2.4.4. GHG Savings Potential

For a more accurate estimation of GHG-related benefits of forest-based ethanol over gasoline, it is necessary to account for the emissions occur throughout the life cycle of ethanol from forest biomass pre-treatment and collection, transportation to biorefinery, conversion to ethanol, transportation to terminals, and the end use of ethanol. While the emissions from the end use or burning of ethanol are assumed to be carbon neutral because they are equivalent to the emissions that are captured during tree growth [44]. Therefore, the total annual GHG savings (*GST*, kg CO2eq) can be expressed as the annual emission credits (*GTgas*, kg CO2eq) obtained from replacing current gasoline minus the life cycle emissions (*GTgas*, kg CO2eq) of ethanol in year *T*.

$$\mathbf{G}\mathbf{S}^T = \mathbf{G}\_{\text{gas}}^T - \mathbf{G}\_{\text{EtOH}}^T \tag{11}$$

The annual GHG emissions (*GTgas* and *GTEtOH*) is calculated by multiplying the amount of energy with an emission factor. The emission factor associated with combusting gasoline is 74.2 kg CO2eq/GJ) [45]. The emission factor for ethanol takes the median life cycle emission per energy unit [25].
