CBAM Fertiliser Calculation: How to Compute Embedded Carbon for Ammonia, Urea, and Nitric Acid
CBAM fertiliser calculation requires producers to compute embedded carbon across a chemistry-driven supply chain: ammonia (synthesised from natural gas via steam methane reforming), urea (from ammonia plus captured CO2), nitric acid (from ammonia oxidation, with significant N2O process emissions if not abated), and downstream NPK fertilisers. Each product has different system boundaries and different defaults.
CBAM Fertiliser Calculation by Product
The CBAM calculation is product-specific because the chemistry is product-specific. The four main products:
- Ammonia (CN 2814): synthesised via Haber-Bosch from hydrogen (typically grey hydrogen from steam methane reforming) and atmospheric nitrogen. Embedded emissions are dominated by the SMR step.
- Urea (CN 3102 10): ammonia + CO2 → urea. Some captured CO2 is reabsorbed; the net carbon balance differs from ammonia.
- Nitric acid (CN 2808): ammonia oxidation. The catalytic step produces N2O (a 273× GWP greenhouse gas) — abatement technology is critical.
- NPK fertilisers (CN 3105): downstream blending with embedded emissions of the precursor nitrogen, phosphorus, and potassium components.
Ammonia Calculation — The Foundation
Steam methane reforming (SMR) of natural gas:
CH4 + 2H2O → CO2 + 4H2
Then Haber-Bosch synthesis:
3H2 + N2 → 2NH3
Typical actual ammonia embedded emissions: 1.6–2.2 tCO2e/t for modern SMR-based plants on natural gas, 2.5–3.5 tCO2e/t for older or coal-gasification-based plants (predominant in China), and 0.1–0.5 tCO2e/t for green-ammonia routes using electrolytic hydrogen from renewables.
Urea Calculation — Net of CO2 Capture
Urea production reabsorbs approximately 0.73 tonnes of CO2 per tonne of urea from the upstream ammonia process. The CBAM calculation reflects this net balance — urea has lower net embedded emissions per tonne of nitrogen content than the ammonia it is made from.
Caveat: the captured CO2 is released back to atmosphere when the urea is applied to soil and hydrolysed. CBAM is a customs-gate measurement, so the soil-stage release is out of scope, but the net carbon balance is debated in academic literature.
Nitric Acid — N2O is the Story
Nitric acid production via catalytic ammonia oxidation produces nitrous oxide (N2O) as a byproduct. N2O has a global warming potential of 273× CO2 over 100 years. Without abatement, N2O process emissions can dominate the nitric acid CBAM calculation:
- Without N2O abatement: 6–10 tCO2e/t nitric acid
- With tertiary N2O abatement (catalytic destruction): 1.5–2.5 tCO2e/t nitric acid
- Modern plant with N2O abatement + low-energy process: 1.0–1.8 tCO2e/t
For nitric acid producers, N2O abatement is the single highest-leverage CBAM intervention. The technology is mature, retrofittable, and pays back rapidly under CBAM economics.
Frequently Asked Questions
What CN codes does CBAM fertiliser calculation cover?
CBAM Annex I covers ammonia (CN 2814), nitric acid (CN 2808), nitrogen fertilisers (CN 3102), and mixed NPK fertilisers (CN 3105). The Annex III calculation applies across these.
How does the ammonia production route affect embedded emissions?
Modern SMR on natural gas: 1.6–2.2 tCO2e/t. Older or coal-gasification-based: 2.5–3.5 tCO2e/t. Green ammonia (electrolytic hydrogen + renewable electricity): 0.1–0.5 tCO2e/t. Route choice dominates the calculation.
Why does N2O matter so much for nitric acid?
N2O has a global warming potential 273× that of CO2. Without abatement, N2O process emissions can be 6–10 tCO2e/t of nitric acid — dominating the total. Tertiary abatement reduces this to 1.5–2.5 tCO2e/t.
Does urea get credit for the CO2 reabsorbed during synthesis?
Yes — the urea CBAM calculation accounts for approximately 0.73 tCO2 reabsorbed per tonne of urea. The net embedded emissions per tonne of nitrogen content are lower than for the ammonia precursor.
Is green ammonia commercially CBAM-compliant today?
Green ammonia produced from renewable-powered electrolytic hydrogen has very low CBAM embedded emissions (0.1–0.5 tCO2e/t) and produces a near-zero CBAM cost. The barrier today is production scale and cost, not the CBAM accounting framework.
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