The Clean Air Act


The federal Clean Air Act (CAA) is the law that regulates air quality in the United States. Many of the more important provisions contained in the CAA were added in 1990 when Congress enacted the Clean Air Act Amendments of 1990. The CAA establishes national ambient air quality standards for criteria pollutants, classifies areas depending on their level of air quality, and requires states to develop implementation plans that reduce air pollution levels.

The Clean Air Act does not directly call for the use of alternative fuel vehicles (AFVs), but it has created an environment that is favorable to them, including NGVs.

The law requires the U.S. Environmental Protection Agency (EPA) to periodically review and revise, if necessary, air quality standards based on new scientific information. Areas that have emission concentrations exceeding the standards established in the Act or updated by EPA are classified as nonattainment areas. The law also instructs EPA to establish a number of national controls on emissions sources such as large power plants and motor vehicles. States generally are preempted from establishing their own emission restrictions on sources regulated by EPA. However, it is the states that are primarily responsible for enforcing the emission controls identified in the law and for developing additional controls that are necessary to bring areas into attainment for the national ambient standards. The controls adopted by states are set out in State Implementation Plans.

Criteria pollutants
The six criteria pollutants regulated under the Clean Air Act:

  • Ozone
  • Carbon monoxide
  • Nitrogen dioxide
  • Sulfur dioxide
  • Particulate matter
  • Lead

EPA has also begun a series of rulemakings to regulate greenhouse gas emissions.

Health and economic benefits of the Clean Air Act Amendments
Air pollution disrupts the lives of millions of Americans and causes both chronic health problems and premature deaths. Reducing air pollution is an important national goal that is being achieved through the Clean Air Act. In a recent study, EPA estimates the CAA Amendments of 1990 will prevent 17 million lost work days, 120,000 emergency room visits, and 230,000 premature deaths by 2020. The economic benefits of the CAA Amendments are expected to total approximately $2 trillion by 2020.

Although the Clean Air Act has successfully reduced air pollution throughout the country, there are still nonattainment areas for criteria pollutants. To see the list of nonattainment areas in the U.S. that do not meet the CAA requirements, visit EPA here.

Regulating motor fuels and vehicles
The CAA addresses vehicle emissions by establishing stringent emission standards for all new motor vehicles, regulating the properties of gasoline and diesel fuels, and requiring most nonattainment areas to adopt vehicle inspection and maintenance programs. These programs require the periodic testing of vehicles to ensure that they continue to meet federal emission standards. Vehicles that fail these tests must be repaired. The federal law also provides EPA with the authority to periodically update vehicle emission standards. To read more about what the CAA says about motor vehicles and emission standards, visit EPA here.

AFVs can help meet emission requirements
State regulators are under increasing pressure to identify new pollution control strategies to offset emissions from the growing number of vehicles on the road. Despite the enactment of new federal motor vehicle emission standards and stringent controls on stationary sources, states still need to make further improvements to achieve healthy air. One strategy is to award credits to manufacturers for producing cleaner vehicles that can be used to offset vehicles with higher emissions. State regulators can also take advantage of the emission reduction benefits of NGVs and other AFVs to meet federal emission levels by incorporating them into public fleets or promoting their public adoption through various programs.

California Air Resources Board
California is the only state given the unique ability to adopt its own vehicle emission standards due to its large vehicle population and the resulting environmental challenges. California’s Air Resources Board (CARB) is the institution that controls California’s vehicle emissions standards. Other states cannot adopt their own vehicle emission standards, but are able to adopt CARB standards; more than a dozen states have now adopted California’s low-emission vehicle standards. California has also been particularly aggressive in regulating the motor vehicle emissions of in-use vehicles. The in-use regulations have focused mostly on heavy-duty vehicles, which have introduced cleaner vehicle technologies by accelerating fleet turnover and by requiring fleets to retrofit existing diesel-fueled vehicles. Many states have followed California’s lead by adopting its regulations affecting new motor vehicles, but few have adopted its regulations for in-use fleet vehicles. To date, regulations requiring fleets to accelerate the turn-over of their older, dirtier vehicles have not been challenged in court.

Other states must largely rely on voluntary programs that encourage both consumers and fleets to use lower emission vehicles. A growing number of states are adopting incentive-based programs to encourage the acquisition of AFVs, including NGVs. To search programs and incentives by state, click here.