If you've read an AdBlue® label, a safety data sheet or a Certificate of Analysis, you'll have seen ISO 22241. It's the international standard that defines the diesel exhaust fluid used in SCR systems, known in Australia as AUS 32 and in the US as DEF. Engine makers design their SCR systems around it, which is why they specify ISO 22241 compliant fluid in the owner's manual.
SCR systems are sensitive. AdBlue is injected into hot exhaust, where it turns into ammonia and reacts over a catalyst to convert NOx into nitrogen and water. The catalyst, dosing pump and injector are all built to work with a fluid of a known concentration and very high purity. Small amounts of the wrong minerals or metals can build up on the catalyst or block fine passages over time.
ISO 22241 gives manufacturers, suppliers and users a common definition of "good" AdBlue, and a common way to test it.
The parts of ISO 22241
The standard is published in several parts. The ones most relevant to buyers are:
- ISO 22241-1: Quality requirements. The specification itself: urea concentration, purity limits and physical properties.
- ISO 22241-2: Test methods. How each property must be measured in the lab, so results from different labs can be compared.
- ISO 22241-3: Handling, transportation and storage. Guidance on compatible materials, keeping the product clean, and how storage temperature affects shelf life.
Further parts deal with the refilling interface, such as filler neck and nozzle design, which is why AdBlue nozzles and vehicle filler necks are a different size from diesel ones.
Key limits in ISO 22241-1
AdBlue is 32.5% high-purity urea in de-ionised water. The standard allows a urea range of 31.8% to 33.2%. That concentration is chosen because it has the lowest freezing point of any urea and water mix, at about −11°C.
Beyond urea content, most of the specification is about what must not be there. Some examples:
| Property | Limit |
|---|---|
| Biuret | ≤ 0.3% |
| Aldehydes | ≤ 5 mg/kg |
| Insoluble matter | ≤ 20 mg/kg |
| Phosphate | ≤ 0.5 mg/kg |
| Calcium, iron, magnesium, sodium, potassium | ≤ 0.5 mg/kg each |
| Copper, zinc, chromium, nickel | ≤ 0.2 mg/kg each |
| Aluminium | ≤ 0.5 mg/kg |
| Density at 20°C | 1087–1093 kg/m³ |
| Refractive index at 20°C | 1.3814–1.3843 |
To put those metal limits in perspective, 0.5 mg/kg is half a part per million. Ordinary tap water can carry far more calcium and magnesium than that, which is why AdBlue has to be made with de-ionised water and must never be topped up from a tap. It is also why the urea must be a technical, low-impurity grade rather than agricultural fertiliser urea, which often contains additives and higher impurity levels.
What ISO 22241-3 means on site
Part 3 is the one most useful to operators, because it's about what happens after the product leaves the plant. In practical terms:
- Use compatible materials: stainless steel (304/316), HDPE, polypropylene, PTFE, EPDM and fluoroelastomer seals.
- Avoid incompatible metals: carbon steel, aluminium, copper, brass and zinc or galvanised steel corrode and release exactly the metals the specification limits.
- Keep it clean: dedicated equipment, closed containers, no reuse of containers that held other products.
- Control temperature: shelf life depends on storage temperature. As a guide, product kept at or below 25°C lasts around 18 months, at or below 30°C around 12 months, and at or below 35°C around 6 months. Above 35°C, test before use.
A product can leave the factory fully compliant and be pushed out of spec by a brass fitting, a reused drum or a summer on a steel roof. Compliance is shared between the producer and the user.
One thing to do today: check the fittings on your AdBlue pump, hose and tank outlet. Any yellow brass or galvanised parts should be swapped for stainless steel or polypropylene, because they will slowly add copper and zinc to your AdBlue.
How to know a product meets ISO 22241
Anyone can print "ISO 22241" on a label. Better evidence is a batch Certificate of Analysis showing lab results against the limits, and a VDA AdBlue licence, which requires the producer to be audited against the standard. You can find more on our certification page and download documents from resources.
How Liquidia can help
Liquidia manufactures AdBlue in Australia under VDA licence No. 0005569, ISO 22241 compliant, with every batch lab-tested and a Certificate of Analysis available on request. Read about our certification or learn more in What is AdBlue.