## Appendix A Data Sources
### Annual Emissions Factors  
The combustion of fuel in an electric power plant is an energy conversion process. The effectiveness of the conversion energy in the fuel to electricity is quantified as the heat rate (GJ/kWh) and is strongly affected by fuel and power plant technology [52]. The combustion process oxidizes the carbon, hydrogen, sulfur, and other constituents in the fuel, releasing both heat and the products of combustion: CO2, H2O, and SO2. The quantity of CO2 emissions per energy content of the fuel, the carbon dioxide emissions coefficient (kgCO2/GJ), is closely associated with the fuel type [53]. For power plants, the product of the heat rate and the carbon dioxide emissions coefficient is called the CO2 emissions factor (kgCO2/kWh). The consequence of the combustion process in power plants is that, for a combination of power plant technology and fuel, the quantity of CO2 emissions is strongly associated with the activity of the power plant. This relationship is demonstrated in Figure A2.  
A power plant consists of one or more generating units, each of which may have a different fuel source and prime mover type, and therefore a different carbon intensity, from other units at the plant. For each unit, an emissions factor (carbon intensity) was calculated through a combination of country-, fuel-, and prime-mover-specific average carbon intensities. Nominal carbon intensity values for combinations of energy source and prime mover technology were derived from a combination of US EPA Clean Air Markets Program Data (CAMPD), US EPA Emissions & Generation Resource Integrated Database (eGRID) ([[https://www.epa.gov/egrid](https://www.epa.gov/egrid)]([https://www.epa.gov/egrid](https://www.epa.gov/egrid)), accessed on 1 August 2022), and European Commission Joint Research Open Power Plants Database (JRC-PPDB-OPEN) ([[https://data.jrc.ec.europa.eu/dataset/9810](https://data.jrc.ec.europa.eu/dataset/9810) feeb-f062-49 cd-8e76-8d8 cfd488a05]([https://data.jrc.ec.europa.eu/dataset/9810](https://data.jrc.ec.europa.eu/dataset/9810) feeb-f062-49 cd-8e76-8d8 cfd488a05), accessed on 1 August 2022) data, and country-specific calibration based on IEA ([[https://www.iea.org](https://www.iea.org)]([https://www.iea.org](https://www.iea.org)), accessed on 1 August 2022) data. The emissions factor of each unit (unit_annual_carbon_intensity), was determined as follows:  
1. A base value (base_carbon_intensity) was gathered from the combination of the unit's energy source (energy_source_type), e.g., coal, gas, oil, and prime mover technology (prime_mover_type), e.g., combined cycle, simple cycle. This factor accounts for the typical efficiency and fuel carbon content differences between fuel and prime mover types.
2. If the combination of the energy source and prime mover did not have a value in the database, the average carbon intensity of the energy source was used.
3. The final emissions factor was calculated by applying an energy source and country-specific calibration factor (country_calibration_factor), a scalar that was multiplied by the base value to account for average regional differences in power plant efficiency (due to age, technology level, and size), fuel quality, and the impact of ambient conditions on carbon intensity that are not currently modeled. Example calculation: unit_annual_carbon_intensity = base_carbon_intensity(energy_source_type,prime_mover_type)  * country_calibration_factor(country,energy_source_type) For a coal-fired boiler with a steam turbine prime mover in the US, the annual carbon intensity would be 934 \([\)kg CO\({}_{2}\)/MWh\(]=1170\)\([\)kg CO\({}_{2}\)/MWh\(]*0.798\).