Commence operation
Commence operation means to have begun any mechanical, chemical, or electronic process, including, with regard to a unit, start-up of a unit's combustion chamber. Except as provided in 97.4, 97.5, or subpart I of this part for a unit that is a NOX Budget unit under 97.4(a) on the date of commencement of operation, such date shall remain the unit's date of commencement of operation even if the unit is subsequently modified, reconstructed, or repowered. Except as provided in 97.4(b), 97.5, or subpart I of this part, for a unit that is not a NOX Budget unit under 97.4(a) on the date of commencement of operation, the date the unit becomes a NOX Budget unit under 97.4(a) shall be the unit's date of commencement of operation.
Source
40 CFR § 97.2
Scoping language
The terms used in this part shall have the meanings set forth in this section as follows: