An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

Clean Air Act Overview

Setting Emissions Standards Based on Technology Performance

The Clean Air Act requires emissions standards for pollution sources such as motor vehicles, power plants and industrial facilities. Most of these provisions call for setting standards based on the emissions performance and cost of technologies.

The Clean Air Act requires EPA to set national air quality standards for common pollutants based solely on protecting public health and welfare. In addition, the Act requires states or EPA (depending on the program) to set emissions standards or limits for air pollution sources such as power plants, industrial facilities or motor vehicles. These emissions standards may be designed to control common pollutants, toxic pollutants, or greenhouse gas pollution.

In most cases, the Act calls for emissions standards to be set based on data concerning the emissions performance and cost of available technologies. In this way, technical feasibility and cost considerations are taken into account when pollution sources are regulated.

Performance standards, not technology requirements

In setting national emissions standards, EPA generally sets emissions performance levels rather than mandating use of a particular technology. In fact, the law mandates that EPA use numerical performance standards whenever feasible in setting national emissions standards for stationary sources. Depending on the program, additional flexibility may be provided through emissions averaging, emissions trading, alternative standards, or other mechanisms. <Learn more about flexibility in Clean Air Act standards>

The importance of data

EPA collects and carefully examines data on the performance levels of currently available technologies when considering Clean Air Act emissions standards for mobile and stationary sources. Examples of national standards set by EPA include “new source performance standards” for new industrial facilities, and emissions standards for new motor vehicles and nonroad engines (such as those used in construction and, agriculture). The Act gives EPA authority to collect data from industries on emissions, control technologies and costs. EPA uses this and other technical information in issuing national rules, and places the information that EPA relies on in the rulemaking docket for public review and comment (except confidential business information). EPA also collects information from states, and makes data on control technology performance available to states and the private sector in information clearinghouses.

State limits based on technology performance and cost

Under the Act, States also set emissions limits for pollution sources considering technology performance and cost. States require “reasonably available” controls for existing stationary sources (e.g., factories) to help meet and maintain air quality standards. Another example is the “best available control technology” requirement in permits for major new pollution sources. Through a public notice-and-comment process, the state permitting authority considers alternative control levels for the proposed facility based on data concerning the emissions performance of technologies applied at other facilities, and the corresponding control costs, before determining a new source’s numerical pollution limits.

Promoting technology improvement

Under some parts of the Act, Congress authorized standards that push development of technology. For example, in provisions for new motor vehicle standards, Congress authorized EPA to set performance levels that, while not achievable immediately, are demonstrated to be achievable in the future based on information available today.

Standards based on the best performers

Other emissions standard-setting provisions of the Act call for an approach that focuses on what the best performers in a particular industry are already doing in practice. For example, section 112 requires EPA to set national emissions standards for major stationary sources of toxic pollution. For existing sources, EPA must set standards that require at least the level of performance already achieved by the top-performing 12 percent of similar sources. These provisions are designed to ensure that the higher-emitting sources in an industry make improvements and bring emissions in line with levels already achieved in practice by the lower-emitting sources. The resulting performance standards give all sources the flexibility to decide the most cost-effective way to comply.

<Learn more about setting performance-based and risk-based air toxics standards>
<Learn more about standard setting and the Clean Air Act generally>