### Question
What does existing unit mean?


### Answer
**Existing unit** has the following meaning in *42 U.S.C. § 7651a*:

> a unit (including units subject to section 7411 of this title) that commenced commercial operation before November 15, 1990

#### Citation:
  - *42 U.S.C. § 7651a*
  - Heading: **CHAPTER 83-ENERGY EXTENSION SERVICE > SUBCHAPTER IV&ndash;A-ACID DEPOSITION CONTROL**

