1. a) A new emissions unit is any emissions unit that is (or will be) newly constructed and that has existed for less than 2 years from the date such emissions unit first operated.
2. b) An existing emissions unit is any emissions unit that does not meet the requirements of subsection (a). A replacement unit, as defined in Section 203.1350, is an existing emissions unit.

"Emissions unit" means any part of a stationary source that emits or would have the potential to emit any regulated NSR pollutant and includes an electric utility steam generating unit as defined in Section 203.1140. For purposes of this Part, there are two types of emissions units.

(Source: Added at 49 Ill. Reg. 6237, effective April 23, 2025)