Measurements, abbreviations, and acronyms used in this subpart and subparts BBB through III are defined as follows: Btu--British thermal unit.CO2--carbon dioxide.H2O--water.Hg--mercury.hr--hour.kW--kilowatt electrical.kWh--kilowatt hour.lb--pound.mmBtu--million Btu.MWe--megawatt electrical.MWh--megawatt hour.NOX--nitrogen oxides.O2--oxygen.ppm--parts per million.scfh--standard cubic feet per hour.SO2--sulfur dioxide.yr--year.