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? Evidence suggests it poses a threat to our lung health.
Diesel engine exhaust fumes contain tiny particles of sooty matter known as particulate materials (PM). Scientists categorise them by size and divide them into two groups: coarse particles less than ten micrometres wide (PM10), and fine particles less than 2.5 micrometres wide (PM2.5).
Larger particles tend to become trapped in the nose, mouth or throat. However, these tiny particles can travel deep into the lungs. Diesel engines also release even smaller particles, about 0.1 micrometres in diameter. Research by Imperial College London shows that these can directly affect the lungs, causing tighter airways and coughing.
Health concerns and cancer risk
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. They argued that they bought the vehicles because they were supposedly the ‘greener’ option.
Why diesel was once considered greener
Policymakers promoted diesel as a more ‘environmentally friendly’ fuel during the EU’s response to the 1997 Kyoto Protocol. The goal was to reduce greenhouse gas emissions, especially carbon dioxide (CO₂).
Diesel engines use less fuel and more air to achieve the same performance as petrol engines. Because of this efficiency, governments encouraged drivers to switch.
Government figures show that sales of new diesel cars peaked in 2016. At that point, they accounted for almost half of all cars sold in the UK.
However, newer petrol engines have become more fuel-efficient and emit less CO₂. These improvements helped petrol regain ground and weakened diesel’s ‘greener’ reputation.
Pollution and the emissions scandal
Diesel engines also emit much higher levels of nitrogen dioxide (NO₂). Scientists link this pollutant to lung problems. In many cases, diesel vehicles produce several times more NO₂ than petrol cars.
The market for diesel cars also suffered a major blow after the Volkswagen emissions scandal. Volkswagen and other manufacturers systematically cheated on emissions tests. They manipulated systems in 11 million vehicles worldwide to show better results. Meanwhile, 95% of diesel cars continued to exceed official limits.
The scandal became a PR disaster for the industry. Public confidence dropped, and diesel sales declined. Reports showed sales falling by 4.3% in January 2017.
New technology and emissions standards
In the past, petrol and diesel cars differed significantly in their emissions. Today, EU emissions standards for new vehicles of both types are quite similar.
To meet these rules, diesel manufacturers introduced technologies such as particulate filters in exhaust systems. These filters can reduce PM emissions by more than 90%.
However, the filters often clog during mainly urban driving. Drivers must therefore ensure proper operating conditions and carry out regular maintenance.
Many modern diesel engines also require owners to add a urea mixture such as AdBlue. This system helps reduce emissions. Petrol emissions systems, by contrast, regulate themselves, which means less work for drivers.
Older cars still dominate the roads
Of course, there are still many older cars on the road that conform to earlier emissions standards.
Data from Germany’s transport watchdog, the KBA, highlights the scale of the issue. Only 2.7 million of Germany’s 15 million diesel cars meet the latest Euro-6 standards.
Possible driving restrictions
In the UK, London’s mayor, Sadiq Khan, has announced plans to extend the Congestion Charge scheme. He also wants to increase the cost of driving heavily polluting cars within the zone. Similar policies could eventually spread across the country.
However, the situation remains uncertain.
The German government has stressed that nothing will change immediately. Officials say 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. Chancellor Angela Merkel added that the ruling concerned only “individual cities”.
About 70 other cities, including Munich and Cologne, are reportedly watching developments closely. For now, though, it remains very much a case of ‘watch this space’.
* The Guardian, 27 February 2018