Diesel vehicles in the EU are allowed a much higher NOx emission level than gasoline cars. In 2000, when the Euro 3 standard was introduced, the allowed level was 0.5 g/km, more than twice as much as for gasoline vehicles. Yet, as vehicle tests show, even back then the real on-road emission levels were closer to 1.0 g/km, i.e., much more than actually allowed by the standard. Still, the vehicles received their type-approval and could be sold, as the Euro emission standards have to be met under laboratory conditions only. Over time, emission limits got stricter, and the current Euro 5 emission standard sets a limit of 0.18 g/km for NOx diesel emissions. This is still more than three times as high as for gasoline vehicles, but of course much lower than back in 2000. However, recent research suggests that the on-road emissions did not really change at all during the last decade. The values measured are in the range of 0.8 g/km, only 20% lower than in 2000 and more than four times higher than allowed by the Euro 5 emission limit.
The on-road emission data comes from a study carried out recently by King’s College London and the University of Leeds for the UK government. In total, emissions data from more than 80,000 vehicles were analyzed, and the authors conclude: “In the case of light duty diesel vehicles it is found that NOx emissions have changed little over 20 years or so over a period when the proportion of directly emitted NO2 has increased substantially”. The UK study is not the only one arriving at these findings. A recently published paper by researchers from the European Commission’s Joint Research Centre (JRC) and IFEU institute summarizes on-road test results for a number of vehicles and comes to the conclusion: “The on-road NOx emissions of diesel cars, furthermore, appear to exceed substantially applicable emissions standards.” The authors even go one step further by raising doubts about whether the new Euro 6 emission standard, to be introduced in 2014, will solve the problem. It says: “Still, all tested cars, including the Euro 6 diesel car, exceed their NOx emissions standards on the road by 260 ±130%”.*