Emissions unit means any part or activity of a stationary source that emits or has the potential to emit any regulated air pollutant or any pollutant listed under section 112 of the Act. This term is not meant to alter or affect the definition of the term unit for purposes of title IV of the Act.
40 CFR § 71.2
The following definitions apply to part 71. Except as specifically provided in this section, terms used in this part retain the meaning accorded them under the applicable requirements of the Act.