Is carbon monoxide counted in a Carbon Border Adjustment Mechanism (CBAM) figure, or only carbon dioxide?
It counts as carbon dioxide. The Commission's guides treat carbon monoxide (CO) released to the air as the molar equivalent amount of carbon dioxide (CO2), and the aluminium guide assumes all CO formed at the anode becomes CO2. If you measure CO yourself, by our arithmetic from molar masses, 1 tonne of CO counts as about 1.57 tonnes of CO2.
Half-burnt smoke
Carbon monoxide is carbon that did not finish burning, like half-burnt smoke from a stove. Carbon dioxide is the finished burn. CBAM is the European Union's (EU) charge on the carbon built into imported goods, and it asks for carbon dioxide equivalent. So the rule is simple: count all the carbon as if it had finished burning.
What the guides say
- Hydrogen guide, worked example: carbon monoxide released to the air is not counted as an outgoing stream in the mass balance but is considered as the molar equivalent amount of CO2 emissions.
- Aluminium guide: all carbon monoxide formed at the anode is assumed to be converted to CO2.
- Annex A of the guides (the cement guide's version covers the oxidation factor), definitions of the conversion factor and the oxidation factor: carbon monoxide emitted to the atmosphere is considered as the molar equivalent amount of CO2.
- Ammonia and hydrogen guides: any carbon monoxide made in steam reforming is almost all converted to carbon dioxide by the process.
The arithmetic
Molar equivalent means one molecule of CO counts as one molecule of CO2. A CO molecule weighs 28 units (carbon 12 plus oxygen 16) and a CO2 molecule 44 (carbon 12 plus oxygen 32). So 1 tonne of CO counts as 44 / 28 = 1.571 tonnes of CO2. This is our arithmetic from those standard weights, not a figure printed in the guides.
Where it matters in practice
- Working from fuel and feedstock carbon, as in the hydrogen guide's example: do not subtract the CO as an outgoing stream and add nothing extra. The guide counts it as the molar equivalent amount of CO2 already, so adding it on top would count the same carbon twice.
- Only a CO figure you measure yourself, for example at the stack, and only if your monitoring plan uses measurement: convert it at 44 / 28 before it joins the direct emissions.
- A smelter, where the anode carbon burns to CO and CO2: the guide says all formed CO is assumed to be converted to CO2. Our reading: so no separate CO line is needed.
Two ways CO shows up in a hydrogen plant (example)
- Carbon balance route: the carbon in the natural gas and feedstock is worked out as CO2. CO leaving the process is not subtracted as an outgoing stream, and nothing is added on top.
- Measurement route, only if your monitoring plan uses it: 4 tonnes of CO measured escaping to the air in the year, counted as 4 x 44 / 28 = 6.29 tonnes of CO2
- Never do both for the same carbon: that would count it twice
The 4 tonnes is an example number.
What Senseible does here
Senseible reads fuel invoices and electricity bills into monthly records. Reading stack gas tests or working out a carbon balance is custom, on request. Senseible builds the verifier-ready file and checks every figure in-house; an accredited verifier Senseible partners with signs it off, or the client sends it to their own.
- Build your CBAM file
- Steam reforming hydrogen worked example
- Verifier checks at an aluminium plant
- Do IPCC default fuel factors assume full burning
Sources: European Commission, CBAM Guidance No. 5b, hydrogen (14 August 2026), European Commission, CBAM Guidance No. 5e, aluminium (14 August 2026), European Commission, CBAM Guidance No. 5c, fertilisers (14 August 2026), European Commission, CBAM Guidance No. 5a, cement (14 August 2026)
Last reviewed 2026-11-07. Check the definitions in Annex A of the guides and Annex II of Implementing Regulation (EU) 2025/2547 for the carbon balance rules. The guides say they are not legally binding.