Regulatory and Guidance Information by Topic: Air | US EPA (2024)

Under the Clean Air Act (CAA), EPA sets limits on certain air pollutants, including setting limits on how much can be in the air anywhere in the United States. The Clean Air Act also gives EPA the authority to limit emissions of air pollutants coming from sources like chemical plants, utilities, and steel mills. Individual states or tribes may have stronger air pollution laws, but they may not have weaker pollution limits than those set by EPA.

Read more at The Plain English Guide to the Clean Air Act

On this page:

  • Greenhouse Gases (GHGs)
    • Climate Change
  • Indoor Air
  • Mold
  • Radiation
  • Stationary Sources
    • Clean Air Markets (includesAcid Rain and Cross State Air Pollution Rule (CSAPR))
    • Criteria Air Pollutants: Carbon Monoxide, Ground-level Ozone, Lead, Nitrogen Oxides, Particulate Matter, and Sulfur Dioxide
    • New Source Performance Standards (NSPS)
    • New Source Review (NSR)/Prevention of Significant Deterioration (PSD)
    • Ozone Layer Protection
    • Operating Permits/Title V
    • Toxic Air Pollutants (Hazardous Air Pollutants)
  • Transportation: Mobile Sources
  • Visibility/Haze

On other pages:

  • Cross-Cutting Issues: Lead
  • Cross-Cutting Issues: Mercury

Greenhouse Gases (GHGs)

Greenhouse Gas Emissions: EPA provides information about emissions levels, sources of GHGs, partnership (voluntary programs), and options for cutting emissions.

Climate Change

EPA studies and reports on Climate Change as it impacts various populations and the natural environment. Learn about climate change's effects on the energy sector, transportation, and water, along with other climate change research.

Indoor Air

Indoor Air Quality: EPA does not regulate indoor air, but we do offer assistance in protecting your indoor air quality. Find information about mold, radon, formaldehyde and other indoor air quality issues.


Currently, there are no EPA regulations or standards for airborne mold contaminants. Learn more about mold on our Mold and Moisture site.

Policy and Guidance

  • Mold Remediation in Schools and Commercial Buildings: guidelines for the remediation/cleanup of mold and moisture problems in schools and commercial buildings. Includes measures designed to protect the health of building occupants and remediators.


Congress designated EPA as the primary federal agency charged with protecting people and the environment from harmful and avoidable exposure to radiation. EPA responds to emergencies, assists in homeland security, assesses radiation risks, sets protective limits on emissions, and informs people about radiation and radiation hazards.

Radiation Resources Outside of EPA: Cell Phones: Wireless technology devices such as cell phones and computer networks are regulated by the US Federal Communication Commission (FCC) and the US Food and Drug Administration (FDA).

Laws and Regulations

  • Radiation Regulations and Laws
  • Radiological Emergency Response
  • Radiation Protection: International Response

Policy and Guidance

  • Radiation Information for Technical Users and the Regulated Community

Stationary Sources

The Clean Air Act (CAA) requires major stationary sources to install pollution control equipment and to meet specific emissions limitations. In addition, under the 1990 CAA amendments, major stationary sources must obtain operating permits.

Clean Air Markets

EPA’s Clean Air Markets Division (CAMD) runs programs that reduce air pollution from power plants to address environmental problems such asacid rain,ozoneandparticle pollution, andinterstate transport of air pollution.

TheClean Air Markets website includes data and progress statistics, compliance resources for program participants, and the main program sites:

  • Acid Rain Program (ARP)
  • Cross-State Air Pollution Rule (CSAPR)

Six Criteria Air Pollutants: Carbon Monoxide, Ground-level Ozone, Lead, Nitrogen Oxides, Particulate Matter, and Sulfur Dioxide

The Clean Air Act (CAA) requires EPA to set National Ambient Air Quality Standards (NAAQS) for six common air pollutants. EPA must designate areas as meeting (attainment) or not meeting (nonattainment) the standard. States are required to develop a general plan to attain and maintain the NAAQS in all areas of the country, and a specific plan to attain the standards for each area designated nonattainment for a NAAQS.

Laws and Regulations

  • National Ambient Air Quality Standards (NAAQS): standards and implementation information for each of the six common air pollutants. Find information on sources for each pollutant, why the pollutant is of concern, health and environmental effects, and current efforts to help reduce the pollutants
  • Six Criteria Air Pollutants: Designations: find information on the process EPA, the states, and the tribes follow to designate areas as "attainment" or "nonattainment" for each of the pollutants
  • State Implementation Plan Status and Information: identifies how states and EPA work together to ensure that the agency'sNAAQSare met and maintained

New Source Performance Standards (NSPS)

The Clean Air Act (CAA) requires EPA to create a list of the important categories of stationary sources of air pollution, and to establish Federal standards of performance for new sources within these categories. These New Source Performance Standards (NSPS) apply to newly constructed sources or those that undergo major upgrades or modifications. The standards include both equipment specifications as well as operation and measurement requirements.

Laws and Regulations

  • New Source Performance Standards: includes selected NSPS. NSPS are published at 40 CFR 60.


  • New Source Performance Standards and State Improvement Plans Compliance Monitoring
  • Applicability Determination Index (ADI): NSPS and NESHAP memoranda and letters, including applicability determinations and regulatory interpretations.

New Source Review (NSR)/Prevention of Significant Deterioration (PSD)

The Clean Air Act (CAA) requires all areas of the country to meet or strive to comply with the National Ambient Air Quality Standards (NAAQS). One of the key programs designed to achieve compliance with the NAAQS is the New Source Review (NSR) program, a preconstruction review process for new and modified stationary sources.

Laws and Regulations

  • NSR: Regulations and Standards


  • RACT/BACT/LAER Clearinghouse (RBLC): database with case-specific information on the "Best Available" air pollution technologies that have been required to reduce the emission of air pollutants from stationary sources


  • Air Enforcement: New Source Review and Prevention of Significant Deterioration

Policy and Guidance

  • NSR: Policy and Guidance
  • New Source Review Policy and Guidance Database: a database with policy and guidance documents interpreting NSR and PSD construction permit regulations.

Ozone Layer Protection

Under Title VI of the Clean Air Act (CAA), EPA is responsible for programs that protect the stratospheric ozone layer.

Laws and Regulations

  • Ozone Layer Protection: Regulatory Programs: Information about the phase-out of chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), stationary refrigeration and air conditioning (Section 608), motor vehicle air conditioning (Section 609), the Montreal Protocol, and more.


  • Importing Bulk Ozone Depleting Substances
  • Stratospheric Ozone Including CFCs Compliance Monitoring


  • Enforcement Actions Under Title VI of the Clean Air Act

Operating Permits/Title V

Operating permits are legally enforceable documents that permitting authorities issue to air pollution sources after the source has begun to operate.

Laws and Regulations

  • Operating Permits: Current Regulations and Regulatory Actions

Policy and Guidance

  • OAR Policy and Guidance: Operating Permits (Title V): including policy and guidance memos and white papers.
  • Title V Policy and Guidance Document Index: a searchable database of policy and guidance documents that interpret title V and its regulations.

Toxic Air Pollutants (Hazardous Air Pollutants)

The Clean Air Act (CAA) requires EPA to regulate emissions of toxic air pollutants from a published list of industrial sources referred to as "source categories." Toxic air pollutants include mercury, polychlorinated biphenyls (PCBs), benzene and volatile organic compounds (VOCs).

Laws and Regulations

  • National Emissions Standards for Hazardous Air Pollutants (NESHAPs): An alphabetical list of NESHAPs by source category, including area sources.


  • NESHAPs Compliance Monitoring: Information about inspections, evaluations and investigations.


  • National Compliance Initiative: Creating Cleaner Air for Communities by Reducing Excess Emissions of Harmful Pollutants

Transportation: Mobile Sources

The Clean Air Act (CAA) mandates controls on air pollution from mobile sources by regulating both the composition of fuels and emission-control components on motor vehicles and nonroad engines. Vehicle fuel standards for gasoline and diesel are met by refiners/ importers, and by other parties in the fuel distribution system.

Regulation of vehicles includes vehicle emission limits for hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx), and particulates in the case of diesel vehicles. These limits, which must be met by the vehicle manufacturers, apply to on-road vehicles, off-road vehicles, and non-road sources (e.g., marine engines, locomotives, and lawn and garden equipment). Under the 1990 CAA amendments, vehicle standards are being made more stringent, in stages, through 2005 or later.

Vehicle safety information is available from the National Highway Traffic Safety Administration.

Browse by vehicle/fuel type:

On-road Vehicles and EnginesNonroad Vehicles and EnginesFuels and Fuel Additives
  • Cars and light trucks
  • Heavy trucks, buses, engines
  • Motorcycles
  • Aircraft
  • Diesel boats and ships
  • Forklifts, generators and compressors (gasoline and propane)
  • Gasoline boats and personal watercraft
  • Lawn and garden (small gasoline equipment)
  • Locomotives
  • Nonroad diesel equipment
  • Ocean vessels and large ships
  • Snowmobiles, dirt bikes, and ATVs
  • E15 (ethanol and gasoline blend)
  • Diesel
  • Gasoline
  • Renewable and alternative fuels

Browse by information type:

Laws and Regulations

  • Emissions Standards Reference Guide: Federal emissions standards for on-road and nonroad vehicles and engines, and related fuel sulfur standards.
  • Engine Testing Regulations, including 40 CFR 1065.
  • Mobile Sources Air Toxics: Regulations: Fuels such as ethanol, diesel fuels and more.
  • Transportation and Climate: Regulations and Standards


  • Compliance Monitoring: Air Mobile Sources Program: Information about inspections, evaluations and investigations for vehicles, engines and fuels.
  • Fuels and Fuel Additives: Compliance Information
  • Importing Vehicles and Engines


  • Air Enforcement: Mobile Sources

Policies and Guidance

  • State and Local Transportation Resources: Policy and Guidance: Directions for state and local governments on how to implement strategies for controlling transportation sector emissions.


One of the most basic forms of air pollution - haze - degrades visibility in many American cities and scenic areas. Since 1988 the federal government has been monitoring visibility in national parks and wilderness area.

Read more on the Visibility website .

Laws and Regulations

  • Visibility Regulatory Actions
Regulatory and Guidance Information by Topic: Air | US EPA (2024)
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