Dewpoint means a measure of humidity stated as the equilibrium temperature at which water condenses under a given pressure from moist air with a given absolute humidity. Dewpoint is specified as a temperature in C or K, and is valid only for the pressure at which it is measured. See 1065.645 to determine water vapor mole fractions from dewpoints using the pressure at which the dewpoint is measured.
40 CFR § 1065.1001
The definitions in this section apply to this part. The definitions apply to all subparts unless we note otherwise. All undefined terms have the meaning the Act gives them. The definitions follow: