October 15, 1997
"Update of Heavy-Duty Emission Levels (Model Years 1988-2004+)
for Use in MOBILE6"
Released for Stakeholder Review and Comment
The Office of Mobile Sources, Assessment and Modeling Division,
announces the release of "Update of Heavy-Duty Emission Levels
(Model Years 1988-2004+) for Use in MOBILES" for stakeholder
review and comment. This document (M6HDE001.WPD) is available at
the MOBILES section of the QMS Web Site
(http:/www.epa.gov/omswww/modeIs.htm).
The aforementioned report was developed by Christian Lindhjem and
Tracie Jackson of the EPA Office of Mobile Sources, Assessment
and Modeling Division. The report details the methodology used
to determine emission rates for use in the development of
emission factors for heavy-duty trucks and buses. These emission
rates are based on engine certification data, and include
emission rates when the vehicle has not accumulated any mileage
(zero mile level) and over the course of the engines life
(deterioration rates). Available certification data used in this
analysis spans the 1988-1995 model years, and projections were
made for model years beyond 1995.
Please note that EPA is seeking any input from stakeholders and
reviewers that might improve our emission rate estimates.
Comments on this report and its proposed use in MOBILE6 should be
sent to the attention of Tracie Jackson. Comments may be
submitted electronically to Jackson.tracie® epamail.epa.gov, or
by fax to (313) 741-7939, or by mail to "MOBILES Comments", US
EPA Assessment and Modeling Division, 2565 Plymouth Road, Ann
Arbor MI 48105. Electronic submission of comments is preferred.
In your comments, please note clearly the document that you are
commenting on including the report title and the code number
listed. Please be sure to include your name, address,
affiliation, and any other pertinent information.
This document is being released and posted on October 17, 1997
Comments will be accepted for sixty (60) days, ending December
16, 1997. EPA will then review and consider all comments
received, and will provide a summary of those comments and how we
are responding to them in the form of a follow-up document within
30 days of the close of the comment period.
-------
Thank you for your continuing interest in the development of
MOBILE6.
Sincerely,
Emission Inventory Group, Assessment and Modeling Division, US
EPA
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Update of Heavy-Duty Emission Levels (Model Years 1988-2004+)
for Use in MOBILE6
Draft Report No. M6HDE.001
Christian Lindhjem
Trade Jackson
U.S. EPA Office of Mobile Sources, Assessment and Modeling Division
Introduction
EPA intends to update the estimates of heavy-duty engine emission factors currently
contained in MOBILESb. To accomplish this, EPA plans to follow the same methodology
employed in previous versions of the MOBILE model, using updated inputs. Succinctly, the
methodology entails determination of a gram per mile (g/mi) emission factor by multiplying a
work-specific emission level (in units of grams per horsepower-hour (g/bhp-hr)) by a conversion
factor which converts work units into mileage units (bhp-hr/mi).
Emission Factor (g/mi) = Work-Specific Emission Level (g/bhp-hr) * Conversion Factor (bhp-hr/mi)
The conversion factors required for development of the g/mi emission factors will be
detailed in another report. The purpose of this analysis is to develop updated work-specific
emission levels necessary for computing heavy-duty emission factors for use in MOBILE6.
Background
EPA defines heavy-duty vehicles as those vehicles exceeding 8,500 Ibs. gross vehicle
weight (GVW). As noted in Table 1, this broad class of vehicles is divided into those requiring
gasoline or diesel fuels, and is further subdivided into more specific classes based on GVW
categories. EPA uses this more detailed subdivision scheme to account for different
characteristics and general uses of the engines included in each GVW class.
Emissions of air pollutants from heavy-duty vehicles, particularly heavy-duty diesel
vehicles, have come under increased scrutiny in recent years. This increased attention is due to
three main factors: 1) EPA's past emphasis on control of emissions from passenger cars and
light-duty trucks has effectively reduced the proportional contribution of these sources to mobile
source air pollution, and hence has increased the relative significance of heavy-duty emissions; 2)
the public has become increasingly concerned about the human health and environmental
impacts of emissions of particulate matter and nitrogen oxides, both of which are emitted in
relatively large amounts from heavy-duty diesel engines; and 3) advances in emission control
technology have increased the cost effectiveness of regulating heavy-duty engines.
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Table 1. Heavy-Duty Vehicle Classifications
Designation
Description
Gross Vehicle Weight
(Ibs.)
Gasoline Vehicles
HDGV (classes 2B-3)
HDGV (classes 4-8)
Diesel Vehicles
HDDV (class 2B)
HDDV (class 3)
HDDV (classes 4-5)
HDDV (classes 6-7)
HDDV (class 8A)
HDDV (class 8B)
Urban Buses
HDGB (school)
HDGB (transit)
HDDB (school)
HDDB ftransif)
Heavy-duty gasoline vehicles
Heavy-duty gasoline vehicles
Light heavy-duty diesel tracks
Light heavy-duty diesel tracks
Light heavy-duty diesel tracks
Medium heavy-duty diesel tracks
Heavy heavy-duty diesel tracks
Heavy heavy-duty diesel tracks
Heavy-duty gasoline school buses
Heavy-duty gasoline transit buses
Heavy-duty diesel school buses
Heaw-dutv diesel transit buses
8,501-14,000
>14,000
8,501-10,000
10,001-14,000
14,001-19,500
19,501-33,000
33,001-60,000
>60,000
all
all
all
all
EPA has been regulating air pollutant emissions from heavy-duty gasoline and diesel
vehicles since the 1970s. Since manufacturers of individual types of heavy-duty engines may sell
these engines to multiple vehicle manufacturers for use in different applications (for both on-
highway and off-highway vehicles), EPA has developed emission standards for heavy-duty
engines instead of vehicles.
In response to the need to further reduce air pollution at the national level, EPA is
currently in the process of finalizing a new set of combined emission standards for nitrogen
oxides (NOx) and nonmethane hydrocarbons (NMHC, hereafter referred to as HC) from heavy-
duty engines, to become effective in model year 2004. Tables 2 and 3 list the emission standards
for heavy-duty gasoline and heavy-duty diesel vehicles respectively since the mid-1980s,
including the proposed new standard. Note that the 2004 standard applies to both heavy-duty
gasoline and diesel vehicles, and is presented separately as NOx and HC .
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Table 2. Emission Standards for New Heavy-Duty Gasoline Engines
Model Year
1987 (A)*
(B)*
1988-1990 (A)*
(B)*
1991-1997 (A)*
(B)*
1998-2003 (A)*
(B)*
2004
Pollutant (g/bhp-hr)
Hydrocarbons
(HC)
1.1 g/bhp-hr
1.9 g/bhp-hr
1.1 g/bhp-hr
1.9 g/bhp-hr
1.1 g/bhp-hr
1.9 g/bhp-hr
1.1 g/bhp-hr
1.9 g/bhp-hr
**2.5 g/bhp-hr
combined NMHC +
NOx
Carbon Monoxide
(CO)
14.4 g/bhp-hr
37.1 g/bhp-hr
14.4 g/bhp-hr
3 7.1 g/bhp-hr
14.4 g/bhp-hr
3 7.1 g/bhp-hr
14.4 g/bhp-hr
3 7.1 g/bhp-hr
15.5 g/bhp-hr
Nitrogen oxides
(NOx)
10.6 g/bhp-hr
10.6 g/bhp-hr
6.0 g/bhp-hr
6.0 g/bhp-hr
5.0 g/bhp-hr
5.0 g/bhp-hr
4.0 g/bhp-hr
4.0 g/bhp-hr
**2.5 g/bhp-hr
combined NMHC +
NOx
Paniculate Matter
(PM)
N/A
N/A
N/A
N/A
N/A
* (A) refers to heavy-duty gasoline engines less than 14,000 Ibs. GVW.
(B) refers to heavy-duty gasoline engines greater than 14,000 Ibs. GVW.
** The 2004 standards apply to all GVW classes, and is defined as a combined non-methane hydrocarbon plus
nitrogen oxides (NMHC + NOx) emission standard of 2.5 g/bhp-hr.
Table 3. Emission Standards for New Heavy-Duty Diesel Engines
Model Year
1985-1987
1988-1989
1990
1991-1992
1993
1994-1995
1996-1997
1998-2003
2004
Pollutant (g/bhp-hr)
Hydrocarbons
(HC)
1.3 g/bhp-hr
1.3 g/bhp-hr
1.3 g/bhp-hr
1.3 g/bhp-hr
1.3 g/bhp-hr
1.3 g/bhp-hr
1.3 g/bhp-hr
1.3 g/bhp-hr
**2.5 g/bhp-hr combined
NMHC + NOx
Carbon
Monoxide
(CO)
15.5 g/bhp-hr
15.5 g/bhp-hr
15.5 g/bhp-hr
15.5 g/bhp-hr
15.5 g/bhp-hr
15.5 g/bhp-hr
15.5 g/bhp-hr
15.5 g/bhp-hr
15.5 g/bhp-hr
Nitrogen oxides
(NOx)
10.7 g/bhp-hr
10.7 g/bhp-hr
6.0 g/bhp-hr
5.0 g/bhp-hr
5.0 g/bhp-hr
5.0 g/bhp-hr
5.0 g/bhp-hr
4.0 g/bhp-hr
**2.5 g/bhp-hr combined
NMHC + NOx
Paniculate Matter
(PM)
None
0.6 g/bhp-hr
0.6 g/bhp-hr
0.25 g/bhp-hr
0.25 g/bhp-hr truck
0.10 g/bhp-hr urban bus
0.10 g/bhp-hr truck
0.07 g/bhp-hr urban bus
0.10 g/bhp-hr truck
0.05 g/bhp-hr urban bus
0.10 g/bhp-hr truck
0.05 g/bhp-hr urban bus"
0.10 g/bhp-hr truck
0.05 g/bhp-hr urban bus"
** The 2004 standards apply to all GVW classes, and is defined as a combined non-methane hydrocarbon plus
nitrogen oxides (NMHC + NOx) emission standard of 2.5 g/bhp-hr.
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In the above tables, one should note that heavy-duty gasoline emission standards are
GVW-specific, while heavy-duty diesel emission standards apply to all GVWs. Also note that,
for the most part, technical changes to engine design over the years were made in response to
these emission standards. That is, engine design changes rather than emission control technology
per se (e.g., catalytic converters, O2 sensors) have been the primary means of compliance with
heavy-duty engine emission standards to date.
Emissions Testing
Testing of heavy-duty vehicles to determine emissions may be performed in two ways.
The first method involves removing the engine from the test vehicle's chassis (frame), mounting
it on a test stand, and operating the engine on a testing apparatus known as an engine
dynamometer. The second method involves testing the engine while it is still in the vehicle by
operating the entire vehicle on what is known as a chassis dynamometer. The latter method is
very similar to the approach used to test light-duty vehicle and light-duty truck emissions.
Emission levels produced on the engine dynamometer are measured in grams per brake
horsepower-hour (g/bhp-hr) or grams per kilowatt-hour (g/kW-hr) for a given test cycle, while
emissions produced on a chassis dynamometer are measured in grams per mile (g/mi) or grams
per kilometer (g/km). The results of these emissions tests are used to develop emission factors
for heavy-duty vehicles that are then used in mobile source modeling and inventory development.
Both testing methods have certain limitations. Use of chassis dynamometers allows the
investigator to directly account for the impacts of factors such as load and grade on emissions,
thus providing a better sense of emissions due to real-world driving conditions. However, in-
use emission factors for heavy-duty engines are more difficult to determine than for light-duty
engines because chassis dynamometers capable of testing these heavy, larger vehicles are not
widely available. Furthermore, manufacturers of heavy-duty engines may sell these engines for
use in a variety of applications. Given these factors, the optimal test procedure for emission
certification is testing the engine on an engine dynamometer.
Heavy-duty engine testing tends to be very costly. Due to the prohibitive costs involved
in obtaining in-use emissions data on heavy-duty vehicles, very little recent test data existed at
the time MOBILESb, the latest version of the MOBILE model, was developed.. Therefore, the
heavy-duty emissions factors in MOBILESb (1996) are the same ones that were developed for
use in MOBILE4 (1989). The 1980 through 1990 model year emissions factors are based on data
derived from a cooperative test program between EPA and engine manufacturers, involving 18
heavy-duty gasoline engines (model years 1979 to 1982) and 22 heavy-duty diesel engines
(model years 1979 to 1984). In MOBILESb, emissions rates from the cooperative program were
used unless the certification rate was higher than that produced from the test program. In cases
were the certification results was greater, that rate was used instead.
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Proposed Changes for MOBILE6
Since the release of MOBILESb, very little new data on in-use heavy-duty engines, using
representative driving cycles, has been produced. In lieu of actual data on in-use engines, EPA
has proposed the use of test data required by EPA from engine manufacturers for new engine
certification as a surrogate for in-use emissions data.
Under the EPA certification test procedure, manufacturers are required to submit
emissions data on new engines using an engine dynamometer test. The engines are run on a
transient engine dynamometer test cycle (developed from in-use data), and emission results are
given in grams of pollutant per brake horsepower-hour.
Using this EPA engine dynamometer test cycle in the cooperative test program between
EPA and engine manufacturers, the test results indicated that emission-control performance in
heavy-duty vehicles does not suffer from significant deterioration. Given that these test data
indicate that emission controls on these engines do not deteriorate greatly over time, and because
the EPA engine dynamometer test cycle was developed to closely represent the in-use behavior
of these engines, EPA assumed for this analysis that the emission levels produced by the
certification test procedure are representative of the average in-use emission levels.
Methodology
Engine certification data consist of zero-mile level (ZML) emissions (new engine
emissions) and rates of deterioration at the end of useful life, typically given in grams of
pollutant per brake horsepower-hour (g/bhp-hr). For heavy-duty diesel engines, the certification
data sets also generally include an intended service class for each engine model (light, medium,
heavy, and bus). Useful life is defined as 110,000 miles for all heavy-duty gasoline engines and
those engines with the intended service class of light heavy-duty diesel, 185,000 miles for
medium heavy-duty diesel engines, and 290,000 miles for heavy heavy-duty diesel engines and
buses.
Table 4. Intended service classes and useful lifetimes for heavy-duty engines
Engine Class
All heavy-duty gasoline engines
Light heavy-duty diesel engines
Medium heavy-duty diesel engines
Heavy heavy-duty diesel engines (incl. buses)
Gross Vehicle
Weight (GVW)
Ob)
8,501-60,000+
8,501 - 19,500
19,501-33,000
33,001-60,000+
Useful Life
(miles)
110,000
110,000
185,000
290,000
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The sum of the ZML and the deterioration rate must be less than the emission standard for each
pollutant for the engine model to receive EPA certification. This is only true for each individual
engine if no averaging, banking and/or trading provisions are used to offset excess emissions.
For the purpose of modeling average, in-use emissions, these programs can be ignored.
For this analysis, the emission levels from the certification data were weighted by engine
sales and rated power to produce average emission levels for gasoline and diesel-fueled heavy-
duty engines, beginning with the 1988 model year and ending with 1995 model year data (the
most current available during this analysis). This calculation was performed for ZML emissions
as well as deterioration rates, and is illustrated by the following equation:
(Sales .* HP .* EL )
Emission Level (EL) = — — - - - - - —
(Sales t* HP t)
A second method of averaging emission levels was identified; this method involve simply
averaging emission level weighted by engine sales. However, EPA opted to use the method
defined by the above equation because this method accounts for differences in rated power of
various engine models, and also because the second method does not produce significantly
different results from those calculated as stated above.
The above calculations were performed using certification and sales data for both
gasoline and diesel heavy-duty engines by engine model year. Separate calculations were
performed for hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOx), and
particulate matter (PM). In addition to calculating average emission levels for all heavy-duty
diesel engines, calculations were performed for each of the service classes as well. Heavy-duty
gasoline engine certification reports do not include intended service class specification; therefore,
a single average emission level for each model year is given.
There are several peculiarities within the certification data that must be noted by anyone
working with the results provided in this report. Manufacturers often supply multiple emission
results for a given engine family, because tests are often run on engines in the same engine family
that are rated at different power levels. For this analysis, multiple results were averaged by
emission level and rated power to avoid double counting the sales information. Another unusual
characteristic of the certification data is that deterioration rates are sometimes given as multiples
of the zero-mile emission rate and at other times as additive emissions to the zero-mile emission
rate. The emission level results presented in this analysis account for these peculiarities and
provide emission rates at the zero mile level and the incremental increase at the end of useful life.
A third caveat involves the reporting of deterioration rates in certification data reports. A
manufacturer is not permitted to report a negative deterioration. In cases where the manufacturer
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observed negative deterioration results, the certification report states that zero deterioration was
found. Therefore, the average deterioration rates calculated from the certification data inflate the
deterioration that the manufacturers have determined. And lastly, because all engines tested for
certification meet the specifications of the manufacturer, the effects of engine malmaintenance
and tampering on emissions are not included in the analysis.
Results of Analysis
Gasoline Engines
The certification data set for heavy-duty gasoline engines is sparsely populated. Close
examination of the data sets seems to indicate that certification data for engine models which
have been "carried over," or sold in subsequent years, have not been recorded in much of the
certification data that EPA acquired for this analysis. This is especially true for the 1992 and
1993 data where only one major manufacturer's engines were reported for 1992 and another
manufacturer's engines were reported for 1993. As it is quite unlikely that only one
manufacturer sold heavy-duty gasoline engines in a given year, EPA assumes that this lack of
sales and emission data is due to a reporting anomaly. This hypothesis is further supported by
the fact that manufacturers of light-duty vehicles may not be required to recertify models that
carry-over; it is possible that the reporting assumptions were made in the heavy-duty gasoline
database. Due to the data limitations, there is some concern as to the reliability of the emission
level calculations derived from these data sets, particularly 1992 and 1993.
The results of the current analysis are compared to emission levels reported in
MOBILESb model. Tables 5, 6 and 7 present these comparisons for hydrocarbon, carbon
dioxide, and nitrogen oxide emissions, respectively, by model year (1988 through 1995).
Particulate matter emissions are not included here because gasoline engines generally produce
negligible amounts of particulate. Model years 1992 and 1993 are in italics to signify the greater
uncertainty involved with the calculations in these years, as explained above.
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Table 5. Comparison of MOBILESb and Certification Calculation Results for Emission Levels of
Hydrocarbon from Heavy-Duty Gasoline Engines
Model
Year
1988
1989
1990
1991
1992
1993
1994
1995
Zero Mile Level (g/bhp-hr)
MOBILESb
0.92
0.92
0.92
0.92
0.92
0.92
0.92
0.92
Certification
0.59
0.65
0.35
0.30
0.32
0.29
0.42
0.38
Deterioration (g/bhp-hr/useful
life)
MOBILESb
1.10
1.10
1.10
1.10
1.10
1.10
1.10
1.10
Certification
0.26
0.24
0.25
0.21
0.27
0.15
0.29
0.23
Table 6. Comparison of MOBILESb and Certification Calculation Results for Emission Levels of Carbon
Monoxide from Heavy-Duty Gasoline Engines
Model
Year
1988
1989
1990
1991
1992
1993
1994
1995
Zero Mile Level (g/bhp-hr)
MOBILESb
12.48
12.48
12.48
12.48
12. 48
12.48
12.48
12.48
Certification
12.18
15.65
6.89
6.11
6.59
9.77
7.57
7.69
Deterioration (g/bhp-hr/userul
life)
MOBILESb
7.92
7.92
7.92
7.92
7.92
7.92
7.92
7.92
Certification
2.32
3.12
2.34
1.95
4.35
1.22
3.76
3.50
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Table 7. Comparison of MOBILESb and Certification Calculation Results for Emission Levels of Nitrogen
oxides from Heavy-Duty Gasoline Engines
Model
Year
1988
1989
1990
1991
1992
1993
1994
1995
Zero Mile Level (g/bhp-hr)
MOBILESb
5.82
5.82
4.78
3.99
3.99
3.99
3.99
3.99
Certification
5.10
4.82
3.61
3.52
3. 13
3.58
2.80
2.79
Deterioration (g/bhp-hr/userul
life)
MOBILESb
0.33
0.33
0.55
0.55
0.55
0.55
0.55
0.55
Certification
0.49
0.48
0.29
0.34
0.62
0.00
0.54
0.56
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Diesel Engines
The following four tables present the calculated emission level results from this analysis
for hydrocarbons, carbon monoxide, nitrogen oxides and particulate matter. Each table includes
a total average emission level of the pollutant by model year (1988 through 1995), plus average
emission levels by intended service class. For purposes of comparison, each table also includes
emission levels used by EPA's emission factor models, MOBILESb and PARTS. Note that
MOBILESb does not compute particulate matter emissions; therefore, for this analysis, results
from EPA's separate particulate matter model, PARTS, have been used.
Table 8. Modeled and Calculated Hydrocarbon Emission Levels for Heavy-Duty Diesel Engines
Model
Year
1988
1989
1990
1991
1992
1993
1994
1995
Zero Mile Level (g/bhp-hr)
MOBILE
5b
Modeled
Total
1.03
1.03
1.03
1.03
1.03
1.03
1.03
1.03
Certification Data Calculations
Total
0.56
0.55
0.52
0.37
0.45
0.35
0.20
0.20
Heavy
0.42
0.51
NA
0.29
0.21
0.33
0.17
0.18
Med.
0.67
0.65
NA
0.40
0.52
0.38
0.24
0.25
Light
0.74
0.54
NA
0.51
0.25
0.31
0.20
0.20
Bus
NA
NA
NA
0.62
NA
0.30
0.11
0.06
Deterioration (g/bhp-hr/useful life)
MOBILE
5b
Modeled
Total
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
Certification Data Calculations
Total
0.03
0.02
0.01
0.01
0.01
0.01
0.01
0.03
Heavy
0.02
0.02
NA
0.00
0.00
0.01
0.02
0.04
Med.
0.05
0.04
NA
0.00
0.01
0.01
0.00
0.03
Light
0.02
0.02
NA
0.01
0.03
0.01
0.01
0.01
Bus
NA
NA
NA
0.01
NA
0.00
0.01
0.00
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Table 9. Modeled and Calculated Carbon Monoxide Emission Levels for Heavy-Duty Diesel Engines
Model
Year
1988
1989
1990
1991
1992
1993
1994
1995
Zero Mile Level (g/bhp-hr)
MOBILE
5b
Modeled
Total
4.68
4.68
4.68
4.68
4.68
4.68
4.68
4.68
Certification Data Calculations
Total
1.87
0.94
1.81
1.32
1.12
1.56
1.05
1.09
Heavy
1.84
0.84
NA
1.81
0.97
1.85
1.09
1.05
Med.
2.11
1.28
NA
1.22
1.23
1.29
0.77
0.98
Light
1.65
0.78
NA
0.28
0.69
0.98
1.20
1.19
Bus
NA
NA
NA
2.70
NA
2.90
1.01
1.12
Deterioration (g/bhp-hr/useful life)
MOBILE
5b
Modeled
Total
1.16
1.16
1.16
1.16
1.16
1.16
1.16
1.16
Certification Data Calculations
Total
0.38
0.13
0.13
0.11
0.05
0.12
0.08
0.10
Heavy
0.34
0.10
NA
0.08
0.00
0.08
0.10
0.10
Med.
0.44
0.22
NA
0.25
0.04
0.16
0.11
0.22
Light
0.40
0.08
NA
0.00
0.07
0.22
0.04
0.01
Bus
NA
NA
NA
0.00
NA
0.00
0.01
0.01
Table 10. Modeled and Calculated Nitrogen Oxide Emission Levels for Heavy-Duty Diesel Engines
Model
Year
1988
1989
1990
1991
1992
1993
1994
1995
Zero Mile Level (g/bhp-hr)
MOBILE
5b
Modeled
Total
7.93
7.93
5.64
4.60
4.60
4.60
4.60
4.60
Certification Data Calculations
Total
6.0
5.7
4.9
4.5
4.5
4.5
4.3
4.6
Heavy
6.47
6.08
NA
4.59
4.46
4.53
4.52
4.70
Med.
6.64
6.21
NA
4.51
4.57
4.53
4.56
4.67
Light
4.38
4.29
NA
4.41
4.06
4.37
3.85
4.36
Bus
NA
NA
NA
4.55
NA
4.26
4.70
5.09
Deterioration (g/bhp-hr/userul life)
MOBILE
5b
Modeled
Total
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
Certification Data Calculations
Total
0.2
0.2
0.1
0.1
0.1
0.
0.
0.
Heavy
0.28
0.27
NA
0.11
0.04
0.11
0.12
0.05
Med.
0.14
0.18
NA
0.23
0.08
0.06
0.01
0.03
Light
0.02
0.02
NA
0.03
0.00
0.01
0.00
0.01
Bus
NA
NA
NA
0.10
NA
0.00
0.01
0.01
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Table 11. Modeled and Calculated Participate Matter Emission Levels for Heavy-Duty Diesel Engines*
Model
Year
1988
1989
1990
1991
1992
1993
1994
1995
Zero Mile Level (g/bhp-hr)
PARTS
Modeled
Total
-0.48
-0.48
-0.48
-0.27
-0.27
-0.27
-0.09
-0.09
Certification Data Calculations
Total
0.45
0.43
0.38
0.23
0.19
0.19
0.09
0.08
Heavy
0.42
0.46
NA
0.24
0.10
0.18
0.09
0.09
Med.
0.44
0.44
NA
0.21
0.20
0.20
0.08
0.08
Light
0.51
0.37
NA
0.24
0.18
0.18
0.09
0.08
Bus
NA
NA
NA
0.46
NA
0.23
0.06
0.06
Deterioration (g/bhp-hr/userul life)
PARTS
Modeled
Total
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
Certification Data Calculations
Total
0.02
0.02
0.01
0.00
0.01
0.01
0.00
0.00
Heavy
0.02
0.02
NA
0.00
0.00
0.01
0.00
0.00
Med.
0.04
0.02
NA
0.01
0.01
0.01
0.00
0.00
Light
0.01
0.01
NA
0.00
0.00
0.00
0.00
0.00
Bus
NA
NA
NA
0.00
NA
0.00
0.00
0.00
* The PART5 model uses slightly different but unique emission levels for various classes of trucks therefore
an average level can be estimated for the assumed travel fraction of the different classes.
The certification data file for 1990 model year heavy-duty engines did not report different
emissions for each of the three service classes or for buses. Therefore, EPA has only reported a
total ZML and a total deterioration rate for this model year.
In most cases, the results of the calculations using the certification data are close to those
being produced by the MOBILESb and PARTS models. However, the modeled emission level
estimates for HC and CO are higher than those produced by the certification data-based
calculations.
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Inputs into MOBILE6
After reviewing the results of the above calculations, EPA decided to recompute the
emission levels and deterioration rates based on specific model year groups. These model year
groups represent changes in EPA emission standards.
Table 12. Model-year groups for heavy-duty gasoline engines, heavy-duty diesel engines and heavy-duty
diesel buses for use in MOBILE6
Heavy-duty gasoline engines
Model Year
Group
1988-1990
1991-1997
1998-2003
2004+
Regulatory Changes
6.0g/bhp-hrNOx
5.0g/bhp-hrNOx
4.0g/bhp-hrNOx
2.5 g/bhp-hr
HC + NOx
Heavy-duty diesel engines
Model Year
Group
1988-1989
1990
1991-1993
1994-1997
1998-2003
2004+
Regulatory
Changes
10.7 g/bhp-hr NOx,
0.6 g/bhp-hr PM
6.0 g/bhp-hr NOx
5.0 g/bhp-hr NOx,
0.25 g/bhp-hr PM
0.10 g/bhp-hr PM
4.0 g/bhp-hr NOx
2.5 g/bhp-hr HC +
NOx
Heavy-duty diesel Buses
Model Year
Group
1988-1989
1990
1991-1992
1993
1994-1995
1996-1997
1998-2003
2004+
Regulatory Changes
6.0 g/bhp-hr NOx
5.0 g/bhp-hr NOx
0.25 g/bhp-hr PM
0.10 g/bhp-hr PM
(urban buses only)
0.07 g/bhp-hr PM
(urban buses only)
0.05 g/bhp-hr PM
(urban buses only)
4.0 g/bhp-hr NOx
2.5 g/bhp-hr
HC+NOx
By re-computing the averages based on these model year groups, we have attempted to
reduced the impact of the data inconsistencies and caveats that were mentioned previously.
To improve the flexibility of MOBILE6's emission factors, EPA has opted to use the
individual emission rates for each intended service class for heavy-duty diesels instead of a single
emission rate. Since no separate intended service classes are defined for heavy-duty gasoline
engines, EPA will continue to have a total emission rate in MOBILE6.
Projections for post-1995 model years were also computed. Tables presenting the
recompute ZMLs and deterioration rates, as well as explanations of the assumptions used in the
projections follow. All tables below present deterioration rates as g/bhp-hr/10,000 miles, for
consistency with the MOBILESb framework. Italicized emission rates are projections.
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Heavy Duty Gasoline Engine Inputs for MOBILE6
The heavy-duty gasoline zero mile levels and deterioration rates for HC, CO and NOx are
presented below in Tables 13 through 15. In 2004, a new standard for combined non-methane
hydrocarbon and nitrogen oxide (NMHC + NOx) emissions becomes effective. This combined
standard sets a limit of 2.5 g/bhp-hr for NOx and NMHC. EPA assumes that this standard will
effectively result in a 2.0 g/bhp-hr for NOx. HC projections are based on the assumption that no
changes occur beyond the 1997 model year.
NOx projections for 1998-2003 are based on proportioning the emission rates calculated
for 1991-1997 by a ratio of the standard in effect in 1998 (4.0 g/bhp-hr) to the standard in effect
for the 1991-1997 model years (5.0 g/bhp-hr). Again, due to the split standard in 2004, EPA has
used a ratio of assumed NOx standard of 2.0 g/bhp-hr to the 1998 standard of 4.0 g/bhp-hr to
project emission rates for the year 2004 and beyond.
Since no standard changes occurred between 1988 and 2004 for CO, EPA has assumed
the same emission rate calculated in 1991-1997 for the 1998-2003 and 2004+ model year classes.
All deterioration rates remain the same as in the 1991-1997 model year group.
Table 13. Heavy-duty Gasoline Engine Emission Rates for Hydrocarbons for use in MOBILE6
Model
Year Class
1988-1990
1991-1997
1998-2003
2004+
Zero Mile Level (g/bhp-hr)
MOBILESb
0.92
0.92
0.92
0.92
Hydrocarbons
0.44
0.33
0.33
0.33
Deterioration (g/bhp-hr/10,000
miles)
MOBILESb
0.10
0.10
0.10
0.10
Hydrocarbons
0.023
0.021
0.021
0.021
Table 14. Heavy-duty Gasoline Engine Emission Rates for Carbon Monoxide for use in MOBILE6
Model
Year Class
1988-1990
1991-1997
1998-2003
2004+
Zero Mile Level (g/bhp-hr)
MOBILESb
12.48
12.48
12.48
12.48
Carbon
Monoxide
9.15
7.10
7.10
7.10
Deterioration (g/bhp-hr/10,000
miles)
MOBILESb
0.72
0.72
0.72
0.72
Carbon
Monoxide
0.224
0.255
0.255
0.255
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Table 15. Heavy-duty Gasoline Engine Emission Rates for Nitrogen Oxides for use in MOBILE6
Model
Year Class
1988-1990
1991-1997
1998-2003
2004+
Zero Mile Level (g/bhp-hr)
MOBILESb
5.82
3.99
3.19
3.19
Nitrogen
Oxides
4.05
3.24
2.59
1.30
Deterioration (g/bhp-hr/10,000
miles)
MOBILE5b
0.05
0.05
0.05
0.05
Nitrogen
Oxides
0.032
0.038
0.038
0.038
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Heavy-duty diesel engines
Zero mile levels and deterioration rates for HC, CO, NOx, and PM are presented for
heavy-duty diesel engines in Tables 16 through 19. Since no standard changes have occurred for
CO or PM during the 1988-2004+ period, emission projections are assumed to be the same as in
the 1994-1997 model year class.
Due to the fact that HC emissions are extremely low in the 1994-1997 model year group,
EPA has assumed that engine manufacturers will not reduce HC emissions as a means of meeting
the 0.5 g/bhp-hr NMHC + NOx emission standard that becomes effective in 2004. Therefore,
emissions for 1998-2003 and 2004+ are assumed to be the same as in the 1994-1997 time frame.
For NOx, a ratio of 4.0 g/bhp-hr to 5.0 g/bhp-hr has been used to proportion the 1994-
1997 emission rates as a means of projecting 1998-2003 emissions. Post-2004 rates are based on
proportioning of the 1988-2003 rate by a ration of 2.0 g/bhp-hr to 4.0 g/bhp-hr, in the same
manner as for heavy-duty gasoline vehicles.
Table 16. Heavy-duty Diesel Engine Emission Rates of Hydrocarbons for use in MOBILE6
Model Year
Class
1988-1989
1990*
1991-1993
1994-1997
1998-2003
2004+
Zero Mile Level (g/bhp-hr)
MOBILESb
1.03
1.03
1.03
1.03
1.03
1.03
Heavy
0.47
0.52
0.30
0.17
0.17
0.17
Med.
0.66
0.52
0.40
0.24
0.24
0.24
Light
0.64
0.52
0.47
0.20
0.20
0.20
Deterioration (g/bhp-hr/10,000 miles)
MOBILESb
0.00
0.00
0.00
0.00
0.00
0.00
Heavy
0.001
0.000
0.000
0.001
0.001
0.001
Med.
0.002
0.001
0.001
0.001
0.001
0.001
Light
0.002
0.001
0.001
0.001
0.001
0.001
Table 17. Heavy-duty Diesel Engine Emission Rates of Carbon Monoxide (for use in MOBILE6)
Model Year
Class
1988-1989
1990*
1991-1993
1994-1997
1998-2003
2004+
Zero Mile Level (g/bhp-hr)
MOBILE5b
4.68
4.68
4.68
4.68
4.68
4.68
Heavy
1.34
1.81
1.82
1.07
1.07
1.07
Med.
1.70
1.81
1.26
0.85
0.85
0.85
Light
1.21
1.81
0.40
1.19
1.19
1.19
Deterioration (g/bhp-hr/10,000 miles)
MOBILESb
0.04
0.04
0.04
0.04
0.04
0.04
Heavy
0.008
0.005
0.003
0.004
0.004
0.004
Med.
0.018
0.007
0.010
0.009
0.009
0.009
Light
0.022
0.012
0.004
0.003
0.003
0.003
Table 18. Heavy-duty Diesel Engine Emission Rates of Nitrogen Oxides (for use in MOBILE6)
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Model Year
Class
1988-1989
1990*
1991-1993
1994-1997
1998-2003
2004+
Zero Mile Level (g/bhp-hr)
MOBILESb
7.93
5.64
4.60
4.60
3.68
3.68
Heavy
6.28
4.85
4.56
4.61
3.68
1.84
Med.
6.43
4.85
4.53
4.61
3.69
1.84
Light
4.34
4.85
4.38
4.08
3.26
1.63
Deterioration (g/bhp-hr/10,000 miles)
MOBILESb
0.00
0.00
0.00
0.00
0.00
0.00
Heavy
0.010
0.004
0.004
0.003
0.003
0.003
Med.
0.009
0.006
0.007
0.001
0.001
0.001
Light
0.002
0.011
0.003
0.001
0.001
0.001
Italics = projections (not based on direct certification data)
Table 19. Heavy-duty Diesel Engine Emission Rates of Participate Matter (for use in MOBILE6)
Model Year
Class
1988-1989
1990*
1991-1993
1994-1997
1998-2003
2004+
Zero Mile Level (g/bhp-hr)
PARTS
-0.48
-0.48
-0.27
-0.09
-O.OP
-O.OP
Heavy
0.44
0.38
0.21
0.08
0.08
0.08
Med.
0.44
0.38
0.20
0.08
0.08
0.08
Light
0.44
0.38
0.23
0.09
0.09
0.08
Deterioration (g/bhp-hr/10,000 miles)
PARTS
0.00
0.00
0.00
0.00
0.00
0.00
Heavy
0.001
0.000
0.000
0.000
0.000
0.000
Med.
0.002
0.000
0.001
0.001
0.000
0.000
Light
0.001
0.000
0.000
0.000
0.000
0.000
Italics = projections (not based on direct certification data)
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Heavy-duty diesel buses engines
Projections for buses essentially follow the same pattern as heavy-duty diesels, with
standard changes for HC and NOx occurring in the years for which projections were made.
However, there is one exception. In 1994, separate standards were implemented for particulate
matter from buses. In 1994, the bus PM standard was 0.07 g/bhp-hr. This standard was changed
to 0.05 g/bhp-hr in 1996. This ratio was used to project PM emissions for the 1996-1997 heavy-
duty diesel bus category. Projections for PM emissions beyond 1997 are assumed to be the same
as in 1996-1997.
Table 20. Heavy-duty Diesel Bus Engine Emission Rates of Hydrocarbons for use in MOBILE6
Model
Year Class
1988-1989
1990
1991-1992
1993
1994-1995
1996-1997
1998-2003
2004+
Zero Mile Level (g/bhp-hr)
MOBILESb
1.03
1.03
1.03
1.03
1.03
1.03
1.03
1.03
Hydrocarbons
0.47
0.52
0.62
0.30
0.08
0.08
0.08
0.08
Deterioration (g/bhp-hr/10,000
miles)
MOBILESb
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
Hydrocarbons
0.001
0.000
0.000
0.000
0.000
0.000
0.000
0.000
Table 21. Heavy-duty Diesel Bus Engine Emission Rates of Carbon Monoxide for use in MOBILE6
Model
Year Class
1988-1989
1990
1991-1992
1993
1994-1995
1996-1997
1998-2003
2004+
Zero Mile Level (g/bhp-hr)
MOBILESb
4.68
4.68
4.68
4.68
4.68
4.68
4.68
4.68
Carbon
Monoxide
1.34
1.81
2.7
2.9
1.06
1.06
1.06
1.06
Deterioration (g/bhp-hr/10,000
miles)
MOBILESb
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
Carbon
Monoxide
0.001
0.005
0.000
0.000
0.000
0.000
0.000
0.000
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Table 22. Heavy-duty Diesel Bus Engine Emission Rates of Nitrogen Oxides for use in MOBILE6
Model
Year Class
1988-1989
1990
1991-1992
1993
1994-1995
1996-1997
1998-2003
2004+
Zero Mile Level (g/bhp-hr)
MOBILESb
7.93
5.64
4.60
4.60
4.60
4.60
3.68
3.68
Nitrogen
Oxides
6.28
4.85
4.55
4.26
4.88
4.88
3.90
1.95
Deterioration (g/bhp-hr/10,000
miles)
MOBILE5b
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
Nitrogen
Oxides
0.000
0.004
0.000
0.000
0.000
0.000
0.000
0.000
: = projections for heavy-duty diesel buses have not been completed.
Table 23. Heavy-duty Diesel Buses Emission Rates of Particulate Matter for use in MOBILE6
Model
Year Class
1988-1989
1990
1991-1992
1993
1994-1995
1996-1997
1998-2003
2004+
Zero Mile Level (g/bhp-hr)
PART5
-0.48
-0.48
-0.27
-0.27
-0.09
-0.09
-0.09
-0.09
Particulate
Matter
0.44
0.38
0.46
0.23
0.06
0.04
0.04
0.04
Deterioration (g/bhp-hr/10,000
miles)
PART5
0.000
0.000
0.000
0.000
0.000
0.000
0.000
0.000
Particulate
Matter
0.001
0.000
0.000
0.000
0.000
0.000
0.000
0.000
M6HDE001 October 15, 1997
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