Diesel Cars Emitting More Pollution During Cold Weather

Car exhaust fumes
The increases in pollution are perfectly legal. Olegusk/Shutterstock

It hasn’t been a great year for the producers of diesel cars. Earlier in 2016, it was revealed how the manufacturers were cheating the emissions tests, making it appear that their cars were pumping out far less pollution under test conditions than they were in reality out on the road. But it seems that now there is even more to be concerned about.

It turns out that some diesel cars are emitting up to twice as much pollution during cold weather. When the air temperature drops to below 18°C (64°F), the levels of poisonous gasses being released spike dramatically, adding to the already massive problem of air pollution smothering the world. Rather than being some strange quirk of chemistry, though, it has become apparent that cars are deliberately designed this way, and what’s more that it is perfectly legal.


The problem has been found to most acutely affect what are called “Euro 5” category diesel cars, which became mandatory in 2011. Fitted with pollution controls designed to remove harmful pollutants such as Nitrogen Oxides, these checks can be turned off if they significantly impact the running efficiency of the engine, such as during cold weather. But the testing company Emissions Analytics, which looked at 213 car models from 31 manufacturers, found that this ruling was seemingly being exploited, as the temperature threshold has been set too high.

It is important to note here that the car manufacturers who have been contacted and responded to queries regarding the news all unequivocally state that they have done nothing illegal. Some have now issued software updates and patches to some of their models.

This has meant that the cars in question, up to 5.1 million of them are currently on the roads, have been emitting up to 4.6 times the legal limit for Nitrogen Oxides, when the temperature fell to below 18°C (64°F). For some models, such as the Ranger Rover Sport, its pollution levels were twice as high early on a cold morning compared to later in the day after it had warmed up. With between 10 and 15 years of life left in many of the vehicles currently affected, the situation could last years.

There is, however, something of a trade-off here. While cutting the emissions of poisonous air pollution is obviously a good thing, under certain conditions, as stated, it can make engines a lot more inefficient. This, then, means that the vehicle will be burning more fuel and thus releasing more carbon dioxide into the atmosphere, the main driver of climate change.


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