What are "emission factors" and what is their role in calculating carbon footprint?

Carbon footprint calculations require knowledge of the relevant emission factors. An emission factor (EF) indicates the rate of released greenhouse gas into the atmosphere (greenhouse gas emissions) caused by a particular activity or process, e.g. fuel burning. Emission factors allow us to create an estimate of the amount of emissions released from different sources of a similar nature. A typical equation for calculating emissions is:

E = A x EF x (1-ER/100)

where:

• E = emissions estimate (usually expressed in tonnes of CO2 equivalent - tCO2e);
• A = activity rate (e.g. mass of fuel burned);
• EF = = emissions factor;
• ER = overall emissions reduction achieved by controls (%)

Emission factors are most commonly calculated as an average by using all data of acceptable quality. More complex processes than the above equation can express are usually expressed by empirically established equations which include multiple parameters/empirical constants [1].

Depending on the complexity of the calculation and the types of emission factors used, the emission calculation procedures described in the IPCC methodology are divided into three tiers - tier 1, tier 2 and tier 3. Tier 1 is characterised by simpler calculations based on basic statistical data and on tabulated global or continental scale emission factors. Tier 2 calculations require more detailed statistical data and are based on a particular country or technology-specific emission factors. Tier 3 calculations are usually considered to be based on the results of direct measurements made under local conditions [2].

The general recommendation is to use, as far as possible, emission factors that are specific for a particular geographical or technological area, i.e. higher level calculations, which should be more accurate and better reflect reality. However, they are more complex to calculate, and the data are usually only available for certain categories or products.

Emission factors can also be calculated for processes composed of several different (sub)processes. As an example, we can demonstrate the national emission factor for electricity generation, which includes different processes of electricity generation on the territory of a particular country - in the case of the Czech Republic, the said (sub)processes would be: electricity generation in nuclear power plants, burning of lignite and coal, use of renewable energy sources (RES), etc. The calculation methodology is as follows: "The primary energy of fossil fuels used (by specific types of fuel) to generate electricity in a given year is multiplied by the specific emission factors for the respective fuels in question (or for related fuels). (…) In the calculation, RES are considered as CO2 neutral, i.e. with zero emissions" [3]. Nuclear energy is also considered emission-free, although considering the total life cycle assessment, both sources produce (low) GHG emissions. In the carbon footprint calculations, the contribution of emissions caused by consumed energy appears to be significant for many companies (especially when only Scope 1 and 2 are assessed). The emission factor used for electricity, natural gas or heat therefore plays a significant role. Fig. 1 shows that the Czech electricity emission factor has mostly decreased between 2010 and 2020, from 0.554 t CO2e/MWh (tonnes of CO2 equivalent emissions per megawatt hour of energy) to 0.382 t CO2e/MWh in 2020, i.e. by around 31% in total. Between 2019 and 2020 alone, it decreased by almost 11%, which was mainly due to the higher share of generated electricity from nuclear power, natural gas and RES in 2020 compared to 2019. Thus, the emissions caused by electricity that is consumed by companies have decreased by 10 %, without the companies even trying.

If you would like to learn more about carbon footprint assessment and how to optimize it, visit our article on carbon footprint monitoring and do not hesitate to contact us at dotazy@enerfis.cz or call us at +420 222 766 950.

Sources:
[1] Recommended Procedures for Development of Emissions Factors and Use of the WebFIRE Database, https://www.epa.gov/system/files/documents/2021-11/final-webfire-procedures-document_nov-2021.pdf
[2] National Greenhouse Gas Inventory Report of the Czech Republic (reported inventories 1990- 2019), https://www.chmi.cz/files/portal/docs/uoco/oez/nis/NIR/CZE_NIR-2021-2019_UNFCCC_ISBN.pdf
[3] https://www.mpo.cz/cz/energetika/statistika/elektrina-a-teplo/hodnota-emisniho-faktoru-co2-z-vyroby-elektriny-za-leta-2010_2020--260559/