Clean Air Act

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Clean Air Act

The Clean Air Act of 1970 is a U.S. federal law intended to reduce air pollution and protect air quality. The actwhich underwent major revisions in 1990 and 2003deals with ambient air pollution (that which is present in the open air) as well as source-specific air pollution (that which can be traced to identifiable sources, such as factories and automobiles). The Clean Air Act sets standards for air quality that limit the amount of various pollutants to specified levels. The Clean Air Act also sets deadlines for governments and industries to meet the standards. The federal Environmental Protection Agency (EPA) is ultimately responsible for establishing standards and enforcing the Clean Air Act, although much of the daily business of fighting air pollution takes place at the state and local levels.

The Clean Air Act affects American businesses in a number of ways. Polluting industries may be forced to control air pollution through end-of-pipe methods, which capture pollution that has already been created and remove it from the air. Or businesses may be required to implement preventative measures, which limit the quantity of pollutants produced in the course of their operations. The cost of compliance with Clean Air Act regulations can be high for companies but the cost to society of air pollution is also quite high. What is clear is that the Clean Air Act has been largely successful in reducing air pollution. According to a report by the National Center for Public Policy Research entitled Earth Day 2004 Fact Sheet, it has contributed to a reduction in total emissions of major air pollutants in the United States of 25 percent between 1970 and 2004, and this despite the fact that U.S. gross domestic product increased 42 percent during the same period.


The original version of the Clean Air Act, which was passed by the U.S. Congress in 1970, was fairly straightforward. It placed the Environmental Protection Agency in charge of monitoring and improving the nation's air quality. The EPA's powers under the act included establishing research programs, setting clean air standards, enforcing regulations, and providing technical and financial assistance to state and local government efforts toward reducing air pollution. The 1970 act also directed the EPA to establish National Ambient Air Quality Standards (NAAQS) to control the emission of a number of substances that threatened air quality. The NAAQS divided pollutants into two categories: primary pollutants, or those directly affecting human health; and secondary pollutants, or those indirectly affecting human welfare.

The Clean Air Act underwent significant changes and amendments in 1990. The amendments brought widespread reform to the government's methods of dealing with all kinds of air pollution. For example, the 1990 revisions specifically targeted acid rain, with the goal of reducing the emissions of sulfur dioxide and nitrogen oxides by half. The reforms also established new limits on ozonea prime contributor to smogin urban areas. Cities that failed to meet the regulations were divided into five different categories of non-attainment areas, with specific ozone emission goals for each category. Another change to the act addressed the depletion of the protective ozone layer in the earth's atmosphere. It mandated the gradual phasing out of chlorofluorocarbons (CFCs) and other ozone-depleting chemicals.

The Clean Air Act of 1990 also placed new regulations on automobile emissions. It set targets for reducing the emissions of hydrocarbons and nitrogen oxides by vehicles and assembly plants. It also required new automobiles to meet stricter pollution standards, whether by installing pollution control equipment like catalytic converters or by burning cleaner fuels. Another major provision of the Clean Air Act dealt with toxic air pollutants. The 1990 amendments expanded the number of regulated substances from 7 to 189, set safety standards for factories where toxic chemicals were used or emitted, and required polluters to install the best available pollution control equipment.

In early 2003 a new law to amend the Clean Air Act was introduced before the Senate. The proposed law, entitled the Clear Skies Act of 2003, is based on an initiative by the same name put forward by President George W. Bush. The Clear Skies Act is controversial because it proposes amending the Clean Air Act substantially, changing many of the mandated emission reduction goals and altering the way in which emission controls would be implemented. According to one of the bill's sponsors, Senator James Inhofe, Republican of Oklahoma, "Moving beyond the confusing, command-and-control mandates of the past, Clear Skies cap-and-trade system harnesses the power of technology and innovation to bring about significant reductions in harmful pollutants." As of early 2006, the Clean Air Act remains in committee, having failed to garner enough support to be passed into law.


In 1997, the EPA established strict new regulations to control the release of ozone and particulates, two dangerous pollutants that agency experts believed are responsible for killing thousands of Americans each year. In fact, Business Week reported that EPA estimates showed that the new rules could prevent 15,000 premature deaths, 350,000 cases of asthma, and one million cases of impaired lung function annually, in addition to saving billions of dollars in health care costs.

But business groups felt that the new regulations were too broad and would impose excessive compliance costs on industry. Associations representing a number of different industries joined in suing to overturn the EPA rules. They argued that the agency had overstepped its authority in imposing the restrictions under the Clean Air Act, and had thus infringed on the constitutional power of Congress to pass laws. The industry groups also argued that the EPA should be forced to consider the costs as well as the benefits of such actions.

The lawsuit, Browner v. American Trucking Associations, went before the U.S. Supreme Court in the fall of 2000. In arguments before the court, the EPA claimed that it was banned by a 20-year-old federal court ruling from considering costs when imposing new regulations. In 2001 the Supreme Court upheld this argument, ruling in favor of the EPA.

see also Environmental Law and Business


Bassett, Susan. "Clean Air Act Update." Pollution Engineering. July 2000.

"Earth Day 2004 Fact Sheet." The National Center for Public Policy Research. Available from Retrieved on 24 January 2006.

Hess, Glenn. "Supreme Court Examines Arguments Concerning Clean Air Act Regulations." Chemical Market Reporter. 13 November 2000.

Kilian, Michael. "Bush Administration Pushes Plan to Change Air Pollution Regulation." Chemical Market Reporter. Chicago Tribune, 27 January 2005.

Marriott, Betty Bowers. Environmental Impact Assessment: A Practical Guide. McGraw-Hill, 1997.

"Regulators: By Whose Authority?" Business Week. 16 October 2000.

Trzupek, Richard. Air Quality Compliance and Permitting Manual. McGraw-Hill Professional, 2002.

Varva, Bob. "The 1970 Clean Air Act Changes Rules on Fuels and the Environment." National Petroleum News. August 2000.

                               Hillstrom, Northern Lights

                                updated by Magee, ECDI

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Clean Air Act

Environmental Defense v. Duke Energy Corporation

The Clean Air Act (CAA), which is enforced by the Environmental Protection Agency (EPA), regulates the release of air pollutants. Since its enactment in 1963 the CAA has been amended by Congress several times to strengthen its regulatory powers. The regulation of power plant emissions has been a major component of EPA oversight because coal has been the fuel of choice for most power plants. Despite statutes and regulations that seek to define the scope of environmental oversight, energy producers sometimes run afoul and trigger legal controversies. Such was the case in Environmental Defense v. Duke Energy Corporation, __U.S.__, 127 S.Ct. 1423, __L.Ed.2d __ (2007), where the U.S. Supreme Court held that the EPA could interpret the word "modification" differently in two sets of air quality regulations. In addition, a power company seeking to force a uniform interpretation of the word was essentially challenging one of the regulations. This approach was not acceptable because challenges to regulations must be addressed within 60 days of the rulemaking in a specific circuit court of appeals.

Duke Energy Corporation operates 30 coal-fired power plants in North and South Carolina which provide power to over two million people. Beginning in 1988 Duke Energy started to modernize more than 24 of these unites. They were refurbished and the central sections of the generators were either rebuilt or replaced. The modernization was long overdue for some of the equipment, which had gone into operation in the 1940s. Between 1988 and 2000 the company updated the boilers to extend the life of the units and to allow them to run longer each day. The EPA filed a lawsuit against Duke Energy in 2000, alleging that the company had not obtained EPA permits and that the modernization program violated a 1977 amendment to the CAA known as the Prevention of Significant Deterioration or PSD. Under the PSD a permit is required before a "major emitting facility" can be constructed; modification of a facility was included in this requirement. Following the enactment of this amendment the EPA issued PSD regulations which limited the need for a review and permit to any "major modification." This was defined as a change in the method of operation that would result "in a significant net emissions increase of any pollutant subject to regulation under the Act." Complications arose because the CAA contained an earlier amendment entitled New Source Performance Standards or NSPS. Under NSPS regulations the word "modification" had a different meaning. A source would not need to use the best pollution-limiting technology if the modification would not increase the rate of discharge of pollutants measured in kilograms per hour.

Duke moved for summary judgment, contending that none of its projects were "major modifications" requiring a PSD permit because none increased hourly rates of emission under NSPS. The EPA and a group of environmental organizations that intervened in the lawsuit contended that the increased use of the units, which can more hours per day, contravened the language of the PSD regulations. The district court ruled in favor of Duke Energy and the case moved to the Fourth Circuit Court of Appeals. The appeals court upheld the lower court, finding that identical statutory definitions of the term "modification" in the NSPS and PSD provisions "mandated that this term be interpreted identically" in the regulations for these two provisions. Therefore, the PSD regulations must use an increase in the hourly rate of emissions as its guide for determining whether a permit is required.

The Supreme Court, in a unanimous decision, overruled the Fourth Circuit. Justice David Souter, writing for the Court, concluded that the appeals court's effort to harmonize the two statutes and sets of regulations and "trim the PSD regulations to match their different NSPS counterparts can only be seen as an implicit declaration that the PSD regulations were invalid as written." This approach was in error for several reasons. First, he pointed out that a given term in a statute may take on a different character when associated with "distinct statutory objects calling for different implementation strategies." Contrary to the appeals court, there was no "irrebuttable" presumption that the same defined term in different provisions of the same law must be interpreted identically. The PSD regulations use of the term "major modification" clearly was not defined to mean an increase in hourly emissions rate. On its face the PSD regulations did not specify a rate, "merely requiring a physical or operational change that would result in significant net emissions. Justice Souter held that the Fourth Circuit's equation of the NSPS and PSD regulations served as "an implicit invalidation" of the PSD regulations. This was incorrect because judicial review of CAA regulations is limited during enforcement proceedings when review could have been obtained by Duke Power in the Court of Appeals for the District of Columbia within 60 days of EPA rulemaking. Therefore, the case was remanded to the district court for further consideration.

Massachusetts v. Environmental Protection Agency (EPA)

The prospect that human activity has significantly contributed to an increase in "greenhouse gases," which, in turn, causes global warming, has suffered from less-than-convincing consensus over the years. It has only been since 2006–2007 that at least a clear majority of respected scientific opinions has so concluded, despite the existence of impressive data supporting that conclusion for at least two decades.

In Massachusetts v. Environmental Protection Agency (EPA), No. 05-1120, 549 U.S.___ (2007), the U.S. Supreme Court was asked to determine whether the U.S. Environmental Protection Agency (EPA) had the statutory authority to regulate greenhouse gas emissions from new motor vehicles; and if so, whether EPA's stated reasons for declining to act were consistent with the statute. In a narrow 5-4 landmark decision, the Court found that gases which cause global warming were pollutants under the federal Clean Air Act; that EPA did indeed have the statutory authority to regulate them; and that it had acted arbitrarily and capriciously in refusing to exercise that authority.

This long-winded controversy centered on Section 202(a)(1) of the Clean Air Act, specifically, 42 USC §7521(a)(1), which states in relevant part:

The [EPA] Administrator shall by regulation prescribe (and from time to time revise) in accordance with the provisions of this section, standards applicable to the emission of any air pollutant from any class or classes of new motor vehicles or new motor vehicle engines, which in his judgment cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare …

The Act defines air pollutants to include "any air pollution agent … including any physical, chemical … substance … emitted into … the ambient air." [§7602(g)].

In 1999, various environmental groups filed an administrative "rule-making" petition formally requesting that EPA establish standards for motor vehicle "greenhouse gas" emissions (primarily carbon dioxide and other heat-trapping gases). Four years later, in 2003, the EPA denied the administrative petition, stating that it lacked authority to regulate such gases. It argued, in part, that carbon dioxide and other greenhouse gases were naturally occurring substances in the atmosphere and therefore did not constitute "air pollutants" within the meaning of the Clean Air Act. Further, even if it did have authority, arguendo, it would discretionarily decline in favor of voluntary programs and further research. The EPA noted that a causal link between greenhouse gases and increased global surface temperatures had not been dispositively established. Therefore, such a piecemeal approach would conflict with the President's more comprehensive environmental package, which included non-regulatory private-sector voluntary reductions and technologically innovative research into other climate-change alternatives.

Next, the State of Massachusetts joined the original petitioners as an intervening party and sought review of EPA's administrative decision in the Court of Appeals for the D.C. Circuit. Although each of the judges wrote a separate opinion, the ultimate decision let stand the EPA's decision and denied appellate review. The U.S. Supreme Court granted review (certiorari ).

In response, the EPA, joined by ten intervening states and six trade associations, argued that the Supreme Court first needed to address whether the petitioners even had legal standing to invoke the Court's jurisdiction. The Court agreed. In order for the petitioners (at least one) to have standing, there needed to be a justiciable controversy under Art. III of the U.S. Constitution, which means that petitioners needed to show that they suffered particular injury (actual or imminent) because of EPA's actions (or failure to act). The Supreme Court found that the petitioners did have standing, particularly Massachusetts, as Congress had ordered EPA to protect Massachusetts and other states; and that EPA's refusal to regulate greenhouse gas emissions presented a risk of actual and imminent harm. This preliminary question being resolved in favor of petitioners, the Court went on to address the case on its merits.

The Court found that greenhouse gases fit well within the definition of "air pollutants" contemplated by the Clean Air Act. Therefore, EPA does have the authority to regulate them. Even though regulating motor vehicle emissions may not by itself reverse global warming, this does not mean that the Court does not have jurisdiction to decide whether EPA has a duty to act to slow or reduce it.

Next, the Court noted that under the Act's clear terms, EPA can decline to promulgate regulations only if it determines that greenhouse gases do not contribute to global climate change, or if it provides explanation as to why it cannot or will not exercise its discretion to determine whether such gases do contribute to climate change. If scientific uncertainty prevents EPA from making such a determination, it must state so. It had not. Nor did the Court find EPA's other arguments persuasive, for example, that regulation of motor vehicle carbon dioxide emissions would require it to tighten mileage standards, which was really the purview of the U.S. Department of Transportation. The Court held that even if there was overlap in responsibilities, EPA may not shirk its duty to protect the public health and welfare under the Clean Air Act. Having found EPA's responsive reasons less than acceptable, the Court held that EPA had acted arbitrarily, capriciously, or otherwise not in accordance with law [§7607(d)(9) of the Act]. Accordingly, the Court remanded the matter for EPA to specifically articulate plausible reasons for its action or inaction.

Justice Stevens delivered the opinion of the court, in which he was joined by Justices Kennedy, Souter, Ginsburg, and Breyer. Chief Justice Roberts filed a dissenting opinion, joined by Justices Scalia, Alito, and Thomas. The dissent addressed the justiciability issue, arguing that the Court used "the dire nature of global warming itself as a bootstrap for finding causation and redressability." Since domestic automobile emissions are but a miniscule part of global greenhouse gas emissions, linking those emissions to Massachusetts' alleged injury was "far too speculative to establish causation."

Justice Scalia also filed a separate dissenting opinion, joined by the same dissenting justices. Justice Scalia addressed the substantive merits of distinguishing air pollutants from air pollution agents. However, he ended his dissent by noting that this was a straightforward administrative-law case for which Congress had given broad agency discretion. No matter how important the issue of global warming, said his dissent, it was not incumbent upon the Supreme Court to substitute its own desired outcome for the judgment of the delegated agency (EPA).

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Clean Air Act (1963)

Craig Oren

Excerpt from the Clean Air Act

  1. to protect and enhance the quality of the Nation's air resources so as to promote the public health and welfare and the productive capacity of its population;
  2. to initiate and accelerate a national research and development program to achieve the prevention and control of air pollution;
  3. to provide technical and financial assistance to State and local governments in connection with the development and execution of their air pollution prevention and control programs; and
  4. to encourage and assist the development and operation of regional air pollution prevention and control programs.

The Clean Air Act (P.L. 88-206 77, Stat. 401) established a program to help clean up dirty air and to maintain clean air. Congress extended its efforts to remedy and prevent air pollution in the Clean Air Act Amendments of 1970, whose provisions form the basics of today's air pollution standards. Congress amended the 1963 act out of concern that, without stricter standards, the air quality in our nation's cities would never be improved to healthful levels. At the time there was also a great deal of public concern about air pollution. Senator Edmund Muskie, a prime sponsor of the 1970 amendments, stated: "Our responsibility is to establish what the public interest requires to protect the health of persons. This may mean that people and industries will be asked to do what seems to be impossible at the present time." President Richard Nixon also pushed for improvements to the Clean Air Act. In fact, the president and Senator Muskie competed to see who could offer a stricter version of the amendments. As a result, the 1970 amendments established stringent deadlines for the achievement of air quality standards, as well as deadlines for auto manufacturers to produce cars with dramatically reduced pollutants in their emissions.


Under the act, the Environmental Protection Agency (EPA) sets "national ambient air quality standards" (NAAQS). These standards limit the allowable concentrations of pollutants in the outdoor air. There are presently standards for carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter, and sulfur oxide. The EPA sets both primary and secondary ambient air quality standards; primary standards protect the public health with an adequate margin of safety, and secondary standards protect public welfare. Neither kind of standard can be based on cost considerations.

The act requires each state to submit a State Implementation Plan (SIP) showing how it will limit emissions from sources of air pollution. The state must demonstrate that its plan will result in attainment of the primary standards by a specific deadline, and of the secondary standards "as expeditiously as possible." Generally, a state may pick any mix of emission control measures that would result in attainment and maintenance on time. Each major source of air pollution receives a permit containing the measures that apply to it. States can, in general, choose to be stricter than the Clean Air Act.

Under the act, the federal government sets emission standards for categories of new motor vehicles. Congress has sometimes set these standards itself, and has sometimes directed the EPA to set them. (California has the authority to set its own standards and other states can adopt them rather than follow the federal standards.) These standards are based on the emission levels the EPA projects can be achieved by vehicle manufacturers after a period of lead time. In addition to standards for motor vehicles, the EPA sets performance standards for categories of new and modified stationary sources of pollutants, such as new power plants. These standards are based on assessments of what is technologically feasible using the best system of emissions reduction.

Each state's plan must also include a Prevention of Significant Deterioration (PSD) program to protect areas whose air quality is better than the levels of the NAAQS. A major stationary source can be constructed or modified in such an area only if the operator (a) installs the best available control technology to minimize pollutants, and (b) shows the source will not cause a violation of "increments" that limit increases in air pollution in clean air areas.

States must also impose requirements on the construction and modification of a major stationary source that would cause or contribute to a violation of the NAAQS. The new source must be subject to strict controls, and the new source's emissions must be offset by extra reductions at other sources.

Another provision of the act attempts to deal with the interstate transport of air pollution. For instance, the act requires power plants to reduce emissions of sulfates that can cause acid rain as well as reduced visibility and damage to human health. Each plant is assigned a set of allowances for sulfur dioxide. Plants that can reduce emissions at low cost can over control their emissions and sell excess allowances to plants that cannot reduce at low cost. In this way, the emission target can be met at the lowest possible cost.

The act also attempts to reduce emissions of air pollutants that may cause cancer or other life threatening diseases. The EPA sets standards that compel new and existing major sources of these pollutants to do the utmost to control their emissions. The EPA must set additional, stricter standards if a risk to public health remains.


In South Terminal v. EPA (1973), the U.S. Court of Appeals held that the constitutional basis for the act is Congress's power to regulate interstate commerce, because air pollution and some of its sources (like motor vehicles) move across state borders. Several important judicial decisions have interpreted the act:

  1. In Sierra Club v. Ruckelshaus (1972), the federal district court in the District of Columbia held that the EPA could not approve state plans unless those plans called for the protection of existing clean air from degradation. This led to the PSD program mentioned above.
  2. In Ethyl Corp. v. EPA (1976), the U.S. Court of Appeals for the District of Columbia Circuit held that the EPA could regulate a substance even though it could not be proved that the substance was harmful. The court said the EPA could proceed if it could show a significant risk of harm. The ruling in this case has been incorporated in the Clean Air Act.
  3. In Union Electric v. EPA (1976), the U.S. Supreme Court held that states may require air pollution sources to achieve tough emission limits, even if the technology does not presently exist to achieve those limits.
  4. In Whitman v. American Trucking Associations (2001), the Supreme Court held that the EPA may not consider costs in setting ambient air quality standards, and that the act's command that primary standards be set to protect public health with an adequate margin of safety gives the EPA sufficient direction in setting these standards.


In 1977 Congress passed a lengthy series of amendments that extended the original deadlines for areas to attain air quality standards but at the same time required more intensive efforts to attain those standards. The amendments also extended the deadlines for auto manufacturers to produce cleaner vehicles, and established the PSD program.

Congress passed an even longer series of amendments in 1990. These amendments again extended deadlines to attain air quality standards in exchange for greater efforts to attain those standards. The amendments further established the act's current programs to combat acid rain and hazardous air pollutants, and tightened the standards for new motor vehicles.


If a source does not obey the emission limits set in an approved SIP, then the state, the federal government, or citizens can enforce the limit. If a state does not establish an SIP, or refuses to carry it out, the federal government can establish and enforce its own plan for the state.

Since 1970 there have been drastic reductions in emissions of most air pollutants. These reductions are especially remarkable considering that the nation's national economic product, as well as the number of vehicle miles traveled in the nation, have doubled since that year. Although important air quality problems remain, an increasing number of areas have come into compliance with the EPA's ambient air quality standards. The EPA estimates that the monetary benefits of controlling air pollution have greatly outweighed its costs.

See also: National Emissions Standards Act; National Environmental Policy Act.


Doland, Edward F. Our Poisoned Sky. New York: Cobblehill Books, 1991.

Gay, Kathlyn. Air Pollution. New York: F. Watts, 1991.


Environmental Protection Association. <>.

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Clean Air Act


By: United States Code

Date: November 15, 1990

Source: U.S. Code. "Air Pollution Prevention and Control." Title 42, Chapter 85, Subchapter I, Part A, Section 7401.

About the Author: The U.S. Code is the set of general and permanent laws that govern the United States. The House of Representatives prepares the Code and revisions are published every six years. The Code is arranged into fifty titles. Title 42 deals with Public Health and Welfare. Chapter 85 describes the laws pertaining to air pollution.


Air pollution is the collective term for any substance that poses a risk to human health or to the environment and that can be found in the air. Common types of air pollutants include particulates, smog, and harmful gases. Examples of these harmful gases include nitrogen oxides and sulfur oxides, which contribute to acid rain; ozone, which contributes to smog; carbon monoxide, which is a poison; and carbon dioxide, which contributes to global warming. Chemicals like chlorofluorocarbons (CFCs) are also considered air pollutants. CFCs reduce the amount of ozone in the stratosphere, increasing the amount of harmful ultraviolet radiation from the Sun that reaches the surface of the Earth.

In 1955 the U.S. Congress passed its first legislation in response to evidence of increased air pollution. This Air Pollution Control Act of 1955 identified air pollution as a problem and launched a public awareness and research campaign into the situation.

The first Clean Air Act was passed in 1963. It set standards for emissions of air pollutants by power plants and steel mills. Amendments to the Act were passed in 1966, 1967, and 1969. These regulations set standards for moving sources of emissions, like cars, trucks, and trains, and established research grants for improving fuel efficiency.

By 1970, Congress realized that the Clean Air Act required major revision. The Clean Air Act of 1970 established much stricter emission controls than its predecessor. It was an extremely ambitious act and industries were economically challenged to comply with its standards. This act was revised throughout the 1970s, extending deadlines and rewriting standards.

After two decades, Congress again revisited the Clean Air Act. In 1990 it underwent a major revision, strengthening standards and improving regulations. The Act contains six subchapters. The first deals with the programs and activities governed by the Act. The second sets emission standards for moving sources. The third subchapter discusses general provisions of the Act, such as impact assessment, monitoring and auditing. The fourth and sixth subchapters are concerned with acid rain and stratospheric ozone depletion. The fifth subchapter deals with permitting for large stationary sources of air pollution. The first section of the Clean Air Act, included below, lays out the purpose of the Act.



7401. Congressional findings and declaration of purpose Sec. 101.

(a) The Congress finds—

  1. that the predominant part of the Nation's population is located in its rapidly expanding metropolitan and other urban areas, which generally cross the boundary lines of local jurisdictions and often extend into two or more States;
  2. that the growth in the amount and complexity of air pollution brought about by urbanization, industrial development, and the increasing use of motor vehicles, has resulted in mounting dangers to the public health and welfare, including injury to agricultural crops and livestock, damage to and the deterioration of property, and hazards to air and ground transportation;
  3. that air pollution prevention (that is, the reduction or elimination, through any measures, of the amount of pollutants produced or created at the source) and air pollution control at its source is the primary responsibility of States and local governments; and
  4. that Federal financial assistance and leadership is essential for the development of cooperative Federal, State, regional, and local programs to prevent and control air pollution.

(b) The purposes of this title are—

  1. to protect and enhance the quality of the Nation's air resources so as to promote the public health and welfare and the productive capacity of its population;
  2. to initiate and accelerate a national research and development program to achieve the prevention and control of air pollution;
  3. to provide technical and financial assistance to State and local governments in connection with the development and execution of their air pollution prevention and control programs; and
  4. to encourage and assist the development and operation of regional air pollution prevention and control programs.

(c) Pollution prevention A primary goal of this chapter is to encourage or otherwise promote reasonable Federal, State, and local governmental actions, consistent with the provisions of this Act, for pollution prevention. [42 U.S.C. 7401]


One of the most important features of the 1990 version of the Clean Air Act is that it gives states significant control over air pollution issues so that they can establish standards and deadlines for improvements locally. Although the Environmental Protection Agency (EPA) sets standards for how much air pollution can be released throughout the country, each state develops its own implementation plan, or SIP, which describes exactly how it will fulfill its obligations under the act.

The Clean Air Act also establishes a permit system for large sources of air pollution, such as factories and power plants. This system clarifies the source's requirements under the SIP and condenses the information on the amount and type of air pollution that the source releases. The source must pay a fee for the permit and the fee is used to fund air pollution control activities.

Another major impact of the 1990 Clean Air Act is that it institutes a market-based approach for cleaning up air pollution. The EPA establishes pollution allowances for different sources of air pollution. If a business produces less pollution than it is allowed, it can trade or sell its allowances to another company. On the other hand, if a company releases air pollutants in excess of its allowance, it must acquire allowances through purchase or trade. This program allows businesses to make their own decisions about how they will best solve their air pollution problems.

The impact that the Clean Air Act has had on the air quality in the United States is extremely large. The EPA has developed computer models that calculate the differences in economic conditions and human health in the United States given the policies enacted by the Clean Air Act and in the absence of those policies. If the Clean Air Act were not in place, the models predicted that by 1990, approximately 200,000 additional Americans would have died prematurely and millions would have suffered from respiratory and heart diseases. The economic benefits of the Clean Air Act during its first twenty years were estimated at approximately $22 trillion, compared to the costs of the pollution reductions during the same time period, which were $523 billion.

A 2004 report by the National Academy of Sciences confirmed the EPA's claims that the Clean Air Act has greatly improved air quality in the United States. The report shows that emissions standards for trucks and cars, as well as controls on the quality of fuel used in vehicles, have greatly reduced the pollutants released in exhaust. The concentrations of air pollutants in most urban areas of the country have also decreased greatly. In particular, the deposition of sulfur through acid rain in the Eastern United States has been greatly reduced. The report also documents the economic benefits imparted by the Clean Air Act.



Committee on Air Quality Management in the United States, National Research Council. Air Quality Management in the United States. Washington D.C.: National Academies Press, 2004.


Lemonick, Michael D. "Forecast: Clearer Skies." Time (November 5, 1990).

Web sites

Fleming, James R., and Bethany R. Knorr "Legislation: A Look at U.S. Air Pollution Laws and Their Amendments." American Meteorological Society. 〈〉 (accessed March 6, 2006).

"The Plain English Guide to the Clean Air Act." U.S. Environmental Protection Agency, April 1993. 〈〉 (accessed March 6, 2006).

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Since the time of the Industrial Revolution, air pollution has been a major public health problem. In 1948, in Donora, Pennsylvania, an air pollution episode resulted in the deaths of nineteen people in a community of 14,000; 43 percent of the population were adversely effected. The cause was industrial emissions of combustion products combined with a thermal inversion. Today, air pollution still causes extensive rates of morbidity and mortality, and it poses a particular risk for children and those with chronic lung disease. Air pollution is a complex mixture of substances discharged into the air in a myriad of ways. Incinerators and combustion sources, including motor vehicles, emit large quantities of carbon dioxide, carbon monoxide, nitrous oxides, and sulfur dioxide; as well as more complex combustion by-products such as polycyclic aromatic hydrocarbons (PAHs), dioxins, furans, and benzo[a]pyrene. Feedstock materials (e.g., wastes that are included in incineration) that do not burn, such as cadmium, lead, chromium, mercury, and other metals also contribute to air pollution. Toxic-air contaminants may be emitted as products of incomplete combustion or in consequence of their manufacture, processing, use, or disposal.

In 1970, Senator Edmund Muskie led the effort to enact the Clean Air Act (CAA). It was a very ambitious statute in scope, technical detail, and in terms of precise timetables for compliance. Amendments in 1977 set new goals for attaining CAA standards, which had not been met in many parts of the United States. Amendments enacted in 1990 were directed to a number of areas that had not previously been addressed, including acid rain, ground-level ozone, stratospheric ozone depletion (by implementing the Montreal Protocol), and air toxics (control of toxic contaminants in air).


The CAA act established six "priority air pollutants": ozone, sulfur dioxide, respirable particulate matter, nitrogen dioxide (NO2), carbon monoxide (CO), and lead. Priority air pollutants are regulated by the Environmental Protection Agency (EPA) strictly on a public health basis, with an adequate margin of safety to protect the population and special attention given to protection of vulnerable populations. Regulations for priority air pollutants are called National Ambient Air Quality Standards (NAAQS). Initially, the EPA was to adopt standards for the priority pollutants within ninety days of enactment of the CAA. The CAA also directed the states to develop state implementation plans (SIPs) that would assure that the NAAQS would be met within those states within nine months of issuance of NAAQS. Automobile manufacturers were given a five to six year deadline to achieve 90 percent reductions in emissions of CO, hydrocarbons, and nitrogen oxides (NOx).

The CAA led eventually to the phaseout of leaded gasoline in the United States, which in turn resulted in the lowering of blood-lead levels across the nation. The act also succeeded in attaining large reductions in sulfur dioxide and carbon monoxide release levels in nearly every area of the country. An innovative pollution trading program for sulfur dioxides has played an important role in reducing acid rain and in creating new mechanisms for environmental protection.

More challenging have been efforts to reduce pollution from two sectors: motor vehicles (cars and trucks) and coal-fired utilities. Difficulties in these areas have been compounded by Congessionally mandated delays in evaluation and tightening of fuel economy standards, the increased demand for energy in a growing economy, and the increased numbers of vehicle miles driven by an expanding population. These pressures have in turn created pressures to change the standards for priority pollutants to include the consideration of costs as well as public health benefits.


Hazardous air pollutants (HAPs) developed a higher public profile in 1985, due to the catastrophic release of methyl isocyanate (MIC) at a pesticide production facility in Bhopal, India. Prior to 1990, HAPs were regulated based on complex risk determinations, and standards had been promulgated for only six of them. Frustrated by the slow progress, Congress, in 1990, directed the EPA to establish standards for nearly two hundred HAPs, listed by name in the statute. These standards are called the National Emissions Standards for Hazardous Air Pollutants (NESHAPs). Congress directed the EPA to establish these standards based on the maximum achievable control technology (MACT). This strategy has resulted in a 90 percent decrease in emissions of toxic air contaminants from regulated industry. In a later phase, the EPA must conduct "residual risk" analyses and tighten the MACT standards if they provide inadequate in protecting the public health. It remains to be seen whether this very complex risk analysis will be successful. Congress directed two studies that are to direct the EPA in the methodology for this effort.

Lynn R. Goldman

(see also: Acid Rain; Ambient Air Quality [Air Pollution]; Carbon Monoxide; Emissions Trading; Hazardous Air Pollutants )


Committee of the Environmental and Occupational Health Assembly of the American Thoracic Society (1996). "Health Effects of Outdoor Air Pollution. State of the Art." American Journal of Respiratory and Critical Care Medicine 153:350; 477498.

National Research Council (1994). Science and Judgment in Risk Assessment. Washington, DC: National Academy Press.

Presidential/Congressional Commission on Risk Assessment and Risk Management (1997) Framework for Environmental Health Risk Management. Washington, DC.

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CLEAN AIR ACT. In 1990, Congress passed substantial amendments to the Clean Air Act of 1970, strengthening the act in a number of ways. Title I imposed new regulations limiting industrial emissions of ozone, carbon monoxide, particulates, nitrogen dioxide, sulfur oxides, and lead. Title II required new emission standards for automobiles and other mobile sources and created a clean-fuel program. Title III substantially limited the emission of hazardous air pollutants, while Title IV established a program to reduce sulfur dioxide emissions from power plants. Title V created an operating permit program for major sources of air pollution that was similar to permit programs found in other major environmental statutes. Title VI implemented the provisions in the Montreal Protocol, an international agreement to halt the destruction of the ozone, by banning the emission of certain chemicals. Finally, Title VII added new enforcement provisions, making it easier to punish violators and substantially increasing both civil and criminal penalties for violations of the act.

Supporters of stronger air pollution controls had fought for over a decade to enact many of these provisions, and they succeeded in 1990 only because of important changes in the political landscape. To begin with, public concern over air pollution had grown due to increased awareness about the effects of acid rain and because of startling revelations about the growing hole in the ozone layer. This concern translated into greater support in Congress and in the administration. In particular, President George H. W. Bush, unlike his predecessor, favored modest strengthening of certain environmental laws, including the Clean Air Act. In the Senate, Democrat George Mitchell of Maine, a clean-air proponent, became majority leader in 1989, replacing Democratic Senator Robert Byrd of West Virginia, who had worked for years to protect the coal mining industry in his state by blocking air pollution legislation. In the House, Democratic Representative Harry Waxman of California used his positionas chair of the Subcommittee on Health and the Environment to support the amendments. Meanwhile, environmental organizations united to form the National Clean Air Coalition, effectively counteracting the influence of the industrial lobby's Clean Air Working Group, even though environmentalists played little role in drafting the amendments. Ultimately, the House voted 401–25 in support of the amendments, the Senate passed the amendments 89–10, and President Bush signed the new clean-air legislation into law on 15 November 1990.

During the 1990s, two forces acted to shape the way the act affected American industry and the environment. First, during the mid-1990s, antienvironmental rhetoric and failed legislative attacks by a new, conservative-led Congress intimidated the federal Environmental Protection Agency (EPA) from implementing and enforcing the act as aggressively as the law required. Second, and more generally, the 1990 amendments preserved the clumsy scheme of federalism, where by the EPA oversaw state implementation plans. In theory, if a state failed to meet the standards set by federal regulation, the EPA had the authority to run the clean-air program within the state. In practice, however, the EPA had neither the resources nor the political support to do this. Despite the strong language of the 1990 amendments, and marked improvements in the national air quality, by the end of the millennium many believed American skies, while cleaner, were not clean enough.


Bryner, Gary C. Blue Skies, Green Politics: The Clean Air Act of 1990 and Its Implementation. 2d ed. Washington, D.C.: Congressional Quarterly Press, 1995.

Reitze, Arnold W. "The Legislative History of U.S. Air Pollution Control." Houston Law Review 36 (1999): 696–702.

Shannon C.Petersen

See alsoAcid Rain ; Air Pollution ; Auto Emission Testing and Standards ; Environmental Protection Agency .

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Clean Air Act

The 1970 Clean Air Act (CAA), significantly amended in 1977 and again in 1990, regulates air pollution emissions from "stationary" sources (e.g., factories, smokestacks, etc.), mobile sources (e.g., motor vehicles), and certain "indirect" sources (e.g., highways, malls, parking lots, etc., that attract mobile sources to the location). Specified "criteria" pollutants such as sulfur dioxide, nitrogen oxide, carbon monoxide, particulates (i.e., soot, fly ash, etc.), and lead are directly regulated, as are "hazardous" air pollutants that the EPA determines are likely to cause death or serious physical injuries. Congress listed some 189 hazardous air pollutants in its 1990 amendments to the original law. Many of these hazardous air pollutants are fairly common chemicals, such as benzene, dry-cleaning solvents, and others that pose scientifically verifiable health dangers. Although it has long been a criteria pollutant, lead is now known to be especially dangerous to human health. The 1990 amendments require further reductions in the criteria oxides that cause smog and acid rain.

Permitted sources have monitoring and reporting requirements. Permitting decisions are based, in part, on whether the location of a stationary source emitting a particular pollutant is in an "attainment area" for that pollutant (i.e., the local pollution generated by that pollutant does not exceed the specified threshold). Conversely, the area may be regarded as "nonattainment" in terms of that pollutant and the applicable standard (i.e., the threshold is exceeded), in which case allowable emissions will be severely curtailed. Mobile source emissions are regulated in the main by the EPA's establishment of specific emission standards for several classifications of vehicles; these are imposed on manufacturers. The 1990 amendments planned the development of "clean fuel" vehicles using hybrid or low polluting fuels and, especially for notoriously dirty urban buses, clean fuel fleets. Vehicle fuel is also regulated in regard to its constituents, with limitations imposed on gasoline sold in ozone or carbon monoxide nonattainment areas. After 1995, leaded gasoline was absolutely barred from commerce.

States exercise responsibility primarily by the formulation of State Implementation Plans (SIPs), which are subject to EPA approval. If a SIP is unavailable or ineffectively carried out by the state, the EPA enforces the act. Citizen suits are also permitted, whereby private citizens, subject to notice requirements, have the authority to act as private attorney generals in seeking judicial enforcement. They may not, however, recover damages.

see also Air Pollution; Dry Cleaning; Electric Power; Laws and Regulations, United States; Toxic Release Inventory; Vehicular Pollution.

Internet Resource

U.S. Environmental Protection Agency. "The Plain English Guide to the Clean Air Act." Available from

Kevin Anthony Reilly