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The SCR catalytic converter (Selective Catalytic Reduction) converts the exhaust constituent nitrogen oxide (NOx) into nitrogen and water without producing undesirable by-products. This conversion takes place using a synthetically produced aqueous urea solution, e.g. AdBlue, which is carried in an auxiliary tank. The substance, containing 32.5 percent urea, is added continuously to the exhaust tract upstream of the SCR catalytic converter. It is metered according to the mass flow rate of the exhaust gas and is precisely regulated by the engine management system, which receives information from the NOx sensor behind the SCR catalytic converter. The NOx exhaust treatment system SCR is one of the efficient and environmentally compatible technologies that Volkswagen links under its BlueMotionTechnologies umbrella brand.