35 Ill. Adm. Code 204.370
Emissions Unit
Section 204.370 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 204.360. For purposes of this Part, there are two types of emissions
units.
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 the emissions unit first
operated.
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
204.620, is an existing emissions unit.