AdBlue® is a biodegradable aqueous liquid based on urea to reduce NOx emissions (nitrogen oxides) from diesel engines. The AdBlue® solution is injected into the exhaust system between the engine and the SCR catalyst (Selective Catalytic Reduction). In the catalytic converter, AdBlue® is converted into ammonia. The ammonia then reacts with the emitted nitrogen oxides to form water and nitrogen gas. These substances are harmless to the environment and are biodegradable.