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Identify and collect relevant emissions factors

> How to identify and collect relevant emissions factors for your company GHG inventory

1. What are emission factors?

Emission factors are ​the average amount of greenhouse gases emitted per unit of consumption or use. Typical units are weight (e.g., tons, kg) of CO2e per unit of consumption.

Example: The emission factor for brick is 241.8 kg CO2e per ton of brick

Please note that many emissions factors databases provide data in CO2 equivalent already, meaning they already account for the GWP of the different GHG. If that is the case, then GWP should not be included in the equation.

However, in some cases, they might be expressed in another GHG (e.g., N2O). In this case, you will have to convert the GHG into CO2eq using the global warming potential (GWP) value, which expresses the relative potency of climate warming of a gas relative to CO2. GWP values are defined by the IPCC and are updated regularly. Best practice is to use the most recent ones (i.e., from the latest IPCC assessment report). You will find the GWP values here.

2. What type of emissions factors can be collected?

Emission factors are calculated ratios relating GHG emissions to a measured activity at an emissions source. They have different specificity levels depending on their sources (e.g., reflect national or industry-based averages or be specific to a product). Best practice is to use the most specific emissions factors whenever possible. Emissions factor specificity is increasing over time as companies are performing product lifecycle assessments enabling to build product-level emission factor.

Emission factors, where they cannot be reliably collected at first, need to be updated over time as higher-quality information becomes available.

What are the best practices in terms of accounting maturity?

3. Where can emission factors be collected?

Some commonly used third party emission factors databases include: