Representing Freight in Air Quality and Greenhouse Gas Models (2010) / Chapter Skim
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A method is defined as a step-by-step approach on how to estimate vehicle and freight activity, how to develop emission factors, and how to calculate freight emissions. A method generally includes the use of several input parameters, as well as one or more models; • Models: current models used to estimate freight activity, emission factors, and total emissions; and • Parameters: input parameters are used in both methods and models to define fuel and vehicle/vessel characteristics, estimate emission factors, and calculate emissions.
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Because the two main national methods to estimate emissions -- Inventory of U.S. Greenhouse Gas Emissions and Sinks (hereafter referred to as the EPA GHG Inventory)
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The following subsections summarize the evaluation of methods, models, and parameters for each transportation mode at the national, state, and local/project level scales. 1.6.1 National At the national level, EPA uses two separate methodologies, reported in the EPA GHG Inventory (1)
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The parameters shown in Exhibit 1-1 are used in allocating fuel consumption to the transportation sector and to individ6 Parameter Methods/Models Impact on Emissions Parameter Uncertainty Marine Equipment Inventory NEI Low/Moderate High Nonroad Equipment Inventory NEI Low/Moderate Moderate On-road Fleet Mix NEI Low/Moderate Low/Moderate Rail GIS Data NEI Low/Moderate Low/Moderate Economic Sector Activity Data GHG Inventory Moderate/High High Modal Activity Data GHG Inventory, NEI Moderate/High High Modal Emissions Factors NEI Moderate/High Moderate Fuel Carbon Content GHG Inventory High Low Fuel Supply Data GHG Inventory High Low Exhibit 1-1. National parameters.
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Second, when used for forecasting truck VMT, travel demand models often do a poor job of representing the complex trip generation and trip distribution patterns of commercial vehicles. Third, the accuracy of average speed at the link level is questioned given that it is not measured directly but is instead estimated from vehicle volume and road capacity.
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, there are other methods at the regional and local/project level scales that estimate fuel consumption by different rail parameters. The only model that calculates rail fuel consumption is the Train Energy Model, which is not analyzed because it is used 8 Parameter Methods/Models Geographi c Scale Impact on Emissions Parameter Uncertainty VMT Share by Time of Day All Regional/Local Low/Moderate Moderate/High Fuel Type Distribution All All Moderate Low/Moderate Average Speed MOBILE6, EMFAC2007 Regional/Local Moderate Moderate Classification of Truck Types All All Moderate Moderate Mileage Accumulation All All Moderate Moderate Empty Miles All All Moderate High Truck Age Distribution All All Moderate/High Moderate VMT Share by Truck Type All All Moderate/High Moderate/High Driving Cycle CMEM Local Moderate/High High Truck VMT All All High Moderate/High Emission Factors All All High High Exhibit 1-2.
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Regional/Local Moderate/High High Employees Emissions by Employees Regional/Local High Low Miles of Active Track Emissions by Active Track Regional/Local High Low Number of Switch Locomotives Emissions by Switchers Regional/Local High Low Hours by Switch Locomotive Emissions by Hours Regional/Local High Moderate Traffic Density Emissions by Traffic Density Regional/Local High Moderate/High Emission Factors All All High High Fuel Consumption National National High High Exhibit 1-3. Rail parameters.
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• Information to describe rail activity data (e.g., traffic density, number of switch locomotives, hours by switch locomotive, miles of active track, number of employees) have a direct impact on emissions, but the level of uncertainty with those estimates varies depending on the parameters.
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From page 11... ...
There are a variety of primary and secondary parameters that feed into the overall uncertainty and include effects of characterization of engine deterioration and engine age distribution, both of which are noted to influence total uncertainty of estimated emissions. The six principal input parameters used to determine H/C emissions -- and therefore the main Parameter Methods/Models Geographi c Scale Impact on Emissions Parameter Uncertainty Boiler Emission Factors Detailed All Low/Moderate Moderate/High Boiler Loads Detailed and Mid-Tier All Low/Moderate High Fuel Type Detailed All Moderate Moderate Port Selection Mid-Tier and Streamlined All Moderate Moderate Auxiliary Emission Factors Detailed All Moderate Moderate/High Auxiliary Load Fac tors Detailed and Mid-Tier All Moderate High Auxiliary Power Detailed and Mid-Tier All Moderate High Propulsion Power Detailed and Mid-Tier All Moderate/High Low/Moderate Calls All All Moderate/High Moderate Time in Modes Detailed All Moderate/High Moderate Propulsion Emission Factors Detailed All Moderate/High Moderate/High Propulsion Load Factors Detailed and Mid-Tier All Moderate/High Moderate/High Exhibit 1-4.
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• The Emissions and Dispersion Modeling System (EDMS) was developed by FAA to specifically address the impacts of airport emission sources, including ground-level sources 12 Parameter Methods/Models Geographi c Scale Impact on Emissions Parameter Uncertainty Auxiliary Engine Population EPA RIA Method, CARB H/C Method National, Regional Moderate High Engine Power All All Moderate/High Low/Moderate Activity All All Moderate/High Moderate/High Emission Factors All All Moderate/High Moderate/High Load Factors All All Moderate/High Moderate/High Main Engine Population EPA RIA Method, CARB H/C Method National, Regional Moderate/High High Exhibit 1-5.
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13 Parameter Methods/Models Geographi c Scale Impact on Emissions Parameter Uncertainty Engine Power All All Moderate/High Low/Moderate Activity All All Moderate/High Moderate/High Emission Factors All All Moderate/High Moderate/High Load Factors All All Moderate/High Moderate/High Equipment Population All All Moderate/High High Exhibit 1-6. CHE parameters.
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Other exhaust parameters that may be considered include emission release height, exit temperature, exit velocity, stack diameter, and initial plume size. Other indirect parameters (e.g., shape of buildings, terrain in the region)
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Based on a set of input parameters, the Conceptual Model will include a set of equations to calculate emissions. The emission outputs will be associated with either a product (or quantity of a given commodity)
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