What is an emission factor?

The release of GHG into the atmosphere depends mainly on the activity and the product. In order to estimate GHG emissions per unit of available activity, we need to use a factor called emission factor (EF).

For example: how many kg of GHG are emitted by 1 kWh of natural gas ?

An emission factor is a coefficient which allows to convert activity data into GHG emissions. It is the average emission rate of a given source, relative to units of activity or process/processes.

For example: the natural gas emits 0.244 kg CO2eq / kWh ICV (European mean) with 5% uncertainty.

Thus, the emission factor is the sum of emissions of CO2eq of the human activity described as mass unit of CO2eq / reference flows. For example: the EF for the natural gas is the sum of the combustion (0.205 kg CO2eq / kWh ICV) and the upstream (i.e. the production and transport of the gas) (0.0389 kg CO2eq / kWh ICV).

A human activity emits different kind of greenhouse gas (GHG) (see below). Their Global Warming Potential (GWP), a physical characteristic of a GHG, represents their impact on the greenhouse effect, and allows to convert 1 kg of GHG into X kg of CO2 equivalent, noted CO2eq. Thus, emissions of different gases can be compared.

What is an EF?

To constitute an emission factor, we need to produce a dataset which describes and quantifies the activity generating GHG.

The Newtral Emission Factor database includes the greenhouse gases covered by the Kyoto Protocol.

Kyoto Protocol GHG

Each GHG emission is converted in CO2eq and then summed. The conversion is made by multiplying gas quantity (kg GHG) with their GWP (kg CO2eq / kg GHG) in order to express impacts in CO2eq. Nitrogen trifluoride (NF3) has been recently added.