Clean Air Act Basics

Clean Air Act Basics

The modern version of the Clean Air Act came into existence in 1970 with the passage of the Clean Air Act. The Act has undergone two major revisions in 1977 and 1990. The Act is broken down into Titles, Parts, and individual Sections. With all of its interconnections and technically complex programs, the Clean Air Act is the most complex environmental law in the United States; in fact it is probably one of the most complex laws ever passed by Congress. It is therefore impossible to give an “overview” of the entire Act. This overview will focus on the basics of some of the most used or important sections.

The Clean Air Act has six major Titles:

  • Title I contains requirements for stationary sources and airsheds.
  • Title II contains requirements for mobile sources, both “on road” and “non road” sources.
  • Title III contains general provisions, including enforcement provisions.
  • Title IV addresses the problem of acid rain.
  • Title V contains the major source operating permit program.
  • Title VI implements the requirements of the Montreal Protocol on Ozone Depleting Substances.


Title I

Title I of the Clean Air Act regulates stationary sources of air pollution. Most regulations and requirements under the Clean Air Act find their basis in Title I. In Part A of Title I, Sections 107 through 110 require the United States Environmental Protection Agency (EPA) to create National Ambient Air Quality Standards (NAAQS) for “criteria” pollutants. Currently there are six criteria pollutants:

–       nitrogen oxides (NOx),

–       sulfur dioxide (SO2),

–       carbon monoxide (CO),

–       ozone (O3),

–       lead (Pb),

–       and particulate matter (PM), which is broken down into particulates less than 10 microns (PM10) and particulates less than 2.5 microns (PM2.5).

The NAAQS standards are set based on the best available data concerning the pollutant’s affect on human health; the cost of achieving these standards is not considered in setting the standards themselves. States must undertake monitoring and modeling to determine whether the airsheds in the state are in “attainment,” are “nonattainment,” or “unclassifiable.” States must then adopt a State Implementation Plan (SIP) that sets out the state’s plan for achieving or maintaining compliance with the NAAQS in these airsheds. These plans must be submitted to and approved by EPA. Once approved by EPA these state regulations become federal law in that state, which, as discussed below under Title III, makes them enforceable by citizens.

Also found in Part A are the New Source Performance Standards (NSPS) and National Emission Standards for Hazardous Air Pollutants (NESHAPs). Section 111 sets out the requirements for NSPS; Section 112 sets out the requirements for NESHAPs.


NSPS regulations set out minimum control requirements for new air pollution sources in specific source categories. These standards are set based on the best system of emissions reduction that, accounting for cost and non-air impacts, has been adequately demonstrated. The NSPS set emission limits and do not require a source to install a specific control technology though in practice sources usually meet these requirements by installing the control technology EPA based the NSPS on. If an existing source would be subject to an NSPS but is not currently regulated under the NAAQS or NESHAPs, EPA can ask states to develop plans to address these existing sources. It is this authority that EPA is currently exploring to regulate green house gas (GHG) emissions from existing coal-fired power plants.


            NESHAP regulations set standards for the most prevalent industrial sources of air toxics. The original NESHAP program was a health-based standard. Unfortunately due to its narrow scope and continuous litigation involving EPA’s judgment on the health effects, this original program was very ineffective. While the regulations passed under this program remain, the only one of real consequence is the regulation of asbestos. Part of the problem with the original program is that EPA first had to determine whether or not a chemical was toxic.

Congress remedied this situation with the 1990 Clean Air Act Amendments. Congress set out a list of 188 hazardous air pollutants (HAPs) and gave EPA the authority to add or remove from this list. This list is much broader than simply 188 chemicals since many are sets of compounds, like “chromium compounds,” that contain hundreds or even thousands of different chemicals. There have been some changes to this list over the years, but most of the list remains as Congress wrote it in 1990.

Congress also worked to create a more concrete standard for EPA to implement than a health-based standard that was subject to constant litigation. Congress required EPA to set out a list of the major and area sources of HAPs. A major source is a source that has the potential to emit more than 25 tons/year of HAPs or 10 tons/year of an individual HAP. An area source is a source other than a major source. The list of regulated source categories is revised every 8 years to ensure the appropriate source categories are regulated.

Congress also modified the NESHAP program to be essentially a pure technology based standard. New major sources must meet the best level of control achieved in practice. Existing major sources are required to meet a level of control that is the average of the best performing 12 percent of existing sources. If there are less than 30 sources in a category, an existing major source must meet a level of control that is the average of the top 5 sources. These standards are known as the maximum achievable control technology (MACT). Much like the NSPS, the NESHAP program does not require the installation of specific control technology only an emission limit. If EPA determines that a source category meets certain requirements, it can pass regulations for area sources that require the sources to implement generally available control technology (GACT).

Risk Management Planning

            Section 112 also includes the Risk Management Planning (RMP) program. The RMP program is contained in Section 112r. This program was passed in response to the Bhopal disaster in India. It requires sources that store or use large amounts of potentially dangerous chemicals to develop plans that include a risk assessment, a program for preventing accidental releases, and a response plan for accidental releases.

 New Source Review

            The review of emissions from new or modified major sources is found in two separate parts of Title I. Part B, Subpart I sets out the Prevention of Siginficant Deterioration (PSD) program. Part D sets out the Nonattainment New Source Review (NaNSR) program. Both of these programs are often referred to as simply “New Source Review.” PSD applies in areas that are designated as attainment or unclassifiable. NaNSR applies in areas that are designated as nonattainment. Both programs only apply to the largest sources. For a designated list of source categories the trigger level is 100 tons per year of a single pollutant. Outside of that designated list, the trigger level is 250 tons per year of a single pollutant.

Generally, under PSD a source has to do modeling to ensure that it won’t cause a violation of the NAAQS. The source must also install the Best Available Control Technology (BACT). The determination of BACT is made on a case-by-case basis and accounts for “energy, environmental, and economic impacts and other costs,” but must be at least as stringent as any NSPS or NESHAP that are applicable to the source.

For NaNSR, a source must comply with the lowest achievable emission rate which is either the most stringent standard included in a SIP or the most stringent standard achieved in practice, whichever is lower. The source must also receive “offsets” from other sources of pollution so that there is no net increase in air emissions within the airshed.

Visibility Protection

            The last major program in Title I is Visibility Protection. This program is aimed at curbing visibility impairment at “mandatory Class I Federal areas” which are places like National Parks and Wilderness areas. A full list can be found here. The Visibility Program requires states to develop plans to reduce the impact of anthropogenic emissions on visibility in these areas. Among other requirements, the largest sources that were “grandfathered” under the New Source Review programs (i.e., built prior to 1977) must install the best achievable retrofit technology (BART).


Title II

Title II regulates mobile sources of air pollution like cars, trucks, and airplanes. EPA can set standards for these mobile sources. With a notable exception, states are prohibited from adopting their own standards. The purpose of this preemption was to allow car companies and engine manufacturers reliability and prevent a patchwork of state regulations from making interstate sales of cars and engines more difficult. However, because it had adopted standards prior to the Clean Air Act and had and has serious problems with air pollution, California was allowed to adopt more stringent standards that those passed by EPA. Other states are then allowed to adopt the California standards in lieu of the federal standards, but are still prohibited from adopting their own, different, standards.

Regulations under Title II have become important in EPA’s actions to address climate change. During the Bush Administration, several states and environmental groups petitioned EPA asking it to regulate GHGs emissions from motor vehicles. EPA denied the petition claiming that it lacked authority to regulate carbon dioxide and other GHGs and even if it did, policy considerations supported not regulating these emissions. The petitioners challenged this decision in court, which eventually lead to the landmark case of Massachusetts v. EPA. In Massachusetts, the Supreme Court ruled that carbon dioxide and other GHGs were “pollutants” under the Clean Air Act and that EPA may not look outside the text of the Clean Air Act and refuse to issue regulations for other “policy” considerations.

During the Obama Administration, EPA issued its first GHGs standards for new cars. Interestingly, under a long standing EPA regulation and interpretation, this meant that major new stationary sources of GHGs were now subject to New Source Review. The regulation of GHGs under Title II has also lead to EPA proposing New Source Performance Standards for GHGs from electric generating units like coal and natural gas power plants.

Title III

Title III contains the general provisions of the Clean Air Act. The most important part of this Title is the citizen suit provision. When first passed in 1970, the citizen suit provision of the Clean Air Act was a bold first. Prior to the 1970’s Clean Air Act, there were very few opportunities for citizens to be directly involved with the enforcement of laws and regulations. Now citizens can be there to step in when the state and federal governments can’t or simply won’t enforce the requirements of the Clean Air Act. The citizen suit provision allows any “person” to file suit in federal court. “Person” is defined very broadly to include individuals, corporations, partnerships, municipalities, and States.

The citizen suit provision has a couple of important caveats. First, to sue a violator in federal court under the Clean Air Act, the requirement must be part of the State Implementation Plan (SIP) approved by EPA. Not all requirements under state law are incorporated into the SIP. For instance, in Oregon there are additional requirements in the Portland Metro area that have not been incorporated into the Oregon SIP; citizens therefore cannot sue a source in federal court for violating these requirements.

In most circumstances citizens also have to give the source, the state, and the federal government “notice” before filing suit. This is done in an “Intent to Sue” letter that lays out why the citizen believes the source violated the Clean Air Act. The citizen must wait 60 days after giving notice to file in federal court. This gives the state and federal governments an opportunity to bring their own lawsuit, which preempts filing a citizen suit, though citizens can join the state or federal lawsuit under most circumstances. The notice also gives the violator an opportunity to fix the violation or negotiate a settlement with the citizen. The notice requirement does not apply if the source is proposing to construct or constructing in violation of New Source Review permitting requirements or is violating the terms New Source Review construction permit.

The citizen suit provision allows citizens to seek injunctive relief in which a federal judge orders a company or individual to undertake some action or prohibits them from taking some action. In other words, remedy the violation. Violations of the Clean Air Act also subject sources to civil penalties, currently up to $37,500 per day per violation.

The citizen suit provision also gives citizens the right to sue the Environmental Protection Agency (EPA) for failure to perform a non-discretionary duty. For instance, the Clean Air Act requires EPA to update NSPS and NESHAPs on a set time table. If EPA fails to meet this time table, which it often does, citizens can sue EPA to force the updates.

Title IV

Added with the 1990 Clean Air Act Amendments, Title IV is aimed at addressing the problem of acid rain. Acid rain is caused by the presence of sulfur and nitrogen oxides. These pollutants, when trapped in the water vapor of clouds, form sulfuric and nitric acid. Acid rain causes significant damage to plants and wildlife. Title IV regulates the emissions of sulfur and nitrogen oxides, mainly from electric generating units like coal and natural gas power plants through a cap-and-trade system of allowances. The first phase, implemented in 1995, targeted the largest sources in the East and Midwest. The second phase, implemented in 2000, expanded the scope of the program.

Title V 

 Title V was added to the Clean Air Act with the 1990 Amendments and is probably the most visible part of the Clean Air Act to the general public. However, the role of Title V is often misunderstood. Title V was added to address a very specific problem. Prior to 1990, a large number of facilities had multiple construction or modification permits. For instance, if an existing facility added a large emergency generator, it would get a construction permit, but only for that generator. This meant that the requirements a facility was subject to were contained in multiple permits. This made it hard for sources to know for sure that they were doing everything they were supposed to be doing and it made it hard for regulators and citizens to assess whether a source was in compliance with the Clean Air Act.

Congress’s solution, at least for large sources, was Title V. Title V establishes an operating permit requirement for large sources. These large sources are required to apply for a Title V operating permit. This operating permit includes all of the applicable requirements for that source, making it much easier to assess compliance. Title V does not add any new requirements, it simply rolls all existing requirements into one place.

Despite the fact that it does not add any new requirements, Title V is important for a number of reasons. It makes it much easier to assess compliance with Clean Air Act requirements. The five year permit term means that the regulators and sources must assess changes to regulations on a regular, if extended, basis. Title V also includes public notice and comment requirements which allow the public to review regulators’s determinations of applicable requirements. Title V also allows citizens to petition EPA to object to state regulators’ determinations.

On the whole, while not adding any new requirements, Title V is an important part of the Clean Air Act because it aggregates all requirements in one place and provides more public oversight of the regulation of the largest sources of air pollution.

Title VI

Most people born after 1990 wouldn’t even know that at one point the international community was concerned about ozone depletion and something called the “Ozone Hole.” The Ozone Layer is a portion of the upper atmosphere that contains ozone (O3). Unlike ground-level ozone which is a health hazard, this atmospheric ozone is vitally important in blocking ultraviolet (UV) radiation from the sun. In the 1970’s, data showed a small but steady decrease in the concentration of ozone in this layer of the stratosphere. In the 1980’s researchers discovered a large area over Antarctica where ozone levels were significantly depressed, a phenomenon referred to as the Ozone Hole.

Response to ozone depletion was tepid until the the discovery of the Ozone Hole. In 1987, representatives from 43 countries signed the Montreal Protocol. The Montreal Protocol froze production levels of chlorofluorocarbons (CFCs) and signatories agreed to reduce production levels by 50% by 1999. These requirements where later strengthened to include the phase-out of CFCs except in “essential” cases. CFCs have generally been replaced by less damaging hydrochlorofluorocarbons (HCFCs). Title VI of the Clean Air Act implements all of the requirements that the United States has signed onto and regulates ozone depleting substances (ODS).

As a result of the international implementation of the Montreal Protocol and subsequent agreements, the concern over the worsening of the Ozone Hole and ozone depletion has for the most part subsided. Given the long atmospheric life of CFCs, recovery will take decades.