The Source of Nitrogen Oxide

Diesel vehicles are the essential cause of an increased NO2 pollution in inner cities. These cars are not disposing of an exhaust purification in the best available technology.
Special attention should be drawn to the fact that diesel vehicles emit a multiple of dangerous nitrogen oxide (NO2) compared to gasoline engines. This comparison finds particular application since the introduction of Euro norms 3, 4, and 5.

A gasoline engine emits only a small quantity of NOx, according to norm Euro 3, and a hardly measurable quantity of NO2. The NOx level of Euro Group 3 diesel vehicles, on the other hand, is already more than four times higher than the one of a gasoline engine. Not to forget that the content of nitrogen oxide NO2 amounting to almost 0.3 g NO2/km is by far the highest level for Euro 3 and is likely to be almost 100 times higher, compared with a gas engine according to Euro 3.
Also Euro 4 and Euro 5 diesel vehicles show similar values as the Euro 3 Diesel. Only the Euro 6 diesel is accompanied with a clear decrease of nitrogen oxide but still 10 times above a comparable Euro 6 gas engine car.

Considering now construction machinery, buses, and other commercial vehicles of the city traffic, high contents of NO2 are found here, too. Reviewed in detail, the problems suffer a severe aggravation due to the quantity of local public transport buses. The NO2 contents exceed approximately 5 to 7 times the level of a diesel vehicle.

Comparatively low speed and frequent stops lead to a lower exhaust gas temperature which in turn makes an efficient decrease of NO2 more difficult. Since the introduction of the Euro 6 norm, however, producers of buses are forced to optimise the exhaust technology by an active temperature management and other technologies in so far as also higher demands on a nitrogen oxide reduction can be observed.