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PSD - Prevention of Significant Deterioration


The program in its entirety is codified at 42 U.S.C. §§ 7470 - 7492 (CAA §§ 160 - 169B).

Implementing regulations for this provision are at 40 C.F.R. 51.166.

For EPA policy and guidance related to review of new air pollution sources, please visit EPA's New Source Review web page.

Goals and Class I Areas

The prevention of significant deterioration (PSD) title of the CAA is an important authority for protecting the resources of parks. One of its express purposes is "to preserve, protect, and enhance the air quality in national parks, national wilderness areas, national monuments, national seashores, and other areas of special national or regional natural, recreational, scenic, or historic value." PSD addresses resource protection through the establishment of ceilings on additional amounts of air pollution over base-line levels in "clean" air areas, the protection of the air quality-related values of certain special areas, and additional protection for the visibility values of certain special areas. The PSD title reserves an important resource protection role to the federal land manager, which the CAA defines as the secretary of the department with authority over the affected lands. For parklands, the secretary of the interior has delegated his authority as federal land manager to the assistant secretary for fish and wildlife and parks.

More specifically, the PSD title reflects Congress' judgment that, among the "clean" air regions of the country, certain areas-the "Class I" areas-deserve the highest level of air-quality protection. Congress designated (42 U.S.C. § 7472 )(CAA § 162) 158 areas as Class I areas, including national parks larger than 6,000 acres and national wilderness areas larger than 5,000 acres, in existence on August 7, 1977. These "mandatory" Class I areas may not be redesignated to a less protective classification. Forty-eight areas within the National Park System are designated Class I. (Large national parks and wilderness areas established since 1977, such as most park areas in Alaska, have not been designated subsequently as Class I.)

The PSD title also contains measures that can protect the remaining "clean" areas-the Class II areas. Furthermore, states and Indian governing bodies may redesignate (42 U.S.C. § 7474 (CAA § 164) Class II (and Class III) areas to Class I.

Preconstruction Permits, Increments and AQRVs

42 U.S.C. § 7475 (CAA § 165)

The principal mechanism of the CAA for implementing the special protection for clean air areas is the PSD preconstruction permit program. To obtain a permit, major new and modified sources proposing to locate in "clean" air areas 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. Get more information on cumulative analyses in PDF format (178 kb).
• not violate a national ambient air-quality standard.
• in most cases, not violate an "increment" as described below.
• not have an "adverse impact" on a Class I area; and ,
• generally have to conduct preconstruction and possibly post-construction monitoring of air quality and, in some cases, additional resources.

In addition, all major new and modified sources with the potential to affect the visibility of a "mandatory Class I" area must obtain a new source permit that assures no adverse impact on the Class I area's visibility, regardless of whether the source proposes to locate in a "clean" or "dirty" air area.

Since 1978, the National Park Service has reviewed many PSD permit applications. Often, the service's involvement has resulted in changes in the proposed permit, such as adoption of more efficient control technology, downsizing of the operation, selection of a new location, commitment for monitoring and study of park resources, and other changes that have helped to protect the potentially affected parks.

• For more information about the NPS's procedure for reviewing a proposed permit, visit our Permit Review web page.

Class I Increments and the Adverse Impact Test

In Class I areas, once baseline is triggered by submission of the first PSD preconstruction permit application from a major new or modified source, the PSD provisions (42 U.S.C. § 7473 (CAA § 163) allow only the smallest increment of certain pollutants-initially, only sulfur dioxide and particulate matter-to be added to the air. Actually, the CAA requires EPA to promulgate increments or equivalent protective measures for all pollutants that have national ambient air quality standards. As a result of litigation based on this requirement, EPA promulgated nitrogen oxide increments in 1988. After another round of litigation, the nitrogen oxide increment was remanded to EPA but left in place pending further review. EPA has recently announced a settlement agreement, including a schedule for responding to the remand.

Of special importance to many parks, the PSD title also establishes a site-specific resource test, known as the adverse impact test, to determine whether emissions from major new and modified sources will cause an "adverse impact" on the "air quality related values" of the Class I Area. "Air quality related values" include all values of an area dependent upon and affected by air quality, such as scenic, cultural, biological, and recreational resources, including visibility itself. In the case of a major new or modified source, the adverse impact test works as follows:

• If the federal land manager determines, and convinces the permitting authority, that the source will adversely affect the Class I area's resources-even though the source's emissions will not contribute to an increment violation-a "PSD permit" shall not be issued.
• If the federal land manager certifies that the source will not adversely affect the Class I area's resources-even though the source's emissions will contribute to an increment violation-the permitting authority may issue a "PSD permit."

The adverse impact test imposes an "affirmative responsibility" on the federal land manager "to protect the air quality related values (including visibility)" of Class I areas, and, as the Senate committee wrote,"[i]n the case of doubt, . . . [to] err on the side of protecting the air quality related values for future generations."
The National Park Service's current working definition of adverse impact under the CAA is any impact that:

• diminishes the area's national significance; and/or
• impairs the structure and functioning of ecosystems; and/or
• impairs the quality of the visitor experience.

EPA has further defined adverse impact on visibility to mean perceptible visibility changes that "interfere with the management, protection, preservation, or enjoyment of the visitor's visual experience."

Class II and III Areas

The Clean Air Act's concern for resource protection is not limited to Class I areas. Congress designated all other "clean" air regions of the country "Class II." In fact, most of the units of the National Park System are "Class II." Congress prohibited redesignation not only of statutory Class I areas to any other classification, but also of certain Class II areas to the dirtier Class III classification. These so-called Class II floor areas include the following areas when greater than 10,000 acres: national monuments, national primitive areas, national preserves, national recreation areas, national wild and scenic rivers, national wildlife refuges, national lakeshores and seashores, in existence on August 7, 1977 , as well as national parks and wilderness areas established since August 7, 1977 .
In Class II areas, the Class II increment ceilings on additional pollution over base-line concentrations allow for moderate development. Class II increments constitute an absolute ceiling on additional pollution in these areas, however, because Congress did not qualify the Class II increment with a variance procedure similar to the adverse impact test for Class I areas.

As part of the PSD permit application, major new and modified sources with the potential to affect a park service Class II area must analyze their impacts on the area's ambient air quality, climate and meteorology, terrain, soils and vegetation, and visibility. The Department of the Interior also has encouraged the park service to seek protection of "integral vistas" associated with Class II areas in individual permit and plan proceedings.

Although the act does not create as many resource protection tools for Class II areas as for Class I areas, it nevertheless creates opportunities. The park service can participate in State Implementation Plan proceedings, new source reviews, and other federal, state, and local activities that potentially affect the air quality of these areas. For example, the service can oppose sources that threaten park resources and values, seek more stringent control technology for sources of concern, and recommend special preconstruction and postconstruction monitoring if more information is needed. In proceedings concerning units of the National Park System, the land manager can invoke the strong language of the park system's Organic Act for protection of park purposes and values from adverse air pollution impacts, in addition to the clear mandate of the CAA. Furthermore, as appropriate, the land manager can undertake or encourage efforts to redesignate the area to Class I. (See discussion below on redesignation.)

At this time, there are no Class III areas. States or Indian governing bodies have the authority to redesignate to Class III any clean air area except a statutory Class I or Class II "floor" area. Class III designation could allow for substantial air pollution increases over base-line concentrations, subject-as with all increments-to the ceiling imposed by the national ambient air quality standards. The redesignation process itself, as well as subsequent new source reviews and implementation proceedings, provide opportunities to seek protection of park values.

updated on 11/02/2006  I   http://www.nature.nps.gov/air/Regs/psd.cfm   I  Email: Webmaster