Emissions findings question official figures

Emissions tests carried out by the Dutch government have found that cars can breach the legal NOx limit by almost 4000% – yet still comply with the law.

Commissioned by the country’s environment ministry, the Organisation for Applied Science Research tested a Mercedes-Benz C220 Tdi BlueTec – which it found to put out 40 times the limit for oxides of nitrogen.

There is no suggestion of wrongdoing on Mercedes’ part, or of technical deficiencies in the vehicle. However, the results appear to highlight shortcomings in the official test regime – which mean the real-world emissions from any given car are likely to be higher than its government-approved figures suggest.

The problem is that the official test is carried out at an ambient temperature of 22°C. For most of the year in most of Europe, the air is far colder than that.

And the Dutch tests were carried out at 5-7°C. That’s much more realistic, certainly at this time of year.

In Germany, clean-air campaigners are calling for city-centre exclusion zones that would come into force at temperatures of less than 10°C. Some even say type approval should be withdrawn from C-Class diesels as a result of the new findings.

With Mercedes having followed all the rules, however, that suggestion sounds more like a bid for headlines than a serious proposal.

Merc says the official test regime gives manufacturers a necessary benchmark against which to set their engines’ emission controls. The exhaust gas recirculation system, for example, doesn’t just have to work – it has to do so consistently for 160,000 kilometres.