Is there a trade-off between carbon emissions and air pollutants?

The so-called Dieselgate affair that erupted in 2015 was about more than the antics of the German car industry. The revelations that Volkswagen and other carmakers rigged emissions tests for diesel cars shattered the notion that there was a cheap and fast way to reduce the carbon emissions that drive climate change.

Europe had favoured diesel over petrol engines for decades, mainly because it has fewer carbon emissions. Support through tax breaks and other incentives helped the market share in the UK alone rise from under 10% in 1995 to over 50% in 2012. But a side-effect was thousands of extra deaths from increased levels of toxic gases like nitrogen dioxide (NO2) and other particulate matter. The dilemma now is: do we choose the petrol engines that endanger our planet or the diesel ones that poison the air we breathe?

The issue is not just about switching between diesel and petrol. Biofuels and biomass have been promoted though EU policies, including the Renewable Energy Directive, as part of the bloc’s carbon-cutting efforts, but wood stoves, popular across Scandinavia and Central Europe, produce dust and high levels of NO2. In June, six EU countries were taken to court for failing to tackle repeated breaches of air pollutant limits.

Since Dieselgate emerged, governments have slashed their support for diesel fuel, and sales of diesel vehicles in Europe are now in decline. Some say the next generation of diesel engines will be cleaner than ever – German engineering giant Bosch has cut NOx emissions to 13 milligrams/km, a fraction of the 2020 limit of 120mg/km.

However, the reputational damage appears to be done. And since Dieselgate occurred just when the viability of electric and hybrid vehicles was starting to take off, the focus is now shifting away from both diesel and petrol.

This still leaves a huge challenge for industry, who have to meet stringent emission targets. The winner from the decline of diesel is not petrol but hybrid or electric technology. These new engines produce neither carbon emissions nor other toxic particulates as they drive, showing that there does not have to be a tech trade-off on the road to cleaner mobility.