Green ammonia certification explained: how mass balance chain of custody works, why book and claim is not allowed, and how co-mingled storage is handled.
Introduction
Hydrogen is hard to ship, so a great deal of green hydrogen is converted to ammonia for export. That makes green ammonia certification a central topic for producers aiming at Europe. It also introduces a specific and underestimated risk: what happens when green and non-green ammonia end up in the same tank. This article explains how green ammonia is certified, how the mass balance chain of custody works, and why co-mingled storage is where most of the certification risk sits.
How green ammonia is certified
Green ammonia has no standard of its own. It is certified as an RFNBO derivative, and qualification rests on three things.
The first is a certified renewable hydrogen input. The hydrogen fed into ammonia synthesis must itself meet the RFNBO rules. The second is the lifecycle greenhouse gas footprint, which must meet the threshold of below 28.2 gCO2e/MJ across the whole chain, including synthesis and shipping. The third is the chain of custody, which keeps the green attribute attached to the right volumes as the ammonia moves through synthesis, storage and transport.
Mass balance, not book and claim
The chain-of-custody method is mass balance. Book and claim is not allowed. This distinction matters.
Book and claim would let a producer sell the green attribute separately from the physical ammonia, so a buyer could claim green ammonia with no physical link to green production. CertifHy does not permit this for RFNBO. It requires mass balance, which keeps a physical connection between the certified attribute and the actual volumes flowing through the system. The green attribute lives in the ledger, not in any particular molecule, but the ledger has to reconcile against real physical flows.
The co-mingled storage rules
Co-mingling is allowed, within strict conditions. Green and non-green ammonia can share one tank if the following hold.
| Condition | Requirement |
|---|---|
| Volume balance | Green drawn out never exceeds green put in, each period |
| Balancing period | No longer than three months, closing with no deficit |
| Attribute transfer | The full attribute set is transferred whole, not split |
| Carry forward | A positive green balance may be carried to the next period |
| Documentation | Each delivery carries a Proof of Sustainability |
If these hold, co-mingling is fine and the green claim stays valid. If they do not, separate mass balances are required.
The molecules mix in the tank. The green attribute must not. Keeping those two facts compatible is what chain of custody is for.
Proof of Sustainability
Each delivery of certified ammonia carries a Proof of Sustainability, a record of the attributes that travels with the consignment. This is what allows a downstream buyer, and the auditor, to trace the certified claim back through the chain. Getting the Proof of Sustainability right at every handover is part of what makes the mass balance defensible.
What this means for producers
The practical lesson is that chain of custody is a design problem, not a paperwork afterthought. How storage is arranged, how balancing periods are defined, and how third-party operators are contracted all determine whether the mass balance holds. For a GCC ammonia export project, this is often the part of the certification that needs the most careful engineering, alongside the electricity qualification.
How ESGweise helps
ESGweise helps producers design a mass balance chain of custody that will pass audit. We map the physical flows, define the balancing boundaries and periods, structure the third-party storage arrangements, and set up the Proof of Sustainability records, so the certified claim reconciles against real volumes. This is readiness work, distinct from the audit itself. See our assurance readiness and carbon accounting services, and the full scheme in the CertifHy pillar guide.
Conclusion
Green ammonia is certified through a certified renewable hydrogen input, a compliant lifecycle footprint, and a mass balance chain of custody. Book and claim is not allowed, so the certified attribute has to stay physically linked to real volumes. Co-mingled storage is where that link is most at risk, especially under third-party operation. Producers who design the chain of custody early, and contract the storage carefully, protect the certification that their export market depends on.
Frequently asked questions
How is green ammonia certified?
Green ammonia has no separate standard. It is certified as an RFNBO derivative through three things: a certified renewable hydrogen input, a lifecycle greenhouse gas footprint that meets the RFNBO threshold of below 28.2 gCO2e/MJ, and a mass balance chain of custody that keeps the green attribute attached to the correct volumes as the ammonia is synthesised, stored, moved and mixed.
What is mass balance chain of custody?
Mass balance is a method for tracking a sustainability attribute through a system where certified and non-certified material is mixed. The green attribute is tracked in a ledger rather than in a specific molecule. Over each balancing period, the certified volume drawn out of the system cannot exceed the certified volume put in. This allows green and non-green ammonia to share infrastructure while keeping the certified claim accurate.
Why is book and claim not allowed for green ammonia?
Book and claim allows a certified attribute to be sold separately from the physical product, so a buyer can claim green ammonia without a physical connection to green production. CertifHy does not allow this for RFNBO. It requires mass balance, which keeps a physical link between the certified attribute and the actual volumes of ammonia flowing through the system. This makes the claim more robust but also more demanding to operate.
How does co-mingled storage work under the rules?
Green and non-green ammonia can be stored together in one tank if the boundaries are precise, the green volume drawn out never exceeds the green volume put in during each period, the period is no longer than three months and closes with no deficit, and the full attribute set is transferred whole rather than split. A positive green balance can be carried to the next period. If the tank is operated by a third party, a written contract is needed to forward the CertifHy claim.