In order to improve air quality, the pollutant exhaust emissions of road vehicles are limited by regulation. Regulatory limits apply to exhaust emission measurements during vehicle type approval procedures1. Over the last two decades limit values were lowered in steps from EURO 0 to EURO 4. Further steps have already been defined for the coming years (EURO 5) or are under discussion (EURO 6). This study aims to provide explanations for the gap, both for cars and heavy duty vehicles (HDVs) on the basis of a comparison of operating conditions under test cycles and operating conditions in real traffic. Possibilities to improve test cycles to match onroad conditions more closely are examined and recommendations made for the introduction of in-use control tests. The study focusses mainly on NOx emissions and heavy duty vehicles.

URL: http://www.cemt.org/pub/pubpdf/NOx%202006E.pdf