In 2018 biochar was acknowledged by the IPCC (the Intergovernmental Panel on Climate Change) as an important Negative Emission Technology (NET). The carbon sequestration potential (100 years) for different biochar is calculated with the three factors below:
The amount of carbon in biochar depends on the type of biomass that is carbonized and the pyrolysis (production) temperature. Higher degrees result in a more condensed carbon structure and increased presence of aromatic carbon1 (stable carbon rings). The more aromatic structures the higher the resistance to biodegradation. Inorganic carbon that may be present in biochar is not part of the condensed aromatic structure and is not expected to remain in soil for 100 years.
Aromaticity of biochar is strongly correlated to its carbon stability2 and can be predicted by the presence of
hydrogen relative to organic carbon (H/Corg) in biochar3. These elemental components of biochar can be
measured using an elemental analyzer. Biochar with low H/Corg values are graphite‐like materials, which exhibit
high stability and resistance to biodegradation.
The ratio between the molar value and the mass value for hydrogen and carbon respectively determines the stability of biochar. The H/Corg value is calculated with the formula H/Corg = (mH/MH)/(mC/MC)
The method to assess stability through H/Corg values does not provide an absolute measure of stability but is acknowledged as a reliable method by the the International Biochar Initiative and the European Biochar Certificate. Biochar that obtain H/Corg values <0,4 is estimated to have 80% of stable carbon left after 100 years. Biochar that obtain values within the range of 0,4 - 0,7 is estimated to have 60% of stable carbon left after 100 years. Biochar that obtain H/Corg values higher than 0,7 are not considered to be biochar.
If all available carbon in biochar was oxidised into carbon dioxide the theoretical calculation would be as follows: 1 kg of carbon + 2,67 kg of oxygen give 3,67 kg of carbon dioxide and heat (1 kg of C = 3,67 CO2-eq) In the table below fictive examples of the CO2 equivalents for biochar are calculated with variations in carbon content and stability ratio (H/Corg).