FEM

Federal equivalent method (FEM) means a method for measuring the concentration of an air pollutant in the ambient air that has been designated as an equivalent method in accordance with part 53 of this chapter; it does not include a method for which an equivalent method designation has been canceled in accordance with 53.11 or 53.16.

Source

40 CFR § 58.1

Scoping language

As used in this part, all terms not defined herein have the meaning given them in the Clean Air Act.