In 1977, Congress amended the Clean Air Act (CAA or Act) to provide for a Prevention of Significant Deterioration (PSD) program. The PSD program protects air quality by requiring all major new and modified sources located in areas whose air quality has been designated under CAA Section 107 as either being in attainment of the National Ambient Air Quality Standards (NAAQS) or as unclassifiable to undergo a preconstruction review for each air pollutant regulated under the PSD program that the new major stationary source or major modification will emit or increase in significant amounts. Areas that are in attainment of the NAAQS are categorized as either “Class I”, “Class II,” or “Class III” which determines the increment of air quality deterioration allowed. Under the PSD program, all international parks, national wilderness areas and national memorial parks that exceed 5,000 acres, and of national parks that exceed 6,000 acres are designated as mandatory federal Class I areas in order to preserve, protect and enhance air quality. All other areas that attain the NAAQS are initially designated as Class II. Section 164 of the CAA, gives states and tribes the ability to request redesignation from Class II to Class I called “non-federal” Class I areas. Redesignation is one of the tools available to tribes (and states) under the CAA to afford special protection to air quality.