1

Emission

Facts

Office of Transportation

and Air Quality

EPA420-F-05-001

February 2005

Average Carbon Dioxide Emissions

Resulting from Gasoline and Diesel

Fuel

The U.S. Environmental Protection Agency (EPA) developed this series

of four fact sheets to facilitate consistency of assumptions and practices

in the calculation of emissions of greenhouse gases from transportation

and mobile sources. They are intended as a reference for anyone

estimating emissions benefits of mobile sources air pollution control

programs.

Carbon content in motor vehicle fuels

One of the primary determinants of carbon dioxide (CO2) emissions

from mobile sources is the amount of carbon in the fuel. Carbon content

varies, but typically we use average carbon content values to estimate

CO2

 emissions.

The Code of Federal Regulations (40 CFR 600.113) provides values for

carbon content per gallon of gasoline and diesel fuel which EPA uses in

calculating the fuel economy of vehicles:

Gasoline carbon content per gallon: 2,421 grams

Diesel carbon content per gallon: 2,778 grams
2

Note that for the "Inventory of U.S. Greenhouse Gas Emissions and

Sinks," EPA estimates CO2

 emissions from fuel from the heat content of

the fuel and carbon content coefficients in terms of carbon content per

quadrillion BTU (QBTU), using data from the Energy Information

Administration (EIA). EIA’s numbers are derived from carbon content

by mass, and equate to roughly the same carbon content per gallon of

fuel as the values provided in 40 CFR 600.113. EPA uses heat content

data from Energy Information Administration’s (EIA) “Annual Energy

Outlook 2003" and carbon content from EIA’s “Emissions of Greenhouse Gases in the United States, 2000.”

Note also that these estimates are based only on an average carbon

content of conventional gasoline and diesel fuel, and do not specifically

address the impact of fuel additives such as ethanol or methyl tertiarybutyl ether (MTBE) that may depend on the feedstock.

Calculating CO2 emissions

The Intergovernmental Panel on Climate Change (IPCC) guidelines for

calculating emissions inventories require that an oxidation factor be

applied to the carbon content to account for a small portion of the fuel

that is not oxidized into CO2. For all oil and oil products, the oxidation

factor used is 0.99 (99 percent of the carbon in the fuel is eventually

oxidized, while 1 percent remains un-oxidized.)1

Finally, to calculate the CO2 emissions from a gallon of fuel, the carbon

emissions are multiplied by the ratio of the molecular weight of CO2

(m.w. 44) to the molecular weight of carbon (m.w.12): 44/12.

CO2 emissions from a gallon of gasoline = 2,421 grams x 0.99 x (44/12)

= 8,788 grams = 8.8 kg/gallon = 19.4 pounds/gallon

CO2 emissions from a gallon of diesel = 2,778 grams x 0.99 x (44/12) =

10,084 grams = 10.1 kg/gallon = 22.2 pounds/gallon

Note: These calculations and the supporting data have associated

variation and uncertainty. EPA may use other values in certain circumstances, and in some cases it may be appropriate to use a range of

values.

1

 Based on emissions data, EPA's Office of Transportation and Air Quality (OTAQ) is

currently examining whether this fraction is higher (closer to 100 percent) for gasoline.
3

For More Information

You can access documents on greenhouse gas emissions on the Office of

Transportation and Air Quality Web site at:

www.epa.gov/otaq/greenhousegases.htm

For further information on calculating emissions of greenhouse gases,

please contact Ed Coe at:

U. S. Environmental Protection Agency

Office of Transportation and Air Quality

1200 Pennsylvania Ave., NW (6406J)

Washington, DC 20460

202-343-9629

E-mail: coe.edmund@epa.gov