Emission Factors are the values associated with the amount of energy-related Carbon Dioxide emissions that are released when these fuels are burned. These values adjust each year based on fuel quality and power plant efficiencies.
The graphs below represent data from October 2022 for fuels burned and used for electricity generated. You'll notice all of the values are the same with the exception of coal.
Through the visualization of the graph, the difference in size of the emission factors is more apparent. Coal's emission factor is 82% higher than natural gas which means there is 82% more emissions being released per MMBtu of electricity being produced. Diesel and Fuel Oil is half that. It is 40% higher than Natural Gas.
The Emission Factors consist of data representing carbon dioxide. However, there are other greenhouse gases that are released along with CO2. Together, emissions can be converted to a Carbon Dioxide Equivalent value (CO2e).
Check out this link for more info about emission factors and equivalents.