Will Euro 6 reduce the NO _x emissions of new diesel cars? - Insights from on-road tests with Portable Emissions Measurement Systems (PEMS)

The nitrogen dioxide (NO ₂) pollution in urban areas of Europe can be partially attributed to the increasing market penetration of diesel cars that show higher distance-specific nitrogen oxides (NO _x) emissions than gasoline cars. The on-road NO _x emissions of diesel cars, furthermore, appear to exceed substantially applicable emissions standards. This observation raises concerns that the introduction of more stringent Euro 6 emissions standards in 2014 may not adequately reduce the distance-specific on-road NO _x emissions of new diesel cars. We address the existing concerns by analyzing the gaseous emissions of one novel Euro 6 diesel car and six Euro 4-5 diesel cars with Portable Emissions Measurement Systems (PEMS). We find that the average on-road NO _x emissions of the Euro 6 car (0.21 ± 0.09 g per kilometer [g km ^-1]) are considerably lower than those of the Euro 4 cars (0.76 ± 0.12 g km ^-1) and the Euro 5 cars (0.71 ± 0.30 g km ^-1). The selective catalytic reduction (SCR) system of the Euro 6 diesel car is suitable to limit NO _x emissions during real-world on-road driving. Still, all tested cars, including the Euro 6 diesel car, exceed their NO _x emissions standards on the road by 260 ± 130%. This finding suggests that the current type-approval procedure does not adequately capture the on-road NO _x emissions of diesel cars. By introducing a complementary emissions test procedure that covers a wide range of normal operating conditions, the European legislative authorities can address this problem and ensure that Euro 6 will indeed deliver an adequate reduction in the NO _x emissions of new diesel cars.