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 ------- |