Prior to 1990, EPA established standards of performance for hazardous air pollutants (HAPs) based on the risk presented by certain chemicals. Because progress was slow, the 1990 Clean Air Act expanded the universe of regulated HAPs to 188 and required EPA to establish technology-based standards. These standards make use of control equipment, work practices, material substitution and other technologies to reduce emissions from stationary and other smaller area sources. The Clean Air Act requires EPA to re-evaluate these technology-based standards every eight (8) years to assure that any remaining "residual risk" is sufficiently reduced. These National Emission Standards for Hazardous Air Pollutants can be found at Title 40, Parts 61 and 63 in the Code of Federal Regulations. For more details, see the e-CFR or links provided on this page.

EPA is also required to conduct a National-Scale Air Toxics Assessment (NATA) that identifies air toxics that present the greatest threat to public health in the largest number of urban areas. This assessment includes the development of toxic inventories from point sources, area sources, and mobile sources. The NATA Assessment is designed to help EPA, state, local and tribal governments and the public to better understand the air toxics problem in the U.S. and the progress being made to reduce emissions.

Since EPA's activities to reduce risk on a national scale may not fully address potential risks at the local level, the agency's air toxics strategy also includes local and community-based initiatives to reduce the level of hazardous air pollutant emissions.

Generally, state and local air pollution control agencies are responsible for implementation, compliance assistance, and enforcement of the MACT and NESHAP standards. EPA retains concurrent enforcement authority and is also available to provide technical assistance when a state or local agency seeks help. EPA also retains a few of the MACT and NESHAP responsibilities -- such as the ability to approve alternative monitoring methods -- to maintain a minimum level of national consistency.

If you have questions about the MACT or NESHAP standards, or the air toxics program in general, we encourage you to discuss with your respective state or local air pollution control agency. If you are located outside of Region 7, please check with your state or local agency or EPA Regional Office. If you are a state or local agency located in Region 7 and need assistance with the interpretation of regulatory language, please see the "State and EPA Contact" links for further assistance.