The purposes of this part are as follows: (1) to protect public health and welfare from any actual or potential adverse effect which in the Administrator's judgment may reasonably be anticipate (!1) to occur from air pollution or from exposures to pollutants in other media, which pollutants originate as emissions to the ambient air) (!2), notwithstanding attainment and maintenance of all national ambient air quality standards; (2) 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; (3) to insure that economic growth will occur in a manner consistent with the preservation of existing clean air resources; (4) to assure that emissions from any source in any State will not interfere with any portion of the applicable implementation plan to prevent significant deterioration of air quality for any other State; and (5) to assure that any decision to permit increased air pollution in any area to which this section applies is made only after careful evaluation of all the consequences of such a decision and after adequate procedural opportunities for informed public participation in the decisionmaking process.