42 U.S.C. § 7472 — Initial classifications

(a) Areas designated as class I: When this part of the law was enacted, the following became "class I" areas and cannot be redesignated (changed to a different class): (1) international parks; (2) national wilderness areas bigger than 5,000 acres; (3) national memorial parks bigger than 5,000 acres; and (4) national parks bigger than 6,000 acres that existed as of August 7, 1977. Any area already redesignated as class I under older regulations (before August 7, 1977) is also class I, but those areas can be redesignated under this part. The exact boundaries of class I areas follow any boundary changes that happened after August 7, 1977, or that happen after November 15, 1990. (b) Areas designated as class II: Any area in a state that has been designated under section 7407(d) as meeting air quality standards (or "unclassifiable"), and that is not already class I under subsection (a), is a class II area - unless it gets redesignated under section 7474.