# Emission Factors for LocomotivesTechnical Highlights 

# 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 emission 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 manufacturedin 2015 and later. This fact sheet describes EPA’s estimates of the typical 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 simplifying assumptions. Thus emission rates calculated as described in this fact sheet should be considered as approximations

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Estimated Locomotive Emission Rates by Tier 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 wasrevised in a 2008 rulemaking (73 FR 37096, June 30, 2008). For example, locomotives 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.

Office of Transportation and Air Quality EPA-420-F-09-025 April 2009It 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 itslife as the engine ages and as ambient conditions change. Thus the values presented here are intended 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 COemissions at pre-control levels (which were relatively low), we have not projected any reductions 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)

PM 10 HC NO
x CO

UNCONtrOlled 0.32 0.48 13.00 1.28

tier 0 0.32 0.48 8.60 1.28

tier 0+ 0.20 0.30 7.20 1.28

tier 1 0.32 0.47 6.70 1.28

tier 1+ 0.20 0.29 6.70 1.28

tier2 0.18 0.26 4.95 1.28

tier 2+ & tier 3 0.08 0.13 4.95 1.28

tier 4 0.015 0.04 1.00 1.28

+ iNdiCates tHat tHese are tHe revised staNdards iN 40 CFr Part 1033Technical Highlights

PM 10 HC NO
x CO

UNCONtrOlled 0.44 1.01 17.40 1.83

tier 0 0.44 1.01 12.60 1.83

tier 0+ 0.23 0.57 10.60 1.83

tier 1 0.43 1.01 9.90 1.83

tier 1+ 0.23 0.57 9.90 1.83

tier2 0.19 0.51 7.30 1.83

tier 2+ 0.11 0.26 7.30 1.83

tier 3 0.08 0.26 4

. 50 1.83

tier 4 0.015 0.08 1.00 1.83

+ iNdiCates tHat tHese are tHe revised staNdards iN 40 CFr Part 1033 

### Table 2 - Switch Emission Factors (g/bhp-hr)

2Technical Highlights 

### Conversion to Gram per Gallon Emission FactorsIt is often useful to express emission rates as grams of pollutant emitted per gallon of fuel consumed (g/gal). This can be done by multiplying the emission rates in Table 1 or 2 by a conversion 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 presentedat the end of this fact sheet can be converted back to g/bhp-hr by dividing them by the conversion factors shown here.

Table 3 Conversion Factors (bhp-hr/gal) locomotive application Conversion Factor (bhp-hr/gal) large line-Haul and Passenger 20.8

small line-Haul 18.2 switching 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 ondata collected by the Association of American Railroads for revenue ton-miles and fuel consumption, 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 EstimationTotal emissions can be calculated by multiplying the emission factors (in g/gal) by the fuel consumption rates (in million-gal/yr) to give annual emission rates (in metric tons per year). Multiplying 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 eachyear. This includes national/regional freight service, switching, local freight service, and passenger 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

Technical Highlights 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 emission 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 meetour regulatory definition of “small railroad” (40 CFR 1033.901) to qualify for small business allowances 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 88% National Freight switching 7% local Freight <2% Passenger 3%



### Other PollutantsThe preceding emission factors include those pollutants for which EPA has set emission standards. However, other pollutants may also be of interest.

The broad category of volatile organic compounds (VOC) is a slightly different way of aggregating 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 10 2.5 includes only those particles up to 2.5 microns in diameter). PM 2.5emissions can be estimated as 0.97 times the PM 10emissions, meaning that nearly all of the PM is less than 2.5 microns in diameter.

Gram per gallon emissions of sulfur dioxide (SO 2 ) and carbon dioxide (CO 2 ) are largely independent of engine parameters and are primarily dependent on fuel properties. Locomotive-specific emission rates are not presented here. Instead, SO 2and CO 2emission rates should be calculated 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 SO 2emission 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 SO 2 , up to 5 percent of the sulfur is oxidized further to sulfate (and forms particulate matter), so that the fraction of fuel sulfur emitted as SO 2 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).

4Technical Highlights sO2(g/gal) = (fuel density) × (conversion factor) × (64 g sO2/32 g s) × (s content of fuel)

Consider the example where the density of diesel fuel is 3200 g/gal, the fraction of fuel sulfur
converted to sO2is 97.8 percent, and the sulfur content of the fuel is 300 ppm.

sO2(g/gal) = (3200) × (0.978) × (2.00) × (300 x 10-6) = 1.88 g/gal

CO2(g/gal) = (fuel density) × (44 g CO2/12 g C) × (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) × (3.67) × (0.87) = 10,217 g/gal

Other trace pollutants such as N 2O, 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 N 2O or methane, you may assume that emissions of these pollutants from locomotives are similar to those of other diesel engines with similar technology. For N 2O, you may assume the emissions are proportional to total NOx.For methane, you may assume the emissions are proportional to total hydrocarbons. Note however, 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 thatair toxic emissions are proportional to total hydrocarbons), EPA has estimated air toxic emissions from locomotives. These estimates are described in the National Emission Inventory documentation (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, PM 10, and HC emission factors by calendar year for the four categories of locomotives (the same four categories as are shown in Table 4). Thesteady decline in these emission factors reflects the penetration of the various tiers of locomotives 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)

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### For More InformationYou can access the rule and related documents on EPA’s Office of Transportation and Air Quality (OTAQ) Web site at: 

### www.epa.gov/otaq/locomotives.htm

.For more information on this rule, please contact the Assessment and Standards Division information line at:

U.S.Environmental Protection Agency Office of Transportation and Air Quality 2000 Traverwood Drive Ann Arbor, MI 48105 Voicemail: (734) 214-4636 E-mail: 

### asdinfo@epa.govTechnical Highlights

Table 5 – NOx Emission Factors (g/gal)Technical Highlights Calendar large line- large small Overall

Year 2006 haul 180 switch 250 railroads 242 Passenger/Commuter 244 average 188 2007 175 249 242 229 183 2008 169 243 242 214 177 2009 165 241 242 200 172 2010 157 236 242 183 165 2011 149 235 242 167 157 2012 144 227 242 157 152 2013 139 225 242 147 147 2014 135 217 242 138 143 2015 129 215 240 131 137 2016 121 208 239 119 129 2017 114 206 237 112 122 2018 108 202 236 105 117 2019 103 200 233 98 112 2020 99 187 231 93 107 2021 94 185 228 88 102 2022 89 177 225 83 97 2023 84 172 223 78 92 2024 79 162 220 73 87 2025 74 150 217 68 81 2026 69 144 215 64 77 2027 65 138 212 60 72 2028 61 132 209 56 68 2029 57 126 206 52 64 2030 53 119 203 49 60 2031 49 112 200 46 56 2032 46 105 197 42 52 2033 43 98 193 39 49 2034 40 91 190 36 46 2035 37 84 187 33 43 2036 35 77 184 30 40 2037 33 71 180 28 38 2038 31 67 177 26 36 2039 29 63 174 24 34 2040 28 60 171 23 32

Table 6 – PM 10Emission Factors (g/gal)Technical Highlights Calendar large line- large small Overall

Year 2006 haul 6.4 switch6.5 railroads6.5 Passenger/Commuter 6.5 average 6.4 2007 6.3 6.5 6.5 6.4 6.3 2008 5.1 5.5 5.7 5.1 5.1 2009 4.9 5.5 5.7 5.0 4.9 2010 4.7 5.4 5.7 4.8 4.7 2011 4.4 5.3 5.7 4.5 4.5 2012 4.1 5.1 5.7 4.2 4.2 2013 3.8 5.0 5.6 3.9 3.9 2014 3.6 4.8 5.6 3.6 3.7 2015 3.4 4.8 5.5 3.4 3.5 2016 3.1 4.6 5.5 3.1 3.3 2017 2.9 4.5 5.4 2.8 3.0 2018 2.7 4.4 5.4 2.6 2.8 2019 2.5 4.4 5.4 2.3 2.6 2020 2.3 4.1 5.3 2.1 2.5 2021 2.2 4.0 5.3 2.0 2.4 2022 2.0 3.9 5.3 1.8 2.2 2023 1.9 3.7 5.2 1.7 2.1 2024 1.7 3.5 5.2 1.5 1.9 2025 1.6 3.2 5.1 1.4 1.8 2026 1.5 3.1 5.1 1.2 1.6 2027 1.4 3.0 5.1 1.1 1.5 2028 1.3 2.8 5.0 1.0 1.4 2029 1.1 2.7 5.0 0.9 1.3 2030 1.0 2.5 4.9 0.8 1.2 2031 1.0 2.4 4.8 0.7 1.1 2032 0.9 2.2 4.8 0.7 1.0 2033 0.8 2.1 4.7 0.6 0.9 2034 0.7 1.9 4.6 0.6 0.9 2035 0.7 1.7 4.6 0.5 0.8 2036 0.6 1.6 4.5 0.5 0.7 2037 0.6 1.5 4.4 0.4 0.7 2038 0.5 1.4 4.4 0.4 0.6 2039 0.5 1.3 4.3 0.4 0.6 2040 0.4 1.2 4.2 0.3 0.5

Table 7 - HC Emission Factors (g/gal)Technical Highlights Calendar large line- large small Overall

Year 2006 haul 9.5 switch 15.0 railroads 11.7 Passenger/Commuter 9.7 average 10.0 2007 9.3 15.0 11.7 9.5 9.8 2008 9.0 14.5 1 1.7 9.3 9.5 2009 8.7 14.5 11.7 9.1 9.1 2010 8.3 14.1 11.7 8.6 8.8 2011 7.7 14.0 11.7 8.1 8.2 2012 7.1 13.3 11.7 7.5 7.6 2013 6.5 13.3 11.7 6.9 7.1 2014 6.1 12.7 11.7 6.3 6.7 2015 5.7 12.6 11.7 5.8 6.3 2016 5.1 12.0 11.7 5.2 5.7 2017 4.6 11.8 11.7 4.6 5.2 2018 4.2 11.5 11.7 4.1 4.8 2019 3.9 11.4 11.7 3.5 4.5 2020 3.6 10.5 11.7 3.1 4.2 2021 3.4 10.4 11.7 2.9 4.0 2022 3.2 9.8 11.7 2.7 3.8 2023 3.0 9.5 11.7 2.4 3.6 2024 2.8 8.9 11.7 2.2 3.4 2025 2.6 8.0 11.7 2.0 3.1 2026 2.5 7.6 11.7 1.8 2.9 2027 2.3 7.3 11.7 1.6 2.8 2028 2.1 6.9 11.7 1.5 2.6 2029 2.0 6.5 11.7 1.3 2.4 2030 1.9 6.2 11.7 1.2 2.3 2031 1.7 5.8 11.7 1.1 2.2 2032 1.6 5.5 11.7 1.0 2.0 2033 1.5 5.1 11.7 0.9 1.9 2034 1.4 4.7 11.7 0.8 1.8 2035 1.3 4.4 11.7 0.7 1.7 2036 1.2 4.0 11.7 0.7 1.6 2037 1.2 3.7 11.7 0.6 1.5 2038 1.1 3.6 11.7 0.6 1.4 2039 1.1 3.4 11.7 0.5 1.4 2040 1.0 3.2 11.7 0.5 1.3

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