Selective Catalytic Reduction Systems (SCR) are methods of reducing NOX emissions. The basis of this technology consists of a urea solution, which is sprayed into the stream in front of a specialized catalytic converter. This converter has a platinum, vanadium or zeolite coating. The urea is passively converted into ammonia NH3, which in turn reacts with the NOX and oxygen to create nitrogen and water. This technology will be introduced into the European truck market beginning in 2006, but its application in the US depends on the development of an infrastructure system to provide urea.