Prevention of Significant Deterioration (PSD) Program

The PSD sections of the Clean Air Act require a permit program for certain new or modified sources of air pollution. One primary purpose of the PSD process is to aid in the protection and enhancement of air quality in national wilderness areas and other locations of scenic, recreational, historic, or natural value. Before the construction of certain new air pollution sources is approved, the applicants must receive a PSD permit from the appropriate air regulatory agency. The Forest Service manager must make three decisions:

1. What are the sensitive air pollution receptors within the wilderness that need protection?
2. What are the concern thresholds for these receptors?
3. Will the proposed facility cause or contribute to pollutant concentrations or atmospheric deposition within the wilderness that will cause the thresholds to be exceeded?

The first two decisions are land management issues based upon the management goals for the wilderness in question. The third is a technical question analyzed by models combining proposed emissions, background levels of pollutants and the sensitivity of visibility and resources to the pollutants.

Close coordination between the Forest Service and the appropriate air regulatory agency is essential in the PSD process. The Forest Service makes a determination of whether a proposed project will adversely impact Forest lands. The air regulatory agency then makes a decision to grant or deny the permit The Forest Service, along with the National Park Service (NPS), and the U.S. Fish and Wildlife Service (FWS), formed The Federal Land Managers' Air Quality Related Values Work Group (FLAG) (link to http://www.nature.nps.gov/air/Permits/flag/) in order to evaluate air pollution effects on air quality related values (AQRVs) and to provide State permitting authorities and potential permit applicants consistent guidance regarding assessment of new and existing source impacts on AQRVs.

Learn More

• Alphabetical List of class I wildernesses
• Map of class I wilderness