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2020 National Emissions Inventory Technical
Support Document: Locomotives
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EP A-454/R-23 -0011
March 2023
2020 National Emissions Inventory Technical Support Document: Locomotives
U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Air Quality Assessment Division
Research Triangle Park, NC
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Contents
List of Tables i
12 Locomotives 12-1
12.1 Sector Descriptions and Overview 12-1
12.2 Sources of data 12-1
12.3 EPA-developed estimates 12-2
12.3.2 Quality assurance 12-3
12.3.3 Improvements/Changes in the 2020 NEI 12-3
List of Tables
Table 12-1: Locomotive SCCs, descriptions, and EPA estimation status 12-1
Table 12-2: Submitting SLT agencies with number of pollutants reported for each SCC 12-1
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12 Locomotives
This section documents (rail) emissions in the nonpoint data category. Refer to Section 3.3 for
information on rail yard emissions in the point data category.
12.1 Sector Descriptions and Overview
The locomotive sector includes railroad locomotives powered by diesel-electric engines. A diesel-electric
locomotive uses 2-stroke or 4-stroke diesel engines and an alternator or a generator to produce the
electricity required to power its traction motors. The locomotive source category is further divided up
into categories: Class I line haul, Class ll/lll line haul, Passenger, Commuter, and Yard. Table 12-1 below
indicates locomotive SCCs and whether they are included in EPA estimated emissions. If not in EPA
estimates, then all emissions from that SCC that appear in the inventory are from S/L/T agencies.
Table 12-1: Locomotive SCCs, descriptions, and EPA estimation status
SCC
Description
EPA Estimated?
Data Category
2285002006
Mobile Sources Railroad Equipment Diesel
Line Haul Locomotives: Class 1 Operations
Yes - at county-level
Nonpoint
2285002007
Mobile Sources Railroad Equipment Diesel
Line Haul Locomotives: Class II / III
Operations
Yes - at county-level
Nonpoint
2285002008
Mobile Sources Railroad Equipment Diesel
Line Haul Locomotives: Passenger Trains
(Amtrak)
Yes - at county-level
Nonpoint
2285002009
Mobile Sources Railroad Equipment Diesel
Line Haul Locomotives: Commuter Lines
Yes - at county-level
Nonpoint
2285002010
Railroad Equipment Diesel Yard Locomotives
No
Nonpoint
28500201
Internal Combustion Engines Railroad
Equipment Diesel Yard
Yes - as point sources
Point
12.2 Sources of data
The locomotives sector includes data from SLT agency-provided emissions data, and an EPA dataset of
locomotive emissions. EPA-estimated emissions from select locomotive SCCs as indicated in Table
above. The agencies listed in Table 12-2 also submitted emissions to locomotive SCCs.
Table 12-2: Submitting SLT agencies with number of pollutants reported for each SCC
SLT dataset
Agency
io
r--
00
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SLT dataset
Agency
2285002006
2285002007
2285002008
2285002009
2285002010
28500201
CTBAM
Connecticut
10
7
2020DDOE
District of Columbia
6
2020Maricopa
Maricopa County, AZ
7
2020MNPCA
Minnesota
44
2020NCDAQ
North Carolina
10
2020TXCEQ
Texas
54
54
54
54
54
54
2020VADEQ
Virginia
43
43
2020WADOE
Washington
10
2020WashoeCty
Washoe County, NV
7
7
7
12.3 EPA-developed estimates
EPA's 2020 rail emissions were developed with the support of the Lake Michigan Air Directors
Consortium (LADCO) and the State of Illinois. The EPA used confidential line-haul activity data, in
millions of gross ton (MGT) route miles per link, from the Federal Railroad Administration (FRA) for
2019. 2020 rail fuel consumption index values were used to allocate each Class 1 railroad's fuel use to
links based on MGT. The Association of American Railroads (AAR) provided EPA with locomotive fleet
mix information for 2020 for emission factor application. EPA then developed county-level emission
summaries.
Rail yard emissions were calculated based on supply fuel use and/or yard switcher counts provided by
rail companies. For Class II and III rail lines, location data is available online as part of Bureau of
Transportation Statistics' National Transportation Atlas Database (NTAD). Detailed documentation
methodology for this work is available in the 2020 NEl Rail 062722 document on the 2020
Supplemental data FTP site.
The EPA effort developed emissions for criteria pollutants and greenhouse gases. The GHG emissions
included in the NEI for this category are calculated using confidential link-level line-haul activity data
from the Federal Railroad Administration combined with emission tier fleet mix information from the
Association of American Railroad and fuel use data from the Surface Transportation Board. While the
NEI calculates locomotive emissions per railway segment link and aggregated those results to the county
level, rail C02 emissions reported in the US GHGI are based on top-down national-level fuel consumption
data. The bottom-up NEI approach applied nationally may not be comparable with national or state
level totals in the US GHGI given the difference in approaches.
12.3.1.1 Hazardous Air Pollutant Emissions Estimates
HAP emissions were estimated by applying speciation profiles to the VOC or PM estimates. These "HAP
fractions" were updated for 2017 NEI. These profiles are posted in the workbook
"2017Rail_HAP_AugmentationProfileAssignmentFactors_20200128.xlsx" on the 2017 Supplemental
data FTP site.
12-2
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HAP estimates were calculated at the yard and link level, after the criteria emissions had been allocated.
Where submitting agencies did not supply HAPs, those estimates were also derived via this VOC/PM
speciation method.
12.3.2 Quality assurance
EPA and agency-submitted values were compared to find instances where point and nonpoint rail yard
SCCs may duplicate. This occurs when agencies submitted nonpoint in the same counties where EPA had
point yards. In this case, where rail yard point locations existed within the county, SLT county-level
emissions were reassigned to yards to avoid double counting point and county emissions estimates.
12.3.3 Improvements/Changes in the 2020 NEI
There were no NEI methodology changes for locomotives from 2017 to 2020.
12-3
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United States Office of Air Quality Planning and Standards Publication No. EPA-454/R-23-0011
Environmental Protection Air Quality Assessment Division March 2023
Agency Research Triangle Park, NC
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