Emission Factors for Locomotives
The Environmental Protection Agency (EPA) has established
emission standards for oxides of nitrogen (NOx), hydrocarbons
(HC), carbon monoxide (CO), particulate matter (PM) and smoke for
newly manufactured and remanufactured locomotives. These standards,
which are codified at 40 CFR part 1033, include several sets of emis-
sion standards with applicability dependent on the date a locomotive is
first manufactured. The first set of standards (Tier 0) applies to most
locomotives originally manufactured before 2001. The most stringent
set of standards (Tier 4) applies to locomotives originally manufactured
in 2015 and later. This fact sheet describes EPAs estimates of the typ-
ical in-use emission rates for locomotives subject to these standards, as
well as the previous standards.
It is important to emphasize that this fact sheet relies on many simpli-
fying assumptions. Thus emission rates calculated as described in this
fact sheet should be considered as approximations.
Estimated Locomotive Emission Rates byTier
EPA has estimated average emission rates, given in grams per brake horsepower-hour
(g/bhp-hr), for uncontrolled locomotives and those required to meet the various
emission standards. Emissions were estimated for two different types of operation: a
low power cycle representing operation in a switch yard, and a higher power cycle
representative of general line-haul operation. These estimates are shown in Tables
1 and 2. Note that plus signs in the table indicate that a given tier of standards was
revised in a 2008 rulemaking (73 FR 37096, June 30, 2008). For example, locomo-
tives originally manufactured in years 2002-2004 were initially subject to the original
Tier 1 standards, but will be required to meet revised Tier 1 standards (also known as
Tier 1+ standards) when remanufactured. See the regulatory text for a more precise
explanation of which standards apply to which locomotives.
United States
Environmental Protection
Agency
Office of Transportation and Air Quality
EPA-420-F-09-025
April 2009
-------
u
u
It is important to note that there can be significant variability in in-use emission rates, especially
for uncontrolled locomotives. Also, a single locomotive's emission rate can vary throughout its
life as the engine ages and as ambient conditions change. Thus the values presented here are in-
tended to reflect the average emission rates. It is also worth noting that these emission estimates
were developed in the context of adopting new emission standards. This is especially important
for the CO emission factors. Because EPA's CO emission standards were intended to cap CO
emissions at pre'Control levels (which were relatively low), we have not projected any reduc-
tions in CO emission factors. However, recent testing indicates that emission controls designed
to reduce PM and HC emissions are also reducing CO emissions. Thus the CO emission rates
presented here may be too high and should be used with some caution. A similar effect may also
apply for HC emissions from Tier 0 and Tier 1 locomotives (but not the Tier 0+ and Tier 1 +
locomotives).
Table 1 - Line-Haul Emission Factors (g/bhp-hr)
UNCONTROLLED
TIERO
TIERO+
TIER1
TIER1+
TIER2
TIER 2+ & TIER 3
TIER 4
PM10
0.32
0.32
0.20
0.32
0.20
0.18
0.08
0.015
HC
0.48
0.48
0.30
0.47
0.29
0.26
0.13
0.04
NOX
13.00
8.60
7.20
6.70
6.70
4.95
4.95
1.00
CO
1.28
1.28
1.28
1.28
1.28
1.28
1.28
1.28
+ INDICATES THAT THESE ARE THE REVISED STANDARDS IN 40 CFR PART 1033
Table 2 - Switch Emission Factors (g/bhp-hr)
UNCONTROLLED
TIERO
TIERO+
TIER1
TIER1+
TIER2
TIER 2+
TIER 3
TIER 4
PM10
0.44
0.44
0.23
0.43
0.23
0.19
0.11
0.08
0.015
HC
1.01
1.01
0.57
1.01
0.57
0.51
0.26
0.26
0.08
NOX
17.40
12.60
10.60
9.90
9.90
7.30
7.30
4.50
1.00
CO
1.83
1.83
1.83
1.83
1.83
1.83
1.83
1.83
1.83
+ INDICATES THAT THESE ARE THE REVISED STANDARDS IN 40 CFR PART 1033
-------
Conversion to Gram per Gallon Emission Factors
It is often useful to express emission rates as grams of pollutant emitted per gallon of fuel con-
sumed (g/gal). This can be done by multiplying the emission rates in Table 1 or 2 by a conver-
sion factor relating the fuel consumption (gal/hr) and the usable power (bhp) of the engine.
EPA has estimated different conversion factors for different types of locomotive service as shown
in Table 3. The two primary reasons for the differences are variations in locomotive age and
duty cycle. Fuel efficiency tends to be worse for older locomotive designs and for locomotives
used in low power applications such as switching. Note that the g/gal emission factors presented
at the end of this fact sheet can be converted back to g/bhp-hr by dividing them by the conver-
sion factors shown here.
Table 3
Conversion Factors (bhp-hr/gal)
Locomotive Application
Large Line-Haul and Passenger
Small Line-Haul
Switching
Conversion Factor (bhp-hr/gal)
20.8
18.2
15.2
Conversion to Gram per Ton-Mile Emission Factors
In some cases, it can be helpful to express emission factors as grams emitted per ton-mile of
freight hauled. However, this can also be very problematic because the amount of engine work
required for each ton-mile varies significantly with a variety of factors. For example, it takes
more work to haul freight through mountainous terrain than across flat areas. Since EPA does
not have detailed information about these variations, we cannot provide accurate g/ton-mile
emission rates. However, very approximate national average values can be calculated based on
data collected by the Association of American Railroads for revenue ton-miles and fuel con-
sumption, which show that about one gallon of fuel is consumed by the railroads to haul 400
tons-miles of freight. Thus dividing g/gal emission rates by 400 ton-miles/gal gives approximate
g/ton-mile emission rates.
Emission Inventory Estimation
Total emissions can be calculated by multiplying the emission factors (in g/gal) by the fuel con-
sumption rates (in million-gal/yr) to give annual emission rates (in metric tons per year). Multi-
plying this metric estimate by 1.102 gives standard U.S. tons (or short tons) per year.
EPA has estimated that locomotives consume approximately 4 billion gallons of diesel fuel each
year. This includes national/regional freight service, switching, local freight service, and passen-
ger service. The relative amounts of fuel used in the United States for these four different types
of operation are shown in Table 4. The great majority of fuel consumed by locomotives each
year is used in line-haul freight service by the largest railroads. Smaller amounts are also used in
-------
switching and passenger service, and by very small railroads. For the purpose of this fact sheet,
we are aggregating the largest railroads with smaller railroads that are fully subject to EPA's emis-
sion requirements. This includes regional railroads as well as other railroads such as those that
are owned by large businesses. The local freight category includes only those railroads that meet
our regulatory definition of "small railroad" (40 CFR 1033.901) to qualify for small business al-
lowances under our regulations. These railroads are included in this fact sheet as local whether
or not they are truly local in nature. The passenger category includes local commuter railroads
and AMTRAK.
Table 4 - Locomotive Fuel Consumption by Service Category
National and Regional Freight Line-haul
National Freight Switching
Local Freight
Passenger
88%
7%
<2%
3%
U
Other Pollutants
The preceding emission factors include those pollutants for which EPA has set emission stan-
dards. However, other pollutants may also be of interest.
The broad category of volatile organic compounds (VOC) is a slightly different way of aggregat-
ing the organic pollutants controlled by our HC emission standards. In our rulemaking analysis
(http://www.epa.gov/otaq/regs/nonroad/420r08001a.pdf), we estimated that VOC emissions
can be assumed to be equal to 1.053 times the HC emissions. Similarly, PM emissions can be
expressed as PM (which includes all particles up to 10 microns in diameter) or PM (which
includes only those particles up to 2.5 microns in diameter). PM emissions can be estimated
as 0.97 times the PM10 emissions, meaning that nearly all of the PM is less than 2.5 microns in
diameter.
Gram per gallon emissions of sulfur dioxide (SO2) and carbon dioxide (CO2) are largely inde-
pendent of engine parameters and are primarily dependent on fuel properties. Locomotive-spe-
cific emission rates are not presented here. Instead, SO2 and CO2 emission rates should be calcu-
lated based on the properties of the specific fuel being used by the locomotives. These emission
rates can also be assumed to be the same as for other diesel engines operating on similar fuel.
Note that special caution should be used when estimating SO2 emission rates since the sulfur
content of diesel fuel varies much more than the carbon content. Also, while the vast majority
of sulfur in the fuel is typically converted to SO2, up to 5 percent of the sulfur is oxidized fur-
ther to sulfate (and forms particulate matter), so that the fraction of fuel sulfur emitted as SO2
may be as low as 95 percent. Examples of these calculations are shown below based on inputs
described in the NONROAD technical document NR-009c (http://www.epa.gov/otaq/models/
nonrdmdl/nonrdmdl2004/420p04009.pdf).
-------
SO2 (g/gal) = (fuel density) * (conversion factor) x (64 g SO2/32 g S) x (S content of fuel)
Consider the example where the density of diesel fuel is 3200 g/gal, the fraction of fuel sulfur
converted to SO2 is 97.8 percent, and the sulfur content of the fuel is 300 ppm.
SO2 (g/gal) = (3200) x (0.978) x (2.00) x (300 x lO'6) = 1.88 g/gal
CO2 (g/gal) = (fuel density) x (44 g CO/12 g C) x (C content of fuel)
Consider the example where the density of diesel fuel is 3200 g/gal and the carbon content of
the fuel is 87 percent by mass.
CO2 (g/gal) = (3200) x (3.67) x (0.87) = 10,217 g/gal
Other trace pollutants such as N2O, methane, and many air toxics are more dependent on
engine parameters. At this time, however, EPA does not have detailed emission rates for these
pollutants from locomotives. Where estimates are needed for N2O or methane, you may assume
that emissions of these pollutants from locomotives are similar to those of other diesel engines
with similar technology. For N2O, you may assume the emissions are proportional to total NOx.
For methane, you may assume the emissions are proportional to total hydrocarbons. Note how-
ever, that the presence of catalyzed components in the exhaust can significantly affect these
ratios. So it is best to compare emissions from uncatalyzed locomotives to emissions from other
uncatalyzed diesel engines. While this same approach could be used for air toxics (assuming that
air toxic emissions are proportional to total hydrocarbons), EPA has estimated air toxic emis-
sions from locomotives. These estimates are described in the National Emission Inventory docu-
mentation (see ftp://ftp.epa.gov/EmisInventory/2002finalnei/documentation/mobile/2002nei_
mobile_nonroad_methods.pdf- appendix C).
Projected Future Emission Factors
Tables 5-7 give the expected fleet average NOx, PM10, and HC emission factors by calendar year
for the four categories of locomotives (the same four categories as are shown in Table 4). The
steady decline in these emission factors reflects the penetration of the various tiers of locomo-
tives into the fleet over time. More detail regarding the assumptions on which these projections
were based can be found in the Regulatory Impact Analysis for the 2008 rulemaking (http://
www.epa.gov/otaq/regs/nonroad/420r08001a.pdf)
-------
For More Information
You can access the rule and related documents on EPA's Office of Transportation and Air Qual-
ity (OTAQ) Web site at: www.epa.gov/otaq/locomotives.htm.
For more information on this rule, please contact the Assessment and Standards Division infor-
mation line at:
U.S. Environmental Protection Agency
Office of Transportation and Air Quality
2000 Traverwood Drive
Ann Arbor, MI48105
Voicemail: (734) 214-4636
E-mail: asdinfo@epa.gov
u
u
-------
Table 5 - NOx Emission Factors (g/gal)
Calendar Large Line- Large Small
Overall
Year haul Switch Railroads Passenger/Commuter Average
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
180
175
169
165
157
149
144
139
135
129
121
114
108
103
99
94
89
84
79
74
69
65
61
57
53
49
46
43
40
37
35
33
31
29
28
250
249
243
241
236
235
227
225
217
215
208
206
202
200
187
185
177
172
162
150
144
138
132
126
119
112
105
98
91
84
77
71
67
63
60
242
242
242
242
242
242
242
242
242
240
239
237
236
233
231
228
225
223
220
217
215
212
209
206
203
200
197
193
190
187
184
180
177
174
171
244
229
214
200
183
167
157
147
138
131
119
112
105
98
93
88
83
78
73
68
64
60
56
52
49
46
42
39
36
33
30
28
26
24
23
188
183
177
172
165
157
152
147
143
137
129
122
117
112
107
102
97
92
87
81
77
72
68
64
60
56
52
49
46
43
40
38
36
34
32
-------
Table 6 - PM Emission Factors (g/gal)
Calendar Large Line- Large Small
Overall
Year haul Switch Railroads Passenger/Commuter Average
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
6.4
6.3
5.1
4.9
4.7
4.4
4.1
3.8
3.6
3.4
3.1
2.9
2.7
2.5
2.3
2.2
2.0
1.9
1.7
1.6
1.5
1.4
1.3
1.1
1.0
1.0
0.9
0.8
0.7
0.7
0.6
0.6
0.5
0.5
0.4
6.5
6.5
5.5
5.5
5.4
5.3
5.1
5.0
4.8
4.8
4.6
4.5
4.4
4.4
4.1
4.0
3.9
3.7
3.5
3.2
3.1
3.0
2.8
2.7
2.5
2.4
2.2
2.1
1.9
1.7
1.6
1.5
1.4
1.3
1.2
6.5
6.5
5.7
5.7
5.7
5.7
5.7
5.6
5.6
5.5
5.5
5.4
5.4
5.4
5.3
5.3
5.3
5.2
5.2
5.1
5.1
5.1
5.0
5.0
4.9
4.8
4.8
4.7
4.6
4.6
4.5
4.4
4.4
4.3
4.2
6.5
6.4
5.1
5.0
4.8
4.5
4.2
3.9
3.6
3.4
3.1
2.8
2.6
2.3
2.1
2.0
1.8
1.7
1.5
1.4
1.2
1.1
1.0
0.9
0.8
0.7
0.7
0.6
0.6
0.5
0.5
0.4
0.4
0.4
0.3
6.4
6.3
5.1
4.9
4.7
4.5
4.2
3.9
3.7
3.5
3.3
3.0
2.8
2.6
2.5
2.4
2.2
2.1
1.9
1.8
1.6
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.9
0.8
0.7
0.7
0.6
0.6
0.5
-------
Table 7 - HC Emission Factors (g/gal)
Calendar Large Line- Large Small
Overall
Year haul Switch Railroads Passenger/Commuter Average
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
9.5
9.3
9.0
8.7
8.3
7.7
7.1
6.5
6.1
5.7
5.1
4.6
4.2
3.9
3.6
3.4
3.2
3.0
2.8
2.6
2.5
2.3
2.1
2.0
1.9
1.7
1.6
1.5
1.4
1.3
1.2
1.2
1.1
1.1
1.0
15.0
15.0
14.5
14.5
14.1
14.0
13.3
13.3
12.7
12.6
12.0
11.8
11.5
11.4
10.5
10.4
9.8
9.5
8.9
8.0
7.6
7.3
6.9
6.5
6.2
5.8
5.5
5.1
4.7
4.4
4.0
3.7
3.6
3.4
3.2
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
11.7
9.7
9.5
9.3
9.1
8.6
8.1
7.5
6.9
6.3
5.8
5.2
4.6
4.1
3.5
3.1
2.9
2.7
2.4
2.2
2.0
1.8
1.6
1.5
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.7
0.6
0.6
0.5
0.5
10.0
9.8
9.5
9.1
8.8
8.2
7.6
7.1
6.7
6.3
5.7
5.2
4.8
4.5
4.2
4.0
3.8
3.6
3.4
3.1
2.9
2.8
2.6
2.4
2.3
2.2
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.4
1.3
------- |