Home | Data and Monitoring | Emission Inventory Scope Study
Scope Study for Expanding the Great Lakes Toxic Emission Regional Inventory to include Estimated Emissions from Mobile Sources
Chapter 7 Estimating Air Toxics Emissions from Locomotives
Locomotives in the United States are primarily of two types, electric and diesel-electric. An electric locomotive uses electricity generated at a stationary power plant not at the locomotive. On the other hand, a diesel-electric locomotive uses a diesel engine and an alternator or generator to produce the electricity to power itself. This chapter illustrates the method for estimating emissions from diesel-electric locomotives only.
Railroads are separated into three classes based on size by the Interstate Commerce Commission (ICC) (EPA, 1992):
Class I railroads operate over a large geographic area and carry most of the interstate freight and passenger service. They represent the largest railroad systems in the country. Also, they are required to keep detailed records of their operations.
Class II and III railroads generally operate within smaller, localized areas. Their operation-record keeping is less extensive. Their fleets of locomotives are older, while the Class I railroads tend to buy almost all of the new locomotives.
Locomotives can perform two different types of operations: line haul and yard (or switch). In the line haul operations, locomotives generally travel between distant locations. In the yard operations, locomotives are primarily responsible for moving railcars within a particular railway yard.
Like other nonroad sources, there could be two potential approaches to deriving toxic air emissions from locomotives:
The following sections briefly discuss these approaches.
7-2. Use Toxic Emission Factors Based on Activity Level
Toxic air emissions from locomotives can be estimated by directly using toxic emission factors based on activity level. However, no emission factors are available for air toxics emitted from locomotives in EPAs current version of the Factor Information Retrieval System (FIRE) (EPA, 1996). Since locomotives use large diesel engines, the emission factors for internal combustion diesel engines can be extrapolated to estimate emissions from locomotives. These emission factors are compiled in SCC codes starting with 201001 and 202001 in the FIRE version 5.1a. Literature searches can also provide useful emission factors. If the emission factors for a pollutant can not be found, the emissions of this pollutant may be estimated by combining TOG and PM emissions with speciation profiles.
Activity level in this approach can be fuel consumption or million British thermal unit (MM Btu) heat input. A heat input value can be calculated by multiplying the fuel consumption by a diesel heating value. The information source for fuel consumption is described in Section 7-3.
7-3. Estimating Toxic Air Emissions from Locomotives by Combining Total Organic Gases and Particulate Matter Emissions with Speciation Profiles
The following equations for line haul and yard operations illustrate the basis for estimating toxic air emissions from locomotives by combining total organic gases and particulate matter emissions with speciation profiles.
Line haul operations
The annual fuel consumption for Class I line haul locomotives can be obtained from the railroad companies because Class I railroads are required to report their operation statistics each year to the ICC. The basis for determining the county-level fuel consumption is to allocate the total amount of fuel consumed systemwide for a Class I railroad system to the interested counties within the system. The detailed explanation of the method is provided in Chapter 6 of the EPA guidance document, Procedures for Emission Inventory Preparation Volume IV: Mobile Sources (EPA, 1992).
Class II and III railroad companies are not required to report to the ICC. For Class II and III railroad companies, annual fuel consumption can be obtained by simply allocating the fuel consumption by track length and track density for each respective company.
Emission factors per yard locomotive were calculated based on the assumptions of an average yard engine fuel consumption of 228 gallons per day and an annual operating time of 365 days.
The number of yard locomotives can be obtained through surveys of railway yard managers. If this approach is unproductive, then the number of yard locomotives can be determined by actually counting the units operating in each railway yard during a day because this number remains relatively constant through the year.
It should be noted that the emission factors shown above are derived from national average railroad fleet and operation data which may differ significantly from actual conditions at the state or local level. If more detailed information regarding locomotive activity can be accessed, the states and province may calculate more precise emission factors based on their actual locomotive fleet data and operational characteristics. The methods for such an emission factor calculation is shown in the EPA guidance document (EPA, 1992).
Converting from hydrocarbon (HC) to total organic gases (TOG)
The emission factors for HC represent total hydrocarbon (THC). EPA recommended a conversion factor from THC to volatile organic compounds (VOC) (Janssen, 1992). Since locomotive emissions are created by large diesel engines, EPA has assumed that the conversion factors for heavy-duty diesel vehicles can also be used for locomotives. Then, the conversion factor from HC to TOG can be calculated by using Equation 7-5.
The appropriate conversion factors from VOC to TOG should be determined before speciating the emissions to individual toxic air pollutants.
Speciation profiles for locomotives can be obtained from the same information sources as identified in Section 4-4-2-3. Table 7-1 shows the existing EPA and the California Air Resources Board (CARB) TOG and PM speciation profiles for locomotives (EPA, 1993; CARB, 1991). Additional speciation information may be obtained through a literature search.
Table 7-1. TOG and PM speciation profiles for locomotives
CARB, Speciation Manual, Volume 1: Identification of Volatile Organic Compound Species Profiles, Volume 2: Identification of Particulate Matter Species Profiles, 2nd Edition, State of California Air Resource Board, August 1991.
EPA, Factor Information Retrieval System (FIRE) Version 5.1a, U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards, Research Triangle Park, NC, May 1996.
EPA, Locomotive Emission Factors for Inventory Guidance Document, Office of Mobile Sources, U.S. Environmental Protection Agency, Ann Arbor, MI, June, 1991.
EPA, Procedures for Emission Inventory Preparation: Volume IV: Mobile Sources, U.S. Environmental Protection Agency, Office of Mobile Sources, Ann Arbor, MI and Office of Air Quality Planning and Standards, Research Triangle Park., NC, EPA-450/4-81-026d (Revised), 1992.
EPA, Volatile Organic Compounds (VOC)/Particulate Matter (PM) Speciation Data System (SPECIATE), Version 1.5, Emission Inventory Branch (MD-14), Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, NC. 1993.
Janssen, G., Memorandum to Lorang, P., Office of Mobile Sources, U.S. Environmental Protection Agency, Ann Arbor, MI, THC to VOC Correction Factors for Nonroad Emission Inventories, April 21, 1992.