What is the difference between an emission factor and an emission intensity factor?
Emission factors allow you to convert the consumption of a fuel into emissions of CO2. The number is : grams of CO2 per unit of energy , for example grams of CO2 per liter of diesel, or per kWh of electricity . Pay attention to whether the number is “from the tank to the exhaust” (Tank-To-Wheel/TTW), or whether the production is included (Well-to-Wheel/WTW). That makes quite a difference. With electric propulsion, this is immediately apparent: the TTW emission factor is 0 (zero) g/kWH, the WTW emission factor around 475 g/KWh.
Emission factors are based on averages and are therefore often shown regionally and/or situation specific.
- See guideline 4: fuel
With an emission intensity factor the emission of CO2 is assigned to transported cargo; this is expressed in g CO2 per transport unit x distance. This figure provides insight into how efficiently an activity is performed. Emission intensity can also be used to estimate the emission of cargo transported. However, it is important to be very careful and to know how the emission intensity factor is calculated. A number does not immediately reveal the allocation method used and the assumptions made by the researchers. Misuse can give very strange results, such as vans that seem to run 1 liter in 3 kilometers when you calculate it backwards.
The best and most widely used emission intensity factor is the one calculated on the COFRET method. It has been given the name CPI, to make it recognizable.
- See guideline 1: Allocating emissions to cargo and customers