£1,000 / 4 Tonnes CO2e Removed
 
Biochar, resembling charcoal, is packed with stable carbon and made by heating biomass in a low-oxygen setting, known as pyrolysis. Its primary use is as a soil enhancer in farming and gardening.
 
Typically, discarded biomass serves as the source material for biochar production. This biomass holds carbon temporarily stored by plants during photosynthesis. If not for pyrolysis, this carbon would return to the atmosphere when the biomass decomposes or burns. By blending biochar with soil, its potential combustion in oxygen is averted.
 
Additionally, applying biochar to farmland offers significant perks like increased crop yields and decreased reliance on fertilisers.
 
The Science
Biochar, a varied material, comprises two carbon pools with differing degrees of stability: labile and recalcitrant (stable, aromatic) fractions. A higher proportion of the recalcitrant fraction indicates greater permanence, as the stable polycyclic aromatic carbon can endure in soils for over 1000 years.
 
The ratio of labile to recalcitrant fraction mainly hinges on pyrolysis conditions like pressure and temperature, with some influence from the feedstock's chemical composition. The hydrogen-to-carbon (H:C) molar ratio serves as a gauge for aromatization, easily and accurately measured. A ratio below 0.4 signals a substantial portion (~75%) of stable, aromatic carbon. Since autumn 2022, all our suppliers have adhered to this requirement.
 
Biochar carbon permanence is also affected by soil type and temperature, with slower degradation in colder soils.
We classify biochar credits as medium permanence (100-1000 years). At 100 years, one credit stores 1 tonne of CO₂, potentially requiring slightly higher initial sequestration. The labile and aromatic carbon pools each exhibit distinct degradation dynamics, with the labile pool degrading over decades to centuries, while the aromatic pool may persist for over 1000 years. As scientific understanding evolves, we'll update permanence estimates accordingly.
 
Biochar boasts a large, porous surface area and a mild electrical charge, enhancing its capacity to retain water and nutrients in soil.
 
These properties translate into improved water retention, mitigating crop vulnerability to drought, and reduced reliance on nitrogen fertilizers (thus lowering nitrogen pollution and nitrous oxide emissions). Additionally, biochar aids in soil organic carbon buildup, fostering carbon removal and fertility enhancement. In tropical regions, biochar has notably boosted crop yields, echoing the success of charcoal's traditional use in soils, exemplified by Brazil's Terra Preta soils.