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New Hampshire Department of Environmental Services

Vehicle Emissions and Fuel Economy

Among the major sources of air pollution (electricity generation, transportation, industry, residences and agriculture) motor vehicles alone account for over 33 percent of the carbon monoxide, 38 percent of the nitrous oxides and 28 percent of the greenhouse gas (GHG) emissions. In addition, motor vehicles emit fine particulates, hydrocarbons and sulfur dioxides that endanger our health, create ground level ozone and cause acid rain. For example, based on a 2013 national average fuel economy of 24.8 miles per gallon, a car emits a little less than one pound of carbon dioxide per mile. If that car is driven 12,000 miles per year, a low estimate, it discharges a whopping 4.7 tons of carbon dioxide and almost 500 pounds of carbon monoxide as well as 55 pounds of hydrocarbon compounds into the atmosphere each year. Increases in the overall vehicle fuel economy not only save consumers money, it reduces this major source of air pollution and greenhouse gases.

Tier 3 emissions reductions

The National Highway Traffic Safety Administration (NHTSA) sets minimum average motor vehicle fuel economy requirements in mile per gallons referred to as Corporate Average Fuel Economy or CAFE standards. In 2012, the U.S. Environmental Protection Agency (EPA) and the NHTSA set new greenhouse gas and CAFE standards for passenger cars, light-duty trucks and medium-duty passenger vehicles that will be phased in for model years 2017 through 2025. Under the new standards, these vehicles are expected to achieve a combined average of 35.5 miles per gallon by 2017, increasing to 54.5 miles per gallon by 2025. Under the new standards, these vehicles are expected to achieve a combined average of 54.5 miles per gallon by 2025.

EPA also establishes fuel composition standards and sets limits on emissions from vehicles such as light-duty and heavy-duty trucks. In 2014, EPA announced it is taking additional steps to further reduce motor vehicle emissions. These are:

  • Gasoline Quality Standards – EPA is requiring refiners to reduce the amount of sulfur in gasoline.  Called "Tier 3" rules, these standards require that by 2017, gasoline at fuel pumps contains no more than an average of 10 parts per million of sulfur. Along with creating sulfur dioxide during combustion, sulfur in gasoline interferes with the vehicle’s catalytic converter and impedes its efficiency at reducing organic gas, nitrous oxide and other combustion emissions such as carbon monoxide.
  • Tailpipe Emissions Standards – EPA is setting standards for nitrogen oxides (NOx) and non-methane organic gases (NMOG) emitted from trucks. Scheduled to be phased in through model years 2017 through 2025, light- and medium-duty trucks’ organic gas and nitrous oxide emissions will be reduced from today’s fleet average of 160 milligrams per mile, to 30 milligrams per mile by 2025. NMOG and NOx emissions from heavy duty trucks will be reduced from today’s average of 396 milligrams per mile, to as low as 178 milligrams per mile by 2022. EPA is also requiring reductions in particulates emissions from 10 milligrams per mile, to as low as 3 milligrams per mile over the same time period.
  • Evaporative Emissions Standards – Even a non-running vehicle emits hydrocarbon vapors as fuel in the tank and fuel system evaporates. Since 1990, emissions from mobile sources have been reduced by about 50 percent. The EPA anticipates a further reduction of up to 80 percent by 2030. As with the other standards, maximum evaporation rates will be phased in over time and will result in a 50 percent reduction in this emission source.

CAFE, fuel quality and emissions standards not only protect the environment, they save vehicle owners fuel and maintenance costs and reduce our dependence on foreign fossil fuels. Although increased fuel efficiency will add about $1,300 to the price of a 2025 vehicle, consumers who drive their MY 2025 vehicle for its entire lifetime will save, on average, about $4,400 in fuel costs.  These standards are also expected to save approximately 4 million barrels of oil and reduce GHG emissions by 2 billion metric tons. 

If you would like to see how much money a more fuel-efficient vehicle can save you, visit By comparing two vehicles’ miles per gallon versus cost per gallon, the calculator will show how much money you can save over the length of time you keep the vehicle. "My MPG" feature allows you to calculate and track your current vehicle’s fuel economy.

Contact Us

  • Timothy White
    Supervisor, Mobile Sources Section
    New Hampshire Department of Environmental Services
    29 Hazen Drive, PO Box 95
    Concord, NH 03302-0095
    Tel: (603) 271-5552
    Fax: (603) 271-1381

NH Department of Environmental Services | 29 Hazen Drive | PO Box 95 | Concord, NH 03302-0095
(603) 271-3503 | TDD Access: Relay NH 1-800-735-2964 | Hours: M-F, 8am-4pm

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