I just got my first lab test back and my Hydrogen to Organic Carbon ratio is 0.45. What does this mean for my project eligibility and credit production?

– Torrefied of My Permanence

Dear Torrefied of My Permanence,

This is a great question, as there are several key factors that typically have an outsized impact on the carbon removal potential of your biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More, with Hydrogen to Organic Carbon (H:Corg) being one of them. 

H:Corg is a critical input in calculating your biochar’s permanence factor, which determines the amount of carbon expected to remain stored over a given time period. This factor is influenced by both H:Corg and the soil temperature where the biochar is applied.

Project developers can only claim credits for the portion of carbon projected to persist within the timeframe defined by the registry, typically ranging from 100 to 1000 years, depending on the selected protocol. The permanence factor is expressed as a percentage and applied to the organic carbon content of the dry biochar to determine the gross amount of carbon dioxide equivalent (CO2e) stored.

Formula:
OC Content of Biochar × 44/12 (Molar Mass of CO₂/C Conversion) × Permanence Factor = Gross Carbon Stored

What is Hydrogen to Organic Carbon and how does it dictate permanence

Hydrogen to Organic Carbon, often abbreviated as H:Corg or H:C, is the molar ratio of these two elements in your biochar. A lower H:Corg ratio indicates fewer reactive compounds and a more condensed, graphite-like carbon structure resulting in a more stable biochar with greater long-term permanence. Conversely, a higher H:Corg ratio reflects a biochar with more reactive, hydrogen-rich compounds and fewer tightly bonded, aromatic carbon structures.

Permanence factor equations that rely on H:Corg generally follow the Woolf et al 2021 model or a modified version of it, incorporating both H:Corg and soil temperature to estimate long-term stability. In these models, higher soil temperatures reduce permanence.

Check out this graph from Puro’s biochar methodology to see how H:Corg and soil temperature interact.

What Causes Low or High H:Cₒᵣg?

The main driver of H:Cₒᵣg is pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More temperature and residence timeResidence time refers to the duration that the biomass is heated during the pyrolysis process. The residence time can influence the properties of the biochar produced.   More.

• Lower temperatures (< 500 C) and shorter residence times retain more volatile, hydrogen- and oxygen-rich compounds, leading to a higher H:Corg ratio and lower stability.
• Higher temperatures (>500 C) and longer residence times drive off these volatiles, creating condensed aromatic structures with a lower H:Corg and greater stability.

How This Relates to Certification Standards

Different certification standards and protocols approach permanence in slightly different ways. Many require an H:Corg below a specific threshold, typically 0.7 or lower, to ensure sufficient carbonization.

Some standards, like Isometric, allow developers to use random reflectance testing as an alternative measure of permanence. Others apply a fixed permanence factor, such as Carbon Standards International, that applies a 75% permanence for biochar with an H:Corg at 0.4 or below.

Designing Your Project With Carbon Permanence in Mind

As you design your project, pyrolysis temperature and residence timeThis refers to the amount of time that the biomass is heated during the pyrolysis process. The residence time can influence the characteristics of the biochar, such as its porosity and surface area.   More should be key considerations to achieve a lower H:Corg, particularly if you plan to sell carbon credits. However, you may avoid this issue by applying biochar to non-agricultural soil uses, such as concrete, where degradation is negligible, though this ultimately depends on the protocol’s accounting ruleset.

Credit buyers want confidence that the carbon removal credits they purchase represent durable, verifiable sequestration to appropriately offset their emissions. Because permanence is directly tied to creditable carbon storage, a lower H:Corg ratio, and therefore a higher permanence factor, leads to greater credit production.

Sustainably yours,

Annie Nichols
GM of Biochar, Mangrove Systems

Sources:

• Woolf et al – Greenhouse Gas Inventory Model for Biochar Additions to Soil
• Puro Biochar Methodology Edition 2025 v1: Section 6.2
• Isometric Biochar Storage in Agricultural Soils v1.1: Section 4.0
• Carbon Standards International Global C-Sink Methodology v3.1: Section 3

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