Noxious diesel emissions may be higher than we think

Since the public first found out about the diesel emissions scandal, car makers across the world have been trying to convince us that diesel engines that meet the official emissions regulations, without any cheating software, can be as clean as we need them to be, and even as clean as a petrol-engined car.

A new survey, based on real-world observed emissions, claims to debunk that, and says emissions of noxious diesel gases, specifically harmful nitrogen oxides (NOx) are far higher in the real world than in the lab, even with regulations-compliant cars.

The Real Urban Emissions (True) initiative is a collaboration of the FIA Foundation, the International Council on Clean Transportation (ICCT), Global NCAP, Transport and Environment (T&E) and 40 leading global cities and it has been collating the data taken from real-world emissions of cars, specifically those which represent some 90 per cent of all sales in Europe. The test involves pointing a beam of light at the emissions "cloud" from a car as it passes a measuring point and uses spectroscopy to analyse what's coming out the tailpipe.

Across 4,850 cars put through the measurement system, all diesel-engined cars exceeded the current NOx limits in real-world conditions, even the cars compliant with current Euro6 regulations – which are supposed to be the standard bearers when it comes to emissions. Four manufacturer groups had NOx emissions averaging 12 times the current legal limit of 80mg/km, while the worst of the Euro6 petrol-engined cars tested was, in NOx terms, only as bad as the best-performing diesel.

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City streets

Stepping back to Euro5 emissions-compliant cars (or, in other words, the cars that have just been banned from some city streets in Hamburg) and even the best performer was at least two times over the NOx limit, with the worst 18 times over.

"This initial project is an important first step," said Rachel Muncrief, programme director for the ICCT, "but remote sensing could take us very much further in terms of our ability to monitor, analyse, and control vehicle pollutant emissions and gain control of Europe's urban air-quality problem."

True is quick to point out that it’s not accusing any car makers of cheating on their emissions tests. Every car in the test passed its exams, whether it was rated to Euro3, Euro4. Euro5, or Euro6. The point of the tests is to demonstrate the yawning gap between even the latest standards and what cars actually emit in real-world conditions. While “defeat devices” are still a worry, True did say that its results could be affected by such things as “include deterioration of emissions control systems, defective parts and driving conditions outside of those covered by the regulation”.

City centres

"If I was a customer, I would look at these figures at the moment and have to conclude I should not buy a diesel car," said Dr Peter Mock from the ICCT. "Even Euro 6 diesel vehicles are not performing well at the moment so pretty much all of them should not have access to city centres."

The car industry has reacted angrily to the True tests. "The claims from the new 'True' study are misleading for consumers," stated Erik Jonnaert, secretary general of the European Automobile Manufacturers' Association (ACEA). "EU policymakers will be equally disappointed that there is no acknowledgment that the latest Euro6 diesel cars complying with the new RDE legislation are very clean. The claims made in this study are based on 'remote sensing' results collected between 2011 and 2017. They therefore do not evaluate the on-road performance of the latest diesel vehicles approved to the Euro 6d standard since September 2017. As all cars tested as part of this 'True' initiative were pre-Euro 6d vehicles, the fact that they do not meet emissions requirements that only became mandatory after they were put on the market is not surprising."