### Question
What is the definition of existing unit?


### Answer
The definition of **existing unit** is as follows 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 85-AIR POLLUTION PREVENTION AND CONTROL > SUBCHAPTER IV&ndash;A-ACID DEPOSITION CONTROL**

