CO2 Emissions from Biofuels

CO2 Emissions from Vehicles Combusting Biofuels

Biofuels such as ethanol and biodiesel, and various blends of biofuels and fossil fuels, may be combusted in a local government’s vehicle fleet. The CO2 emissions from the combustion of biofuels must be reported separately from fossil fuel CO2 emissions due to their biogenic as opposed to anthropogenic origin. ("Biogenic" means that the fuels were rendered from recently living organic matter, while "anthropogenic" means derived from fossil fuels and contributing to manmade global warming.)

For pure biofuels such as B100 (100 percent biodiesel), the methodology presented in Mobile Combustion CO2 Emissions can be used to calculate biogenic CO2 emissions.

For biofuel blends, such as E85 (85 percent ethanol and 15 percent gasoline), CO2 emissions for each fuel must be reported separately to account for biogenic CO2 emissions and anthropogenic CO2 emissions.

The LGOP provides steps for calculating biogenic and anthropogenic CO2 emissions:

  1. Identify the biofuel blend being used (e.g. E85, B20, etc.)
  2. Identify total annual fuel consumption.
  3. Based on the blend, determine the annual consumption of the petroleum-based fuel component and the biomass-based fuel component. For example, for B20, annual consumption would be split into 20 percent biodiesel and 80 percent diesel fuel.
  4. Select the appropriate emission factor for each fuel component to calculate anthropogenic and biogenic CO2 emissions using Table G.9.
  5. Multiply each fuel consumed by its emission factor to calculate total CO2 emissions and convert to metric tons using Equation 7.2. Remember to keep calculations for anthropogenic and biogenic fuel use separate.
  6. To calculate the CH4 and N20 emissions from biofuels, follow the guidance given in Mobile Combustion CH4 and N2O Emissions.