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AdBlue is appearing in more and more cars, including VW, Skoda, Seat, BMW and Mercedes; as more vehicles comply with the Euro 6 diesel standard the use of AdBlue is likely to increase. The German Association of the Automotive Industry (VDA) controls the “AdBlue” trademark and uses it to ensure quality standards are maintained in accordance with DIN 70070 and ISO 22241 specifications. 

Diesel exhaust fluid (DEF), commonly referred to as AdBlue in Europe, Australia and New Zealand, and standardised as ISO 22241, is a solution composed of 32.5% urea and 67.5% demineralised water. It is non-toxic, colourless, odourless and non-flammable.


AdBlue is injected into the engine’s exhaust gases and in the resulting chemical reaction, the nitrogen oxides in the exhaust are converted into harmless nitrogen and water vapour. It is a consumable used in selective catalytic reduction (SCR) in order to lower the concentration of nitrogen oxides in the exhaust emissions from diesel engines. DEF is stored in a tank on board the vehicle, and injected into the exhaust stream by a metering system.

The injection rate depends on the specific after-treatment system, but is typically 2-6% of diesel consumption volume. This low dosing rate ensures long fluid refill intervals and minimises the tank’s size. An electronic control unit adjusts the addition of fluid in accordance with such parameters as engine operating temperature and speed. A passenger car will consume approximately 1.5 litres of AdBlue every 620 miles.

AdBlue belongs to the lowest water pollution hazard category but is a skin irritant and a corrosive liquid that can cause injury if it touches the skin, eyes or respiratory organs. The urea solution is clear, non-toxic and safe to handle. However, it can corrode some metals and so must be handled, stored and transported carefully. It is recommended that DEF be stored in a cool, dry, and well-ventilated area that is out of direct sunlight.

Although not toxic, DEF can cause the catastrophic de-oxidation of water bodies leading to damage of the aquatic environment and so careful handling and storage is essential.