Durability is the whole point of a carbon removal. For biochar, durability is governed by a single, measurable property: the hydrogen-to-organic-carbon (H:Corg) ratio. Here is what it means and why buyers should care.
Why permanence matters
A removal that reverses in a decade is not really a removal. Corporate buyers paying a premium for durable CDR need confidence that the carbon stays locked away for centuries, not years. Biochar's appeal is that this durability is physically measurable — not modelled from assumptions.
What H:Corg measures
During pyrolysis, biomass loses hydrogen and oxygen relative to carbon, and the remaining carbon reorganises into stable, aromatic structures. The H:Corg ratio captures how far that transformation has gone:
- H:Corg < 0.7 — generally associated with centuries-scale stability (the common threshold in methodologies).
- H:Corg < 0.4 — associated with even longer durability, often cited for 1,000+ year permanence.
Lower is more durable. The ratio is driven by pyrolysis temperature and residence time, which is why technology selection directly affects the credits you can claim.
How it is measured
Accredited labs run elemental analysis on representative biochar samples. Robust projects pair this with a sampling plan that captures variability across production batches and feedstocks, so the reported ratio reflects what is actually applied — not a single favourable sample.
What buyers should check
Before purchasing biochar removals, ask for:
- H:Corg (organic) lab results from an accredited laboratory.
- The sampling plan — how many samples, how often, across which batches.
- The methodology's permanence treatment — how the standard converts H:Corg into a durability claim.
- Production records linking biochar quality to specific feedstock and pyrolysis conditions.
- Application records — where and how the biochar was used, ensuring it is genuinely sequestered.
The bigger picture
H:Corg is necessary but not sufficient. High-integrity removals also require sound additionality, conservative baselines, and traceable delivery. But on the question that defines a removal — will the carbon stay put? — H:Corg is the number that matters most.
If you are buying biochar removals and want an independent read on permanence and MRV quality, explore our buyer-side support.