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article imageDiesel cars are more polluting at lower temperatures

By Tim Sandle     Jun 22, 2016 in Environment
A new study suggests that pollution from diesel run cars is far worse when it is colder than 18 degrees Celsius (64 degrees Fahrenheit) outside.
The finding comes from a study by a company called Emissions Analytics. The company report that various poisonous gas emissions, produced from a wide range of models, rises as the temperature drops. In total the research looked at 213 models across 31 manufacturers. All of the cars were in Europe.
The reason for the rise in pollution is not so much linked to an environmental affect, but due to the programming in the cars as set by the manufacturers. Although European Union laws have strict controls on emissions for new cars (cars manufactured from 2011 on wards), European rules also allow manufacturers to program pollution controls to switch off or to run at a lower level under very hot conditions or during cold weather. This is in order to protect the engine.
Some commentators argue that the engine damage argument is not supported and they go so far as to contend that some car companies are deliberately switching off all controls, and even that this option is being extended to times when the weather is relatively mild. This is in order to boost the 'miles per gallon' performance of the car. Miles per gallon remains a key selling point for new cars, and margins of efficiency can help with car sales.
Speaking with BBC Environment, Emissions Analytics head Nick Molden said: "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."
Euro 5 is a reference to the latest tranche of European emission standards. These define the acceptable limits for exhaust emissions of new vehicles sold.
In the study, it was found that a typical Euro 5 vehicle was 3.6 times above the legal limit for Nitrogen Oxides when it was above 18 degrees Celsius. However, this rose to 4.6 times over the limit when the air temperature dropped. This has caused some annoyance from drivers, judging by the tweets on social media.
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