Measurements, abbreviations, and acronyms used in this subpart and subparts BBB through III are defined as follows: Btu--British thermal unitCO2--carbon dioxideH2O--waterHg--mercuryhr--hourkW--kilowatt electricalkWh--kilowatt hourlb--poundmmBtu--million BtuMWe--megawatt electricalMWh--megawatt hourNOX--nitrogen oxidesO2--oxygenppm--parts per millionscfh--standard cubic feet per hourSO2--sulfur dioxideyr--year [71 FR 25387, Apr. 28, 2006]