Environmental Protection Agency: Light Duty Vehicle Emissions

Cars, SUVs, and light duty trucks that are fueled by gasoline, diesel, and E85 emit both greenhouse gases and smog-forming pollutants from their tailpipes.

On this page:


Greenhouse Gas Emissions

  • Greenhouse gases (GHGs) are emitted from the tailpipes of cars and trucks that combust fuel.
  • Once GHGs are released, they can stay in the atmosphere for 100 years or more.
  • GHGs act like a blanket around Earth, trapping energy in the atmosphere and causing it to warm. This can change Earth’s climate, raise sea levels, and result in dangerous effects to human health and welfare, and to ecosystems.

Smog Forming Emissions

  • Cars and trucks that combust fuel also emit smog forming emissions, such as nitrogen oxide, non-methane organic gases, carbon monoxide, particulate matter, and formaldehyde.
  • These emissions are usually trapped close to the ground and can form a brownish haze that pollutes our air, particularly over cities in the summertime.
  • Smog can make it difficult for some people to breathe, triggering lung diseases such as asthma, emphysema, and chronic bronchitis, which may lead to premature death.

Electric and hydrogen fuel cell vehicles do not produce tailpipe emissions. Emissions that are related to the production of the fuel used to power vehicles are known as “upstream” emissions. Visit our Beyond Tailpipe Emissions Calculator for specific information on upstream emissions from electric vehicles.

Environmental Ratings on the Label

GHG and Smog ratings on fuel economy label

We rate greenhouse gas (GHG) and smog forming emissions separately on the fuel economy label.

The GHG rating reflects carbon dioxide (CO2) emissions. CO2 makes up roughly 99% of the total greenhouse gases emitted from the tailpipe.

The smog rating reflects the current federal emission standards, which cover:

  • Oxides of Nitrogen (NOx), which combine with hydrocarbons to create smog
  • Particulate Matter (PM), tiny particles of solid matter that lodge in the lungs and deposit on buildings
  • Carbon-containing compounds (NMOG [non-methane organic gases], NMHC [non-methane hydrocarbons], or THC [total hydrocarbon content]), that contribute to the formation of ozone and smog
  • Carbon Monoxide (CO), a colorless, odorless, and poisonous gas
  • Formaldehyde (HCHO), a lung irritant and carcinogen.

The Good News … Vehicles are getting more efficient.

  • The more efficient a vehicle, the fewer greenhouse gases it emits and farther it goes on a single tank of gas, saving people money at the pump.
  • Average new vehicle fuel economy increased from 13 mpg in 1975 to 25 mpg today. This means that today a typical passenger car will go, on average, 2 times further on a single tank of gas than it did in 1975. Visit our automotive trends page for more details on how much fuel efficiency is improving.
  • Cars and trucks are 98-99% cleaner than they were in the late 1960s for smog-related pollutants, and they’re getting cleaner every year. Visit our vehicle emissions page for more details on cleaner emission standards for cars and trucks.
  • No matter what size car or truck you need, you now have more efficient, cleaner options. Look for greenhouse gas and smog ratings on the window stickers of all new vehicles.


For more information, visit EPA’s sites on:

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See: Infographic version of this information

1970: Clean Air Act (CAA) passed; emission standards set for cars and light-duty truck

1975: Emission Standards Take Effect

1979: Congress amends the CAA and passes more stringent standards

1981: Congress further tightens standards

1990: CAA amended again; Tier 1 standards set

1994: Tier 1 Standards Take Effect

2000: Tier 2 standards set; cars and light trucks now held to same standards

2004: Tier 2 Standards Fully Take Effect

2014: Tier 3 standards set

2017: Tier 3 Standards begin phase-in

2025: Tier 3 Standards Fully Take Effect

Science Topics
Atmospheric Sciences, Fossil Fuels, Pollution
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