Key Federal Laws

The Clean Air Act (CAA)

(as amended)

The CAA is a very complex statute codified at 42 U.S.C. 7401-7671q. The regulations issued by EPA to implement the Act contain thousands of pages and appear at 40 CFR 50-95. The origin of the CAA was the 1967 Air Quality Act. The 1967 Act established the concept of air quality control regions. Under the Act, the federal government developed air quality criteria for selected pollutants (e.g., SO2, NOx, and particulate matter) reflecting the latest scientific knowledge about air pollutants. The states, in turn, were to use the criteria as the basis for air quality standards for the designated regions.

The 1970 CAA amendments gave the federal government a more prominent role and established the basic regulatory structure that exists today. Under the 1970 amendments, the recently created Environmental Protection Agency (EPA) was directed to establish national ambient air quality standards (NAAQS) for the criteria pollutants. The NAAQS were to be used by states as the basis for individual source emission limitations in state implementation plans (SIPs). SIPs remain the principal CAA tool for control of criteria pollutant emissions from existing stationary sources. The 1970 amendments also contained provisions to regulate hazardous air pollutants and to establish a special set of standards for certain new sources (i.e., New Source Performance Standards).

The 1977 CAA amendments codified the prevention of significant deterioration (PSD) program (40 CFR 51.166, 52.21), added nonattainment provisions applicable to areas not meeting the NAAQS, expanded the program for hazardous air pollutants to include certain specific pollutants, and required EPA to review the air quality criteria and NAAQS every five years.

The 1990 CAA amendments added many substantive provisions to the CAA while leaving in place much of the pre-existing system of air pollution control. Specifically, the 1990 amendments contained new requirements for areas that do not meet ambient air quality standards, tightened mobile source emission standards, significantly altered the scheme for regulation of hazardous air pollutants, established a new operating permit program, and established new programs to control electric utility emissions of SO2 and NOx and substances that deplete stratospheric ozone. Because of the complexity of CAA programs, EPA has established an extensive network of CAA compliance assistance programs.

National Ambient Air Quality (Title I of the 1990 CAA Amendments)

EPA has issued NAAQS for six criteria pollutants: SO2, particulate matter, NO2, carbon monoxide, ozone, and lead (40 CFR 50). The NAAQS for particulate matter and ozone were revised in 1997.

SIPs are used by each state to implement, maintain, and enforce the NAAQS. Regions that have failed to meet the NAAQS for one or more criteria pollutants are designated as nonattainment areas. For ozone, carbon monoxide, and particulate matter nonattainment areas, the 1990 CAA Amendments set new, detailed requirements for controlling emissions based on the seriousness of the attainment problem in a specific area. For example, five categories of ozone nonattainment areas are established ranging from "marginal" to "extreme." Dates for achieving attainment are also provided. Various sanctions for not achieving attainment by the scheduled date are included in the amendments.

To meet SIP requirements, existing air pollution sources in nonattainment areas must install reasonably available control technology [CAA, §172(c)(1)].   New sources in both nonattainment and PSD areas must perform a New Source Review, described in detail below.

New major stationary sources or major modifications of existing major sources which would emit a nonattainment pollutant must obtain a nonattainment permit before construction begins. This permit will include requirements to: 1) offset projected emissions of the specific pollutants which do not meet the NAAQS with emission reductions of the pollutants at existing facilities, and 2) install pollution control technology to achieve the lowest achievable emission rate (40 CFR 51.165).

A "major" source is generally one with the potential to emit more than 100 tons per year (tpy) or more of a nonattainment pollutant. In ozone nonattainment areas, this level is reduced to 50 tpy (of ozone precursors VOCs or NOx) in serious areas, 25 tpy in severe areas, and 10 tpy in extreme ozone nonattainment areas. For serious carbon monoxide nonattainment areas, any source with the potential to emit 50 tpy or more would need a nonattainment permit. For serious particulate matter nonattainment areas, a major source is one with emissions of 70 tpy or more.

In a parallel track,  new sources in areas that attain the NAAQS must obtain a PSD preconstruction permit. The PSD permit includes a requirement to comply with ambient air quality levels and to install "best available control technology" (BACT) for criteria pollutants emitted in "significant" levels.   (Note that some states extend BACT coverage to air toxics as well.)

A "new" source for PSD purposes, is one of 28 listed sources in sec. 169 of the CAA with the potential to emit 100 tpy or more of any air pollutant subject to regulation under the CAA or any other source with the potential to emit 250 tpy of any air pollutant subject to regulation under the CAA [40 CFR 52.21(b)].

For both nonattainment and PSD new source review, a modified source is "any physical change in, or change in the method of operation of, a stationary source which increases the amount of any air pollutant emitted by such source or which results in the emission of any air pollutant not previously emitted" [CAA, sec. 111(a)(4)]. However, in its implementing regulations, EPA has limited application of PSD and nonattainment permit requirements to those major modifications that constitute a nonroutine physical or operational change and which result in a significant net increase in emissions. The term "significant" for nonattainment permits is defined at 40 CFR 51.165(a)(1)(x) and specifies 100 tpy for CO and 40 tpy for NOx, sulfur dioxide, and VOCs. The term "significant" for PSD permits is defined at 40 CFR 52.21(b)(23)(i). It is similar to the nonattainment definition except that additional chemicals are included.

In 1996 EPA proposed changes to existing requirements affecting new and modified sources in attainment and nonattainment areas (61 FR 38249). EPA expects to issue a final rule in December 1998.

As can be seen from the preceding text, the PSD and nonattainment regulations are quite complicated; the actual regulations, EPA interpretation and guidance documents, and relevant court decisions need to be closely studies for details that may be applicable to a particular fact situation.

NSPS (Title I of the 1990 CAA Amendments)

EPA has issued New Source Performance Standards for over 70 specific source categories. These source-based standards apply to new and modified facilities. Example source categories subject to NSPS are incinerators, sulfuric acid plants, petroleum refineries, lead smelters, and equipment leaks of VOCs in the synthetic organic chemicals manufacturing industry.  NSPS are incorporated into the facility's operating permit.

To date, NSPS pollutants are acid mist, carbon monoxide, particulate matter, fluorides, hydrogen sulfide in acid gas, lead, nitrogen oxides, sulfur oxides, total reduced sulfur, and VOCs.  This list reflects a compilation of the pollutants that EPA has included in the NSPS, and can be expanded with any new NSPS regulations adopted.

The NSPS set a minimum level of control for new and modified sources of air pollution in the 70+ source categories included at 40 CFR 60. More stringent control can be required by PSD and nonattainment permit requirements. Each individual new source performance standard defines what new sources are subject to the standard.

Reconstructed facilities are also subject to NSPS. The regulations at 40 CFR 60.15 set out what constitutes a reconstructed facility. Basically, reconstruction means the replacement of equipment and components to such an extent that the capital cost of the new equipment/components exceed 50% of the cost of a new facility.

The regulations at 40 CFR 60.14 set out what constitutes a modified facility for purposes of the NSPS. The requirements stem from sec. 111(a)(4) of the CAA which defines the term "modification" as "any physical change in, or change in the method of operation of, a stationary source which increases the amount of any air pollutant emitted by such source or which results in the emission of any air pollutant not previously emitted." Various EPA guidance documents, case-specific interpretations, and court decisions supplement the requirements in 40 CFR 60.14.

Mobile Sources and Clean Fuels (Title II of the 1990 CAA Amendments)

EPA regulates most mobile sources of air pollution (e.g., automobiles at 40 CFR 85-86, airplanes at 40 CFR 87, etc.) under Title II of the CAA. Performance standards issued by EPA limit the emissions of certain pollutants from these sources. Fuel-related requirements under Title II at 40 CFR 79-80 are designed to further reduce emissions from mobile sources.

Air Toxics (Hazardous Air Pollutants) (Title III of the 1990 CAA Amendments)

The 1990 CAA Amendments significantly changed the pre-existing system for control of hazardous air pollutants. The pre-1990 CAA approach required EPA to establish a list of hazardous air pollutants and impose health-based emission standards for each pollutant. Section 112(b) of the CAA identifies 189 Air Toxics (hazardous air pollutants), directs EPA to identify sources of the 189 pollutants, and establishes a ten year time period for EPA to issue technology-based emissions standards for each source category. Title III provides for a second phase under which EPA is to assess residual risk after the implementation of the first phase of standards and impose new standards, when appropriate, to protect public health.

Section 112(r) of the CAA also contains requirements that address accidental releases of hazardous substances from stationary sources that potentially can have serious adverse effects to human health or the environment. Facilities with more than a threshold quantity of regulated substances have a general duty to prevent the accidental release of the substances and to minimize the consequences of any such release. Owners of such facilities must prepare a risk management plan (40 CFR 68) to detect and prevent or minimize accidental release of the substances and to provide a prompt emergency response to any such release.

The Chemical Safety Information, Site Security and Fuels Relief Act (PL 106-40) of 1999 primarily concerns the public availability of the Off-site Consequence Analysis (OCA) sections of Risk Management Plans (RMPs) submitted by facilities under regulations implementing Section 112(r) of the Clean Air Act (CAA). The new law prohibits government officials from disclosing to the public the OCA sections of RMPs and other materials until at least August 5, 2000. However, the law does not prohibit facilities from sharing with the public the OCA sections of their RMPs, and it requires most facilities to provide the public with at least a summary of their OCA information by February 1, 2000.

Acid Deposition Control (Title IV of the 1990 CAA Amendments)

Title IV of the 1990 CAA Amendments established a new program to control emissions of SO2 and NOx, which are precursors of acid deposition (i.e., acid rain). The acid rain rules are found at 40 CFR 72-78. Title IV is designed to reduce electric utility emissions of SO2. Phase I of the program applies to the 110 electric power plants listed at 40 CFR 73.10. More stringent requirements apply for Phase II which will become effective January 1, 2000 and will extend coverage to an additional 700 plants. The result of these requirements is an anticipated reduction in electric utility emissions of SO2 by ten million tons per year from 1980 levels by the year 2010.  Title IV creates a system of SO2 emission allowances that can be freely traded. Each allowance entitles the holder to emit one ton of SO2.

Operating Permits (Title V of the 1990 CAA Amendments)

EPA’s operating permit rule (40 CFR 70) implements Title V of the 1990 CAA Amendments. Before passage of the 1990 amendments, the CAA was the only major regulatory statute implemented by EPA which did not have a permit program as the basic vehicle for applying source-specific control requirements at regulated facilities. The Title V requirements are generally modeled after the national pollution discharge elimination system permit program that has been part of the Clean Water Act since 1972 (33 U.S.C. 1342). The Title V operating permit requirements are primarily procedural and were not intended by Congress to create new substantive requirements.

The Title V requirements do not change the review process for new or modified sources of air pollutants. When applicable, the following air-related permits are still required: 1) state emission permits designed to ensure that new or modified sources of emissions will not violate a federal or state ambient air standard, 2) nonattainment permits (42 U.S.C. 7502), 3) PSD permits (42 U.S.C. 7475), and 4) permits to construct or modify sources of hazardous air pollutants (40 CFR 61.07).

Congress intended that the states administer the operating permit program. States retain the right to impose more stringent operating permit requirements than contained in 40 CFR Part 70, provided the Part 70 requirements are also met (42 U.S.C. 7416, 40 CFR 70.1).

The categories of air pollution sources subject to the operating permit rule requirements are set out in §502(a) of the CAA and 40 CFR 70.3. At a minimum, the following categories of sources will require an operating permit:
  • major sources as defined at 40 CFR 70.2
  • sources subject to a new source performance standard established under §111 of the CAA (the standards are set out at 40 CFR Part 60).
  • any source, including an area source subject to a standard or other requirement under §112 of the CAA relating to hazardous air pollutants
  • affected sources, i.e., sources (principally fossil-fired power plants) that are subject to emission reductions, requirements, or limitations under Title IV of the CAA relating to acid deposition control (CAA, §402).

Stratospheric Ozone Protection (Title VI of the 1990 CAA Amendments)

Title VI of the 1990 CAA Amendments addresses stratospheric ozone depletion. It provides for the phaseout of certain ozone depleting substances and reflects the Montreal Protocol on Substances that Deplete the Ozone Layer. Regulations implementing Title VI are in 40 CFR 82. Section 602 of the CAA identifies certain class I (e.g., chlorofluorocarbons) and class II (e.g., hydrochlorofluorocarbons) ozone depleting substances. The Protocol and sections 604 and 605 of the CAA impose limits on the production and consumption of class I and II substances according to specified schedules. Title VI and regulations issued thereunder also call for reduction in the use and emission of class I and II substances to the lowest achievable level [§608(a)(3), 40 CFR 82 Subpart F]; ban nonessential products containing class I substances or containing or manufactured with class II substances (40 CFR 82 Subpart C); contain requirements for the servicing of motor vehicle air conditioners (40 CFR 82 Subpart B); require warning statements on containers of, and products containing or manufactured with, class I or II substances (40 CFR 82 Subpart E); and promote the use of substitutes for ozone-depleting substances that reduce overall risks to human health and the environment (40 CFR 82 Subpart G).

Title VI also has some provisions covering global warming, which focus mostly on conducting studies.

Program office links:

Office of Air and Radiation

40 CFR 73 - Sulfur Dioxide Allowance System
40 CFR - Protection of Stratospheric Ozone 82

Related sites:
EPA's Plain English Guide to the Clean Air Act
List of Air Toxics


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