Greenhouse Gas Emissions from a Typical Passenger Vehicle

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.
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How much tailpipe carbon dioxide (C02) is emitted from driving one mile?
The average passenger vehicle emits about 404 grams of C02 per mile. This number can vary
based on two factors: the fuel economy of the vehicle and the amount of carbon in the vehicle's
fuel. Most vehicles on the road in the U.S. today are gasoline vehicles, and they average about
22.0 miles per gallon.2 Every gallon of gasoline creates about 8,887 grams of C02 when burned.
Therefore, the average vehicle when driving one mile has tailpipe C02 emissions of about:
C02 per gallon 8,887
CO, emissions per mile = = = 404 srams
2 MPG 22.0
What are the average annual carbon dioxide (C02) emissions of a typical passenger vehicle?
A typical passenger vehicle emits about 4.6 metric tons of carbon dioxide per year. This number
can vary based on a vehicle's fuel, fuel economy, and the number of miles driven per year. The
average gasoline vehicle on the road today has a fuel economy of about 22.0 miles per gallon
and drives around 11,500 miles per year3. Every gallon of gasoline burned creates about 8,887
grams of C02, and there are one million grams per metric ton. Therefore, the average vehicle
over a year of driving has tailpipe C02 emissions of about4:
C02 per gallon 8,887
Annual CO^ emissions = X miles X 11,500 = 4.6 metric tons
2 MPG 22.0
EPA uses this to compare C02 emissions from other sources to emissions from passenger vehicles.
For example, an energy efficiency program that reduces greenhouse gas emissions by 4,600 metric
tons of C02 per year has the same impact as removing 1,000 vehicles from the road.
Are there other sources of greenhouse gas (GHG) emissions from a vehicle?
In addition to carbon dioxide (C02), automobiles produce methane (CH4) and nitrous oxide
(N20) from the tailpipe and hydrofluorocarbon (HFC) emissions from leaking air conditioners.
2 Federal Highway Administration Highway Statistics 2016. This is representative of the light duty passenger
vehicle fleet as a whole, including both new and existing vehicles. The average passenger vehicle fuel economy is
expected to increase over time as a result of greenhouse gas and fuel economy standards developed in coordination
between EPA, DOT and California.
3 Federal Highway Administration Highway Statistics 2016.
4 This calculation provides a simple way to determine the average annual C02 emissions from a passenger vehicle.
Anyone that needs a more detailed approach should use the EPA's Motor Vehicle Emission Simulator (MOVES)
model. This model contains detailed data about the light duty fleet and driving patterns in the United States.
Although simplified, the calculated annual C02 emissions above are consistent with analyses performed by the EPA
using MOVES.
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The emissions of these gases are small in comparison to C02; however, the impact of these emis-
sions can be important because they have a higher global warming potential (GWP) than COr
The global warming potential of a gas relates the impact of that gas relative to an equivalent
amount of COr Using global warming potentials, the impact of various GHGs can be directly
compared using a common metric. This metric is expressed in units of carbon dioxide equiva-
lent, written as C02e. Multiplying the amount of a GHG times the global warming potential of
that GHG results in the amount of GHG in terms of C02e. For automotive-related gases, these
global warming potentials are:
Greenhouse Gas
Abbreviation
GWP5
Carbon Dioxide
co.
1
Methane
ch4
25
N itrous Oxide
n2o
298
Air Conditioning Refrigerant
HFC-134a
1,430
It is more difficult to estimate vehicle emissions of CH4, N20, and HFCs than COr Emissions
of CH4 and N20 are dependent on the design of the engine and emission control system, rather
than fuel consumption per mile. The amount of HFC leakage from air conditioners is dependent
on system design, amount of use, and maintenance. On average, C02 emissions are 95-99%
of the total greenhouse gas emissions from a passenger vehicle, after accounting for the global
warming potential of all GHGs. The remaining 1-5% is CH4, N20, and HFC emissions.
What are the tailpipe emissions from a plug-in hybrid electric vehicle (PHEV) or an electric
vehicle (EV)? What about hydrogen fuel cell vehicles?
A vehicle that operates exclusively on electricity (an EV) will not emit any tailpipe emissions.
A fuel cell vehicle operating on hydrogen will emit only water vapor.
Calculating tailpipe emissions for PHEVs is more complicated. PHEVs can operate on electric-
ity only, gasoline only, or some combination of electricity and gasoline. A PHEV operating on
electricity only (like an EV) does not generate any tailpipe emissions. When a PHEV is operat-
ing on gasoline only, it creates tailpipe emissions based on the PHEV's gasoline fuel economy.
Tailpipe emissions for a PHEV operating on both electricity and gasoline cannot be calculated
without detailed information about how the PHEV operates. The overall tailpipe emissions for
a PHEV can vary significantly based on the PHEV's battery capacity, how it is driven, and how
often it is charged.
5 These 100-year time horizon GWP values are from the 2007 Intergovernmental Panel on Climate Change
(IPCC) Fourth Assessment Report. The IPCC released updated values in the Fifth Assessment Report (2014),
however international reporting guidelines still use the values shown here.
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Are there any greenhouse gas emissions associated with the use of my vehicle other than
what comes out of the tailpipe?
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
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 (EVs) have no tailpipe emissions; however, emissions are created during both
the production and distribution of the electricity used to fuel the vehicle. Visit the Beyond
Tailpipe Emissions calculator to estimate GHG emissions for an EV in your region of the country.
I thought my gasoline was blended with ethanol. Does that change my tailpipe C02 emissions?
Most of the gasoline sold in the U.S.is a mixture of gasoline and up to 10% ethanol (often
referred to as E10). The exact formulation of the gasoline in your vehicle will vary depending 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 gasoline without ethanol, the C02
tailpipe emissions per mile will be similar. This is because ethanol has less carbon per gallon
than gasoline.
How does the EPA measure C02 emissions from vehicles?
The EPA and automobile manufacturers measure vehicle fuel economy and C02 emissions 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 manufacturers meet federal greenhouse gas and corporate average fuel economy (CAFE)
standards.
For every new vehicle, the test results are used to determine real world fuel economy and C02
emissions. These adjusted results are used on the Fuel Economy and Environment Labels and
on Fueleconomy.gov.
For more information, see Frequent Questions on Fuel Economy Testing and Labeling and
How Vehicles Are Tested.
How can I find and compare C02 emission rates for specific vehicle models?
Visit Fueleconomy.gov and click on "Find a Car." From the vehicle search results page, click
on the "Energy and Environment" tab. A vehicle's greenhouse gas emissions rate (g/mile) and
GHG rating can be found there.
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When shopping at a dealership, check out tailpipe C02 emission rates on vehicle Fuel Economy
and Environment Labels. The labels also feature a 1 -to 10 Fuel Economy and Greenhouse Gas
Rating to enable easy comparison shopping.
Where can I find information on the emissions of the transportation sector as a whole?
You can find documents on greenhouse gas emissions on the EPA's Carbon Pollution from
Transportation website.
The EPA also publishes industry-wide data in the report, "Light-Duty Automotive Technology,
Carbon Dioxide Emissions, and Fuel Economy Trends." This report analyzes trends in fuel
economy and C02 emissions for new light duty vehicles from 1975 to the present.
Other useful sources include:
- Fueleconomy.gov
- Green Vehicle Guide
- Inventory of U.S. Greenhouse Gas Emissions and Sinks
- Greenhouse Gas Equivalencies Calculator
- Household Carbon Footprint Calculator
For additional information on calculating emissions of greenhouse gases, please contact
OTAQ@epa.gov, or you can contact the OTAQ library for document information at:
U. S. Environmental Protection Agency
Office of Transportation and Air Quality
2000 Traverwood Drive
Ann Arbor, MI 48105
734-214-4311 & 734-214-4434
E-mail: Group_AAlibrary@epa.gov
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