The European Union has established some rules on vehicle emissions as part of its efforts to reduce environmental pollution caused by heavy machinery. All vehicle manufacturers already fulfill these requirements. The legislation, known as Euro 4, allows NOx emissions of up to 3.5 g/kWh from October 2006.
The next directive, known as Euro 5, which must be fulfilled by vehicle manufacturers by October 2009, regulates NOx emissions as 2.0 grKh.
The automobile industry has arrived at Selective Catalytic Reduction (SCR) after evaluating various solutions to fulfill these requirements.