29th March 2018

The Diesel Dilemma

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One of the highest courts in Germany recently ruled that heavily polluting vehicles could be banned from the urban centres of the cities of Stuttgart and Dusseldorf.

Reporting the decision, the Guardian* suggested it might “dramatically hit the value of diesel cars”.

So why single out diesel?  There is evidence that it represents a threat to our lung health.

Exhaust fumes from diesel engines contain tiny particles of sooty matter known as particulate materials (PM). These are categorised by size and divided into two groups: coarse particles less than ten micrometres wide, known as PM10, and fine particles less than 2.5 micrometres wide, PM2.5.

While larger particles tend to be trapped in the nose, mouth or throat, these tiny particles can be drawn deep into the lungs. There are even smaller diesel particles, just 0.1 micrometres in diameter, and research by Imperial College London shows that these can directly affect the lungs, causing tighter airways and coughing.

In 2012, the World Health Organisation (WHO) reclassified diesel exhaust as a Category 1 carcinogen – the highest grade of cancer-causing chemical or substance, basing its decision on research by the International Agency for Research on Cancer (IARC).

Some diesel car owners reacted angrily, arguing they bought the vehicles because they were supposedly the ‘greener’ option.

Diesel was promoted as a more ‘environmentally friendly’ fuel as part of the EU’s response to the 1997 Kyoto Protocol to reduce greenhouse gas emissions, especially carbon dioxide (CO₂). Diesel engines use less fuel and more air to get the same performance as a petrol engine.

According to government figures, sales of new diesels reached a peak in 2016 when they accounted for almost half of all cars sold in the UK. However, newer generations of petrol engines are more fuel efficient and emit less CO₂. These developments may have been better news for drivers loyal to petrol, but they dented diesel’s ‘greener’ image.    

Emissions of nitrogen dioxide (NO₂), which is also linked to lung problems, are several times higher from diesel than from petrol vehicles.

On top of this, the market for diesel cars was dealt a significant blow with the revelation that Volkswagen and other manufacturers had systematically cheated on emission tests. They manipulated the systems on 11million vehicles worldwide to fake better results, while 95% of diesel cars continued to break official limits.

It was a PR disaster, and the tide turned. Diesel sales slumped, reportedly down by 4.3% in January 2017.

For all the differences between petrol and diesel cars in the past, current EU emissions standards for new vehicles of both types are quite similar.

In order to achieve these standards, diesel engine manufacturers have had to resort to technologies such as particulate filters in car exhausts which can reduce PM emissions by more than 90%. However, they tend to clog up when used mainly for urban driving, so require good operating conditions and regular maintenance.

The latest emissions technology also requires the owner to regularly add a urea mixture such as AdBlue to the engine. By contrast, petrol emissions systems regulate themselves, meaning less work for drivers.

Of course, there are still many older cars on the road that conform to earlier emissions standards.

According to data from the KBA, Germany’s transport watchdog, only 2.7 million of the country’s 15 million diesel cars meet the latest Euro-6 standards.

Here in the UK, the Mayor of London, Sadiq Kahn, has announced plans to extend the Congestion Charge scheme and to increase the cost of driving heavily polluting cars within it, so perhaps we will see similar moves extended across the whole country at some point.

However, the situation is not quite clear-cut as yet: the German government has insisted that nothing would change right away and that the bans are ‘not inevitable’.

“The court has not issued any driving bans but created clarity about the law,” said Environment Minister Barbara Hendricks. “Driving bans can be avoided, and my goal is and will remain that they do not come into force,” she added. Chancelor Angela Merkel added that the ruling concerned only “individual cities”.

About 70 other cities, including Munich and Cologne, are reported to be taking a keen interest. For now, though, it’s very much a case of ‘watch this space’.

* The Guardian, 27 February 2018