Principles & requirements

Project Developers shall demonstrate that they comply with all principles and requirements outlined in the Rainbow Standard Rules, and described below with a specific focus on distributed biochar production.

Rainbow Standard Rules

Additionality

Regulatory surplus analysis

Regulatory surplus analysis shall demonstrate that there are no regulations that require or mandate project activities (for removal and avoidance activities). It is acceptable if regulations promote or set targets for these activities, because the resulting increase in activities shall be accounted for in the baseline scenario.

At the European Union level, projects automatically pass the regulatory surplus analysis, which has been conducted by the Rainbow Science Team. Project Developers are only required to provide a country-level regulatory surplus analysis.

Investment analysis

Barrier analysis

Durability

Durability threshold

All projects certified under this methodology shall prove durable carbon removals for at least 100 years. Project Developers may claim an extended durability threshold of 1000 years if they choose the 1000-year pathway for GHG quantification and measurements.

Reversal risk assessment

The major carbon reversal risks from biochar carbon storage are:

1. Insufficient biochar stability, where biochar carbon is not sufficiently carbonized and is decomposed by microbes and soil organisms, resulting in re-emission of CO₂.

2. Failure to durably incorporate into a permanent matrix (e.g. soil or soil-like material), where biochar is instead burned or destroyed, intentionally or unintentionally (e.g. as fuel, in storage fires, or via waste incineration).

This methodology establishes the following mandatory project design requirements to mitigate these risks, detailed in the following sections:

• measuring the durable carbon fraction

• verification of biochar end use

Upon meeting these requirements for each verification and credit issuance, the risk of reversal is considered negligible for biochar application to soils. There are no further project requirements to assess reversal risks or conduct post-crediting monitoring for reversals.

All projects certified under this methodology shall contribute the default minimum 2% of their verified removal RCCs to the Rainbow Buffer Pool, as defined in the Rainbow Standard Rules.

Risk mitigation: Measuring permanent carbon fraction

Not all biomass carbon that is converted to biochar is expected to remain durably stored. The durability of biochar carbon depends on the its physicochemical stability, which is influenced by factors such as carbonization temperature and biomass feedstock.

Project Developers shall measure one of the following well-known proxy indicators of biochar durability for each Production Batch. These indicators serve both as eligibility thresholds, and as inputs to quantify the permanent fraction of carbon ($F_{perm}$) expected to remain durably stored beyond the applicable durability threshold.

The fraction of permanently stored carbon shall be quantified using the models and equations specified in the GHG quantification section. Only this fraction shall be issued as removal RCCs.

Pathway	Indicator	Threshold requirement
100-year pathway	Hydrogen-to-organic-carbon atomic ratio ($H/C_{\text{org}}$)	$H/C_{\text{org}}$ must be less than 0.7
1000-year pathway	Random reflectance distribution	The fraction of the biochar residual organic carbon that has a random reflectance of 2% or higher can be considered inertinite, which is an extremely stable, permanent storage of mineral-like organic carbon. Must also have $H/C_{\text{org}}$ less than 0.7

The distinction between the 100-year and 1,000-year durability pathways provides supplementary qualitative information and does not affect the inherent attributes of the removal RCC.

These indicators are suitable proof that a substantial fraction of the carbon present in biochar is permanently stable. The specific amount of permanently stored carbon is determined using the models and equations detailed in the GHG quantification section.

These durability indicators shall be monitored for each Production Batch according to this methodology's Sampling Requirements.

Issuing removal RCCs only for the verified, highly stable fraction of biochar carbon mitigates the risk of biological decomposition and re-emission after soil application.

Risk mitigation: Proof of biochar end use

Project Developers shall prove that all biochar has been used in the intended durable storage application and eligible biochar end use (e.g. incorporated into soils, added to fertilizer mixes, mixed in concrete). This shall be done by documenting all of the following information in dMRV:

• Proof of delivery and use of the biochar to its point of end use, specifying the date, GPS coordinates, address, amount of biochar, name of the user/buyer, and Production Batch ID.

• Photo diary of biochar application and/or mixing, including time-stamped and geo-located photos of the process.

No double counting

Project Developers shall sign the Rainbow MRV & Registry Terms & Conditions, committing to follow the requirements outlined in the Rainbow Standard Rules, including not double using or double issuing carbon credits.

Project Developers shall demonstrate that they hold the sole right to issue carbon credits for all biochar produced under the project, and that no third party will seek to issue credits for the same biochar.

• If biochar is applied to soils by participants within the project network (e.g., farmers who also provide biomass or operate kilns), this is considered to remain within the project scope through to end use, and no additional double counting documentation is required.

• If biochar is transferred to third parties, such as farmers outside the project network or companies incorporating it into construction materials, then Project Developers shall obtain recognition that the Project Developer holds the sole right to issue credits for that biochar, and that the recipient will not seek to issue credits for its use.

Co-benefits

Projects should support at least two quantifiable and verifiable environmental or social co-benefits, aligned with the UN Sustainable Development Goals (SDGs) framework. Any co-benefits claimed by the Project Developer shall be quantified, monitored, and audited for each verification and credit issuance.

Common co-benefits under this methodology are detailed in the table below. Project Developers may suggest and prove other co-benefits not mentioned here.

SDG 13 on Climate Action by default is not considered a co-benefit here, since it is implicitly accounted for in the issuance of carbon credits. If the project delivers climate benefits that are not accounted for in the GHG reduction quantifications, then they may be considered as co-benefits.

Table 1 Common co-benefits that projects under this methodology may provide are detailed, including types of proof that can be used to justify each co-benefit.

UN SDG	Example	Proof
SDG 1.5: Build the resilience of the poor and those in vulnerable situations, ensure significant mobilization of resources from a variety of sources	Kiln Operators, who are often smallholder farmers, receive direct payments from carbon finance generated (mandatory, see Benefit sharing requirements).	Payment slips, bank transaction records, contracts.
SDG 2.4: Ensure sustainable food production systems, increase productivity, help maintain resilient ecosystems, improve land and soil quality.	Biochar application to agricultural soils can increase crop yields.	Proof of biochar sales to farmers for agricultural use, invoices, receipts of sale of biochar to farmers.
SDG 3.9: reduce the number of deaths and illnesses from hazardous chemicals and air, water and soil pollution and contamination	Agricultural residues (feedstock) are pyrolyzed instead of open-field burning, improving air quality.	Biomass type records, local data on traditional burning practices.
SDG 12.2: Sustainable management and efficient use of natural resources	Biomass waste is converted into valuable biochar instead of being burned or discarded.	Biomass type records, local statistics on traditional biomass disposal methods.

Environmental and social safeguards

Project Developers shall prove that the project does not contribute to substantial environmental and social harms.

Projects must follow all national, local, and European (if located in Europe) environmental regulations related to, for example, pyrolysis, gasification, waste feedstock management, and biochar spreading on soils.

Biomass requirements

Waste status

Project Developers shall provide proof of waste status for any biomass feedstock categorized as waste. This can be done via any one of the following three methods:

• Price: if Project Developers did not pay for the biomass, or if they were paid to handle it, the biomass can be considered waste. Acceptable proof includes invoices, receipts, or contracts.

• Contextual analysis: Project Developers may submit an analysis supported by reputable sources that the biomass 1) could not be used as main material products, and 2) was not grown for the purpose of CDR.

• Positive list of wastes: if the biomass is included in the following list, it can be considered waste. Acceptable proof includes invoices, receipts, contracts, or photographic evidence and is required for validation:

• sawmill residues

• shavings

• bark

• forestry tops and branches

• wildfire management residues

• sugar beet pulp

• straw

• corn cobs

• wood from horticulture (trimmings or whole plants)

• nut shells

• bagasse

Invasive species status

Project Developers shall provide proof of invasive species status for any biomass feedstock categorized as invasive species. This may include but is not limited to peer-reviewed scientific literature documenting the species as invasive in the specific region, national or regional government invasive species lists or registers, regional intergovernmental lists (e.g. IUCN Invasive Species Specialist Group database), or local official weed management orders.

Project Developers shall provide an Ecosystem Restoration Plan, outlining all of the following:

• the extent of invasive species harvesting, and how much biomass is left in the field after harvesting

• procedures to ensure only targeted invasive species are harvested

• impacts on biodiversity and habitat loss

• impacts on ecosystem carbon loss

Forestry certification

Biomass feedstock originating from forests shall provide at least one of the following forestry sustainability certificates (or similar, with a sufficient justification):

• FSC (Forest Stewardship Council)⁠

• PEFC (Program for the Endorsement of Forest Certification)⁠

• RSB (Roundtable on Sustainable Biomaterials)⁠

• SFI (Sustainable Forestry Initiative)⁠

• SBP (Sustainable Biomass Program)⁠

These certifications are used to prove:

• Legal and transparent chain of custody

• Proper forest regeneration

• Safeguarding biodiversity and soil health

• Historically stable or increasing forest carbon stocks

• Sound socio-environmental practices in forestry operations⁠

Biomass stakeholder consultation

In addition to the general Rainbow stakeholder consultation requirements, Project Developers shall explicitly consult stakeholders on the project's use of biomass. This shall cover the Project Developer's right to use the biomass, the biomass status as waste or invasive species, and the alternative fate of the biomass.

Kiln operation requirements

Distributed biochar production may pose health and safety risks to Kiln Operators, including but not limited to risk of burns and inhalation of smoke and pollutants. Project Developers shall prove all of the following:

• Kiln Operators and Supervisors follow required safety training

• Kiln Operators are equipped with and use burn protection equipment such as fire resistant gloves or appropriate footwear

• Kiln Operators are equipped with and use smoke protection equipment such as eyewear and masks

• pyrolysis occurs in ventilated outdoor spaces

Biochar requirements

Biochar applied to soils must be below the pollutant concentration thresholds outlined in Table 2, defined by the World Biochar Certificate Guidelines (for WBC-Agro). This shall be measured on a representative composite sample of biochar anytime biomass feedstock changes, or annually, if biomass feedstock does not change.

PAH measurement is not required for open kilns under this methodology because open flame curtain kilns using clean agricultural residue feedstocks have been shown in the scientific literature to produce biochar with sufficiently low PAH concentrations.

Table 2 The thresholds for pollutant concentrations allowed in biochar, as detailed in the World Biochar Certificate Guidelines.

Substance	Limit amount (g/tonne dry matter)
Pb	300
Cd	5
Cu	200
Ni	100
Hg	2
Zn	1000
Cr	200
As	20

Disclaimer: The European Biochar Certificate (EBC) and the World Biochar Certificate (WBC) are independent certification programs designed to ensure the quality of biochar products. These certifications are administered and trademarked by Carbon Standards International (CSI) and are distinct from the Rainbow certification and the issuance of carbon credits.

The threshold values provided here are based on the voluntary guidelines of the World Biochar Certificate (WBC), reproduced with permission. While these values have been adopted by the Rainbow standard as pollutant thresholds, they are only indicative. Meeting these thresholds for Rainbow certification does not imply eligibility for or any association with the EBC or WBC programs. Project Developers certified under the Rainbow standard shall not make claims or use any trademarked materials from CSI, unless explicitly allowed by CSI.

Voluntary certification under the WBC and EBC schemes is overseen by CSI and includes additional requirements beyond pollutant thresholds.

Environmental and social risk evaluation

Project Developers shall fill in the Rainbow Distributed biochar risk evaluation, to evaluate the identified environmental and social risks of projects. The identified risks include:

• Heavy metal or other pollutants in biochar applied to agricultural soils

• Disruption of soil health when collecting and exporting organic matter

• Presence of heavy metals, toxins or other chemical pollutants in the biomass⁠

• Spread of diseases or invasive species

• Cultivation of feedstock

• Deforestation from use of forestry products as feedstock

• Distant transport of feedstock inputs (>100 km)

• Timely and fair payments to smallholder farmers

• Safe kiln operation and training events to prevents burns

• Use of large amounts of water, if water is scarce, for quenching

Project Developers shall assign a likelihood and severity score of each risk, and provide an explanation of their choices. The VVB and Rainbow’s Certification team shall evaluate the assessment and may recommend changes to the assigned scores.

Any identified material risk (defined as issues with a risk score of moderate or higher) shall be subject to a Risk Mitigation Plan, which outlines how Project Developers will mitigate, monitor, report, and if necessary, compensate for any environmental and/or social harms.

Additional proof may be required for certain high risk environmental and social problems.

The Project Developer, the Rainbow Certification Team, or the VVB may suggest additional risks to be considered for a specific project.

Note that the life-cycle GHG reduction calculations account for the climate change impacts of most environmental risks. Nonetheless, Project Developers shall transparently describe any substantial and sensitive GHG emission risks in the risk evaluation template.

All risk assessments must also address the Minimum environmental and social risks defined in the Rainbow Standard Rules.

Project Developers shall follow the requirements in the Rainbow Standard Rules for conducting stakeholder consultation, and where IPLCs are involved, obtaining free prior and informed consent (FPIC). Although the Rainbow Standard Rules requires benefit sharing only if IPLCs are involved, this methodology requires it in all cases, as detailed in the following section.

Benefit sharing

Project Developers shall demonstrate that Kiln Operators are fairly compensated for their contribution to the project. This includes timely payments that are not deferred until credits are issued and sold, and allocation of a fair share of carbon finance revenues.

The committed timing and amount of benefit sharing shall be defined by Project Developers and disclosed transparently in project documentation on the Rainbow registry.

Project Developers shall demonstrate adherence to this commitment annually by providing payment slips, bank transaction records, or other ex-post evidence of payments having occurred.

Leakage

Project Developers shall source biomass in a way that reduces leakage. Project Developers shall assess and, if identified to be material, quantify the leakage caused by the distributed biochar project and deduct the associated emissions from the project removals. This shall be done by first identifying the alternative use of biomass, and then assessing the leakage risks from the following identified leakage sources:

• Biomass diversion and replacement

• Counterfactual biomass carbon storage

Where leakage risks are identified, Project Developers shall mitigate the risk, and document such efforts to do so. Where leakage cannot be fully mitigated, leakage emissions shall be counted towards the project induced GHG emissions and therefore deducted from project removals.

Alternative use

Project Developers shall evaluate the most likely alternative use/s of each type of biomass used, in order to assess leakage risks associated with the baseline carbon storage and the diversion of biomass. The assessment shall be transparent and conservative.

The alternative use shall address questions such as:

• was the biomass used for a product or service, that now needs to be replaced (e.g. bioenergy production)?

• was the biomass going to store carbon anyway (in the biomass itself and/or in the soil)?

Proof shall be provided and may include signed statements from the biomass provider, historical records from the biomass provider, regional statistics or reputable reporting.

A short list of likely alternative uses may be provided for descriptive purposes, but for the purpose of further analysis, one single alternative use per biomass shall be proposed.

Biomass diversion and replacement

Using waste biomass helps mitigate activity shifting leakage. However, waste biomass or invasive species may still have valuable alternative uses.

If the Alternative use of biomass assessment concludes that the biomass has a valuable existing use, Project Developers shall assess the impacts of diverting it for biochar production. This assessment must address, at a minimum:

• The availability of substitute materials (either the same material, if locally abundant, or alternative materials that fulfill the same function).

• The risk of indirect land use change or deforestation, particularly if diverting the biomass creates demand for new materials to replace its original function,

Specifically, Project Developers shall identify the most likely replacement product or process for the diverted biomass. Project Developers shall justify the amount of replacement product needed to replace the original function of the biomass based on the business-as-usual (BAU) function, using an appropriate conversion factor.

Proof shall be provided and may include signed statements from the biomass provider, historical records from the biomass provider, regional statistics or reputable reporting.

Counterfactual biomass carbon storage

Projects shall only be credited for carbon storage that is genuinely additional. If the alternative use of biomass was to be left on the soil or reapplied to soils for nutrient recycling, then any permanent carbon storage that would have occurred anyway in the absence of the project shall be deducted from the project's carbon removal capacity.

• Any carbon that is demonstrated to remain stored in the feedstock for up to 50 years shall be considered as baseline carbon storage.

• A minimum of 0.5% of the feedstock carbon content is assumed to remain stored and deducted from the project removals.

Details are outlined in the GHG quantification section.

Upstream and downstream emissions

Upstream and downstream emissions are accounted for in the life-cycle based GHG quantifications in companion modules.

Monitoring

Monitoring Plans for this module shall include, but are not limited to, tracking of the following information:

Measurement frequency	Parameters
Each Production Batch, on a single representative sample of biochar	$H/C_{\text{org}}$ and organic carbon content (full description here) Inertinite content (fraction of the distribution sample that has a random reflectance of 2% or higher) and residual carbon (if calculating 1000-year removals) (full description here) Biochar moisture content, on at least 3 biochar samples (if measuring biochar amount via mass) (full description here)
Once per year, or anytime biomass feedstock changes	Methane emissions, on three runs representative of all other kilns in the same Production Batch (full description here) Environmental pollutants of biochar, on one composite sample mixing biochar from each kiln run (full description here) Dry bulk density of biochar, on at least one sample from each kiln (i.e. 20 different kilns, 20 bulk density measurements) (if measuring biochar amount via volume) (full description here) Biomass to biochar conversion factor (if not weighing the biomass input of each kiln run) (full description here) Updated biomass leakage assessment (full description here)
Each kiln run	Moisture content of biomass input (full description here) Type of biomass input (full description here) Amount of biomass input, via precise mass measurements if using a feedstock mix, or estimates if using a singular biomass (full description here) Mass or volume of fresh biochar produced (full description here) Temperature curve measured in each kiln using real-time sensors, proving pyrolysis has occurred (full description here) Photographs of the pyrolysis process, showing for example a lack of white smoke and ash, and the duration of the kiln run (full description here) Sampling records (proof of setting aside a small sub-sample of biochar, to be combined with sub-samples from all other kiln runs in the same Production Batch) (full description here)
All biochar used	Proof of eligible, durable biochar end use, with names and GPS coordinates of spreading locations, among other information (full description here)
Once per year	Kiln Operator training (full description here) Proof and findings from the visits of Kiln Supervisor to each Kiln Operator (full description here) Proof of calibration and accuracy of onsite scales for weighing biochar to determine biochar amount (full description here)
Once per verification and credit issuance	Quality oversight report from the Project Developer (full description here) Environmental sustainability and Leakage compliance of biomass feedstock (full description here and here)

The Project Developer is the party responsible for adhering to the Monitoring Plan.

dMRV requirements

Distributed biochar uniquely heavily relies on third-party dMRV platforms to allow for detailed tracking of operations across a network of Kiln Operators.

Project Developers shall select the dMRV to be used by Kiln Operators and Supervisors to document the operating procedures. The chosen dMRV shall provide step by step procedures to Kiln Operators and be able to track the following:

Item to track	Further requirements
Eligible kiln use	Scanned QR codes of individual kilns and photos of the kiln displaying the required technical features
Biomass moisture content	Photos of sensor readings
Biomass preparation and amount	Photos of the biomass to be pyrolyzed before each kiln run and The mass or volume of biomass used
Pyrolysis temperature and duration	Continuous thermocouple readings
Pyrolysis process quality	Photos taken throughout the pyrolysis process, including at least one after the last addition of biomass to the kiln, showing the intact and clean flame curtain
Rapid quenching	Through time-stamped photos or short videos showing the start and end time of quenching
Amount of biochar produced	Volume of biochar produced from each kiln run, and bulk density measurements conducted by the Kiln Supervisor, or Mass of biochar produced from each kiln run, and moisture content measurements
Biochar sampling records	Scanned QR codes of the original biochar bags from which the sample is taken, and photos of the sample
Biochar delivery and application	Scanned QR codes of biochar bags for delivery and photos
Aggregated measurements and data	For GHG quantification

Methane emissions testing, including results and photos of the process, may be handled in the dMRV platform or in a separate report shared with Rainbow and the VVB.

All photographs must include a timestamp and GPS coordinates. All temperature curves must include a timestamp.

Any data tracked directly in the dMRV platform and uploaded with a delay must:

• include a timestamp of when the upload occurred, and

• be uploaded as a batch with all relevant data upon connectivity, as opposed to manually uploading individual chosen files from chosen kiln runs, to prevent selective submission of preferred data.

The dMRV platform must prevent Kiln Operators from modifying data once it has been uploaded. Data from dMRV shall be made available and verifiable by Rainbow, the Project Developer and the VVB, through an oversight-only view, and exportable files.

All project records must be retained for a minimum of five years following the end of the project's final monitoring period.

At project validation, Rainbow will review the proposed dMRV platform to ensure it is capable of providing the above-mentioned data and proof. After a dMRV platform design is validated and approved as eligible, the platform will be added to Rainbow’s published list of eligible platform. For any future projects using the same dMRV platform, the platform shall be considered automatically eligible.

The use of an approved dMRV platform is not sufficient to ensure project compliance with the present methodology. All listed data points and proof shall be uploaded to the dMRV platform in order to issue credits.

If any piece of operational proof or documentation is missing in dMRV, the entire kiln run is ineligible.

Role	Use of dMRV platform
Kiln Operators	Directly upload the required information to the dMRV platform, and flag any known anomalies.
Kiln Supervisors	Directly upload any biochar bulk density and/or moisture content measurements to the dMRV platform (depending on the measurement method for the amount of biochar produced), and flag any known anomalies.
Project Developer	Check the information and proof for every kiln run recorded on the dMRV platform, ensuring its accuracy and data preparation (unless outsourcing this task to the dMRV provider, see the Raw data checking section) Provide a report on oversight findings, listing non-conformities, adjusted data, and kiln runs excluded from certification.
VVB	Check the complete raw records in dMRV of a random sample of kiln runs, to cover at least 20% of all events. Check all records related to biochar bulk density and/or moisture content measurements conducted by Kiln Supervisors, as detailed in the biochar amount produced section. Findings shall follow the non-conformity procedure outlined in the Rainbow Procedures Manual. Major non-conformities shall trigger a more thorough audit of a larger sample of events.

Quality and oversight

Raw data checking

The Project Developer is ultimately responsible for the quality and accuracy of raw records submitted to the VVBs for audit, and identifying and flagging runs that do not meet the quality threshold. All records from each kiln run shall be individually checked, ensuring at a minimum all of the following components:

• the duration of the kiln run is consistent with the amount of biochar produced

• the amount of biomass feedstock used is broadly consistent with the amount of biochar produced, based on photographic evidence of the feedstock pile prior to the run

• the amount of biochar produced is broadly consistent with the amount of biochar reported as applied in an eligible end use

• flame curtain photos show a clean burn

• pyrolysis temperature is consistently high throughout the duration of the kiln run. Project Developers shall suggest their own definition for acceptable temperature curves upon validation. Full details are in the temperature curve section

• quenching was rapid enough to mitigate methane emissions

Any kiln run with incomplete data, or that demonstrates unsatisfactory practices, is rendered ineligible for crediting (except for the tolerance threshold of temperature curve failures).

Raw data checking may be completed by the Project Developer, or may be delegated to the Rainbow-approved dMRV provider. Data checking may be completed manually, or via a dMRV-enabled system for automatically scanning for and flagging anomalies. Criteria and anomalies shall be either defined at the dMRV level and applied across all projects, or according to project-specific criteria, and shall be approved by Rainbow. If opting for an automatic flagging approach, the dMRV provider must demonstrate via trial runs that it is capable of flagging deviations from the criteria, and define a protocol for random manual checks.

The VVB shall also manually review the complete raw dMRV records for a random sample of kiln runs, covering at least 20% of all events.

Kiln Supervisor site visits

The Kiln Supervisor shall visit each Kiln Operator annually and observe one kiln run, ensuring:

• feedstock is properly added to the kiln

• biomass moisture content measurements are taken appropriately

• storage conditions for biomass and biochar are appropriate

• biochar sampling procedures are followed

The Kiln Supervisor shall also collect the Site Composite Sample during this site visit, which is mixed with other Site Composite Samples to generate the Production Batch Representative Sample. Biochar durability indicators and bulk density measurements (if using the biochar volume approach) are done on this biochar sample. See the Biochar sampling procedure section for more details.

Proof of the site visits shall be included in the Monitoring Plan and submitted at least once per year, including the name of the Kiln Supervisor, date of visit, and the findings and follow up actions of each Kiln Operator.

Note that the Kiln Supervisor site visits are in addition to the annual VVB site audits, described in the Certification Requirements section.

Quality oversight report

Project Developers shall prepare a report, upon each verification and credit issuance, summarizing the findings of dMRV oversight via raw data checking and site visits, as described above. This report shall detail:

• the cumulative biomass used, biochar produced, and biochar applied in an eligible end use, noting any discrepancies and justification,

• any kiln runs that were excluded from certification and the reason for exclusion

• any non-conformities in data uploaded to dMRV and their remediation

• any non-conformities or failure to adhere to best practices in onsite visits, and their remediation

Temperature curves

All kilns shall be equipped with fixed, continuously-logging thermocouples, producing a documented temperature curve over time for each kiln run. The purpose is twofold: to ensure pyrolysis actually occurred, and to assess the quality of the pyrolysis run.

To ensure pyrolysis actually occurred, the temperature curve must show that the temperature of the pyrolysis zone remained above 350°C for the entire process, excluding the ramp up and quenching phases.

To assess pyrolysis quality, Project Developers shall submit project-specific criteria for evaluating temperature curves during project validation. These criteria shall be used to flag and exclude ineligible kiln runs, and shall be approved by Rainbow and the VVB. Criteria shall be designed to flag:

• Incomplete biomass drying prior to pyrolysis, and

• Improper feedstock loading rates, such as overloading events that cause a drop in pyrolysis temperature or extinguish the flame curtain.

Criteria definitions shall address target temperatures, durations, and allowable variance, and ramp-up period, quenching, and main pyrolysis time.

Placement: Thermocouples should be placed inside the kiln at an appropriate number and spacing to meet the above-mentioned performance requirements. For kilns where it is not technically feasible to place thermocouples inside, they may be placed on the outside of kilns and heat-transfer or energy-balance models shall be used to demonstrate that pyrolysis zone remained above 350°C for the entire process.

Checking temperature curves: Temperature curve results from all kiln runs shall be individually checked, according to the Raw data checking requirements.

Tolerance for thermocouple failures: some kiln runs are expected to experience thermocouple failures. Biochar from kiln runs that experience a thermocouple failure may still be credited if all other required proof is still available for the kiln run, if the reason for the failure can be explained and justified, and if a kiln does not experience consecutive failures. This is applicable to kiln runs that make up a cumulative maximum of 5% of the biochar in the Production Batch. Beyond this 5%, any kiln runs with thermocouple failures shall be discarded and not credited. The biochar in such excluded kiln runs does not count towards the size-limit of the Production Batch.

Calibration: All thermocouples shall undergo regular calibration.

Integrated temperature sensors are a promising and relatively new pathway to verify pyrolysis quality and consistency for certification of distributed biochar production, ensuring low methane emissions and proper biochar production. Strict methodology-level requirements are not set because:

• Thermocouple setups (number, placement, spacing) vary by kiln design.

• Different biomass feedstocks produce distinct temperature curves due to varied energy content.

• Universal temperature thresholds are not yet established.

Ideally temperature sensors will be used to prove that pyrolysis remains above 500-550°C, which is a more robust sign of high-quality pyrolysis than 350°C. However, due to the novelty and expected difficulties in this technology's early deployment, this requirement remains flexible for the time being.

Trainings

Upon validation, Project Developers shall submit their Training Protocol, describing how they ensure:

• frequency of trainings for Kiln Operators and Kiln Supervisors

• testing or proof of adequate completion of training

• ongoing training and support

Kiln Operator training

Project Developers are responsible for ensuring regular trainings are provided to Kiln Operators involved in their project. The Kiln Supervisor or the Project Developer may be the party providing training. Training shall cover at least the following aspects of kiln operation:

• safety provisions for operating the kiln

• biomass preparation (drying, eligible biomass size, appropriate size of biomass)

• taking biomass moisture content measurements

• feeding biomass into the kiln to ensure consistent pyrolysis

• rapid quenching

• managing the biochar sampling procedure

• use of dMRV

Kiln Supervisor training

Project Developers shall justify the expertise and qualifications of Kiln Supervisors. This may be through dedicated training or previous relevant experience. This shall cover at a minimum:

• all points listed above, to be transmitted to Kiln Operators

• biochar amount measurements, including bulk density and moisture content