25 Pa. Code § 127.1
The purpose of this article is to regulate air contamination sources for the public welfare. Air quality shall be maintained at existing levels in areas where the existing ambient air quality is better than the applicable ambient air quality standards, and air quality shall be improved to achieve the applicable ambient air quality standards in areas where the existing air quality is worse than the applicable ambient air quality standards. In accordance with this purpose, this chapter is designed to insure that new sources conform to the applicable standards of this article and that they do not result in producing ambient air contaminant concentrations in excess of those specified in Chapter 131 (relating to ambient air quality standards). New sources shall control the emission of air pollutants to the maximum extent, consistent with the best available technology as determined by the Department as of the date of issuance of the plan approval for the new source.
25 Pa. Code § 127.1