Diesel cars are ‘more polluting’ than thought, study finds

Even the newest diesel-engine cars are dirtier than previously thought, according to a new study that calls into question why European regulators continue to favour diesel over petrol engines.

Transport & Environment, a Brussels-based organisation lobbying for sustainable transport, has found that a typical diesel car emits 42.65 tonnes of carbon dioxide over its lifecycle, or 3.65 tonnes more than a petrol car. 

“This analysis debunks carmakers’ claim that diesel cars are needed to meet their climate targets,” T&E said. “Diesel cars are not only more polluting” in terms of air pollutants including harmful nitrogen oxides and particulate matter, “but also churn out more CO2 and cost on average €2,000 to €3,000 more than petrol”. 

The sale of diesel cars in Europe has been in steady decline since US regulators exposed the decade-long Volkswagen diesel emissions scandal two years ago on Monday. The scandal led to closer scrutiny of environmental claims, with various cities across Europe considering bans on diesel in the near future. The negative headlines are likely to reduce diesel’s share of EU car registrations from about half to less than one-third by 2020, according to JPMorgan. 

Carmakers, however, are fighting for diesel’s clean credentials. “The latest generation of diesel vehicles is a very effective lever to achieve climate goals in the near future, because they emit 15-20 per cent less CO2 than equivalent petrol vehicles,” Dieter Zetsche, Daimler chief executive and president of the European Automobile Manufacturers’ Association, said last week. 

But what the T&E study shows is that diesels only emit less CO2 when regulators narrowly look at tailpipe emissions. T&E offers instead a lifecycle analysis — a wider view of emissions comprising the production of the car, including the sourcing of fuel and materials used in its manufacturing, plus the car’s usage and the recycling of its components. 

Diesel cars were found to be more polluting than petrol cars over the lifecycle because of three reasons: One, diesel fuel undergoes a more intensive refinery process. Two, diesel combusts at a higher temperature than petrol, so the components used are heavier and more robust. Three, diesel fuel is cheaper, leading to increased usage on the road. 

Even if one looks just at tailpipe emissions, Julia Poliscanova, manager of clean vehicles and air quality at T&E and the main author of the report, notes the petrol engines have reduced carbon emissions so much in the past decade that the advantage of diesel engines is almost nil. 

“In the 1990s, diesel probably was a better choice, but today it is just not the case,” she said. “They don’t deserve a revival. Today we simply have much better alternatives, in hybrids and electrics.” 

BMW and Daimler reviewed a synopsis of the study at the weekend but could not offer immediate comment. Volkswagen said that “several studies” in the past have shown that diesel cars emit less CO2 than a petrol equivalent over their complete lifetime. 

“Our own analysis documented that recent comparison of diesel and gasoline cars with similar mileage, performance and other important car attributes are leading to the same conclusion: diesel cars do have a relevant advantage of CO2 emissions over lifetime,” Volkswagen said. 

T&E, which represents 50 organisations from 26 countries across Europe, reserves most of its blame not for carmakers but for the “biased regulations and taxes” responsible for “bloated sales of diesel cars in Europe”. 

For instance, European taxes on diesel fuel are significantly less than petrol taxes, “making it 10 to 40 per cent cheaper at the pump”. The UK is the only country in the EU without this “diesel bonus”, although France and Belgium have recently pledged to close the gap. 

T&E calls for the next iteration of European emissions standards to be “technology neutral”. It asks for regulations favouring heavier vehicles to be scrapped, and says “fair fuel and vehicle taxes” should be introduced based on real-world carbon emissions. 

“It is time Europe stopped pouring money and energy into a globally niche 20th century technology,” the report said.

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