### Question
How is the "mandatory class I Federal areas" defined?


### Answer
The term **mandatory class I Federal areas** is defined in *42 U.S.C. § 7491* as follows -

> Federal areas which may not be designated as other than class I under this part

#### Citation:
  - *42 U.S.C. § 7491*
  - Heading: **CHAPTER 85-AIR POLLUTION PREVENTION AND CONTROL > SUBCHAPTER I-PROGRAMS AND ACTIVITIES > Part C-Prevention of Significant Deterioration of Air Quality > subpart ii-visibility protection**

