percent)       (percent)       (percent)       (percent)       (percent)       (percent)
--------------------------------------------------------------------------------------------------------------------------------------------------------
<= -50..................................................  ..............  ..............  ..............  ..............  ..............  ..............
> -50 to <= -25.........................................  ..............  ..............             0.1  ..............  ..............  ..............
> -25 to <= -10.........................................             2.8             0.7            56.8  ..............  ..............  ..............
> -10 to <= -5..........................................            23.7            36.8            30.8  ..............  ..............  ..............
> -5 to <= -2.5.........................................            54.5            43.7             7.1             1.2            33.0             0.3
> -2.5 to <= -1.........................................            17.7            15.3             3.4            63.2            55.3            25.1
> -1 to < 1.............................................             1.4             3.5             1.7            35.6            11.6            74.6
>= 1 to < 2.5...........................................  ..............  ..............             0.0  ..............  ..............  ..............
>= 2.5 to < 5...........................................  ..............  ..............  ..............  ..............  ..............  ..............
>= 5 to < 10............................................  ..............  ..............  ..............  ..............  ..............  ..............
>= 10 to < 25...........................................  ..............  ..............  ..............  ..............  ..............  ..............
>= 25 to < 50...........................................  ..............  ..............  ..............  ..............  ..............  ..............
>= 50...................................................  ..............  ..............  ..............  ..............  ..............  ..............
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ This analysis assumed emissions reductions from Tier 3 vehicle standards would occur in all states and did not account for emission reductions
  associated with LEV III vehicle standards in California and other states that have subsequently adopted it. The analysis for the final rule will
  account for LEV III vehicle standards.

5. Visibility
    Air quality modeling conducted for this proposed action was used to
project visibility conditions in 139 mandatory class I federal areas
across the U.S. The results show that in 2030 all the modeled areas
would continue to have annual average deciview levels above background
and the proposed rule would improve visibility in all these areas.\194\
The average visibility at all modeled mandatory class I federal areas
on the 20 percent worst days is projected to improve by 0.04 deciviews,
or 0.28 percent, in 2030. Section <IP_ADDRESS> of the draft RIA contains
more detail on the visibility portion of the air quality modeling.
---------------------------------------------------------------------------

    \194\ The level of visibility impairment in an area is based on
the light-extinction coefficient and a unitless visibility index,
called a ``deciview'', which is used in the valuation of visibility.
The deciview metric provides a scale for perceived visual changes
over the entire range of conditions, from clear to hazy. Under many
scenic conditions, the average person can generally perceive a
change of one deciview. The higher the deciview value, the worse the
visibility. Thus, an improvement in visibility is a decrease in
deciview value.
---------------------------------------------------------------------------

6. Nitrogen and Sulfur Deposition
    Our air quality modeling projects substantial decreases in nitrogen
deposition as a result of the proposed standards. The standards would
result in annual percent decreases of greater than 5 percent in most
major urban areas and greater than 7 percent in a few areas. In
addition, smaller decreases, in the 1 to 1.5 percent range, would occur
over most of the rest of the country. The impacts of the proposed
standards on sulfur deposition are smaller, ranging from no change to
decreases of over 2 percent in some areas. For maps of 2030 deposition
impacts and additional information on these impacts see Section <IP_ADDRESS>
of the draft RIA.
7. Environmental Justice
    Environmental justice (EJ) is a principle asserting that all people
deserve fair treatment and meaningful involvement with respect to
environmental laws, regulations, and policies. EPA seeks to provide the
same degree of protection from environmental health hazards for all
people. As referenced below, numerous studies have found that some
environmental hazards are more prevalent in areas with high population
fractions of racial/ethnic minorities and people with low socioeconomic
status (SES), as would be expected on the basis of those areas' share
of the general population.
    As discussed in Section II of this document, concentrations of many
air pollutants are elevated near high-traffic roadways. If minority
populations and low-income populations disproportionately live near
such roads, then an issue of EJ may be present. Such disparities may be
due to multiple factors.\195\
---------------------------------------------------------------------------

    \195\ Depro, B.; Timmins, C. (2008) Mobility and environmental
equity: do housing choices determine exposure to air pollution?
North Caroline State University Center for Environmental and
Resource Economic Policy.
---------------------------------------------------------------------------

    People with low SES often live in neighborhoods with multiple
stressors and health risk factors, including reduced health insurance
coverage rates, higher smoking and drug use rates, limited access to
fresh food, visible neighborhood violence, and elevated rates of
obesity and some diseases such as asthma, diabetes, and ischemic heart
disease. Although questions remain, several studies find stronger
associations between air pollution and health in locations with such
chronic neighborhood stress, suggesting that populations in these areas
may be more susceptible to the effects of air

pollution.196 197 198 199 Household-level stressors such as
parental smoking and relationship stress also may increase
susceptibility to the adverse effects of air
pollution.200 201
---------------------------------------------------------------------------

    \196\ Clougherty, J.E.; Kubzansky, L.D. (2009) A framework for
examining social stress and susceptibility to air pollution in
respiratory health. Environ Health Perspect 117: 1351-1358.
Doi:10.1289/ehp.0900612 [Online at http://dx.doi.org].
    \197\ Clougherty, J.E.; Levy, J.I.; Kubzansky, L.D.; Ryan, P.B.;
Franco Suglia, S.; Jacobson Canner, M.; Wright, R.J. (2007)
Synergistic effects of traffic-related air pollution and exposure to
violence on urban asthma etiology. Environ Health Perspect 115:
1140-1146. doi:10.1289/ehp.9863 [Online at http://dx.doi.org].
    \198\ Finkelstein, M.M.; Jerrett, M.; DeLuca, P.; Finkelstein,
N.; Verma, D.K.; Chapman, K.; Sears, M.R. (2003) Relation between
income, air pollution and mortality: a cohort study. Canadian Med
Assn J 169: 397-402.
    \199\ Shankardass, K.; McConnell, R.; Jerrett, M.; Milam, J.;
Richardson, J.; Berhane, K. (2009) Parental stress increases the
effect of traffic-related air pollution on childhood asthma
incidence. Proc Natl Acad Sci 106: 12406-12411. doi:10.1073/
pnas.0812910106 [Online at http://dx.doi.org].
    \200\ Lewis, A.S.; Sax, S.N.; Wason, S.C.; Campleman, S.L (2011)
Non-chemical stressors and cumulative risk assessment: an overview
of current initiatives and potential air pollutant interactions. Int
J Environ Res Public Health 8: 2020-2073. Doi:10.3390/ijerph8062020
[Online at http://dx.doi.org].
    \201\ Rosa, M.J.; Jung, K.H.; Perzanowski, M.S.; Kelvin, E.A.;
Darling, K.W.; Camann, D.E.; Chillrud, S.N.; Whyatt, R.M.; Kinney,
P.L.; Perera, F.P.; Miller, R.L (2010) Prenatal exposure to
polycyclic aromatic hydrocarbons, environmental tobacco smoke and
asthma. Respir Med (In press). doi:10.1016/j.rmed.2010.11.022
[Online at http://dx.doi.org].
---------------------------------------------------------------------------

    To address the existing conditions in areas near major roadways, in
comparison with other locations, we reviewed existing scholarly
literature examining the topic, and conducted our own evaluation of two
national datasets: the U.S. Census Bureau's American Housing Survey for
calendar year 2009 and the U.S. Department of Education's database of
school locations.
    Existing publications that address EJ issues generally report that
populations living near major roadways (and other types of
transportation infrastructure) tend to be composed of larger fractions
of nonwhite residents. People living in neighborhoods near such sources
of air pollution also tend to be lower in income than people living
elsewhere. Numerous studies evaluating the demographics and
socioeconomic status of populations or schools near roadways have found
that they include a greater percentage of minority residents, as well
as lower SES (indicated by variables such as median household income).
Locations in these studies include Los Angeles, CA, Seattle, WA, Wayne
County, MI, Orange County, FL, and the State of California
202 203 204 205 206 207
---------------------------------------------------------------------------

    \202\ Marshall, J.D. (2008) Environmental inequality: air
pollution exposures in California's South Coast Air Basin.
    \203\ Su, J.G.; Larson, T.; Gould, T.; Cohen, M.; Buzzelli, M.
(2010) Transboundary air pollution and environmental justice:
Vancouver and Seattle compared. GeoJournal 57: 595-608. doi:10.1007/
s10708-009-9269-6 [Online at http://dx.doi.org].
    \204\ Chakraborty, J.; Zandbergen, P.A. (2007) Children at risk:
measuring racial/ethnic disparities in potential exposure to air
pollution at school and home. J Epidemiol Community Health 61: 1074-
1079. doi: 10.1136/jech.2006.054130 [Online at http://dx.doi.org].
    \205\ Green, R.S.; Smorodinsky, S.; Kim, J.J.; McLaughlin, R.;
Ostro, B. (2003) Proximity of California public schools to busy
roads. Environ Health Perspect 112: 61-66. doi:10.1289/ehp.6566
[http://dx.doi.org].
    \206\ Wu, Y; Batterman, S.A. (2006) Proximity of schools in
Detroit, Michigan to automobile and truck traffic. J Exposure Sci &
Environ Epidemiol. doi:10.1038/sj.jes.7500484 [Online at http://dx.doi.org].
    \207\ Su, J.G.; Jerrett, M.; de Nazelle, A.; Wolch, J. (2011)
Does exposure to air pollution in urban parks have socioeconomic,
racial, or ethnic gradients? Environ Res 111: 319-328.
---------------------------------------------------------------------------

    We analyzed two national databases that allowed us to evaluate
whether homes and schools were located near a major road. One database,
the American Housing Survey (AHS), includes descriptive statistics of
over 70,000 housing units across the nation. The study is conducted
every two years by the U.S. Census Bureau. We analyzed data from the
2009 AHS. The second database we analyzed was the U.S. Department of
Education's Common Core of Data, which includes enrollment and location
information for schools across the U.S.
    In analyzing the 2009 AHS, we focused on whether or not a housing
unit was located within 300 feet of ``4-or-more lane highway, railroad,
or airport.'' \208\ We analyzed whether there were differences between
houses and householders in such locations and those not in them.\209\
We found that houses with a nonwhite householder were 22-34 percent
more likely to be located within 300 feet of these large transportation
facilities, while houses with a Hispanic householder were 17-33 percent
more likely. Households near large transportation facilities were, on
average, lower in income and educational attainment, more likely to be
a rental property and located in an urban area.
---------------------------------------------------------------------------

    \208\ This variable primarily represents roadway proximity.
According to the Central Intelligence Agency's World Factbook, in
2010, the United States had 6,506,204 km or roadways, 224,792 km of
railways, and 15,079 airports. As such, highways represent the
overwhelming majority of transportation facilities described by this
factor in the AHS.
    \209\ Bailey, C. (2011) Demographic and Social Patterns in
Housing Units Near Large Highways and other Transportation Sources.
Memorandum to docket.
---------------------------------------------------------------------------

    In examining schools near major roadways, we examined the Common
Core of Data (CCD) from the U.S. Department of Education, which
includes information on all public elementary and secondary schools and
school districts nationwide.\210\ To determine school proximities to
major roadways, we used a geographic information system (GIS) to map
each school and roadways based on the U.S. Census's TIGER roadway
file.\211\ We found that minority students were overrepresented at
schools within 200 meters of the largest roadways, and that schools
within 200 meters of the largest roadways also had higher than expected
numbers of students eligible for free or reduced-price lunches. For
example, Black students represent 21.57 percent of students at schools
located within 200 meters of a primary road, whereas Black students
represent 16.62 percent of students in all U.S. schools. Hispanic
students represent 30.13 percent of students at schools located within
200 meters of a primary road, whereas Hispanic students represent 21.93
percent of students in all U.S. schools.
---------------------------------------------------------------------------

    \210\ http://nces.ed.gov/ccd/.
    \211\ Pedde, M.; Bailey, C. (2011) Identification of Schools
within 200 Meters of U.S. Primary and Secondary Roads. Memorandum to
the docket.
---------------------------------------------------------------------------

    Overall, there is substantial evidence that people who live or
attend school near major roadways are more likely to be of a minority
race, Hispanic ethnicity, and/or low SES. The reduction of near-roadway
concentrations of many pollutants, discussed above, is likely to help
in mitigating this disparity in racial, ethnic, and economically-based
exposures.

IV. Proposed Vehicle Emissions Program

    In the more than 10 years since EPA finalized the Tier 2 Vehicle
Program, manufacturers of light-duty vehicles have continued to develop
a wide range of improved technologies capable of reducing key exhaust
emissions, especially hydrocarbons, nitrogen oxides (NOX),
and particulate matter (PM). The California LEV II program has been
instrumental in the continuous technology improvements by requiring
year after year reductions in fleet average hydrocarbon levels in
addition to requiring the introduction of advanced exhaust and
evaporative emission controls in partial zero emission vehicles
(PZEVs). This progress in vehicle technology has made it possible for
manufacturers to achieve

emission reductions well beyond the requirements of the Tier 2 program
if gasoline sulfur levels are lowered further.
    Extensive data from existing Tier 2 (and California LEV II)
vehicles show the opportunity for further reductions, especially in
addressing emissions produced at start-up, emissions under high-speed,
high-load conditions, the effects of sulfur in gasoline, the effects of
increased oil consumption, and the effects of vehicle and control
systems age. For these reasons, we are proposing more stringent
standards designed to reduce emissions, primarily non-methane organic
gases (NMOG), NOX, and PM from new vehicles. As discussed in
detail below and in the draft RIA, we have concluded that, in
conjunction with the reductions in fuel sulfur proposed in this action,
the proposed vehicle emissions standards are feasible and cost-
effective across the fleet in the proposed timeframe. We believe that
simultaneous reductions in fuel sulfur would be a key factor in
enabling the entire fleet of light-duty vehicles to meet the proposed
emission standards in-use, throughout the life of the vehicle.
    This section describes in detail the proposed program for reducing
tailpipe and evaporative emissions from light-duty vehicles (LDVs, or
passenger cars), light-duty trucks (LDT1s, 2s, 3s, and 4s), Medium-Duty
Passenger Vehicles (MDPVs), and heavy-duty vehicles (HDVs). Sections
IV.A and B discuss the proposed tailpipe emission standards and time
lines, and other provisions for new light-duty vehicles and MDPVs and
for new heavy-duty vehicles up to 14,000 lbs Gross Vehicle Weight
Rating (GVWR). Section IV.C presents the proposed evaporative emissions
standards and program as well as proposed improvements to the existing
Onboard Diagnostics (OBD) provisions. In Section IV.D, we describe our
proposal to update our federal certification fuel to better match
today's in-use fuel and to be forward-looking with respect to potential
future gasoline ethanol and sulfur content. We also discuss in this
section proposed compliance flexibilities for small companies and
small-volume manufacturers (IV.E) and test procedure and other
compliance provisions (IV.F).

A. Tailpipe Emission Standards for Light-Duty Vehicles, Light-Duty
Trucks, and Medium-Duty Passenger Vehicles

1. Overview
    The proposed Tier 3 standards are very similar in structure to
those in the Tier 2 program. As with the Tier 2 program, the proposed
standards would apply to all LDVs and LDTs below 8,500 lbs GVWR, and
MDPVs (8,500 to 10,000 lbs GVWR). (We discuss the proposed standards
for heavy-duty vehicles up to 14,000 lbs GVWR other than MDPVs, in
Section IV.B below.) Also as with Tier 2, manufacturers would select
from several ``bins'' of emission standards such that the average of
their vehicles' emissions complies with the proposed fleet-average
standards.
    In the discussions of the various elements of our proposed program
for light- and heavy-duty vehicles throughout this preamble, we
describe how the provisions would be consistent with the California Air
Resources Board (CARB) LEV III program.\212\ Auto manufacturers have
stressed to us the importance of their being able to design and produce
a single fleet of vehicles in all 50 states that would comply with
requirements under the Tier 3 program and the LEV III program, as well
as greenhouse gas/CAFE requirements in the same timeframe. Consistency
among the federal and California programs means that special versions
of vehicles with different emission control hardware and calibrations
would not be necessary for different geographic areas. This would allow
manufacturers to avoid the additional costs of parallel design,
development, calibration, and manufacturing. Consistency among programs
would also eliminate the need to supply aftermarket parts for repair of
multiple versions of a vehicle. We believe that the most cost-effective
national program will result from close coordination of CARB LEV III
and federal Tier 3 program elements and their implementation. To that
end, we worked closely with CARB and the vehicle manufacturers, both
individually and through their trade associations, to align the two
programs.
---------------------------------------------------------------------------

    \212\ LEV III program as approved by the California Air
Resources Board, January 2012.
---------------------------------------------------------------------------

    The Tier 3 program we are proposing is identical to LEV III in most
major respects for both light-duty and heavy-duty vehicle exhaust and
evaporative emissions requirements, as discussed in detail below in
this section. The levels and the timing of the light-duty and heavy-
duty declining fleet-average NMOG+NOx standards that we are proposing
would be identical to those in LEV III. Also, the Tier 3 emissions bins
to which manufacturers would certify individual vehicle models in order
to comply with the average standards, for both light- and heavy-duty
vehicles, would also be identical to those in LEV III. Similarly, the
proposed Tier 3 per-vehicle PM standards match LEV III standards
through MY 2024. In addition, our proposed primary evaporative
emissions standards and onboard diagnostics requirements are also
identical to the LEV III requirements.
    We note there are a few proposed Tier 3 provisions that CARB and
EPA understand would be different, for reasons discussed below.
Specifically, these include the LEV III program and our proposed Tier 3
program would have different light-duty PM requirements late in the
program (i.e., after MY 2024 (IV.A.3.b.)), would require different test
fuels (E10 and E15, respectively (IV.A.3.c)), and only EPA would have
an evaporative leak test (IV.C.5.b). EPA and CARB will continue to work
toward additional consistency between our programs whenever practicable
as both programs are implemented. Beyond these three provisions, the
differences between the programs would not be major and would exist
only in the early transitional years of the Tier 3 program. These
differences would result from the fact that the LEV III requirements
begin slightly earlier and that a limited phase-in of some provisions
would be necessary for a smooth transition to overall aligned programs.
These temporary differences would include the process for how early
compliance credits would be generated and used (e.g., Section
IV.A.7.a); how quickly manufacturers would need move toward certifying
all of their vehicle models to longer useful-life values (e.g., Section
IV.A.7.b) and on the new test fuel (e.g., Section IV.A.7.c); and
transitional emissions bins to facilitate the transition from Tier 2 to
Tier 3 (IV.A.7.m). Similarly, the primary Tier 3 evaporative standards
would have a brief phase in period, temporarily resulting in
requirements that would be slightly different from those in LEV III.
    The proposed Tier 3 program is designed primarily to reduce exhaust
and evaporative emissions during summer ambient temperature conditions
when NMOG, NOX and PM emissions contribute to air quality
concerns. We are not proposing new emission requirements for any
vehicle or fuel over the cold temperatures test cycles (i.e., the
20[emsp14][deg]F cold CO and NMHC tests). However, we seek comment on
the need for doing so, including vehicles operating on E85 fuel, and on
the appropriate form and level for any such cold-temperature
requirements.

2. Summary of Proposed FTP and SFTP Tailpipe Standards
    We are proposing a comprehensive program that would address the key
pollutants of concern. We are proposing new standards for the sum of
NMOG and NOX emissions, presented as NMOG+NOX,
and PM. As discussed in Section III above, these proposed standards
would result in very significant improvements in vehicle emissions from
the levels of the Tier 2 program. For these pollutants, we are
proposing standards as measured on test procedures that represent a
range of vehicle operation, including the Federal Test Procedure (FTP)
and the Supplemental Federal Test Procedure (SFTP). Unless otherwise
specified, the proposed FTP and SFTP standards would apply to vehicles
operating on gasoline, diesel, and alternative fuels, including both
flexible fuel and dedicated alternative fuel vehicles.
    The proposed FTP and SFTP NMOG+NOX standards would be
fleet-average standards, meaning that the manufacturer would calculate
the average emissions of the vehicles it sells in each model year and
compare that average to the applicable standard for that model year.
The proposed fleet average standards for NMOG+NOX evaluated
over the FTP are summarized in Table I-1. (For comparison, the average
NMOG and NOX standard for the Tier 2 program, when added
together, equal 160 mg/mi). The standards would begin in MY 2017 at a
level representing a 46 percent reduction from the current Tier 2
requirements for lighter vehicles and would become increasingly
stringent, culminating in an 81 percent reduction in MY 2025. The
proposed FTP NMOG+NOX program includes separate fleet
average standards for lighter and heavier vehicles that would converge
at 30 milligrams per mile (mg/mi) in MY 2025 and
later.213 214
---------------------------------------------------------------------------

    \213\ The proposed declining NMOG+NOX fleet-average
standards would consist of one set of declining standards that would
apply to light-duty vehicles (LDVs) and small light trucks (LDT1s)
and a second set of declining standards that would apply to heavier
light trucks (LDT2s, LDT3s. LDT4s), and MDPVs.
    \214\ This preamble presents the proposed standards in terms of
milligrams per mile for convenience. The associated regulatory
language will continue to present the standard in terms of grams per
mile for consistency with earlier programs.
---------------------------------------------------------------------------

    Manufacturers would determine their fleet average FTP
NMOG+NOX emission values based on the per-vehicle ``bin
standards'' to which they certified each vehicle model. As with the
Tier 2 program, manufacturers would be free to choose to certify
vehicles to any of the bins, so long as the sales-weighted average of
the NMOG+NOX values from the selected bins met the fleet
average standard for that model year. Table IV-1 presents the per-
vehicle bin standards. Similarly, the proposed fleet average
NMOG+NOX standards measured over the SFTP are summarized in
Table I-2. The proposed SFTP NMOG+NOX fleet average
standards decline from MY 2017 until MY 2025. In this case, the same
standards would apply to both lighter and heavier vehicles. In MY 2025,
the SFTP NMOG+NOX standard would reach its fully phased-in
fleet average level of 50 mg/mi. We are also proposing PM standards as
part of this Tier 3 program. The proposed PM standards would apply to
each vehicle separately (i.e., not as a fleet average). Also, in
contrast to the declining NMOG+NOX standards, the proposed
certification PM standard on the FTP is 3 mg/mi for all vehicles and
for all model years, but phasing in beginning in MY 2017 for vehicles
at or below 6,000 lbs GVWR and in MY 2018 for vehicles above 6,000 lbs
GVWR. Based on EPA and CARB test programs, most current light duty
vehicles are already performing at or below this level. However, some
vehicles are emitting above this level, due to such factors as
combustion chamber designs, and fuel and oil consumption controls that
are not optimized for low PM emissions. The intent of the proposed 3
mg/mi standard is to bring all light-duty vehicles to the PM level
typical of that being demonstrated by most light-duty vehicles today.
    To address the uncertainties that will accompany the introduction
of new technologies, the proposed program also includes a separate in-
use FTP PM standard of 6 mg/mi for the testing of in-use vehicles
during the phase-in period, as described in more detail below. As
presented in Table I-3, for vehicles at or below 6000 lbs GVWR, these
FTP certification and in-use standards would be phased in beginning
with a requirement that at least 20 percent of a company's U.S. sales
meet the standards in MY 2017 and reaching a 100 percent compliance
requirement in MY 2021. The proposed standards represent a significant
numerical reduction from the Tier 2 PM emission standards of 10 mg/mi
for light-duty vehicles. Finally, the proposed Tier 3 program includes
PM standards evaluated over the US06 cycle (a component of the SFTP
test, discussed further below) at a level of 10 mg/mi for vehicles at
or below 6,000 lbs GVWR and 20 mg/mi for heavier vehicles. We are
proposing separate standards for different sizes of vehicles because PM
generation typically increases when vehicles are carrying heavier loads
and/or when they are pulling trailers. The US06 PM standards would
phase in on the same schedule as the FTP PM standards, reaching 100
percent of each company's U.S. sales by MY 2022. These US06 standards
would apply to the same vehicle models that a manufacture chose to
certify to the FTP PM standard during the percent phase in period. PM
levels over the US06 are typically higher than the PM emitted over the
FTP due to the increased load on the vehicle. As in the case of the FTP
PM standards, the intent of the proposed standard is to bring the
emission performance of all vehicles to that already being demonstrated
by many vehicles in the current light-duty fleet.
    As with the FTP PM standard, we propose a separate in-use US06 PM
standard during the percent phase-in period of 15 and 25 mg/mi for
vehicles of 6000 lbs GVWR and less, and for vehicles above 6,000 lbs
GVWR, respectively.
    The next subsections describe in more detail the proposed
standards, how they would be implemented over time, and the
technological approaches that we believe will be available to
manufacturers in order to comply.
3. Proposed FTP Standards
    As summarized above, we propose new standards for the primary
pollutants of concern for this rule (NMOG, NOX, and PM) as
measured on the FTP. The following paragraphs describe in more detail
these FTP standards for NMOG+NOX and PM, as well as for
carbon monoxide (CO) and formaldehyde (HCHO).
a. FTP NMOG+NOX Standards
    We propose that the Tier 3 NMOG and NOX standards, both
of which are important to reduce ambient ozone concentrations, be
expressed in terms of the sum of the two pollutants, or as
NMOG+NOX in mg/mi.\215\ This approach contrasts with the
Tier 2 standards, which were expressed as separate NMOG and
NOX standards. We believe that the combined standard is
appropriate for this proposed program for several reasons. At the
stringent proposed emission levels, combining NMOG and NOX
would provide a small amount of compliance flexibility, while at the
same time significantly reducing both NMOG and NOX emission
levels.

For example, the combined standard would allow a gasoline vehicle
manufacturer to have slightly higher NMOG if it were offset by lower
NOX, or allow a diesel vehicle manufacturer to have slightly
higher NOX if offset by lower NMOG. This approach still
ensures major reductions in both pollutants compared to today's levels.
This is because the very stringent level of the fully phased-in
proposed combined standard (30 mg/mi NMOG+NOX) means that
even with a degree of allowed trading off of one pollutant for the
other, the maximum emissions of either pollutant would need to be well
below current levels. The standards of the California LEV III program
would also be expressed as NMOG+NOX; aligning Tier 3 with
LEV III in this respect would facilitate an important element of a
national program.
---------------------------------------------------------------------------

    \215\ In the past, EPA has taken a similar combined-standard
approach for heavy-duty highway engines and many categories of
nonroad engines.
---------------------------------------------------------------------------

    We believe that a fully phased-in level for the proposed fleet-
average standard of 30 mg/mi is the most stringent level that we could
reasonably propose in the context of our proposed 10-ppm average
standard for gasoline sulfur. As discussed in the feasibility Section
IV.A.5 below, when necessary margins of compliance are considered, this
proposed standard is very close to zero. We request comment on this
level for the proposed standard, as well as the declining standards
during the transition years (see Table IV-3 below). EPA is proposing
compliance mechanisms for the new Tier 3 FTP standards that are the
same in most respects as those of the Tier 2 program. Using the Tier 2
approaches as much as possible would streamline the implementation of
the program by maintaining most of the compliance processes that
manufacturers are familiar with today.
    A key compliance mechanism adapted from the Tier 2 program is a
``bin'' structure for the proposed emission standards. For these
purposes, a bin is a set of several standards that are intended to be
complied with as a group. Thus each Tier 3 bin would have an
NMOG+NOX standard and a PM standard, as well as CO and HCHO
standards. A manufacturer choosing to certify a vehicle to a certain
bin would need to meet each of that bin's standards for the full useful
life of the vehicle. In this approach, manufacturers could certify
vehicles to any of the bins, but they would have to ensure that average
NMOG+NOX of the bins to which all of its vehicles were
certified met the fleet average standard specific to the vehicle
category (i.e., LDV/LDT1 and LDT2/3/4/MDPVs) for that model year. That
is, a manufacturer would comply by ensuring that the sales-weighted
average of the NMOG+NOX values of the bins to which each of
its vehicle models was certified was lower than the fleet average
standard that applied for that model year.
    For each proposed bin, we are including CO and HCHO standards at
levels intended to prevent new engine and emission control designs that
would result in increases in today's CO and HCHO emissions. The
standards are based on the comparable current LEV II and Tier 2 bin
standards for these pollutants. The current standards do not appear to
be technology-forcing, and we believe that this would continue to be
the case as Tier 3 technologies are developed.
    The bin structure that we are proposing for light duty vehicles,
light-duty trucks, and MDPVs standards is presented in Table IV-1.

                       Table IV-1--Proposed FTP Standards for LDVs, LDTs and MDPVs (mg/mi)
----------------------------------------------------------------------------------------------------------------
                                                   NMOG+NOX (mg/
                       Bin                              mi)       PM \a\ (mg/mi)     CO (g/mi)     HCHO (mg/mi)
----------------------------------------------------------------------------------------------------------------
Bin 160.........................................             160               3             4.2               4
Bin 125.........................................             125               3             2.1               4
Bin 70..........................................              70               3             1.7               4
Bin 50..........................................              50               3             1.7               4
Bin 30..........................................              30               3             1.0               4
Bin 20..........................................              20               3             1.0               4
Bin 0...........................................               0               0               0               0
----------------------------------------------------------------------------------------------------------------
\a\ In MYs 2017-20, the PM standard applies only to that segment of a manufacturer's vehicles covered by the
  percent of sales phase-in for that model year.

    Consistent with the Tier 2 principle of vehicle and fuel
neutrality, we are proposing that the same standards apply to LDVs,
LDTs, or MDPVs, regardless of the fuel they use. That is, vehicles
certified to operate on any fuel (e.g., gasoline, diesel fuel, E85,
CNG, LNG, hydrogen, and methanol) would all be subject to the same
standards.
    We propose to maintain the fleet-average approach of the Tier 2
standards. Unlike Tier 2, the proposed Tier 3 fleet-average standards
would decline annually to a fully phased-in level of 30 mg/mi
NMOG+NOX. (The Tier 2 program, after a period of transition,
established a single fleet average standard for all model years.)
Specifically, we are proposing NMOG+NOX standards as
measured on the FTP that would reduce the combined fleet-average
emissions gradually from MY 2017 through 2025, as shown in Table IV-2
below. Beginning in MY 2017, we propose separate fleet average
standards for lighter and heavier vehicles that would both decline
annually, converging in MY 2025. These proposed declining average
standards are identical to CARB's LEV III standards.\216\
---------------------------------------------------------------------------

    \216\ See California Low-Emission Vehicles (LEV) & GHG 2012
regulations adopted by State of California Air Resources Board,
March 22, 2012, Resolution 12-21 incorporating by reference
Resolution 12-11, which was adopted January 26, 2012. Available at
http://www.arb.ca.gov/regact/2012/leviiighg2012/leviiighg2012.htm
(last accessed November 19, 2012).
---------------------------------------------------------------------------

    The declining fleet-average NMOG+NOX standard
requirement would begin in 2017 for light-duty vehicles and light-duty
trucks with a GVWR up to and including 6,000 lbs and in 2018 for all
other light-duty vehicles and light-duty trucks (i.e., those with a
GVWR greater than 6,000 lbs). The standards would apply to the heavier
vehicles a year later to facilitate the transition to a 50-state
program for all manufacturers. During this transition period, there
would be two fleet-average NMOG+NOX standards for each model
year, one for LDVs and LDT1s and a second fleet-average standard for
all other LDTs (LDT2s, LDT3s, and LDT4s) and for MDPVs. We are
proposing that the fleet-average standards decline in a linear way from
MY 2017 through MY 2025, at which point the two fleet-average standards
would converge and stabilize for later model years at the same level,
30 mg/mi, as shown in Table IV-2. Note that these fleet average
standards are for LDT2 and larger vehicles, and for LDVs and LDT1s that

manufacturers certify to the 150,000 mile useful life value. Section
IV.A.7.b discusses how the Clean Air Act defines the useful life values
for certification purposes and how EPA proposes to also provide for
certification to slightly lower emissions standards to a useful life
value of 120,000 miles, representing a level of stringency that is
equivalent to that of the emission standards corresponding to the
150,000 mile useful life, for LDVs and LDT1s.

                                      Table IV-2--Proposed LDV, LDT, and MDPV Fleet Average FTP NMOG+NOX Standards
                                                                         [mg/mi]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Model Year
                                                      --------------------------------------------------------------------------------------------------
                                                                                2025 and
                                                        2017 \a\     2018       2019       2020       2021       2022       2023       2024      later
--------------------------------------------------------------------------------------------------------------------------------------------------------
LDV/LDT1\b\..........................................         86         79         72         65         58         51         44         37         30
LDT2,3,4 and MDPV....................................        101         92         83         74         65         56         47         38         30
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ For vehicles above 6,000 lbs GVWR, the fleet average standards would apply beginning in MY 2018.
\b\ These proposed standards apply for a 150,000 mile useful life. Manufacturers could choose to certify all of their LDVs and LDV1s to a useful life of
  120,000 miles. If any of these families are certified to the shorter useful life, a proportionally lower numerical fleet average standard would apply,
  calculated by multiplying the respective 150,000 mile standard by 0.85 and rounding to the nearest mg.

    EPA is also proposing an alternative phase-in of the 30 mg/mi FTP
NMOG+NOX standard that would be available if a manufacturer
prefers a stable standard and four full years of lead time, as
specified in the Clean Air Act for vehicles above 6,000 lbs GVWR. For
MYs 2017 and 2018, a manufacturer would certify vehicles up to 6,000
lbs GVWR to the primary declining FTP fleet average standards, as in
the primary program. Then, beginning in MY 2019, a stable fleet average
standard of 30 mg/mi would apply to an increasing percentage of a
manufacturer's light-duty vehicles, light-duty trucks, and MDPVs, both
up to and above 6,000 lbs GVWR. The percent phase-in would match the
proposed PM percent phase-in schedule, as discussed below--specifically
40 percent of sales in MY 2019, 70 percent in MY 2020, and 100 percent
in MY 2021 and later model years. A manufacturer choosing to certify
any vehicle to this alternative phase-in would need to use this
approach for all its models in MYs 2019 and later; certifying part of
its fleet to the declining fleet average after MY 2018 would not be
permitted, since the structures of the two approaches, including the
early credits provisions of the NMOG+NOx fleet average program, would
not be consistent. A manufacturer certifying to this alternative phase-
in would also need to comply with the alternative SFTP NMOG+NOx phase-
in and the alternative FTP PM and US06 PM phase-ins as described below.
Vehicles covered by the alternative phase-in programs would be
considered ``final Tier 3'' vehicles and thus would also comply with
the Tier 3 certification fuel and full useful life provisions. EPA
requests comment on this alternative phase-in approach as well as on
the primary option above.
b. FTP PM Standards
    We also propose new FTP standards for PM emissions, as summarized
in Table IV-3 below. For many years, EPA's focus for mobile source PM
was on diesel engine emissions. In recent years, the very effective
controls on PM exhaust emissions that manufacturers have developed for
heavy-duty diesel engines have been successfully applied to light-duty
diesel engines as well. At the same time, attention to gasoline engine
PM emissions has increased as research has demonstrated that the level
of PM from gasoline light duty vehicles is more significant than had
been previously thought.\217\
---------------------------------------------------------------------------

    \217\ Nam, E.; Fulper, C.; Warila, J.; Somers, J.; Michaels, H.;
Bauldauf, R.; Rykowski, R.; and Scarboro, C. Analysis of Particulate
Matter Emissions from Light-Duty Gasoline Vehicles in Kansas City,
EPA420-R-08-010. Assessment and Standards Division Office of
Transportation and Air Quality U.S. Environmental Protection Agency
Ann Arbor, MI, April 2008.
---------------------------------------------------------------------------

    Under typical driving, as simulated by the FTP, the PM emissions of
most current-technology gasoline vehicles are fairly low, well below
the Tier 2 PM standards. At the same time we see considerable variation
in PM emissions among vehicle models not consistently associated with
any specific engine or emission control technology (Section 1.5.1 of
the draft RIA). As a result, we are proposing a new FTP PM standard
that is set to ensure that all new vehicles would perform at a level
representing what is already being achieved by well-designed Tier 2
emission control technologies.
    PM emissions over the FTP are generally attributed to the cold
start, when PM formation from combustion of the fuel is facilitated by
the operating conditions, including a cold combustion chamber and fuel
enrichment. During cold start, PM control via oxidation of semi-
volatile organic compounds from the lubricating oil by catalytic
converters is less effective. We believe that the proposed FTP PM
standard can be achieved with improvements to the fuel controls during
the cold start without the need for any new technology or hardware.
Improvements in cold-start exhaust catalyst performance for NMOG+NOx
control will also reduce emissions of semi-volatile organic PM. As
such, cold start PM levels are relatively independent of vehicle
application and therefore we are proposing a single FTP PM standard for
all light-duty and MDPV vehicles. The PM standard level we are
proposing would ensure that future PM performance is consistent with
current well-performing Tier 2 vehicles. Unlike the NMOG+NOX
FTP standard, the PM standard would not decline over time, since most
manufacturers are already producing vehicles that would meet the
proposed new standards.
    Although we believe it is important that the proposed FTP PM
standard apply from the beginning of the Tier 3 program, we are
proposing several provisions to provide a degree of flexibility for
manufacturers in how many vehicle models would need to meet that
standard in the early years of the program. Manufacturers have raised
several issues that we believe these provisions would address.
    In meetings with EPA, several manufacturers have expressed concerns
about how a PM standard in the range of the proposed 3 mg/mi standard
would be implemented. One concern related to the initial uncertainties
about PM emissions performance that will accompany the development of
new engine technologies, including those that may be introduced to
address the GHG emissions/fuel economy standards that EPA and NHTSA
recently finalized for these vehicles. Also, manufacturers expressed
concerns related to the testing

of PM on the FTP, particularly about potential updates to the test
procedures required to accurately measure PM at very low levels.
Finally, related to the concerns about the new test procedures are the
current limitations that exist for some manufacturers regarding the
capacity of their test facilities to perform a significant volume of
gasoline vehicle PM testing.
    For these reasons, we are proposing a percent-of-sales phase-in
during the first 5 years of the program to address these concerns.
Beginning in MY 2017 (and in MY 2018 for vehicles over 6,000 lbs GVWR),
manufacturers would comply with the PM standard with a minimum of 20
percent of their U.S. sales. As shown in Table IV-3, the percentage of
the manufacturer's sales that would need to comply would increase each
year, reaching 100 percent in MY 2021. In addition to this percent
phase-in, we are proposing a separate PM standard of 6 mg/mi that would
apply only for in-use testing of vehicles certified to the new
standards, and only during the percent phase-in period.
    Due to the MY 2018 start date for vehicles over 6,000 lbs GVWR,
manufacturers that have few or no vehicle models over 6,000 lbs GVWR
would be required to certify a larger percentage of their total light-
duty sales in MY 2017 than full line manufacturers. While we believe
that most manufacturers would likely choose a single large-volume
durability group to meet the 2017 requirements, we seek comment on an
option to comply with the MY 2017 PM requirements by allowing
manufactures to certify 10 percent of all their light-duty vehicle
sales in MY 2017 to the new PM standards, including light-duty vehicles
over 6,000 lbs GVWR and MDPVs. This approach would be consistent with
the CARB LEVIII program, which requires that 10 percent of all light-
duty vehicle sales meet the new PM standards in MY 2017.
    Because of the expected time and expense of performing emission
tests on the improved PM test procedures, we are proposing to limit the
number of tests using the new procedures that a manufacturer would need
to perform at certification and during in-use testing. Specifically,
manufacturers would be required to test vehicles representing a minimum
of 25 percent of a model's durability test groups during certification
each model year (and a minimum of 2 durability groups).\218\
Manufacturers could select which durability groups to test, but would
need to rotate the groups tested each year to eventually cover their
whole fleet. Similarly, manufacturers performing in-use testing under
the In-Use Verification Program could limit their testing to 50 percent
of their low- and high-mileage test vehicles. Again, manufacturers
would need to rotate their vehicle models so that each model would be
tested every other year. Overall, we believe that the flexibility that
these proposed provisions would provide would facilitate the
expeditious implementation of the proposed program, with no significant
impact on the potential benefits of the program.
---------------------------------------------------------------------------

    \218\ Durability groups are a subset of engine families. Several
engine families may have the same durability group.
---------------------------------------------------------------------------

    The PM standards that we are proposing are the most stringent
technically feasible standards within the implementation timeframe of
this proposal. Although the CARB LEV III program includes a 1 mg/mi
standard which will begin phasing in starting in MY 2025, they
acknowledge that there is a need for continuing PM measurement method
development prior to implementing this standard.\219\ In order for EPA
to propose a standard at this level, there must be established methods
to reliably and consistently measure PM below that standard, for
compliance purposes.
---------------------------------------------------------------------------

    \219\ California Air Resources Board (CARB) Initial Statement of
Reasons, Public Hearing to Consider LEV III, December 7, 2011
---------------------------------------------------------------------------

    We request comment on all of the proposed FTP standards, their
structure, and their implementation schedules.

                                                      Table IV-3--Summary of Proposed FTP Standards
--------------------------------------------------------------------------------------------------------------------------------------------------------

--------------------------------------------------------------------------------------------------------------------------------------------------------
                    Program Element                          Units                                Model Year                                 Notes
                                                        ---------------------------------------------------------------------
                                                                          \a\      2018     2019     2020     2021     2022     2023
                                                                          2017
--------------------------------------------------------------------------------------------------------------------------------------------------------
NMOG+NOX Standard (fleet average)                            mg/mi          Per declining fleet average for cars and trucks (see Table IV[dash]2) \b\
--------------------------------------------------------------------------------------------------------------------------------------------------------
PM Standards
--------------------------------------------------------------------------------------------------------------------------------------------------------
Phase-in                                                 %............       20       20       40       70      100      100      100  .................
--------------------------------------------------------------------------------------------------------------------------------------------------------
FTP..............................  Certification.......  mg/mi........        3        3        3        3        3        3        3  Note c
                                  ----------------------------------------------------------------------------------------------------------------------
                                   In-use..............  mg/mi........        6        6        6        6        6        3        3  Note d
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ For vehicles above 6,000 lbs GVWR, the proposed FTP PM would apply beginning in MY 2018.
\b\ The percent phase-in would not apply to the declining fleet average standards.
\c\ Manufacturers would be required to test 25 percent of each model year's durability groups, minimum of 2.
\d\ Manufacturers would be required to test 50 percent of their low and high mileage in-use vehicles.

    As with the proposed FTP NMOG+NOX standards, EPA is also
proposing an alternative phase-in of the 3 mg/mi FTP PM standard that
would be available if a manufacturer prefers 4 full years of lead time
for vehicles above 6,000 lbs GVWR. A manufacturer that chooses the
alternative phase-in for the FTP NMOG+NOX program above
could also postpone the beginning of the phase-in for PM compliance for
vehicles above 6,000 lbs GVWR until MY 2019. For MYs 2017 and 2018, a
manufacturer would certify vehicles up to 6,000 lbs GVWR to the 3 mg/mi
FTP PM standard (and have a 6 mg/mi in-use PM standard) for 20 percent
of its sales in each of those years, as with the primary PM percent
phase-in schedule. Then, for MYs 2019 and later, it would comply with
the 3 mg/mi (and 6 mg/mi in-use) PM standards for their LDVs, LDTs, and
MDPVs, both up to and above 6,000 lbs GVWR. For MYs 2019 and 2020
(i.e., before the phase-in is fully implemented in MY 2021),
manufacturers choosing this alternative would be required to meet the
PM standard on the same segment of their fleet vehicles being used to
meet the NMOG+ NOX fleet average standard, and at the
applicable phase-in percentage of sales for the given model year.
Manufacturers

certifying to the alternative PM phase-in standard would also need to
comply with the alternative US06 PM phase-in as described below, as
well as the NMOG+ NOX FTP and SFTP phase-ins. EPA requests
comment on this alternative phase-in approach as well as on the primary
PM phase-in option above.
4. Proposed SFTP Standards
    In addition to the proposed FTP standards, we are proposing
NMOG+NOX and PM standards as measured on the SFTP. The SFTP
(and specifically the US06 component of the test) is designed to
simulate higher speeds and higher acceleration rates (and thus higher
loads) when substantially more heat can be generated during the
combustion process. It is during these kinds of operation that engines
can go into a fuel ``enrichment'' mode, where the engine's controls may
temporarily create a rich air/fuel mixture to protect exhaust
components from thermal damage. Enrichment can increase emissions of
NMOG+NOX and PM, primarily due to the incomplete combustion
that occurs under rich conditions and the diminished effectiveness of
the catalyst in these circumstances. However, enrichment can be
minimized or eliminated in current and future engines, where components
can be thermally protected even under high-load conditions by careful
electronic management of the air/fuel mixture and the combustion
process. To reduce emissions caused by excessive enrichment, we are
proposing new SFTP standards. Further, as described in Section IV.A.4.c
below, we are proposing limitations on the magnitude of enrichment that
could be commanded by the vehicle operator. We describe the proposed
SFTP standards in the following paragraphs.
    We are also proposing an SFTP composite CO standard of 4.2 g/mi for
all model years 2017 (or 2018) and later. This standard represents no
effective change from the current Tier 2 SFTP CO standard, which we
believe is already at a level that is sufficiently stringent.
a. SFTP NMOG+NOX Standards
    We have reviewed certification and in-use NMOG and NOX
data on a wide range of recent vehicles as tested on the US06 cycle.
See Chapter 1 of the draft RIA for an analysis of this data. It is
clear that most current vehicles are generally avoiding significant
enrichment events during high-load operation and thus achieve
relatively low NMOG+NOX emissions on the US06 test. The data
shows that with minor (if any) improvements to engine calibrations and
with no significant loss of performance, manufacturers are able to
essentially eliminate enrichment events and their emissions
consequences. Thus, as presented in Table IV-5 below, we are proposing
new composite SFTP standards for NMOG+NOX at levels that
would be more stringent than those required by the existing Tier 2
program. We believe that the new standards would require emission
performance at levels currently achieved today by most vehicles under
high-load operation, and we do not believe that significant additional
reductions would result from SFTP standards more stringent than the
proposed 50 mg/mi fully phased-in level. The SFTP emissions value for
certification of gaseous pollutants would continue to be calculated as
a weighted composite value of emissions on three cycles (0.35 x FTP +
0.28 x US06 + 0.37 x SC03), as is done for the Tier 2 SFTP standards.
    We believe that the proposed standards could be more challenging in
the early years of the program. Thus, we propose a declining fleet
average standard that would become increasingly stringent from MY 2017
to MY 2025. Manufacturers would comply with a declining
NMOG+NOX fleet-average SFTP standard for each year beginning
in MY 2017 (MY 2018 for vehicles over 6000 lbs GVWR) and culminating
for MY 2025 and later with a fleet-average standard of 50 mg/mi.
    To provide flexibility in meeting the fleet-average standards,
manufacturers would determine for themselves what the specific SFTP
composite standard would be for an individual vehicle family and report
that self-selected standard and the measured emission performance.
(These self-selected standards are analogous to ``family emission
limits,'' or ``FELs,'' used in other programs (e.g., heavy-duty highway
engine standards).) For each family, a manufacturer would choose any
composite NMOG+NOX standard, up to 180 mg/mi, in even 10 mg/
mi increments. The manufacturer would then calculate the sales-weighted
average of all the selected standards of the families across its fleet
and compare that emissions value to the applicable fleet-average
standards for that model year. Table IV-4 presents the proposed
declining fleet-average SFTP NMOG+NOX standards.
    As with the proposed FTP NMOG+NOX and PM standards, EPA
is also proposing an alternative phase-in of the 50 mg/mi SFTP
NMOG+NOX standard that would be available if a manufacturer
prefers a stable standard and four full years of lead time for vehicles
above 6,000 lbs GVWR. For MYs 2017 and 2018, a manufacturer would
certify vehicles up to 6,000 lbs GVWR to the primary SFTP declining
fleet average standards, as in the primary program. Then, beginning in
MY 2019, a stable fleet average standard of 50 mg/mi would apply to an
increasing percentage of a manufacturer's light-duty vehicles, light-
duty trucks, and MDPVs, both up to and above 6,000 lbs GVWR. The
percent phase-in would match the proposed PM percent phase-in schedule,
as discussed below. A manufacturer certifying to this alternative
phase-in would also need to comply with the alternative FTP
NMOG+NOX phase-in and the alternative FTP PM and US06 PM
phase-ins, as described elsewhere in this section. EPA requests comment
on this alternative phase-in approach as well as on the primary option
above.
b. US06 PM Standards
    Our proposed approach to addressing PM emissions on the US06 test
(a component of the composite SFTP standard) is somewhat different from
the SFTP standards that we are proposing for NMOG and NOX
emissions. In the case of PM, US06 data on recent vehicles shows that
current gasoline vehicles can have very low PM emissions, but US06 PM
emission levels vary depending on many factors. In some cases,
manufacturer emission control strategies that are sensitive to
variations in operating conditions (e.g., variation due to driver
behavior or automatic transmission shift points) appear to result in
very low PM levels during some tests and yet higher PM on other tests
on the same vehicle when driven slightly differently. We also believe
that some of the observed high PM emissions may be partly due to
increasing oil consumption in vehicles as they age, especially under
higher-load conditions or hard closed-throttle deceleration conditions.
Thus, we now believe that more focus on vehicles as they age is
important.
    We have designed the proposed US06 PM standards in light of all of
these factors, which relate to PM emission formation under relatively
extreme driving conditions. For these standards, we are proposing to
focus on the US06 cycle component of the composite SFTP, since most of
our concern about PM formation and sensitivity of engine controls
arises from high-speed, high-load driving conditions. Similarly, the
quantity of PM emissions from warmed-up engines is closely related to
engine load, since the higher rate of fuel consumption results in more

opportunities for PM to form. For this reason, we propose that heavier
vehicles, which face high-load conditions more frequently than lighter
vehicles, comply with a higher US06 standard and lighter vehicles
comply with a lower standard. The proposed US06 PM standard would be 10
mg/mi for vehicles at or below 6,000 lbs GVWR and 20 mg/mi for heavier
vehicles.
    EPA is seeking comment on the use of vehicle weight to establish
separate US06 PM standards for cars and trucks. The data presented in
Chapter 1 of the draft RIA demonstrate that today's heavier vehicles
are already achieving PM emission levels well below our proposed 20 mg/
mi standard and are approximately equivalent to the performance of
lighter vehicles. According to our data, manufacturers appear to be
controlling PM emissions in heavier vehicles over severe duty cycles.
Thus, EPA seeks comment on the proposed US06 PM standards in general,
including whether EPA should adopt a common US06 standard of 10 mg/mi
for all light-duty vehicles.
    As is the case for the proposed FTP PM standards, we are proposing
a single per-vehicle maximum standard to apply in each model year, with
an allowable percentage phase-in schedule identical to the FTP PM
phase-in.
    Finally, as with the FTP PM standard (and for the same reasons), we
propose a slightly less stringent in-use US06 PM standard that would
apply during the percent phase-in period only. The proposed in-use SFTP
PM standards would be 15 mg/mi for vehicles at or below 6,000 lbs GVWR
and 25 mg/mi for heavier vehicles.
    As with the proposed FTP and SFTP NMOG+NOX standards and
FTP PM standards, EPA is also proposing an alternative phase-in of the
20 mg/mi PM standard as measured on the US06 cycle, that would be
available if a manufacturer prefers 4 full years of lead time for
vehicles above 6,000 lbs GVWR. A manufacturer that chooses the
alternative phase-in for the FTP NMOG+NOX program above
could also postpone the beginning of the phase-in for US06 PM
compliance for vehicles above 6,000 lbs GVWR until MY 2019. For MYs
2017 and 2018, a manufacturer would certify vehicles up to 6,000 lbs
GVWR to the 10 mg/mi FTP PM standard (and have a 15 mg/mi in-use
standard) for 20 percent of its sales in each of those years, as with
the primary PM percent phase-in schedule. Then, for MYs 2019 and later,
it would comply with the respective standards for vehicles up to and
above 6,000 lbs GVWR for their LDVs, LDTs, and MDPVs (i.e., 10 mg/mi
and 15 mg/mi (in-use) for vehicles up to 6,000 lbs GVWR, and 20 mg/mi
and 25 mg/mi (in-use) for vehicles above 6,000 lbs GVWR.) For MYs 2019
and 2020, manufacturers choosing this alternative would be required to
meet both the FTP PM and the US06 PM standards on the same segment of
their fleet vehicles being used to meet the 30 mg/mi fleet average
NMOG+NOX standards, at the applicable percent phase-in
requirement for the given model year. Manufacturers certifying to the
alternative US06 PM phase-in standard would also need to comply with
the alternative FTP PM phase-in as described above, as well as the
NMOG+NOX FTP and SFTP phase-ins. EPA requests comment on
this alternative phase-in approach as well as on the primary US06
phase-in option above.
    All of the proposed SFTP/US06 standards are shown in Table IV-4 and
Table IV-5.

                                         Table IV-4--Proposed LD and MDPV SFTP Composite Fleet Average Standards
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Model year
                                                      --------------------------------------------------------------------------------------------------
                                                                                2025 and
                                                          2017       2018       2019       2020       2021       2022       2023       2024      later
--------------------------------------------------------------------------------------------------------------------------------------------------------
NMOG+NOX (mg/mi).....................................    \a\ 103         97         90         83         77         70         63         57         50
--------------------------------------------------------------------------------------------------------------------------------------------------------
CO (g/mi)............................................                                               \a\ 4.2
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ For vehicles above 6,000 lbs GVWR, the NMOG+NOX and CO standards would apply beginning in MY 2018.

                                                     Table IV-5--Summary of Proposed SFTP Standards
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Model year
            Program element                     Units        ----------------------------------------------------------------------         Notes
                                                              \a\ 2017    2018      2019      2020      2021      2022      2023
--------------------------------------------------------------------------------------------------------------------------------------------------------
NMOG+NOX Standard (fleet average).....  mg/mi...............           Per declining fleet average for cars and trucks (see Table IV[dash]4) \b\
                                                             -------------------------------------------------------------------------------------------
PM Standards:
    Phase-in..........................  %...................        20        20        40        70       100       100       100
US06:
    LDV, LDT1&2 Certification.........  mg/mi...............        10        10        10        10        10        10        10  Note c.
    LDV, LDT1&2 In-use................  mg/mi...............        15        15        15        15        15        10        10  Note d.
US06:
    LDT3&4, MDPV Certification........  mg/mi...............        20        20        20        20        20        20        20  Note c.
    LDT3&4, MDPV In-use...............  mg/mi...............        25        25        25        25        25        20        20  Note d.
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ For vehicles above 6,000 lbs GVWR, the standards would apply beginning in MY 2018.
\b\ The percent phase-in would not apply to the declining fleet average standards.
\c\ Manufacturers would be required to test 25 percent of each model year's durability groups, minimum of 2.
\d\ Manufacturers would be required to test 50 percent of their low and high mileage in-use vehicles.

    We request comment on our proposed SFTP NMOG+NOX and PM
standards, their structure, and their implementation schedules.
c. Enrichment Limitation for Spark-Ignition Engines
    To prevent emissions from excessive enrichment during operating
conditions represented by the SFTP cycles, we are proposing limitations
on the magnitude of enrichment that could be commanded, including
enrichment episodes encountered during in-use

operation. During conditions where enrichment was demonstrated to be
present on the SFTP, the nominal air to fuel ratio could not be richer
at any time than the leanest air to fuel ratio required to obtain
maximum torque (lean best torque or LBT). An air to fuel ratio of LBT
plus a tolerance of 4 percent additional enrichment would be allowed in
actual vehicle testing to protect for any in-use variance in the air to
fuel ratio from the nominal LBT air to fuel determination, for such
reasons as air or fuel distribution differences from production
variances or aging.
    LBT is defined as the leanest air to fuel ratio required at a speed
and load point with a fixed spark advance to make peak torque.
Specifically, an increase in fuel would not result in an increase in
torque while maintaining a fixed spark advance. LBT is determined by
setting the spark advance to a setting that is less than or equal to
the spark advance required for best torque (MBT) and maintaining that
spark advance when sweeping the air to fuel ratio. This fixed spark
advance requirement is intended to prevent torque changes related to
spark changes masking true LBT. Manufacturers may request approval of
an alternative LBT definition for a unique technology or control
strategy. The Agency could determine that an enrichment amount was
excessive or not necessary and therefore deem that the approach did not
meet the air to fuel ratio requirements.
    Enrichment required for thermal protection would continue to be
allowed upon demonstration of necessity to the Agency, based upon
temperature limitations of the engine or exhaust components.
Manufacturers would be required to provide descriptions of all
components requiring thermal protection, temperature limitations of the
components, how the enrichment strategy will detect over-temperature
conditions and correct them, and a justification regarding why the
enrichment is the minimum necessary to protect the specific components.
The Agency may determine that the enrichment is not justified or is not
the minimum necessary based on the use of engineering judgment using
industry-reported thermal protection requirements.
5. Feasibility of the Proposed NMOG+NOX and PM Standards
    In this section, with additional support in Chapter 1 of the draft
RIA, we describe how we reached our conclusion that the proposed Tier 3
standards would be technologically feasible in the time frame of the
program. For each of the proposed emission standards, the lead time
provided by the proposed program is more than sufficient for all
manufacturers to comply. First, manufacturers in many cases are already
adopting complying technologies for reasons other than this proposed
rulemaking. For example, many of the technologies that manufacturers
will begin to develop as early as MY 2014 in response to the CARB LEV
III FTP and SFTP NMOG+NOX standards for the California
market will likely represent steps toward compliance with this proposed
national program. Similarly, manufacturers are already building some
vehicles that comply with our proposed evaporative emissions standards
in response to the CARB LEV III evaporative standards. In addition, as
described above, our proposed program incorporates a number of phase-in
provisions that would ease the transition to compliance, including time
some manufacturers would need to install PM testing capability and to
ramp up production on a national scale. We invite comment on our
conclusions relating to the feasibility of the proposed program for
each of the standards, as discussed below, including our overall
conclusion that technological lead time is not a driving factor in
complying with any of the proposed standards.
    This feasibility assessment is based on a variety of complementary
technical data, studies, and analyses. As described below, these
include our analysis of the stringency of the proposed standards as
compared to current Tier 2 emission levels. We also discuss below our
observation that manufacturers are currently certifying several vehicle
models under the California LEV II program that could likely achieve
the proposed Tier 3 NMOG+NOX and PM standards or similar
levels. EPA has assessed the emissions control challenges manufacturers
would generally face (e.g., cold start NMOG reductions and running
(warmed-up) NOX emissions under typical and more aggressive
driving conditions) and the corresponding technologies that we expect
to be available to manufacturers to meet these challenges. Our
feasibility assessment accounts for the fact that the proposed Tier 3
program would apply to all types of new vehicles, ranging from small
cars to large pick-up trucks and MDPVs and representing a wide
diversity in applications and in specific engine designs.
    It is important to note that our primary assessment of the
feasibility of engine and emission control technologies is based on the
assumption that vehicles would be certified on gasoline with a fuel
sulfur content of 10 ppm and operated on in-use gasoline with 10 ppm
sulfur or less.\220\ Therefore, our primary assessment does not
incorporate the degradation of emission control system caused by higher
levels of sulfur content, as is discussed in Section IV.6 below and in
the draft RIA. This assessment reinforces the critical role of gasoline
sulfur control, as proposed in Section V below, in making it possible
for EPA to propose emission standards at these very stringent levels.
See Section IV.6 below for a full discussion of our current knowledge
of the effects of gasoline sulfur on current vehicle emissions as well
as our projections of how we expect that sulfur would affect compliance
with standards in the range of the proposed Tier 3 standards.
---------------------------------------------------------------------------

    \220\ Our technology, feasibility, and cost assessments are also
consistent with an assumption that certification fuel would contain
15 percent ethanol and would have other properties as specified in
Section IV.D below.
---------------------------------------------------------------------------

    Since there are multiple aspects to the Tier 3 program, it is
necessary to consider technical feasibility in light of the different
program requirements and their interactions with each other. In many
cases, manufacturers would be able to address more than one requirement
with the same general technological approach (e.g., faster catalyst
light-off can improve both FTP NMOG+NOX and PM emissions).
At the same time, the feasibility assessment must consider that
different technologies may be needed on different types of vehicle
applications (i.e., cars versus trucks) and must consider the relative
effectiveness of these technologies in reducing emissions for the full
useful life of the vehicle while operating on expected in-use fuel. For
example, certain smaller vehicles with correspondingly small engines
may be less challenged to meet FTP standards than larger vehicles with
larger engines. Conversely, these smaller vehicles may have more
difficulty meeting the more aggressive SFTP requirements than vehicles
with larger and more powerful engines. Additionally, the ability to
meet the proposed SFTP emission requirements can also be impacted by
the path taken to meet the FTP requirements (e.g., larger volume
catalysts for US06 emissions control vs. smaller catalysts for improved
FTP cold-start emissions control). Throughout the following discussion,
we address how these factors, individually and in interaction with each
other, affect the feasibility of the proposed program. We

invite comment on our assessments of these or any other such potential
interactions. Also, although we are not aware of any technological
reasons that vehicle emission controls responding to new Tier 3
requirements should affect vehicle CO2 emissions or fuel
economy in any significant way, it is possible that such interactions
could occur. For example, there may be some slight change in vehicle
mass if manufacturers explore lighter exhaust manifold materials in
order to reduce thermal mass and promote earlier catalyst light-off or
add emissions control equipment such as hydrocarbon adsorbers. We
invite comment on any such potential effects as well.
a. FTP NMOG+NOX Standards
    The proposed new emission requirements include stringent
NMOG+NOX standards on the FTP that would require new vehicle
hardware in order to achieve the 30 mg/mi fleet average level in 2025.
The type of new hardware that would be required would vary depending on
the specific application and emission challenges. Smaller vehicles with
corresponding smaller engines would generally need less new hardware
while larger vehicles may need additional hardware and improvements
beyond what would be needed for the smaller vehicles. While some
vehicles, especially larger light trucks, may face higher costs in
meeting the proposed standards, it is important to remember that not
every vehicle needs to meet the standard. The proposed program has been
structured to provide higher emission standard ``bins'' (see Table IV-1
above) to which manufacturers may certify more challenged vehicles, so
long as these vehicles are offset with vehicles certified in lower
emission bins such that the fleet-wide average meets the standard. We
believe that the availability of the proposed less-stringent bins would
allow for feasible and cost-effective compliance for all vehicles. In
the Tier 2 program, manufacturers took advantage of this flexibility,
especially in the early years of the program. Then, as technologies
improved and/or became less expensive and the need for averaging
diminished, manufacturers began certifying all or most of their fleets
to the average bin (Tier 2 Bin 5). We anticipate that manufacturers
will follow a similar trend with the proposed Tier 3 standards, relying
on fleet averaging more significantly in the transitional years but
certifying increasing numbers of their vehicles to the final fleet
average standard of 30 mg/mi in the later years of the program.
    In order to assess the technical feasibility of a 30 mg/mi
NMOG+NOX national fleet average FTP standard, EPA conducted
two supporting analyses. The initial analyses performed were of the
current Tier 2 and LEV II fleets. This provided a baseline for the
current federal fleet emissions performance, as well as the emissions
performance of the California LEV II fleet. The second consideration
was a modal analysis of typical vehicle emissions under certain
operating conditions. In this way EPA determined the specific emissions
performance challenges that vehicle manufacturers would face in meeting
the lower fleet average emission standards. Each of these
considerations is described in greater detail below.
    The current federal fleet is certified to an average of Tier 2 Bin
5, equivalent to 160 mg/mi NMOG+NOX.\221\ For MY 2009, 92
percent of LDVs and LDT1s were certified to Tier 2 Bin 5 and 91 percent
of LDT2s through LDT4s were certified to Tier 2 Bin 5. This was not an
unexpected result as there is currently no motivation for vehicle
manufacturers to produce a federal fleet that over-complies with
respect to the current Tier 2 standards. By comparison, in the
California fleet, where compliance with the ``PZEV'' program encourages
manufacturers to certify vehicles to cleaner levels, only 30 percent of
the LDVs and LDT1s are certified to Tier 2 Bin 5 and 60 percent are
certified to Tier 2 Bin 3. The situation regarding the truck fleet in
California is similarly stratified, with 37 percent of the LDT2s
through LDT4s being certified to Tier 2 Bin 5 and 55 percent being
certified to Tier 2 Bin 3. In many cases identical vehicles are being
certified to a lower standard in California and a higher standard
federally. We note that vehicles certified to a lower standard in
California are operated on gasoline with an average sulfur content of
10 ppm and thereby are able to maintain their emissions performance in-
use. Based on these patterns of federal and California certification,
EPA believes that much of the existing Tier 2 fleet could be certified
to a lower federal fleet average immediately, with no significant
feasibility concerns, if lower sulfur gasoline were made available
nationwide.
---------------------------------------------------------------------------

    \221\ The current Tier 2 program does not combine NMOG and
NOX emissions into one fleet-average standard. The fleet-
average standard in that program is for NOX emissions
alone.
---------------------------------------------------------------------------

    Regardless of the Tier 2 bin standards at which manufacturers
choose to certify their vehicles, actual measured emissions performance
of these vehicles is typically well below the numerical standards. This
difference is referred to as ``compliance margin'' and is a result of
manufacturers' efforts to address all the sources of variability,
including:

 Test-to-test variability (within one test site and lab-to-lab)
 Build variation expectations
 Manufacturing tolerances and stack-up
 Vehicle operation (for example: driving habits, ambient
temperature, etc.)
 Fuel composition
 The effects of fuel sulfur on exhaust catalysts and oxygen
sensors
 The effects of other fuel components, including ethanol and
gasoline additives
 Oil consumption
 The impact of oil additives and oil ash on exhaust catalysts
and oxygen sensors

    For MY 2009, the compliance margin for a Tier 2 Bin 5 vehicle
averaged approximately 60 percent. In other words, actual vehicle
emissions performance was on average about 40 percent of a 160 mg/mi
NMOG+NOX standard, or about 64 mg/mi. By comparison, for
California-certified vehicles, the average Super Ultra Low Emission
Vehicle (SULEV) compliance margin was somewhat less for the more
stringent standards, approximately 50 percent. We believe that the
recent California experience is a likely indicator of compliance
margins that manufacturers would design for in order to comply with the
proposed Tier 3 FTP standards. Thus, a typical Tier 2 Bin 5 vehicle,
performing at 40 percent of the current standard (i.e., at about 64 mg/
mi) would need improvements sufficient to reach about 15 mg/mi (50
percent of a 30 mg/mi standards).
    To understand how the several currently-used technologies described
below could be used by manufacturers to reach the stringent proposed
Tier 3 NMOG+NOX standards, it is helpful to consider
emissions formation in common modes of operation for gasoline engines,
or modal analysis.\222\ The primary challenge faced by manufacturers
for producing Tier 3 compliant light-duty gasoline vehicle powertrains
would be to reduce the emissions during cold-start operation which,
based on modal analysis of a gasoline powered vehicle being operated on
the FTP cycle, occurs during about the first 50 seconds after engine
start. Thus, effective control of

these cold-start emissions would be the primary technological goal of
manufacturers complying with the proposed Tier 3 FTP standards. As
discussed below, light-duty manufacturers are already applying several
technologies capable of significant reductions in these cold start
emissions to vehicles currently on the road.
---------------------------------------------------------------------------

    \222\ A modal analysis provides a second-by-second view of the
total amount of emissions over the entire cycle being considered.
---------------------------------------------------------------------------

b. SFTP NMOG+NOX Standards
    The increase in the stringency of the SFTP NMOG+NOX
standards, specifically across the US06 cycle, would generally only
require additional focus on fuel control of the engines and diligent
implementation of new technologies that manufacturers are already
introducing or are likely to introduce in response to the current and
2017 LD GHG emission standards. These include downsized gasoline direct
injection (GDI) and turbocharged engines, which may also include
improvements to the engine and emission control hardware to tolerate
higher combustion and exhaust temperatures expected in these future
GHG-oriented engine designs. The upgraded materials or components would
enable manufacturers to rely less on fuel enrichment during high-speed/
high-load operation to protect components from overheating. This fuel
enrichment is currently the source of elevated VOC, NOX, and
PM emissions seen in a subset of the current Tier 2 fleet.
    With respect to enrichment, changes to the fuel/air mixture by
increasing the fuel fraction has historically been the primary method
available to manufacturers to protect the catalyst and other exhaust
components from over-temperature conditions. Changing the fuel/air
mixture is no longer the only tool available to manufacturers for this
purpose. With the application of electronic throttle controls, variable
valve timing, exhaust gas recirculation and other exhaust temperature
influencing technologies on nearly every light-duty vehicle, the
manufacturer has the ability to systematically control the operation
and combustion processes of the engine to minimize or altogether avoid
areas and modes of operation where thermal issues can occur. While some
of these solutions could in some cases result in a small and temporary
reduction in vehicle performance (absolute power levels), we believe
that it could be an effective way to reduce NMOG+NOX
emissions over the SFTP test.
    Additionally, some components, especially catalysts, can experience
accelerated thermal deterioration that occurs when operating at higher
temperatures for more time than expected under normal operation (e.g.,
trailer towing, mountain grades). Some upgrades of existing vehicle
emission control technology, like catalyst substrates and washcoats may
be required to limit thermal deterioration and ensure vehicle emissions
compliance throughout the useful life of the vehicle.
    In order to assess the technical feasibility of a 50 mg/mi
NMOG+NOX national fleet average SFTP standard, EPA conducted
an analysis of SFTP levels of Tier 2 and LEV II vehicles. The analysis
was performed on the US06 results from current Tier 2 and LEV II
vehicles tested in the in-use verification program (IUVP) by
manufacturers and submitted to EPA. This analysis provided a baseline
for the current Tier 2 and LEV II fleet emissions performance, as well
as the SFTP emissions performance capability of the cleanest vehicles
meeting the proposed Tier 3 FTP standards. The analysis concluded that
most vehicles in the IUVP testing program are already capable of
meeting the composite SFTP standard of 50 mg/mi when the Tier 3 FTP
standard levels are factored into the composite calculation. With the
technological improvements already underway as discussed above, we
believe all 2017 and later vehicles would be able to comply with the
proposed SFTP standards, directly, or through the flexibility of the
averaging, banking and trading program. For further information on the
analysis see Chapter 1 of the draft RIA.
c. FTP and SFTP PM Standards
    As described above for NMOG+NOX over the SFTP, the
increase in the stringency of the FTP and SFTP PM standards would
generally also only require additional focus on fuel control of the
engines and diligent implementation of new technologies like gasoline
direct injection (GDI) and turbocharged engines. Some upgrades of
existing vehicle emission control technology may be required to ensure
vehicle emissions performance is maintained throughout the useful life
of the vehicle. These upgrades may include improvements to the engine
to control wear that could result in increased PM from oil consumption
and selection of GDI systems that would be capable of continuing to
perform optimally even as the systems age.
    We based our conclusions about the ability of manufacturers to meet
the proposed PM standards largely on the PM performance of the existing
fleet, both on the FTP and SFTP. In the case of FTP testing of current
vehicles, data on both low and high mileage light-duty vehicles
demonstrate that the majority of vehicles are currently achieving
levels at or below the proposed Tier 3 FTP standards.
    The testing results can be found in Chapter 1 of the draft RIA. A
small number of vehicles are at or just over the proposed FTP PM
standard at low mileage and could require calibration changes and/or
catalyst changes to meet the new standards. It is our expectation that
the same calibration and catalyst changes required to address NMOG
would also provide the necessary PM control. Vehicles that currently
have higher PM emissions over the FTP or SFTP at higher mileages would
likely be required to control oil consumption and combustion chamber
deposits.
    We also analyzed PM test data on US06 emissions for current Tier 2
vehicles. The data show that many vehicles are already at or below the
proposed standards on the US06. Vehicles that have high PM emission
rates on the US06 would likely need to control enrichment, and oil
consumption particularly later in life. As described above for SFTP
NMOG+NOX control, enrichment can be more accurately managed
through available electronic engine controls. The strategies for
reducing oil consumption are similar to those described above for
controlling oil consumption on the FTP. However, given the higher
engine speeds experienced on the US06 and the increase in oil
consumption that can accompany this kind of operation, manufacturers
would most likely focus on oil sources stemming from the piston to
cylinder interface and positive crankcase ventilation (PCV).
    Manufacturers have informed us that they have already reduced or
are planning to reduce the oil consumption of their engines by improved
sealing of the paths of oil into the combustion chamber and improved
piston-to-cylinder interfaces. They are already taking or considering
these actions to address issues of customer satisfaction and cost of
ownership. In addition, many vehicle manufacturers acknowledge the
relationship between combustion chamber deposits and PM formation and
are actively pursuing design changes to mitigate fuel impingement
within the combustion chamber and its commensurate PM effects. Both
types of controls are being widely applied by manufacturers today.
d. Technologies Manufacturers Are Likely To Apply
    Most of the technologies expected to be applied to light-duty
vehicles to meet

the stringent proposed standards would address the emissions control
system's ability to control emission during cold start. The
effectiveness of current vehicle emissions control systems depends in
large part on the time it takes for the catalyst to light off, which is
typically defined as the catalyst reaching a temperature of 250 [deg]C.
In order to improve catalyst light-off, we expect that manufacturers
would add technologies that provide heat from combustion more readily
to the catalyst or improve the catalyst efficiency at lower
temperatures. These technologies include calibration changes, thermal
management, close-coupled catalysts, catalyst platinum group metals
(PGM) loading and strategy, and secondary air injection, all which
generally improve emission performance of all pollutants. In some cases
where the catalyst light-off and efficiency are not enough to address
the cold start NMOG emissions, hydrocarbon adsorbers may be applied to
trap hydrocarbons until such time that the catalyst is lit off. Note
that with the exception of hydrocarbon adsorbers each of these
technologies addresses NMOG, NOX, and PM performance. The
technologies are described in greater detail below. Additional
information on these technologies can also be found in Chapter 1 of the
RIA.
     Engine Control Calibration Changes--These include changes
to retard spark and/or adjust air/fuel mixtures such that more
combustion heat is created during the cold start. Control changes may
include injection strategies in GDI applications, unique cold-start
variable valve timing and lift, and other available engine parameters.
Engine calibration changes can affect NMOG, NOX and PM
emissions.
     Catalyst PGM Loading--Additional PGM loading, increased
loading of other active materials, and improved dispersion of PGM and
other active materials in the catalyst provide a greater number of
sites available to catalyze emissions and addresses NMOG,
NOX and PM emissions. Catalyst PGM loading, when implemented
in conjunction with low sulfur gasoline, will effectively eliminate
NOX emissions under warmed-up conditions.
     Thermal Management--This category of technologies includes
all design attributes meant to conduct the combustion heat into the
catalyst with minimal cooling. This includes insulating the exhaust
piping between the engine and the catalyst, reducing the wetted area of
the exhaust path, reducing the thermal mass of the exhaust system, and/
or using close-coupled catalysts (i.e., the catalysts are packaged as
close as possible to the engine's cylinder head to mitigate the cooling
effects of longer exhaust piping). Thermal management technologies
primarily address NMOG emissions, but also affect NOX and PM
emissions.
     Secondary Air Injection--By injecting air directly into
the exhaust stream, close to the exhaust valve, combustion can be
maintained within the exhaust, creating additional heat by which to
increase the catalyst temperature. The air/fuel mixture must be
adjusted to provide a richer exhaust gas for the secondary air to be
effective.
     Hydrocarbon Adsorber--Traps hydrocarbons during a cold
start until the catalyst lights off, and then releases the hydrocarbons
to be converted by the catalyst.
     Gasoline Sulfur--The relative effectiveness for NMOG and
NOX control of the exhaust-catalyst related technologies are
constrained by gasoline fuel sulfur levels. Thus, reduced sulfur in
gasoline is an enabling technology to achieve the standards and
maintain this performance during in-use operation. We discuss the
relationship between gasoline sulfur and emissions in greater detail in
Section IV.6 below and in the draft RIA.
    Discussions between EPA, CARB, vehicle manufacturers, and major
component suppliers indicated that large light-duty trucks (e.g.,
pickups and full-size sport utility vehicles (SUVs) in the LDT3 and
LDT4 categories) would be the most challenging light-duty vehicles to
bring into compliance with the proposed Tier 3 NMOG+NOX
standards at the 30 mg/mi corporate average emissions level. A similar
challenge was addressed when large light-duty trucks were brought into
compliance with the Tier 2 standards over the past decade. Figure IV-1
provides a graphical representation of the effectiveness of Tier 3
technologies for large light-duty truck applications. A compliance
margin is shown in both cases. Note that the graphical representation
of the effectiveness of catalyst technologies on NOX and
NMOG when going from Tier 2 to Tier 3 levels also includes a reduction
in gasoline sulfur levels from 30 ppm to 10 ppm.

[GRAPHIC] [TIFF OMITTED] TP21MY13.000

6. Impact of Gasoline Sulfur Control on the Feasibility of the Proposed
Vehicle Emission Standards
---------------------------------------------------------------------------

    \223\ The technologies and levels of control in this figure are
based on a combination of confidential business information
submitted by auto manufacturers and suppliers, public data, and EPA
staff engineering judgment.
---------------------------------------------------------------------------

a. Fuel Sulfur Impacts on Exhaust Catalysts
    Modern three-way catalytic exhaust systems utilize platinum group
metals (PGM), metal oxides and other active materials to selectively
oxidize organic compounds and carbon monoxide in the exhaust gases.
These systems simultaneously reduce nitrogen oxides when air-to-fuel
ratio control operates in a condition of relatively low amplitude/high
frequency oscillation about the stoichiometric point. Sulfur is a well-
known catalyst poison. There is a large body of work demonstrating
sulfur inhibition of the emissions control performance of PGM three-way
exhaust catalyst
systems.224 225 226 227 228 229 230 231 232 233 The nature
of sulfur interactions with washcoat materials, active catalytic

materials and catalyst substrates is complex and varies with catalyst
composition and exhaust gas composition and exhaust temperature. The
variation of these interactions with exhaust gas composition and
temperature means that the operational history of a vehicle is an
important factor; continuous light-load operation, throttle tip-in
events and enrichment under high-load conditions can all impact sulfur
interactions with the catalyst.
---------------------------------------------------------------------------

    \224\ Beck, D.D., Sommers, J.W., DiMaggio, C.L. (1994). Impact
of sulfur on model palladium-only catalysts under simulated three-
way operation. Applied Catalysis B: Environmental 3, 205-227.
    \225\ Beck, D.D., Sommers, J.W. (1995). ``Impact of sulfur on
the performance of vehicle aged palladium monoliths.'' Applied
Catalysis B: Environmental 6, 185-200.
    \226\ Beck, D.D., Sommers, J.W., DiMaggio, C.I. (1997). Axial
characterization of oxygen storage capacity in close coupled
lightoff and underfloor catalytic converters and impact of sulfur.
Applied Catalysis B: Environmental 11, 273-290.
    \227\ Waqif, M., Bazin, P., Saur, O. Lavalley, J.C., Blanchard,
G., Touret, O. (1997), Study of ceria sulfation. Applied Catalysis
B: Environmental 11, 193-205.
    \228\ Bazin, P., Saur, O. Lavalley, J.C., Blanchard, G.,
Visciglio, V., Touret, O. (1997). ``Influence of platinum on ceria
sulfation.'' Applied Catalysis B: Environmental 13, 265-274.
    \229\ Takei, Y., Kungasa, Y., Okada, M., Tanaka, T. Fujimoto, Y.
(2000). Fuel Property Requirement for Advanced Technology Engines.
SAE Technical Paper 2000-01-2019.
    \230\ Takei, Y., Kungasa, Y., Okada, M., Tanaka, T. Fujimoto, Y.
(2001). ``Fuel properties for advanced engines.'' Automotive
Engineering International 109 12, 117-120.
    \231\ Kubsh, J.E., Anthony, J.W. (2007). The Potential for
Achieving Low Hydrocarbon and NOX Exhaust Emissions from
Large Light-Duty Gasoline Vehicles. SAE Technical Paper 2007-01-
1261.
    \232\ Shen, Y., Shuai, S., Wang, J. Xiao, J. (2008). Effects of
Gasoline Fuel Properties on Engine Performance. SAE Technical Paper
2008-01-0628.
    \233\ Ball, D., Clark, D., Moser, D. (2011). Effects of Fuel
Sulfur on FTP NOX Emissions from a PZEV 4 Cylinder
Application. SAE Technical Paper 2011-01-0300.
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    Sulfur from gasoline is oxidized during spark-ignition engine
combustion primarily to SO2 and, to a much lesser extent,
SO3-2. Sulfur oxides selectively chemically bind
(chemisorb) with, and in some cases react with, active sites and
coating materials within the catalyst, thus inhibiting the intended
catalytic reactions. Sulfur oxides inhibit pollutant catalysis chiefly
by selective poisoning of active PGM, ceria sites, and alumina
washcoatings (see Figure IV-2).\234\ The amount of sulfur retained by
the catalyst is primarily a function of its operating temperature, the
active materials and coatings used within the catalyst, the
concentration of sulfur oxides in the incoming exhaust gases, and air-
to-fuel ratio feedback and control by the engine management system.
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    \234\ Heck, R.M., Farrauto, R.J. (2002). Chapter 5: Catalyst
Deactivation in Catalytic Air Pollution Control, 2nd Edition. John
Wiley and Sons, Inc.
[GRAPHIC] [TIFF OMITTED] TP21MY13.001

Selective sulfur poisoning of platinum (Pt) and rhodium (Rh) is
primarily from surface-layer chemisorption. Sulfur poisoning of
palladium (Pd) and ceria appears to be via chemisorption combined with
formation of more stable metallic sulfur compounds, e.g. PdS and
Ce2O2S, present in both surface and bulk form
(i.e., below the surface layer.235 236 237 238 Ceria,
zirconia and other oxygen storage components (OSC) play an important
role that is crucial to NOX reduction over Rh as the engine
air-to-fuel ratio oscillates about the stoichiometric closed-loop
control point.\239\ Water-gas-shift reactions are important for
NOX reduction over catalysts combining Pd and ceria. This
reaction can be blocked by sulfur poisoning and may be responsible for
observations of reduced NOX activity over Pd/ceria catalysts
even with exposure to fairly low levels of sulfur (equivalent to 15 ppm
in gasoline).240 241 Pd is also of increased importance for
meeting Tier 3 standards due to its unique application in the closed-
coupled-catalysts location required for vehicles certifying to very
stringent emission standards. Pd is required in closed-coupled
catalysts due to its resistance to high temperature thermal sintering.
Sulfur removal from Pd requires rich operation at higher temperatures
than required for sulfur removal from other PGM catalysts.\242\
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    \235\ Luo, T. Gorte, R.J. (2003). A Mechanistic Study of Sulfur
Poisoning of the Water-Gas-Shift Reaction Over Pd/Ceria.'' Catalysis
Letters, 85, Issues 3-4, pg. 139-146.
    \236\ Li-Dun, A., Quan, D.Y. (1990). ``Mechanism of sulfur
poisoning of supported Pd(Pt)/Al2O3 catalysts
for H2-O2 reaction.'' Applied Catalysis 61,
Issue 1, pg. 219-234.
    \237\ Heck, R.M., Farrauto, R.J. (2002). Chapter 6: Automotive
Catalyst in Catalytic Air Pollution Control, 2nd Edition. John Wiley
and Sons, Inc.
    \238\ Maricq, M. M. Chace, R.E., Xu, N., Podsiadlik, D.H.
(2002). The Effects of the Catalytic Converter and Fuel Sulfur Level
on Motor Vehicle Particulate Matter Emissions: Gasoline Vehicles.
Environmental Science and Technology, 36, No. 2 pg. 276-282.
    \239\ Heck, R.M., Farrauto, R.J. (2002). Chapter 6: Automotive
Catalyst in Catalytic Air Pollution Control, 2nd Edition. John Wiley
and Sons, Inc.
    \240\ Luo, T. Gorte, R.J. (2003) A Mechanistic Study of Sulfur
Poisoning of the Water-Gas-Shift Reaction Over Pd/Ceria. Catalysis
Letters, 85, Issues 3-4, pg. 139-146.
    \241\ Ball, D., Clark, D., Moser, D. (2011). Effects of Fuel
Sulfur on FTP NOX Emissions from a PZEV 4 Cylinder
Application. SAE Technical Paper No. 2011-01-0300.
    \242\ Beck, D.D., Sommers, J.W. (1995) Impact of sulfur on the
performance of vehicle aged palladium monoliths. Applied Catalysis
B: Environmental 6, 185-200.
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    In addition to its interaction with catalyst materials, sulfur can
also react with the washcoating itself to form alumina sulfate, which
in turn can block coating pores and reduce gaseous diffusion to active
materials below the coating surface.\243\ This may be a significant
mechanism for the observed storage of sulfur compounds at light and
moderate load operation with subsequent, rapid release as sulfate
particulate matter when high-load, high-temperature conditions are
encountered.\244\
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    \243\ Maricq, M. M. Chace, R.E., Xu, N., Podsiadlik, D.H.
(2002). The Effects of the Catalytic Converter and Fuel Sulfur Level
on Motor Vehicle Particulate Matter Emissions: Gasoline Vehicles.
Environmental Science and Technology, 36, No. 2 pg. 276-282.
    \244\ Maricq, M. M. Chace, R.E., Xu, N., Podsiadlik, D.H.
(2002). The Effects of the Catalytic Converter and Fuel Sulfur Level
on Motor Vehicle Particulate Matter Emissions: Gasoline Vehicles.
Environmental Science and Technology, 36, No. 2 pg. 276-282.
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    Operating the catalyst at a sufficiently high temperature under net
reducing conditions (e.g., air-to-fuel equivalence that is net fuel-
rich of stoichiometry) can effectively release the sulfur oxides from
the catalyst components. Thus, regular operation at sufficiently high
temperatures at rich air-to-fuel ratios can minimize the effects of
fuel sulfur levels on catalyst active materials and catalyst
efficiency. However, it cannot completely eliminate the effects of
sulfur poisoning. A study of Tier 2 vehicles in the in-use fleet
recently completed by EPA shows that emission levels immediately
following high speed/load operation is still a function of fuel sulfur
level, suggesting that lower fuel sulfur levels will bring emission
benefits unachievable by catalyst regeneration procedures alone.\245\
Furthermore, regular operation at these temperatures and at rich air-
to-fuel ratios is not desirable, for several reasons. The temperatures
necessary to release sulfur oxides are high enough to lead to thermal
degradation of the catalyst over time via thermal sintering of active
materials. Sintering reduces the surface area available to participate
in reactions. Additionally, it is not always possible to maintain these
catalyst temperatures (because of cold weather, idle conditions, light
load operation) and the rich air-to-fuel ratios necessary can result in
increased PM, NMOG and CO emissions. Thus, reducing fuel sulfur levels
has been the primary regulatory mechanism to minimize sulfur
contamination of the catalyst and ensure optimum emissions performance
over the useful life of a vehicle. The impact of gasoline sulfur has
become even more important as vehicle emission standards have become
more stringent. Some studies have suggested an increase in catalyst
sensitivity to sulfur (in terms of percent conversion efficiency) when
standards increase in stringency and emissions levels decrease.
Emission standards under the programs that preceded the Tier 2 program
(Tier 0, Tier 1 and National LEV, or NLEV) were high enough that the
impact of sulfur was considered negligible. The Tier 2 program
recognized the importance of sulfur and reduced the sulfur levels in
the fuel from around 300 ppm to 30 ppm in conjunction with the new
emission standards.\246\ At that time, very little work had been done
to evaluate the effect of further reductions in fuel sulfur, especially
on in-use vehicles that may have some degree of catalyst deterioration
due to real-world operation.
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    \245\ See Chapter 1 of the RIA (Section <IP_ADDRESS>) for more
details on this study and its results.
    \246\ Tier 2 Regulatory Impact Analysis (EPA 420-R-99-023,
December 22, 1999), available at http://epa.gov/tier2/finalrule.htm#regs.
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    In 2005, EPA and several automakers jointly conducted a program
that examined the effects of sulfur and other gasoline properties,
benzene, and volatility on emissions from a fleet of nine Tier 2
compliant vehicles. Section 1.2.3 of the draft RIA provides details of
the Mobile Source Air Toxics (MSAT) Study.\247\ The study found
significant reductions in NOX, CO and total hydrocarbons
(HC) when the vehicles were tested on low sulfur fuel, relative to 32
ppm fuel.\248\ In particular, the study found a nearly 50 percent
increase in NOX over the FTP when sulfur was increased from
6 ppm to 32 ppm. Given the prep procedures related to catalyst clean-
out and loading used by these studies, these results may represent a
``best case'' scenario relative to what would be expected under more
typical driving conditions. Nonetheless, these data suggested the
effect of sulfur loading was reversible for Tier 2 vehicles, and that
there were likely to be significant emission reductions possible with
further reductions in gasoline sulfur level. For more discussion of the
impact of gasoline fuel sulfur on the current light-duty vehicle fleet,
see Section III.A.
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    \247\ This test program is described in Chapter 6 of the RIA of
the MSAT2 final rulemaking, EPA 420-R-07-002, February 2007,
available at http://www.epa.gov/otaq/regs/toxics/420r07002chp6.pdf.
    \248\ See Chapter 6 of the Regulatory Impact Analysis for the
Control of Hazardous Air Pollutants from Mobile Sources Final Rule,
EPA 420-R-07-002.
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b. EPA Gasoline Sulfur Effects Testing
    Both the MSAT and Umicore studies showed the emission reduction
potential of lower sulfur fuel on Tier 2 and later technology vehicles
over the FTP cycle. However, assessing the potential for reduction on
the in-use

fleet requires understanding how sulfur exposure over time impacts
emissions, and what the state of loading is for the typical vehicle in
the field. In response to these data needs, EPA conducted a new study
to assess the emission reductions expected from the in-use Tier 2 fleet
with a reduction in fuel sulfur level from current levels. It was
designed to take into consideration what was known from prior studies
on sulfur build-up in catalysts over time and the effect of periodic
regeneration events that may result from higher speed and load
operation over the course of day-to-day driving.
    The study sample described in this analysis consisted of 81 cars
and light trucks recruited from owners in southeast Michigan, covering
model years 2007-9 with approximately 20,000-40,000 odometer miles. The
makes and models targeted for recruitment were chosen to be
representative of high sales vehicles covering a range of types and
sizes. Test fuels were two non-ethanol gasolines with properties
typical of certification test fuel, one at a sulfur level of 5 ppm and
the other at 28 ppm. A nominal concentration of approximately 25 ppm
was targeted for the high level to be representative of retail fuel
available to the public in the vehicle recruiting area. All emissions
data was collected using the FTP cycle at a nominal temperature of 75
[deg]F.
    Using the 28 ppm test fuel, emissions data were collected from
vehicles in their as-received state as well as following a high-speed/
load ``clean-out'' procedure consisting of two back-to-back US06 cycles
intended to reduce sulfur loading in the catalyst. A statistical
analysis of this data showed highly significant reductions in several
pollutants including NOX and hydrocarbons, suggesting that
reversible sulfur loading exists in the in-use fleet and has a
measurable effect on aftertreatment performance (Table IV-6). For
example, Bag 2 NOX emissions dropped 32 percent between the
pre- and post-cleanout tests on 28 ppm fuel.

                                   Table IV-6--Average Clean-Out Effect on In-Use Emissions Using 28 ppm Test Fuel\a\
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                           NOX (p-value)   THC (p-value)   CO (p-value)   NMHC (p-value)   CH4 (p-value)   PM (p-value)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Bag 1...................................................  ..............  ..............            4.7%  ..............  ..............           15.4%
                                                                                (0.0737)                                       (<0.0001)
Bag 2...................................................           31.9%           16.5%  ..............           17.8%           15.3%  ..............
                                                                (0.0009)        (0.0024)                        (0.0181)        (0.0015)
Bag 3...................................................           38.3%           21.4%           19.5%           27.8%           12.0%           24.5%
                                                               (<0.0001)       (<0.0001)        (0.0011)       (<0.0001)       (<0.0001)       (<0.0001)
FTP Composite...........................................           11.4%            4.1%            7.6%            3.0%            6.9%           13.7%
                                                               (<0.0001)        (0.0187)        (0.0008)        (0.0751)        (0.0003)       (<0.0001)
Bag 1-Bag 3.............................................  ..............  ..............            4.2%  ..............  ..............  ..............
                                                                                (0.0714)
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\a\ The clean-out effect is not significant at [alpha] = 0.10 when no reduction estimate is provided.

    To assess the impact of lower sulfur fuel on in-use emissions,
further testing was conducted on a representative subset of vehicles on
28 ppm and 5 ppm fuel with accumulated mileage. A first step in this
portion of the study was to assess differences in the effectiveness of
the clean-out procedure when done using different fuel sulfur levels.
Table IV-7 presents a comparison of emissions immediately following
(<50 miles) the clean-out procedures at the low vs. high sulfur level.
These results show significant emission reductions for the 5 ppm fuel
relative to the 28 ppm fuel immediately after this clean-out; for
example, Bag 2 NOX emissions were 47 percent lower on the 5
ppm fuel vs. the 28 ppm fuel. This indicates that the catalyst is not
fully desulfurized, even after a clean out procedure, as long as there
is sulfur in the fuel.

   Table IV-7--Percent Reduction in Exhaust Emissions When Going From 28 ppm to 5 ppm Sulfur Gasoline for the First Three Repeat FTP Tests Immediately
                                                                   Following Clean-Out
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                           NOX (p-value)   THC (p-value)   CO (p-value)   NMHC (p-value)   CH4 (p-value)       PM\a\
--------------------------------------------------------------------------------------------------------------------------------------------------------
Bag 1...................................................            5.9%            5.4%            7.3%            4.6%           11.1%  ..............
                                                                (0.0896)        (0.0118)        (0.0023)        (0.0465)       (<0.0001)
Bag 2...................................................           47.3%           40.2%            -\a\           34.4%           53.6%  ..............
                                                                (0.0010)       (<0.0001)                        (0.0041)       (<0.0001)
Bag 3...................................................           51.2%           35.0%           10.1%           45.0%           25.4%  ..............
                                                               (<0.0001)       (<0.0001)        (0.0988)       (<0.0001)       (<0.0001)
FTP Composite...........................................           17.7%           11.2%            8.3%            8.8%           21.4%  ..............
                                                                (0.0001)       (<0.0001)        (0.0003)        (0.0003)       (<0.0001)
Bag 1-Bag 3.............................................            -\a\            -\a\            5.8%            -\a\            -\a\  ..............
                                                                                (0.0412)
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\a\ Sulfur level not significant at [alpha] = 0.10.

    To assess the overall in-use reduction between high and low sulfur
fuel, a mixed model analysis of all data as a function of fuel sulfur
level and miles driven after cleanout was performed. This analysis
found highly significant reductions for several pollutants, as shown in
Table IV-8. Reductions for Bag 2 NOX were particularly high,
estimated at 59 percent between 28 ppm and 5 ppm overall. For some
pollutants, such as Bag 2 NOX, the model fitting did not
find a significant miles-by-sulfur interaction, suggesting the relative
differences were not dependent on

miles driven after clean-out. Other results, such as Bag 1
hydrocarbons, did show a significant miles-by-sulfur interaction. In
this case, determination of a sulfur level effect for the in-use fleet
required estimation of a miles-equivalent level of sulfur loading,