National Ambient Air Quality Standards

National Ambient Air Quality Standards in the United States

National Ambient Air Quality Standards

(NAAQSs) in Environmental Law

Limits set by the Environmental Protection Agency (EPA) for air pollutants it believes may endanger public health (primary standards) or welfare (secondary standards). The standards apply to ambient air, not indoor air. They are stated as maximum permissible concentrations in outdoor air.

For many years, the air pollutants regulated by the National Ambient Air Quality Standards have been these: nitrogen oxides, carbon monoxide, sulfur dioxide, ozone, small particulates (called PM10), and lead. The EPA may revise the list as necessary. Hazardous air pollutants and air toxics are not subject to these standards but are regulated separately, under the National Emission Standards for Hazardous Air Pollutants.

Steps in Standard Setting

The process of regulating air pollutants under the NAAQSs begins with listing. In order to list a substance, the EPA must determine that it is an air pollutant, that it is emitted from numerous or different types of sources, and that the emissions may endanger public health or welfare. From the EPA’s point of view, an air pollutant may be any chemical, physical, biological, or radioactive substance that enters the air. The EPA’s definition does not include ozone, since ozone is not directly emitted. Instead it includes the precursors of ozone, such as volatile organic compounds and nitrogen oxides, which combine under certain conditions to form ozone. The National Ambient Air Quality Standards focus on the substances that are common, and these substances are commonly emitted from factories and businesses as well as motor vehicles.

Once an air pollutant has been listed, the EPA must establish limits in terms of yearly average and maximum permissible concentration within twelve months. Air pollutants regulated under the NAAQSs are often called criteria pollutants because standards exist for them. Primary standards address the health concerns created by the pollutant, while the secondary standards deal with public welfare. Examples of issues the secondary standards confront are effects of the pollutant on wildlife, soils, weather, personal comfort, and economic values. Historically, the limits specified in the primary standards have been the same as those in the secondary standards for most pollutants. Review of the standards is required every five years.

The Effects of the Standards

The National Ambient Air Quality Standards determine the acceptable quality of air throughout the United States. Once a standard is set or revised, each state must revise its law to ensure compliance with the standard [see state implementation plan].

Air quality impacts not only human health, but also economic development. Industrial growth may be severely restricted by programs designed to improve air quality within an area that has not met the NAAQSs, and governmental control over businesses tightens dramatically as noncompliance worsens. See also New Source Performance Standards; New Source Review; nonattainment areas; Prevention of Significant Deterioration.
Based on “Environment and the Law. A Dictionary”.

The Core of the Program: National Ambient Air Quality Standards in Environmental Law

With the 1970 amendments, basic assumptions in the law were changed, and the Clean Air Act came into its own. It had become clear that the states would not regulate air pollution voluntarily. Congress, acknowledging that a stronger federal role was necessary, gave the job to the EPA and required that the agency develop National Ambient Air Quality Standards (NAAQSs) for certain pollutants. This time the standards were mandatory.

Ambient air was not defined in the Clean Air Act, but the EPA defined it in its regulations as any air outside buildings that is generally accessible to the public. The Natural Resources Defense Council v. Train case upheld the agency’s definition.

The act requires that the EPA set two types of standards for ambient air quality: primary standards, designed to protect human health (with an ample margin of safety); and secondary standards, designed to protect public welfare. The standards are to be reviewed every four years and modified as necessary. Pollutants regulated initially included carbon monoxide, nitrogen dioxide [see nitrogen oxides], particulates, ozone, sulfur dioxide, lead, and hydrocarbons, although hydrocarbons are no longer part of the standards. Most of the secondary standards are identical to the primary ones.

This time states did not get to choose whether they would go along with the new federal limits. They were required to designate air quality control regions within their states and submit a state implementation plan (SIP) to the EPA showing how the state would achieve the National Ambient Air Quality Standards.

If, as has often been the case, an air quality control region cannot achieve all of the standards, it is declared nonattainment for the pollutant it has not controlled. At that point, the state must either demonstrate that its implementation plan will bring the area into attainment or revise its plan. If the EPA believes the plan is inadequate, it may, at any time, require a revision. This required revision is described as a SIP call. Plans must also be amended whenever the statute requires it.

Congress included a deadline for meeting the NAAQSs in the 1970 act, but for the most part, the standards were not met. The 1977 revisions extended the compliance deadline but gave the EPA no discretion to extend it further. Still, over seventy cities missed the 1987 deadline for compliance. So when it was again time to review the act in 1990, Congress took its task very seriously.

Regulating Existing Sources of Air Pollution

State implementation plans include several methods of air pollution control: technology changes, end of process control equipment, and restrictions on new sources. Most of the regulations are implemented through permitting. Air pollution standards are often technology based, with baffling names such as “best available control technology” and “lowest achievable emission rate.”

Existing major stationary sources of air pollution must meet reasonably available control technology. The traditional manner of reducing pollutants at an existing facility is retrofitting, which means improving existing technology. Often it simply means adding control equipment to the end of the process, such as adding an incinerator to burn volatile components of a discharge.

Regulating New Sources

Congress established several programs in the Clean Air Act to control sources of air pollution: New Source Performance Standards, Prevention of Significant Deterioration, and nonattainment permitting. All of these programs focus on major stationary sources. Generally, a major source is one capable of emitting 100 tons or more per year of a regulated pollutant. A new source may be a completely new construction or a major modification of an existing source.

The issue of when a change to an existing facility becomes subject to permitting was discussed in the Wisconsin Electric Power Co. v. Reilly case (generally called the WEPCo). In that case, the company had begun a massive reconstruction of its plant. The EPA determined that the changes were significant enough to require regulation under the new source provisions; the company argued that the construction was only a routine replacement of equipment and therefore a New Source Review should not be required. The case had important implications for utilities, but other industries also watched with interest.

The court upheld the EPA’s right to consider the work a major modification but did not agree with its manner of calculating the potential to emit. As a result of the case, the EPA wrote regulations to clarify the criteria for New Source Review, and its position is no longer as harsh as its original determination.

New Source Performance Standards

Certain businesses, including most industrial processes, have so much potential to release air pollutants that limits on their emissions are stated in federal regulations. New companies falling within one of these categories must meet these standards if they begin construction after the date the regulations are proposed. So far, the EPA has listed sixty-one such categories and created regulations for them. Examples include portland cement plants, municipal waste combustors, incinerators, copper smelters, steel plants, glass manufacturing plants, and industrial surface coating.

Certain businesses, including most industrial processes, have so much potential to release air pollutants that limits on their emissions are stated in federal regulations. New companies falling within one of these categories must meet these standards if they begin construction after the date the regulations are proposed. So far, the EPA has listed sixty-one such categories and created regulations for them. Examples include portland cement plants, municipal waste combustors, incinerators, copper smelters, steel plants, glass manufacturing plants, and industrial surface coating.

New Source Review in Attainment Regions

Even if the operation isn’t listed within the established categories, new major sources (or modifications of existing sources) must go through a review and permitting process. The stringency of permit requirements will depend on whether the area is an attainment or nonattainment region.

Prevention of Significant Deterioration

The Clean Air Act regulates maintenance of air quality through the Prevention of Significant Deterioration (PSD) provisions. Once an air quality region meets the standards, the state is required to maintain them.

Under this part of the law, each air quality region is designated as a Class I, II, or III area, and the class determines how much deterioration is allowed. (This does not mean that the state can allow the region to become nonattainment.) Class I areas are national parks. For the most part the rest of the nation is Class II, which means that a small amount of degradation is permitted as long as the NAAQSs are met. At this time, there are no Class III areas.

New source review in an attainment area includes obtaining a permit if the operation could discharge 250 tons per year of any regulated pollutant or 100 tons per year if the source fits within certain categories. Major modifications or reconstruction of existing facilities are also subject to the program. New sources in attainment regions must use best available control technology (BACT). The states, with guidance from the EPA, determine what is best, taking cost into consideration.

Nonattainment Permits

If a new source will be located in a nonattainment area [see nonattainment areas], the applicable technology is called the lowest achievable emission rate (LAER). Because the area already has a problem, smaller sources are considered major and subject to permitting. Sources that could discharge 10 tons per year of the pollutant in question or 100 tons per year of any regulated pollutant fall into the major category in nonattainment areas. For example, if the region is nonattainment for particulates only and the source can emit 10 tons or more of particulates per year, it must have a permit; but if it can release 10 tons or more of sulfur dioxide and nothing else, it will not be considered a major source.

Offsets and Bubbles

In nonattainment regions, the state may require the new source to obtain reductions from other plants in the area to offset the additional emissions it will contribute. If the new source itself has other plants in the area, it is possible for it to achieve this goal itself by shutting down operations, changing control equipment, or installing other technology at one of its own plants. Otherwise, the permit hopeful may have to purchase credits or cooperate with other sources.

When a new source wants to build in a nonattainment area, it is sometimes required to obtain reductions from existing sources that exceed the amount of pollutant it will emit. The excess is called an offset. For example, if a company wants to build and will have the capacity to emit 10 tons of sulfur dioxide in a nonattainment region for sulfur dioxide, it may be required to get another source to reduce the same emissions by 11 tons. The ratio will be greater in areas that have bigger problems. The purpose of these offsets is to improve air quality rather than simply maintaining the status quo.

An offset applies to a reduction at a different facility, but a bubble involves a single facility or complex at which adjustments are made from more than one emission source within a company in order to bring the entire business into compliance. Bubbles were controversial when finally sanctioned by the EPA. Allowing a source to shift processes around or control one emission point tightly so more of the same pollutant can be allowed to escape from another was determined to be permissible, but not everyone agreed.

Chevron U.S.A. v. Natural Resources Defense Council was the case that finally determined that the EPA could allow bubbles. The court decided the statute gave a lot of discretion to the EPA to establish permits and get the nation into compliance with the Clean Air Act. How the agency accomplished this, the court stated, was a matter of policy

Mobile Sources

The 1970 Clean Air Act introduced control of vehicular pollution. Design of vehicles was the primary focus in the beginning; Congress required and the EPA implemented changes in fuel usage, emission controls, and reduction of hydrocarbons and carbon monoxide. As in many environmental provisions, availability of technology was not considered, so vehicle manufacturers were forced to create the methods of control.

Hazardous Air Pollutants or Air Toxics

In addition to more common pollutants, the Clean Air Act also addressed hazardous air pollutants. The regulatory program was designated the National Emission Standards for Hazardous Air Pollutants, and the EPA ion. By 1990, only a few had been listed: vinyl chloride, benzene, asbestos, coke oven emissions, beryllium, mercury, inorganic arsenic, and radionuclides. Congress changed the program in 1990 to list 189 substances as air toxics and bring them under the regulations. See Clean Air Act Amendments of 1990.
Based on “Environment and the Law. A Dictionary”.

National Ambient Air Quality Standards: Open and Free Legal Research of US Law

Federal Primary Materials

The U.S. federal government system consists of executive, legislative, and judicial branches, each of which creates information that can be the subject of legal research about National Ambient Air Quality Standards. This part provides references, in relation to National Ambient Air Quality Standards, to the legislative process, the federal judiciary, and the primary sources of federal law (cases, statutes, and regulations).

Federal primary materials about National Ambient Air Quality Standards by content types:

Laws and Regulations

US Constitution
Federal Statutory Codes and Legislation

Federal Case Law and Court Materials

U.S. Courts of Appeals
United States courts of appeals, inclouding bankruptcy courts and bankcruptcy appellate panels:

Federal Administrative Materials and Resources

Presidential Materials

Materials that emanate from the President’s lawmaking function include executive orders for officers in departments and agencies and proclamations for announcing ceremonial or commemorative policies. Presidential materials available include:

Executive Materials

Federal Legislative History Materials

Legislative history traces the legislative process of a particular bill (about National Ambient Air Quality Standards and other subjects) for the main purpose of determining the legislators’ intent behind the enactment of a law to explain or clarify ambiguities in the language or the perceived meaning of that law (about National Ambient Air Quality Standards or other topics), or locating the current status of a bill and monitoring its progress.

State Administrative Materials and Resources

State regulations are rules and procedures promulgated by state agencies (which may apply to National Ambient Air Quality Standards and other topics); they are a binding source of law. In addition to promulgating regulations, state administrative boards and agencies often have judicial or quasi-judicial authority and may issue administrative decisions affecting National Ambient Air Quality Standards. Finding these decisions can be challenging. In many cases, researchers about National Ambient Air Quality Standards should check state agency web sites for their regulations, decisions, forms, and other information of interest.

State rules and regulations are found in codes of regulations and administrative codes (official compilation of all rules and regulations, organized by subject matter). Search here:

State opinions of the Attorney General (official written advisory opinions on issues of state law related to National Ambient Air Quality Standards when formerly requested by a designated government officer):

Tools and Forms

Law in Other Regions

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