Q771. What is the difference between the Greenhouse Gas (GHG) emission data reported by electric generating units (EGUs) to EPA’s Clean Air Markets Division (CAMD) under Part 75 and to EPA’s Greenhouse Gas Reporting Program under Subpart D of Part 98?

A771.  All EGUs that are required to use Part 75 to monitor and report carbon dioxide (CO 2) mass emissions to EPA year-round must also report annual CO2 mass emissions under Subpart D (electricity generation) of Part 98. This currently includes only EGUs that are subject to the Acid Rain Program (ARP) and/or the Regional Greenhouse Gas Initiative (RGGI).

There is, however, a difference in emissions reported to each program.  The ARP and RGGI require reporting of CO2 mass emissions only, whereas Subpart D of Part 98 requires reporting of CO2 mass emissions and emissions of methane (CH4) and nitrous oxide (N2O) expressed in terms of CO2 equivalent (CO2e) emissions.  CO2e emissions are calculated by multiplying the GHG’s mass emissions by its global warming potential (GWP).  The GWP is a relative measure of how much heat a GHG traps in the atmosphere.  For each calendar year, the same annual CO2 mass emissions reported under Part 75 must also be reported under Subpart D of Part 98, except that the Part 75 data must first be converted from short tons to metric tons.