Measurements, abbreviations, and acronyms used in this subpart and subparts BB through II are defined as follows:Btu--British thermal unit.CO2--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 25381, Apr. 28, 2006]