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Air Pollution and Car Emissions

Cars that Produce the Most NOx

By Adrian Porter

Article 2 of 3

Which? reveals the cars that produce the most amount of harmful NOx (and NO2) emissions in our realistic car emission and air pollution tests.

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NOx (or specifically NO2, one of the gasses within NOx), is perhaps the most talked about of the emissions and with good reason - it's one of the most harmful gasses that cars produce.

Both petrol and diesel vehicles produce NOx, but diesel-powered cars produce it in vastly higher quantities than petrol - 16.5 times as much on average, in our tests.

Keep reading to discover which cars produced the most NOx in our tests.

If a car can't keep its NOx levels down below the Euro 3 limit (passed in 2001) in Which? emission tests, we withhold making it a Best Buy. That means the best cars we recommend are not the biggest NOx offenders.

In a nutshell: why our car emission findings matter

  • Acute NOx exposure can trigger asthma attacks and worsen respiratory diseases
  • In our tests, a quarter of diesel cars emit so much NOx that we couldn't make them Best Buys
  • We found there is no strong link between MPG and NO2/NOx - just because you have low fuel bills doesn't mean you have a clean car.

The 10 diesel cars that produce the most NOx

These cars are the ones that produced the most NOx in our tests. 

All of them officially met their respective official Euro 5 or Euro 6 requirements. But in our more realistic tests, the worst car produced 15 times the limit of NOx than Euro 5 limits allow.

  • Euro 5 limit - 0.18g/km
  • Euro 6 limit - 0.08g/km

Jeep Grand Cherokee, 3.0-litre (2011-) - emits 2.7g/km of NOx.
By far the biggest NOx creator in our tests. Shovels 15 times the amount of NOx into the atmosphere than its Euro 5 engine is allowed to.

Subaru Forester, 2.0-litre (2013-) - emits 1.19g/km of NOx
Its Euro 5 engine pumps out more than six-and-a-half times as much NOx as its engine should permit.

Nissan X-Trail, 1.6-litre (2014-) - emits 1.05g/km of NOx
The Nissan X-Trail is the only official Euro 6 engine we’ve tested that fails to meet even Euro 1 standards from 1993. In our tests, it emitted 13 times as much NOx as the Euro 6 limit.

Nissan Qashqai, 1.6-litre (2014-) - emits 0.99g/km of NOx
A top-selling car, it chugs out so much NOx that it also wouldn’t meet Euro 1 standards.

Subaru Outback, 2.0-litre (2015-) - emits 0.94g/km
Its Euro 6 engine should mean its cleaner than most, but it still claims the fifth-biggest producer of NOx.

Kia Sportage, 2.0-litre (2010-) - emits 0.92g/km of NOx
The four-wheel-drive version of this Kia only just meets Euro 1 criteria. That's OK - if you happen to do your driving in 1993.

Hyundai Santa Fe, 2.2-litre (2012-) - emits 0.89g/km of NOx
Look beyond the exotic name, and the bonnet, and you'll find a Euro 5 engine that chucks out large amounts of NOx.

Kia Sorento, 2.2-litre (2010-2015) - emits 0.89g/km of NOx
The second entry from Kia in this top 10, the Sorento isn't far behind the Sportage in terms of NOx production

Dacia Duster, 1.5-litre diesel (2013-) - emits 0.89g/km of NOx
The price of the Duster may draw you in, but it's far from a squeaky clean purchase despite having a Euro 6 engine

Land Rover Range Rover Sport, 3.0-litre (2005-2013) - emits 0.87g/km of NOx
This Range Rover produces nearly five times the Euro 5 allowed amount of NOx.

Highest NOx-emitting diesel-hybrid

Peugeot 508 RXH, diesel-electric hybrid (2012-) - 0.53g/km
While it's not in the top ten, this Peugeot is worth mentioning. Although it’s a hybrid, it still pushes out three times the Euro 5 NOx legal limit.

The five petrol cars that produce the most amount of NOx

  • The three worst petrol cars listed here produce so much NOx that they would fail the Euro 3 standards.

Petrol engines produce NOx – most in such small quantities that it’s not of consequence. However, there are some that are worth avoiding:

Euro 5 and Euro 6 limit - 0.06g/km

Mercedes-Benz SL, 3.5-litre (2012-) - emits 0.2g/km of NOx
This sporty car from Mercedes creates three times as much NOx as petrol limits allow. To put that in perspective, it’s the only petrol car we've seen that would also fail diesel-equivalent Euro 5 limits.

Mercedes-Benz E-Class, 2.0-litre (2009-) - emits 0.17g/km of NOx
In terms of cars that produce the most amount of NOx from their petrol engines, Mercedes also takes the second spot. The E-Class is almost as bad as the SL, despite the fact it has what should be a cleaner Euro 6 engine.

Mini Cooper, 5-door, 1.5-litre (2014-) - emits 0.16g/km of NOx
It might be fun to drive, but its Euro 6 engine pushes out nearly three times the amount of NOx that it’s supposed to.

Nissan Pulsar, 1.2-litre (2014-) - emits 0.15g/km of NOx
The small-family sized hatchback may not be the biggest car about, but it creates a big stink in our tests. It only just complies with Euro 3 emission levels.

Nissan Qashqai, 1.2-litre (2014-) - emits 0.12g/km of NOx
Just like the diesel version, the petrol version of the Qashqai also exceeds NOx limits. It's not as bad as the diesel, but it's still the fifth-highest creator of NOx of all petrol cars we've tested so far.

Best Buys removed

We’ve found that of the diesel cars we’ve tested, nearly a quarter would exceed Euro 3 limits (passed in 2001) when faced with our more realistic tests. This means these cars don't pass the earliest emission regulations from this century.

Some of these cars had previously performed well enough in other areas of our testing to be named as Best Buys – but considering how much they pollute, they are no longer Best Buys.

Looking something clean? Find your perfect new car among our Best cars.

What you need to know about car emissions

The Environment Research Group at King’s College London completed a study in 2015 estimating that Londoners lost up to 88,113 life years to NO2 during 2011 – the equivalent of nearly 5,900 deaths. But that assumed a 30% crossover with PM, and is a figure that the report itself advises should be used with caution.

Its effects are more pronounced on those who are vulnerable, such as the elderly and those who have an existing lung condition.

Unlike CO, NO2 levels haven’t reduced across urban areas as much as was hoped in the past 20 years after the introduction of emissions laws, and are currently contributing to the widespread public health issue of poor air quality, alongside PM emissions.