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The Plain English Guide to the Clean Air Act

Cars, Trucks, Buses, and "Nonroad" Equipment

Did you know?
  • The Clean Air Act requires the installation of vapor recovery nozzles at gas stations in certain areas. These gas pump nozzles reduce the release of gasoline vapor into the air when people put gas in their cars.
  • In the past, buses released large quantities of pollutants. Cleaner, less-polluting buses resulted from the 1990 Clean Air Act Amendments.
  • More cars driving more miles! This is why air pollution from cars has not improved as much as we had hoped, even though individual cars produce less pollution than they used to.

Today, motor vehicles are responsible for nearly one half of smog-forming volatile organic compounds (VOCs), more than half of the nitrogen oxide (NOx) emissions, and about half of the toxic air pollutant emissions in the United States. Motor vehicles, including nonroad vehicles, now account for 75 percent of carbon monoxide emissions nationwide.

The total vehicle miles people travel in the United States increased 178 percent between 1970 and 2005 and continues to increase at a rate of two to three percent each year. In the United States, there are more than 210 million cars and light-duty trucks on the road. In addition, the types of cars people drive have changed greatly since 1970. Beginning in the late 1980s, Americans began driving more vans, sport utility vehicles (SUVs), and pickup trucks as personal vehicles. By the year 2000, these "light-duty trucks" accounted for about half of the new passenger car sales. These bigger vehicles typically consume more gasoline per mile and many of them pollute three to five times more than cars.

The Clean Air Act takes a comprehensive approach to reducing pollution from these sources by requiring manufacturers to build cleaner engines; refiners to produce cleaner fuels; and certain areas with air pollution problems to adopt and run passenger vehicle inspection and maintenance programs. EPA has issued a series of regulations affecting passenger cars, diesel trucks and buses, and so-called "nonroad" equipment (recreational vehicles, lawn and garden equipment, etc.) that will dramatically reduce emissions as people buy new vehicles and equipment.

Cleaner Cars

The Clean Air Act required EPA to issue a series of rules to reduce pollution from vehicle exhaust, refueling emissions and evaporating gasoline. As a result, emissions from a new car purchased today are well over 90 percent cleaner than a new vehicle purchased in 1970. This applies to SUVs and pickup trucks, as well. Beginning in 2004, all new passenger vehicles - including SUVs, minivans, vans and pick-up trucks - must meet more stringent tailpipe emission standards. This marks the first time that light-duty trucks, including SUVs, pickups, and minivans are subject to the same national pollution standards as cars. As more of these cleaner vehicles enter the national fleet, harmful emissions will drop dramatically.

These reductions would not be possible without cleaner, very low sulfur gasoline and diesel fuel. In addition to their direct emissions benefits, cleaner fuels enable sophisticated emission control devices to effectively control pollution. Congress recognized the importance of cleaner fuels to reducing motor vehicle emissions and gave EPA authority to regulate fuels in the Clean Air Act.

Lead and Other Toxic Pollutants

One of EPA's earliest accomplishments was the elimination of lead from gasoline. Elevated levels of lead can damage organs and the brain and nervous system, and affect the heart and blood. Adverse health effects range from behavior disorders and anemia to mental retardation and permanent nerve damage. Children are especially susceptible to lead's toxic effects on the nervous system, which can result in learning deficits and lowered IQ. In the mid-1970s, EPA began its lead phase-out effort by proposing to limit the amount of lead that could be used in gasoline. By the summer of 1974, unleaded gasoline was widely available around the country, improving public health and providing protection for the catalytic converters that manufacturers began to install on all new vehicles. This effort was followed by even stronger restrictions on the use of lead in gasoline in the 1980s. In 1996, leaded gasoline was finally banned as a result of the Clean Air Act.

Under the Clean Air Act, EPA has also put into place standards to reduce toxic air emissions from mobile sources. These standards will cut toxic emissions from gasoline, vehicles, and even gas containers.

Reformulated Gasoline

The Clean Air Act requires certain metropolitan areas with the worst ground-level ozone pollution to use gasoline that has been reformulated to reduce air pollution. Other areas, including the District of Columbia and 17 states, with ground-level ozone levels exceeding the public health standards, have voluntarily chosen to use reformulated gasoline. Reformulated gasoline reduces emissions of toxic air pollutants, such as benzene, as well as pollutants that contribute to smog.

Low Sulfur Fuels

Beginning in 2006, refiners have been supplying gasoline with sulfur levels much lower than in the past, reducing the sulfur levels in gasoline by 90 percent. Sulfur in gasoline inhibits a vehicle's catalytic converter from effectively cleaning up the exhaust. The advanced vehicle emission control systems in passenger cars and light trucks are even more sensitive to sulfur, so reducing the sulfur content of gasoline will ensure that vehicle emission control devices are effective in reducing pollution. In addition to cutting emissions from new vehicles, lower sulfur fuel will result in lower emissions from vehicles currently on the road.

Since 2006, refiners have begun supplying diesel fuel with very low sulfur levels for highway diesel vehicles. As with gasoline vehicles, efficient new emission controls on diesel engines require this "Ultra- Low Sulfur Diesel" (ULSD) fuel to function properly. Highway diesel fuel sulfur levels are 97 percent cleaner than diesel prior to 2006. In 2007, refiners began reducing sulfur in diesel fuel used for nonroad diesel engines, such as construction equipment.

Alternative Fuels

The Clean Air Act encourages development and sale of alternative fuels. Alternative fuels are transportation fuels other than gasoline and diesel, including natural gas, propane, methanol, ethanol, electricity, and biodiesel. These fuels can be cleaner than gasoline or diesel and can reduce emissions of harmful pollutants. Renewable alternative fuels are made from biomass materials like wood, waste paper, grasses, vegetable oils, and corn. They are biodegradable and reduce carbon dioxide emissions. In addition, most alternative fuels are produced domestically, which is better for our economy, energy security and helps offset the cost of imported oil.

The Clean Air Act also requires EPA to establish a national renewable fuel (RF) program. This program is designed to significantly increase the volume of renewable fuel that is blended into gasoline and diesel.

Cleaner Trucks, Buses and "Nonroad" Equipment

Diesel engines are more durable and are more fuel efficient than gasoline engines, but can pollute significantly more. Heavy-duty trucks and buses account for about one-third of nitrogen oxides emissions and one-quarter of particle pollution emissions from transportation sources. In some large cities, the contribution is even greater. Similarly, nonroad diesel engines such as construction and agricultural equipment emit large quantities of harmful particle pollution and nitrogen oxides, which contribute to ground-level ozone and other pervasive air quality problems.

EPA has issued rules to cut emissions from onroad and nonroad vehicles by more than 90 percent by combining stringent emissions standards for diesel engines and clean, ultra-low sulfur diesel fuel. Under the Clean Air Act, EPA is also addressing pollution from a range of nonroad sources, including locomotives and marine vessels, recreational vehicles, and lawn and garden equipment. Together these sources comprise a significant portion of emissions from the transportation sector.

Transportation Policies

Congress required "conformity" in the Clean Air Act Amendments of 1990. In other words, transportation projects such as construction of highways and transit rail lines cannot be federally funded or approved unless they are consistent with state air quality goals. In addition, transportation projects must not cause or contribute to new violations of the air quality standards, worsen existing violations, or delay attainment of air quality standards.

The conformity provisions require areas that have poor air quality now, or had it in the past, to examine the long-term air quality impacts of their transportation system and ensure that it is compatible with the area's clean air goals. In doing so, those areas must assess the impacts of growth on air pollution and decide how to manage growth. State and local agencies must work together to either change the transportation plan and/or the state air plan to achieve the necessary emission reductions.

Inspection and Maintenance Programs

Proper maintenance of a car's engine and pollution control equipment is critical to reduce excessive air pollution. To help ensure that such maintenance occurs, the Clean Air Act requires certain areas with air pollution problems to run inspection and maintenance (I/M) programs. The 1990 Act also established the requirement that passenger vehicles be equipped with on board diagnostics. The diagnostics system is designed to trigger a dashboard "check engine" light alerting the driver of a possible pollution control device malfunction. To help ensure that motorists respond to the "check engine" light in a timely manner, the Act requires that I/M programs include an inspection of the on board diagnostic system.

For more information about transportation and air quality, visit www.epa.gov/otaq.

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