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Please note: This summary is provided to help you understand the regulations. Consult the references provided for links to the full text of the regulations.

Clean Air Act (CAA)

Road Rail Air Water


Until Congress passed the Clean Air Act (CAA) in 1970, there was no comprehensive federal response to address air pollution. That same year Congress created the EPA and gave it the primary role in carrying out the law. Since 1970, EPA has been responsible for a variety of Clean Air Act programs to reduce air pollution nationwide.

The CAA defines EPA's responsibilities for protecting and improving the nation's air quality and the stratospheric ozone layer. The last major change in the law, the Clean Air Act Amendments (CAAA) of 1990, was enacted by Congress in 1990. Legislation passed since then has made several minor changes. State and local governments oversee, manage, and enforce many of the requirements of the CAA.

The Clean Air Act is a federal law covering the entire country. However, states and local governments do a lot of the work to meet the Act's requirements. For example, representatives from these agencies work with companies to reduce air pollution. They also review and approve permit applications for industries or chemical processes, monitor air quality, inspect facilities under their jurisdictions, and enforce Clean Air Act regulations.

The CAA consists of six sections, referred to as Titles. Titles I-VI regulations can be found in 40 CFR 50-95. Each section is summarized below.

Title I - Air Pollution Prevention and Control

Title I gives EPA the authority to establish National Ambient Air Quality Standards (NAAQSs) to limit levels of six criteria pollutants including carbon monoxide, lead, nitrogen oxides, particulate matter (PM), ozone, and sulfur dioxide (40 CFR 50).

Title I, Section 110 of the CAA, requires each state to develop a State Implementation Plan (SIP) to identify sources of air pollution and to determine what reductions are required to meet federal air quality standards. The SIP must be approved by EPA, or EPA may promulgate a plan of its own. Once a SIP is approved, it may be enforced by both federal and state authorities (CAA Section 110, 42 U.S.C., Section 7410(a) (2)). Geographic areas that meet NAAQSs for given pollutants are classified as Attainment Areas; those that do not meet NAAQSs are classified as Nonattainment Areas. Those areas that are classified as nonattainment must update their SIPs in order to improve air quality. Transportation facilities located in nonattainment areas may be required to install Reasonably Available Control Technology (RACT). RACT is defined as "devices, systems, process modifications, or other apparatus or techniques that are reasonably available" in order to obtain attainment status.

Title I also authorizes EPA to establish New Source Performance Standards (NSPSs), which are nationally uniform emission standards for new stationary sources falling within particular industrial categories (CAA Section 111). NSPSs are based on the pollution control technology available to that category of industrial source but allow the affected industries the flexibility to devise a cost-effective means of reducing emissions.

Title II - Emission Standards for Moving Sources

Title II of the CAA (Section 201-250) pertains to mobile sources, such as cars, trucks, locomotives, ships and planes. 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.

Under the Clean Air Act, standards for trucks, buses, locomotives and ships using diesel engines were strengthened. For trucks, new vehicle engine emission standards began to take effect in model year 2007, which are based on the use of high-efficiency catalytic exhaust emission control devices or comparably effective advanced technologies. Similarly, in 2008, EPA passed new standards for locomotive and marine engines, including requirements for newly-built engines that are based on aftertreatment technology. These standards are enabled by the availability of ultra-low sulfur diesel fuel and will be fully phased in for new engines by 2015.

EPA began regulating the emissions from aircraft engines in 1973. Since that time, they have worked with the FAA and later with the International Civil Aviation Organization (ICAO) to develop international standards and other recommended practices pertaining to aircraft engine emissions. The emission regulations published by EPA in 2012 contain standards and related provisions for NOx control. In 2022 EPA published particulate matter (PM) emission standards (more information on aircraft emissions standards).

Title III - Air Toxics

Under Title I, EPA established and enforced the National Emissions Standards for Hazardous Air Pollutants (NESHAPs), NESHAPs are nationally uniform standards oriented towards controlling particular hazardous air pollutants (HAPs). Title III further directed EPA to develop a list of sources that emit any of 187 HAPs listed under Section 112 of the CAA, and to develop regulations for these categories of sources. To date, EPA has listed 174 categories and developed a schedule for the establishment of emission standards. The emission standards are being developed for both new and existing sources based on maximum achievable control technology (MACT). The MACT is defined as the control technology achieving the maximum degree of reduction in the emission of the HAPs, taking into account cost and other factors.

Various transportation operations and equipment are impacted by NESHAPs, including aerospace, boilers, gasoline dispensing, oil/water separators, and reciprocating internal combustion engines.

Title IV - Acid Deposition Control

Acid rain occurs when sulfur dioxide and nitrogen oxide emissions are released into the atmosphere and return to the earth in rain, fog, or snow. Title IV establishes a sulfur dioxide emissions program designed to reduce the formation of acid rain by requiring power plants and other utilities to reduce sulfur dioxide emissions. Reduction of sulfur dioxide releases will be obtained by granting certain sources limited emissions allowances. This program began in 1995 and set levels of sulfur dioxide releases below previous levels.

Title V - Permits

Title V of the CAAA of 1990 created a permit program for all major sources (and certain other sources) regulated under the CAA. One purpose of the operating permit is to include, in one document, all air emissions requirements that apply to a given facility. States continue to develop their permit programs in accordance with guidance and regulations from EPA. Once a state program is approved by EPA, permits are issued and monitored by that state (see Air Pollution State Resource Locator).

In order to assess whether one requires a Title V permit it is necessary to estimate potential emissions from each manufacturing step/operation, including receiving and shipping. Principal pollutant emission factors for some transportation-related operations (e.g., painting, solvent cleaning) have been tabulated to aid in determining annual emissions. Those without factors need to be experimentally measured or estimated based on like processes .

If emission estimates exceed or potentially may exceed Title V permits then an operating permit must be sought. Most Title V permits are issued by state and local permitting authorities. These permits are often called part 70 permits because the regulations that establish minimum standards for State permit programs are found in the Code of Federal Regulations at 40 CFR part 70.

Two documents that can be employed to help you determine if your business is a minor or major source of air pollution are Potential to Emit, A Guide for Small Businesses and AP 42, Fifth Edition Compilation of Air Pollutant Emission Factors. The reference Potential to Emit provides a good explanation of the rules and examples of calculations using emissions factors. AP-42 contains emission factors and process information for more than 200 air pollution source categories, including some transportation-related operations.

Title VI - Stratospheric Ozone

Title VI is intended to protect stratospheric ozone by phasing out the manufacture of ozone-depleting chemicals and restricting their use and distribution. Title VI requires EPA to list all regulated substances along with their ozone depletion potential, atmospheric lifetimes, and global warming potentials.

Stationary refrigeration and air-conditioning used by the transportation industry is regulated under Section 608 of the Clean Air Act to minimize refrigerant emissions by maximizing the recovery and recycling of such substances during the service, repair, or disposal of refrigeration and air-conditioning equipment (I.e., appliances).

State and local governments also play an important role in meeting the national goal of reducing greenhouse gas. They are participating in national voluntary programs and initiatives, analyzing the costs and benefits of actions and developing and applying innovative programs and strategies that achieve wide-ranging benefits to businesses, the environment and public health. Use our Climate Change State Resource Locator to access resources developed by a variety of state and local environmental agencies.

EPA Resources

Small Business Environmental Assistance Program. Section 507 of the 1990 Clean Air Act Amendments requires each state establish a Small Business Environmental Assistance Program (SBEAP) to assist small businesses with environmental compliance and emissions reduction. Find your SBEAP state contact.