Tailpipe Greenhouse Gas Emissions
from a Typical Passenger Vehicle

a

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 (C02) is created from
burning one gallon of fuel?

The amount of CO? created from burning one gallon of fuel depends on the amount of
carbon in the fuel. Typically, more than 99% of the carbon in a fuel is emitted as C07
when the fuel is burned. Very small amounts are emitted as hydrocarbons and carbon
monoxide, which are converted to CO, relatively quickly in the atmosphere. Carbon
content varies by fuel, and some variation within each type of fuel is normal. EPA and
other agencies use the following average carbon content values to estimate CO, emissions:

CO, Emissions from a gallon of gasoline: 8,887 grams CO, /gallon1
CO, Emissions from a gallon of diesel: 10,180 grams CO, /gallon2

Diesel creates about 15% more CO, per gallon. However, many vehicles that use
diesel fuel achieve higher fuel economy than similar vehicles that use gasoline, which
generally offsets the higher carbon content of diesel fuel.

How can burning one gallon of gasoline produce 8,887 grams
(approximately 20 pounds) of tailpipe carbon, when one gallon of
gasoline weighs only about six pounds?

Most of the weight of the CO? doesn't come from the gasoline itself, but the oxygen
in the air. When gasoline burns, the carbon and hydrogen separate. The hydrogen
combines with oxygen to form water (H70), and carbon combines with oxygen to
form carbon dioxide (C02). Visit fileleconomv.gov for more details, including
the calculations.

1	This gasoline factor is from a regulation establishing GHG standards for model year 2017-2025 vehicles
(77 FR 62773, October 15, 2012).

2	This diesel factor is from the calculations that vehicle manufacturers use to measure fuel economy
(40 C.F.R 600.113).

Jk United States

Environmental Protection
^1	Agency

Office of Transportation and Air Quality

EPA-420-F-23-014
June 2023


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How much tailpipe carbon dioxide (C02) is emitted from driving
one mile?

The average passenger vehicle emits about 400 grams of CO, per mile. The average fuel economy
for all vehicles on the road today is 22.2 miles per gallon.3 The majority of vehicles run on gasoline,
and every gallon of gasoline creates about 8,887 grams of C02 when burned. Therefore, the
average vehicle when driving one mile has tailpipe CO, emissions of about:

^	CO, per gallon 8,887 ^

CU7 emissions per mile =	 	= -rr~r- = 400 grams

MPG	22.2

Electric vehicles (EVs) have zero tailpipe emissions.

What is the average annual carbon dioxide (C02) emissions of a
typical passenger vehicle?

A typical passenger vehicle emits about 4.6 metric tons of C02 per year. This number can vary
based on a vehicle's fuel, fuel economy, and the number of miles driven per year. The average
vehicle on the road today has a fuel economy of about 22.2 miles per gallon (MPG) and drives
around 11,500 miles per year.4 Every gallon of gasoline burned creates about 8,887 grams of C02,
and there are one million grams per metric ton. Therefore, the average gasoline vehicle over a year
of driving has tailpipe CO, emissions of about5:

C07 per gallon	8,887

C07 emissions per mile =		 * miles = ~ * 11 500 = 4.6 metric tons

MPG	22.2

EPA uses this to compare CO? 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 CO, 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 CO?, automobiles using gasoline produce methane (CH4) and nitrous oxide (N70)
from the tailpipe and all vehicles can emit hydrofluorocarbon (HFC) from leaking air conditioners.
For gasoline vehicles, the emissions of HFCs are small in comparison to CO?; however, the impact
of these emissions can be important because they have a higher global warming potential (GWP)
than CO,.

3	Federal Highway Administration Highway Statistics 2020, data for calendar year 2019. Data for 2020 was not used
due to the impacts of the COVID-19 outbreak. The average passenger vehicle fuel economy is expected to increase
over time because of greenhouse gas and fuel economy standards developed in coordination between EPA, DOT,
and California.

4	Federal Highway Administration Highway Statistics 2020.

5	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. MOVES contains detailed data about the light duty fleet and driving patterns in the United States. Although
simplified, the calculated annual 0O2 emissions above are consistent with analyses performed by EPA using MOVES.


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The GWP of a gas relates the impact of that gas relative to an equivalent amount of C02. Using
GWP, the impact of various GHGs can be directly compared using a common metric. This metric
is expressed in units of carbon dioxide equivalent, written as CO?e. Multiplying the amount
of a GHG times the GWP of that GHG results in the amount of GHG in terms of CO?e. For
automotive-related gases, these GWPs are:

Greenhouse Gas

Abbreviation

Global Warming Potential6

Carbon Dioxide

CM

o
o

1

Methane

ch4

25

Nitrous Oxide

n2o

298

Air Conditioning Refrigerant

HFC-134a

1,430

It is more difficult to estimate vehicle emissions of CH4, N?0, and HFCs than CO?. Emissions of
CH4 and N?0 are dependent on the design of the gasoline 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, CO, emissions are
95-99% of the total GHGs from a gasoline passenger vehicle, after accounting for the GWP of all
GHGs. The remaining 1-5% is CH4, N?0, and HFC emissions. EVs also emit a small amount of
GHGs due to air conditioner/HFC leakage.

What are the tailpipe emissions from a plug-in hybrid electric vehicle
(PHEV) or an electric vehicle (EV)? What about hydrogen fuel cell
vehicles (FCEV)?

Electric vehicles (EVs) have a battery instead of a gasoline tank, and an electric motor instead of
an internal combustion engine. EVs do not emit any tailpipe emissions. A fuel cell electric vehicle
(FCEV) operating on hydrogen will emit only water vapor. Calculating tailpipe emissions for
PHEVs is more complicated because they use both gasoline and electricity as fuel sources. When
operating on electricity only, a PHEV does not generate any tailpipe emissions. When a PHEV
is operating on gasoline only, it creates tailpipe emissions based on its gasoline fuel economy.
Tailpipe emissions for a PHEV operating on both electricity and gasoline cannot be calculated
without detailed information about how the specific PHEV operates. The overall tailpipe emissions
for a PHEV can vary significantly based on its battery capacity, how it is driven, and how often it is
charged. For more information, see the My Plug-In Hybrid calculator.

6 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 (GHG) emissions associated with the
use of my vehicle other than what comes out of the tailpipe?

Driving gasoline vehicles results in tailpipe GHG emissions. Producing and distributing the gasoline
used to power your vehicle also creates GHGs. For example, the production of gasoline 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 GHGs.

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 carbon dioxide (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 carbon dioxide (C02) emissions
from vehicles?

EPA measures vehicle fuel economy and CO, emissions using a set of standardized laboratory tests.
These tests were designed by EPA to mimic typical driving patterns. Both 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.

Visit Testing at the National Vehicle and Fuel Emissions Laboratory and Frequent Questions on
Fuel Economy Testing and Labeling for more information.

How can I find and compare carbon dioxide (C02) emission rates for
specific vehicle models?

Visit Fueleconomy.gov and click on "Find a Car." Select your vehicle of interest. From the vehicle
search results page, click on the "Energy and Environment" tab. A vehicle's GHG emissions rate
(g/mile) and GHG rating (1-10 scale) can be found on that search results page.

When shopping at a dealership, check out tailpipe carbon dioxide (C02) emission rates on vehicle
Fuel Economy and Environment Labels. The labels also feature a 1-to 10 Fuel Economy and GHG
rating to enable easy comparison shopping.


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Where can I find information on the emissions of the transportation
sector as a whole?

Visit EPA's Fast Facts on Transportation Greenhouse Gas Emissions and Carbon Pollution from
Transportation.

Annually EPA also publishes industry-wide data in the report, "Light-Duty Automotive
Technology, Carbon Dioxide Emissions, and Fuel Economy Trends." This report analyzes trends
fuel economy and CO? emissions for new light duty vehicles from 1975 to the present.

Other useful sources include:

Beyond Tailpipe Emissions Calculator
Fueleconomy.gov

Greenhouse Gas Equivalencies Calculator

Green Vehicle Guide

Household Carbon Footprint Calculator

Inventory of U.S. Greenhouse Gas Emissions and Sinks

For additional information on calculating emissions of greenhouse gases, please contact
greenvehicles@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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