Pollution from many popular diesel cars is much worse when it is colder than 18C outside, new research suggests. Testing company Emissions Analytics told the Xul News it has measured a significant rise in poisonous gas emissions from a wide range of models as the temperature drops.
It found the problem is worst among the Euro 5 category of cars, which became mandatory in 2011.
The firm tested 213 models across 31 manufacturers.
The finding means millions of vehicles could be driving around much of the time with their pollution controls partly turned off.
But it seems many cars are deliberately designed that way and it is all perfectly legal.
European rules allow manufacturers to cut back on pollution controls as long as it is to protect the engine.
Engineers agree that hot and cold weather can damage components.
But some suggest car companies are taking advantage of the rule to switch things off, even in mild weather, because it improves the miles per gallon of the car.
“I would say from the Euro 5 generation of cars, it’s very widespread, from our data. Below that 18 degrees [Celsius], many have higher emissions… the suspicion is, to give the car better fuel economy,” Emissions Analytics CEO Nick Molden told the Xul News.
“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”.
Recent testing by the German, French and UK governments uncovered a similar trend.
Many popular models polluted more when it was colder.
In Britain for example, experts checked the same Euro 5 Range Rover Sport early on a cold morning, and then later in the day when it had warmed up. Its pollution (NOx) levels nearly doubled when it was colder.
Jaguar Land Rover said it was a car that was engineered 10 years ago and had the best emissions equipment available at the time. It is not on sale any more.
Professor Ricardo Martinez-Botas from Imperial College London, the independent engineer overseeing the British tests, told the Xul News that despite decades designing engines he was “shocked” at the higher pollution levels on the real road compared to the lab.
What the car firms say
Carmakers keep engineering details close to their chest, so we don’t know for certain how any of their systems work and at what temperatures. They argue that this information is commercially sensitive and stress they haven’t broken any rules.
But there is some information available that gives clues.
Vauxhall has been accused by German media of not using one of its diesel cleaning systems for 80% of the time on one model. It is something the company flatly denies.
“Exhaust gas recirculation [the emissions cleaning system] remains active at temperatures below 17C, however, for physical reasons related to engine protection as permitted by the regulations, with differing rates”, a spokesperson for the firm said.
The down side of cutting NOx gases is that the engine uses more fuel. The more fuel you use, the more carbon dioxide the car puts out and that’s a greenhouse gas that harms the planet.
Emissions Analytics found that, in 2015, average mpg dropped for the first time in years. Probably because the car firms are concentrating more on cleaning up NOx.
“That is evidence that the tightening emissions regulations are having a negative effect on mpg,” Mr Molden says. Although he thinks vehicle engineers will eventually find a way around the problem.
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.