Greenhouse Gas Emissions from a
Typical Passenger Vehicle
The U.S. Environmental Protection Agency (EPA) developed this
fact sheet to answer common questions about greenhouse gas
emissions from passenger vehicles. This fact sheet provides emission
rates and calculations consistent with EPA's regulatory work.
How much tailpipe carbon dioxide (CO2) is created from burning one gallon
of fuel?
The amount of CO2 created from burning one gallon of fuel depends on the amount
of carbon in the fuel. After combustion, a majority of the carbon is emitted as CO2
and very small amounts as hydrocarbons and carbon monoxide. Carbon content
varies by fuel, and some variation within each type of fuel is normal. The EPA and
other agencies use the following average carbon content values to estimate CO2
emissions:
CO2 Emissions from a gallon of gasoline:
CO7 Emissions from a gallon of diesel:
8,887 grams CO2/gallon1
10,180 grams CO7/gallon2
Vehicles that use diesel fuel generally have higher fuel economy than comparable
gasoline vehicles. However, when comparing carbon dioxide emissions, the higher
CO7 emissions from diesel fuel partially offset the fuel economy benefit.
1 This gasoline factor is from a recent regulation establishing GHG standards for model year 2012-
2016 vehicles (75 FR 25324, May 7, 2010).
2 This diesel factor is from the calculations that vehicle manufacturers use to measure fuel economy
(40 C.F.R 600.113).
SEPA
United States
Environmental Protection
Agency
Office of Transportation and Air Quality
EPA-420-F-11-041
November 2011
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Emissions of greenhouse gases are typically expressed in a common metric so that their impacts
can be directly compared. The international standard is to express greenhouse gases in units of
carbon dioxide equivalent, commonly written as CO2e. For a given amount of a greenhouse gas,
multiplying the amount of gas times the global warming potential (GWP) for that gas results
in the amount of greenhouse gas in terms of CO2e. For automotive-related gases, these global
warming potentials are:
Greenhouse Gas Abbreviation GWP5
Carbon Dioxide CO2 1
Methane CH4 25
Nitrous Oxide N2O 298
Air Conditioning Refrigerant HFC-134a 1,430
It is more difficult to estimate vehicle emissions of CH,, N2O, and HFCs than of COr Emissions
of CH4 and N2O are dependent on vehicle miles traveled rather than fuel consumption per mile.
The amount of HFC leakage from air conditioners is dependent on many factors, including
system design, amount of use, and maintenance. On average, CO, emissions represent 95-99%
of the total greenhouse gas emissions from a passenger vehicle. CH,, N2O, and HFC emissions
represent roughly 1-5% of the total greenhouse gas emissions from passenger vehicles, after
accounting for the global warming potential of each greenhouse gas.
What are the tailpipe emissions from a plug-in hybrid or an electric vehicle? What about
hydrogen fuel cell vehicles?
A vehicle that can only operate on electricity will not emit any tailpipe emissions. A fuel cell
vehicle operating on hydrogen will emit only water vapor.
Plug-in hybrid vehicles (PHEVs) can operate on either electricity or gasoline. When a PHEV is
operating on electricity, it does not create any tailpipe emissions. However, when it is operating
on gasoline, it creates tailpipe greenhouse gas emissions based on the PHEV's gasoline fuel econ-
omy. These emissions can be calculated as shown in the second question. The overall tailpipe
emissions for a PHEV depend on the percentage of miles the vehicle drives on electricity versus
gasoline. This can vary significantly based on the PHEV's battery capacity, how it is driven, and
how often it is charged.
Are there any greenhouse gas emissions associated with the use of my vehicle other than
the tailpipe emissions?
Driving most vehicles creates tailpipe greenhouse gas emissions. Producing and distributing the
fuel used to power your vehicle also creates greenhouse gasses. Gasoline, for example, requires
5 These 100-year time horizon GWP values are from the 2007 Intergovernmental Panel on Climate Change
(IPCC) Fourth Assessment Report.
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extracting oil from the ground, transporting it to a refinery, refining the oil into gasoline, and
transporting the gasoline to service stations. Each of these steps can produce additional green-
house gas emissions.
Electric vehicles have no tailpipe emissions; however, greenhouse gas emissions are created during
both the production and distribution of the electricity used to fuel the vehicle. Calculators on
Fueleconomy.gov allow you to estimate grams of greenhouse gas emissions per mile for an electric
vehicle in your region of the country.
I thought my gasoline was blended with ethanol. Does that change the tailpipe CO2 emissions?
It is common in the U.S. to blend gasoline with a small percentage of ethanol. Most of the
gasoline sold in the U.S. is really a mixture of gasoline and up to 10% ethanol (this mixture is
often referred to as E10)6. The exact formulation of the gasoline in your vehicle will vary de-
pending on season, region in the U.S., and other factors. While your fuel economy when using
an ethanol blend in your vehicle will be slightly lower than when using pure gasoline, the CO2
tailpipe emissions per mile will be similar. This is because ethanol has less carbon per gallon
than gasoline,
How does the EPA measure CO2 emissions from motor vehicles?
The EPA and automobile manufacturers test vehicles using a set of standardized laboratory
tests. These tests were designed by the EPA to mimic typical driving patterns. The EPA and the
Department of Transportation use these values to ensure that the vehicle meets federal corporate
average fuel economy (CAFE) standards. The test results are then adjusted to reflect different
driving conditions and estimate fuel economy and greenhouse gas emissions for an average
driver. These adjusted results are used on the Fuel Economy and Environment Label seen on all
new vehicles and on Fueleconomy.gov. Detailed information on the test cycles is available on
the EPA's National Vehicle and Fuel Emissions Laboratory website,
How can I find and compare CO2 emission rates for specific vehicle models?
You can find and compare vehicle CO2 emissions at Fueleconomy.gov. Beginning with model
year 2013, vehicle manufacturers will include tailpipe CO2 emission rates on the vehicle Fuel
Economy and Environment labels. These new labels also feature a convenient 1-to 10 Fuel
Economy and Greenhouse Gas Rating to enable easy comparison shopping. A Smartphone QR
Code ® on the label will direct consumers to the website Fueleconomy.gov for more information.7
6 The amount of ethanol in gasoline has historically been limited to 10%; however, the E15 waiver increases that
amount to 15% for some vehicles. For more information see: http://www.epa.gov/otaq/regs/fuels/additive/el5/
7 QR (or "quick response") Codes are simply two-dimensional bar codes used to store information. In this case, the
information is a web site URL. The term QR Code ® is a registered trademark of Denso Wavve Incorporated.
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The EPA publishes additional data in the report "Light-Duty Automotive Technology,
Carbon Dioxide Emissions, and Fuel Economy Trends." The Trends Report analyzes trends in
fuel economy and CO2 emissions for new light duty vehicles from 1975 to the present.
Where can I find information on the emissions of the transportation sector as a whole?
How can I compare this to other sectors?
You can find documents on greenhouse gas emissions on the EPA's Transportation and Climate
website. This website is maintained by the Office of Transportation and Air Quality,
• U.S. Greenhouse Gas Inventory Report
• Light-Duty Greenhouse Gas Standards
• Light-Duty Automotive Technology, Carbon Dioxide Emissions, and
Fuel Economy Trends
• Fueleconomy.gov
For additional 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: Ed Coe at coe.edmund@epa.gov
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