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Diesel cars even more polluting than previously thought

Some new diesel cars emitting 11 times more pollution than the legal limit, while black cabs are even worse

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A new report has revealed that diesel cars on British roads are even more polluting than previously believed, with some vehicles emitting 11 times more pollution than the legal limit.

A study by the FIA Foundation and the International Council on Clean Transport (ICCT) measured the actual tailpipe emissions of 100,000 vehicles (including cars, vans, buses, taxis, trucks and motorcycles) at nine locations in London.

The emissions were measured by firing infrared and ultraviolet light through the car’s exhaust plumes, before recording the contents.

As has been repeatedly found by independent testing, claimed improvements in toxic nitrogen oxide (NOx) emissions by car manufacturers have been exposed as false, with most car companies still exceeding legal limits.

Local air pollution vs. global climate impact

For many years, the EU and national governments have set limits and taxes based on carbon dioxide (CO2) emissions. This led to car manufacturers selling more and more diesel cars, which naturally produce less CO2 than petrol equivalents – at least in very gentle laboratory tests.

However, a major issue has arisen over the increase in NOx emissions, which are much higher in diesel engines than in petrol engines. These emissions affect local air quality rather than global climate change, which has resulted in far more local pollution in cities in exchange for an imperceptible reduction in global CO2 levels.

London pollution will theoretically be reduced when the ULEZ arrives in 2019
A typical summer’s day in London

Our air is getting worse while global CO2 levels are still going up anyway

The key findings published by the International Council on Clean Transport are:

  • Nitrogen oxide (NOx) emissions from diesel cars in London are, on average per kilometer, six times those of petrol cars. NOx emissions from petrol cars have declined, and on average for Euro 5 and Euro 6 vehicles are within 1.35 times the regulatory limits. Average NOx emissions from Euro 5 and 6 diesel cars, however, are approximately six times higher than the standards.
  • Particulate matter (PM) emissions from passenger cars are low for new diesel and petrol cars. Diesel cars, Euro 5 and newer, come equipped with particulate filters and demonstrate significantly lower PM emissions than older vehicles without filters.
  • London’s famous black taxi diesel models produce, on average, higher NOx emissions than diesel passenger cars covered by the same emissions standard. NOx emissions from Euro 5 taxis are higher than those from taxis certified to previous Euro standards and are approximately three times those of other Euro 5 diesel cars.
  • Average NOx emissions from buses in London have declined significantly over the past five years. NOx emissions (grams per kilogram of fuel burned) from buses sampled were 65% lower than those from buses sampled in similar studies conducted in 2012 and 2013. A similar comparison for other vehicle types shows that over the same time period average emissions from the diesel passenger car and light commercial vehicle fleet have decreased by 22% and 15%, respectively, while average NOx emissions from the taxi fleet have not improved.

Diesel cars are still terrible for local air pollution

Even newer Euro 6 (2014 – present) diesel cars are still worse for local air pollution than some Euro 3 (2000 – 2005) petrol cars.

More than 90% of current Euro 6 diesel cars were rated “poor”, with less than 10% rated “moderate” and none rated “good”. Every diesel car prior to 2010 is rated “poor”. By contrast, 67% of Euro 6 petrol cars are rated good, 32% rated “moderate” and only 1% “poor”.

Relative emissions of petrol and diesel cars
Diesel cars are still overwhelmingly bad for local air quality. (C) ICCT

Rules are getting tougher, but will they bring any improvements?

The results do not take into account the very latest emissions regulations that came into force in September 2018, known as Euro 6d-temp, as the data was recorded earlier this year when there were very few of these vehicles on the road.

As usual, the car industry will probably moan that it’s not fair and that the newest Euro 6d-temp cars really are very clean, and yes they did say that last time but they really mean it this time. Then they’ll throw in an unrelated reference to Brexit because that’s the car industry excuse for everything.

The reality remains that air quality on London streets right now (and in every other busy part of the UK) remains very poor and that’s largely because of diesel cars.

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Renault the worst performer again

The ICCT tested a variety of vehicles and found that on average, car companies emitted more than six times the legal limits of NO(0.08g/km).

those produced by the RenaultNissanMitsubishi alliance were the worst performers, emitting on average 11 times the legal limit. This echoes a report by Which? magazine earlier this year that found Renault had five of the ten worst-polluting cars tested.

Diesel vehicles from the Fiat Chrysler Alliance (Fiat, Abarth, Alfa Romeo, Jeep and Maserati) and Hyundai Motor Group (Hyundai and Kia) weren’t too far behind.

Perhaps surprisingly, the disgraced Volkswagen Group (Volkswagen, Audi, SEAT and Skoda) performed second-best – with only JLR (Jaguar and Land Rover) proving cleaner. However, even JLR still emitted more than double the legal limit of nitrogen oxides.

The best diesel engine recorded was the latest-generation Euro 6 Mercedes-Benz 2.0-litre diesel engine, although it is still only considered “moderate” rather than “good”.

The worst Euro 6 petrol engine, and the only one to be rated “poor”, is the 1.2-litre BMW engine used in many Mini models. However, it is still cleaner than the average Euro 6 diesel.

Mercedes-Benz C-Class test drive wallpaper | The Car Expert
The Mercedes C 220d is one of the least-worst diesel cars for air pollution

Black cabs, by name and nature

The research also found that London has a serious problem with black cabs – with the study finding them to be some of the capital’s most polluting vehicles. In fact, the most common black cab models in London produce NOx emissions of up to 30 times that of personal cars.

This is hardly surprising, as black cabs have not had to comply with the same standards applied to normal passenger cars for many years, and have effectively been generations behind passenger cars in terms of emissions requirements.

It’s only this year that laws were introduced to make them zero-emissions capable in London, although no rules yet exist to force cabs to actually run on electric power at any time. They merely have to be capable of doing so.

One diesel black cab can produce as much pollution as 30 diesel passenger cars
One diesel black cab can produce as much pollution as 30 diesel passenger cars

The latest from The Car Expert

Stuart Masson
Stuart Massonhttps://www.thecarexpert.co.uk/
Stuart is the Editorial Director of our suite of sites: The Car Expert, The Van Expert and The Truck Expert. Originally from Australia, Stuart has had a passion for cars and the automotive industry for over thirty years. He spent a decade in automotive retail, and now works tirelessly to help car buyers by providing independent and impartial advice.