National Air Quality Standards

The Clean Air Act of 1970 set National Ambient Air Quality Standards (NAAQS) across the United States. To further protect public health and welfare, environmental health, and preserve and protect air quality, the Prevention of Significant Deterioration (PSD) program was included in amendments to the Clean Air Act in 1977. 

          --> Link: More information on NAAQS

The goal of the PSD program is to protect public health and welfare from the adverse effects of increased air pollution. The PSD program works to achieve these aims while ensuring that economic growth occurs in harmony with the preservation of air quality. PSD provisions do not affect current air emissions, the provisions are designed to prevent significant deterioration from baseline air quality. 



Prevention of Significant Deterioration Classifications

The PSD program created three classifications:

three PSD classifications transparent v4



Prevention of Significant Deterioration Program Criteria

The PSD program contains specific criteria for determining which areas were federally-mandated as Class I by the Clean Air Act. Criteria was also set for areas that may be redesignated from Class II to Class I at a later date.

          --> Link: 40 CFR § 52.21


class 1 area criteria table transparent 2



A Venn diagram better shows what kinds of areas have been mandated as Class I areas and which areas may be redesignated as Class I areas.


Class I mandatory non venn diagram transparent



Federal Class I Areas

The Prevention of Significant Deterioration (PSD) program set all land in the United States as Class II and created 158 Federal Class I areas that met the outlined requirements. These Federal Class I areas are administered by the National Park Service, the U.S. Forest Service, and the U.S. Fish and Wildlife Service.

          --> Link: List of Federally-mandated Class I areas


Federal Class 1 map v4



Non-Federal Class I Areas

At this time, all state lands have remained as Class II. Five tribal reservations have been redesignated from Class II to Class I since 1977. For more information on these tribal redesignations, please see the information compiled on this page:

          --> Link: Forest County Potawatomi Community's Class I for Tribes



Redesignating an Area as a Different Class

The PSD program mandated certain federal Class I areas when initially passed by Congress. In addition, the PSD program allows for States and Tribal Nations to redesignate areas from Class II to Class I or Class III. The redesignation procedure is described in 40 C.F.R. § 52.21.

          --> Link: Bad River Class I Redesignation

PSD redesignating transparent v3



Prevention of Significant Deterioration Increments

Increments in Class II and Class I areas are triggered by submission of the first PSD preconstruction permit application from a major new or modified source (Clean Air Act § 163). PSD provisions allow a modest increase in Class II areas, while allowing a smaller increase in Class I areas. Class I ensures economic growth will occur in a manner consistent with the preservation of existing clean air resources.

National Ambient Air Quality Standards were set nationwide by the Clean Air Act in 1970. Class III, II, and I increments were set in the 1977 Amendments and are separate from the NAAQS. 


PSD Increments graphic transparent 2

Increments are a maximum allowable increase in the concentration of a pollutant above baseline. Baseline is the level of air quality before the first large air pollution source moves into the area. Increments only apply to the three pollutants designated in the PSD program - sulphur dioxide, nitrogen dioxide, and particulates.

     --> Link: Wisconsin DNR minor source baseline dates (Feb 2014)


WI set baselines transparent


Prevention of Significant Deterioration Allowable Increments

     --> Link: 40 CFR 52.21(c)

     --> Link: Wisconsin NR §405.05

increment table v3 transparent



Major Sources and Permits

     To obtain a permit, major new and modified sources must:

    • install "best available control technology"
    • analyze all impacts of the proposed source's emissions
      • together with emissions from "secondary growth" associated with the source
      • as well as emissions from already existing and permitted sources
    • not violate the National Ambient Air Quality Standards
    • not violate a PSD Increment
    • not have an adverse impact on a Class I area
    • may have to conduct preconstruction (and possibly post-construction) monitoring of air quality
    • must assure no adverse impact on the Class I area's visibility if there is potential to affect the visibility of a Class I area


     --> Link: U.S. EPA Region 5 Air Permits 



Class I Areas in the Western Great Lakes Region

For more information, click each Class I area on the map to go to each Class I area's website (you will be directed to the relevant land manager's website - either National Park Service, U.S. Forest Service, U.S. Fish and Wildlife Serive, or the Forest County Potawatomi Community).

Class I areas map western great lakes transparent






Bad River Air Quality Program 

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► Bad River's Treatment as a State (TAS) for air quality

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