Study finds diesel cars emit more pollution when cold

Diesel cars | Smarter Travel Ltd

New research has revealed that millions of diesel cars on British roads are emitting more pollution when the weather is cold, specifically below 18 degrees Celsius.

Emissions Analytics, a pollution and air quality testing company, have said that they’ve measured a significant rise in the emissions of poisonous gas from certain car models in cooler temperatures. This means using the cars on roads given the climate, are a greater threat to human health and the environment.

The problem is caused by engine management systems installed by manufacturers, which are designed to partially switch off emission controls when it gets cold outside. The firm tested 213 models across 31 manufacturers and found the problem is worst among cars approved between 2009 and 2011, known as “Euro 5” cars.

The data shows that the average Euro 5 vehicle is 3.6 times over the legal limit for poisonous Nitrogen Oxide emissions above 18c, and 4.6 times over when below. However, it seems the newer Euro 6 category cars are safer.

Under European law, manufacturers are allowed to install engine management systems which alter emissions based on the outside temperature in order to protect components. But industry critics suggest car companies are taking advantage of the rule to switch things off, even in mild weather, because it improves the car’s mpg.

That said, it seems that lots of cars are designed this way on purpose, and it’s legal even under the emissions guidance. European rules allow manufacturers to cut back on pollution controls as long as it’s to protect the engine; and as engineers agree extremes of either hot or cold can be dangerous, there’s leeway to turn off pollution controls.

And of course, turning the software off helps sale ability, as lesser pollution controls improve the miles per gallon. The manufacturers themselves say it’s simply a safety precaution, to stop engine damage and the resulting breakdowns.

Nick Molden, chief executive of Emissions Analytics, said: “I would say from the Euro 5 generation of cars, it’s very widespread, from our data. Below 18 degrees, many have higher emissions. The suspicion is, to give the car better fuel economy.”

“If we were talking about higher emissions below zero, that would be more understandable and there are reasons why the engine needs to be protected. But what we’ve got is this odd situation where the temperature threshold has been set far too high, and that is a surprise”.

The Society of Motor Manufacturers and Traders, which represents car makes, comments: “The temporary reduction or switching off of some emissions control systems under certain temperatures is allowed by law and necessary to avoid damage to vehicles’ engines.

“Without it, there could be a significant cost to the consumer for major repair work. In its recent report, government recognised the need for such technology and was satisfied with how vehicle manufacturers were using it.

Manufacturers are investing billions of pounds in developing ever-more advanced technology, and this along with new Real Driving Emissions regulation from next year will see significant lowering of emissions across a full range of driving conditions and temperatures.”

Why does it matter?

Pollution has been linked to heart attacks, strokes, breathing problems and premature babies. There is a suggestion that children going to school near busy roads may develop smaller lungs.

Professor Frank Kelly at King’s College London has been calling for tighter rules for years, especially with diesel vehicles. “On average we think pollution is probably taking away about six months of life for the average British citizen,” he says.

Are you concerned about the pollution levels of your car? Help cut carbon by filling your spare seats and keeping other vehicles off the road.

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