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Environment

Methodology

Overview

We created our Carbon Dioxide Emissions by Fuel table by using information in our Monthly Energy Review as well the U.S. Environmental Protection Agency’s (EPA) Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2020 and Greenhouse Gas Emissions Factor Hub. In this document, we outline the steps for creating the values shown in the table.

Step 1: Obtain emissions factors

Unless noted otherwise, we take the carbon dioxide (CO2) emissions factors in this table from Appendix Tables A-22, A-27, A-34, and A-230 of EPA’s Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2020. Factors are provided in terms of million metric tons of carbon per quadrillion British thermal units (quads), which is equivalent in value to kilograms of carbon per million British thermal units (MMBtu). To convert from carbon to CO2, we multiply this factor by 44/12, the weight ratio of CO2 to carbon.

Emissions factors for municipal solid waste, tire-derived fuels, and waste oil are not listed in the greenhouse gas inventory, so we collect them from EPA’s Greenhouse Gas Emissions Factor Hub. Other fuels have emissions factors listed in both the greenhouse gas inventory as well as the emissions factor hub. Occasionally, these factors differ from one another. In such cases, because the factors in the emissions factors hub aren’t always updated on a regular basis, we treat the factors presented in the greenhouse gas inventory as the official values.

We adjust the emissions factor for finished motor gasoline based on its ethanol content, which we explain in detail later in this document.

Step 2: Convert CO2 weights from kilograms to pounds

We use the weight ratio of 2.20462 pounds per kilogram to convert each fuel’s emissions factor from kilograms per MMBtu to pounds per British thermal units (Btu).

Step 3: Apply heat rates for fuels

We calculate emissions by mass (or volume) by multiplying the emissions factor of each fuel (in pounds per MMBtu) by its associated heat rate. We collect heat rates from Appendix A of our Monthly Energy Review. For petroleum products with heat rates expressed in terms of MMBtu per barrel, we divide this value by 42 to convert from barrels to gallons. Table 1 shows heat rates for each fuel.

Table 1. Heat rates for select fuels
Fuel Value Units
For homes and businesses
Propane 3.841 MMBtu per barrel
Diesel and home heating fuel (distillate fuel oil) 5.770 MMBtu per barrel
Kerosene 5.670 MMBtu per barrel
Coal (all types) 18.297 MMBtu per short ton
Natural Gas 1.037 MMBtu per thousand cubic feet
Finished motor gasoline 5.052 MMBtu per barrel
Motor gasoline (not including fuel ethanol) 5.222 MMBtu per barrel
Residual heating fuel (businesses only) 6.287 MMBtu per barrel
Other transportation fuels
Jet fuel 5.670 MMBtu per barrel
Aviation gas 5.048 MMBtu per barrel
Industrial fuels and others not listed above
Petroleum coke 6.130 MMBtu per barrel
Nonfuel uses
Asphalt and road oil 6.636 MMBtu per barrel
Lubricants 6.065 MMBtu per barrel
Naphthas for petrochemical feedstock use 5.248 MMBtu per barrel
Other oils for petrochemical feedstock use 5.825 MMBtu per barrel
Special naphthas (solvents) 5.248 MMBtu per barrel
Waxes 5.537 MMBtu per barrel
Coals by type
Anthracite 25.000 MMBtu per short ton
Bituminous 24.000 MMBtu per short ton
Subbituminous 17.500 MMBtu per short ton
Lignite 13.000 MMBtu per short ton
Coke 28.717 MMBtu per short ton
Other fuels
Geothermal (steam) NA NA
Geothermal (binary cycle) NA NA
Municipal solid waste 14.120 MMBtu per short ton
Tire-derived fuel 28.000 MMBtu per short ton
Waste oil 5.796 MMBtu per barrel
Data source: U.S. Energy Information Administration
Note: MMBtu = million British thermal units

Step 4: Convert CO2 weights from pounds to kilograms

We use the weight ratio of 2.20462 pounds per kilogram to convert each fuel’s emissions from kilograms to pounds per unit of mass (or volume).

Motor gasoline adjustments

This table adjusts the heat rate and carbon factor of motor gasoline to distinguish between finished motor gasoline, which contains some portion of fuel ethanol, and raw motor gasoline, which does not.

The carbon factor for raw motor gasoline, not taking into account fuel ethanol, appears in Table A-22 of EPA’s Inventory of U.S. Greenhouse Gas Emissions and Sinks. Finished motor gasoline contains a blend of both raw motor gasoline, which is emissive, and fuel ethanol, which we treat as non-emissive in this calculation.

We calculate the carbon factor of finished motor gasoline by weighting the carbon factor of raw motor gasoline by the annual share of raw motor gasoline present in finished motor gasoline on an energy basis (Table 2). Energy consumption values appear in Tables 3.6 and 10.3 of our Monthly Energy Review.

Table 2. Percentage shares of motor gasoline and fuel ethanol in finished motor gasoline by total energy, 2010–2020
Year Motor gasoline supplied (trillion Btu) Fuel ethanol, excluding denaturant, losses, and co-products (trillion Btu) Percentage share of motor gasoline in finished motor gasoline Percentage share of ethanol in finished motor gasoline
2010 16,631.509 725.970 95.82% 4.18%
2011 16,175.038 753.993 95.55% 4.45%
2012 16,085.454 709.127 95.78% 4.22%
2013 16,332.108 711.235 95.83% 4.17%
2014 16,472.647 764.221 95.57% 4.43%
2015 16,941.485 788.345 95.55% 4.45%
2016 17,237.809 818.059 95.47% 4.53%
2017 17,201.350 844.342 95.32% 4.68%
2018 17,209.271 851.961 95.28% 4.72%
2019 17,166.234 831.945 95.38% 4.62%
2020 14,883.263 731.951 95.31% 4.69%
Data source: U.S. Energy Information Administration
Btu = British thermal units

As an example of this weighting method, in 2019, the United States consumed around 17.2 quads of finished motor gasoline. Fuel ethanol made up 796 trillion Btu (4.64%) of this consumption, and the remaining 95.36% of this energy came from raw motor gasoline. The 2019 carbon factor for finished motor gasoline would then be the carbon factor for raw motor gasoline multiplied by 95.36%, or 0.9536.

We also use separate heat rates for finished motor gasoline and raw motor gasoline (excluding fuel ethanol). Appendix A of the Monthly Energy Review provides data for both types. Table A3 shows the heat rate for finished motor gasoline, and Table A2 shows the heat rate for raw motor gasoline.