Guest opinion: don't ban diesel - sort the clean from the dirty

As the Government loses a second high court ruling brought by ClientEarth*, many are now sounding the death knell for diesel cars.

Not so fast. Diesels can be clean and governments are highly unlikely to give up the greenhouse gas advantage of diesel in the short or medium-term. 

Since the introduction of Euro 6 in September 2014, manufacturers have been forced to improve their after-treatment systems to meet the stricter legislated limits for NOx. exhaust gas recirculation, lean NOx traps, and selective catalytic reduction technologies have been employed as part of a complex strategy to reduce tailpipe emissions.

There have been variable successes, with some achieving the regulated limits even in real-world driving and the worst more than 20 times the legal limit.

Overall, average NOx emissions from Euro 6 diesels are down 55% compared to Euro 5s.

Nonetheless, there is still the fact many new cars do not meet the legislated limits in real-world operation.

Our data shows NOx emissions are on average 4.3 times over the limit for Euro 6 cars and, after a period of improvement, this Conformity Factor is rising.

This is the heart of the issue, as to whether diesels are the major and unavoidable cause of poor air quality in towns and cities.

Consequently, there have been many suggestions made to combat the problem of dirty diesels.

These range from the London Mayor’s T-charge, to a diesel scrappage scheme, to a total ban on diesel vehicles in certain zones.

However, Emissions Analytics’ data shows that modern diesels in their own right can be clean.

Since the launch of our EQUA Air Quality Index six months ago, 12 cars have how achieved an A-rating including the latest Volkswagen Tiguan, meaning it has met the 0.08g/km limit in real-world driving.

Emissions Analytics' air quality rating for the 2016 Volkswagen Tiguan diesel

This proves that diesels can be clean and the reason most are not is down to a failure of regulation and enforcement and not the technical impossibility.

There is also the issue of CO2 emissions to be considered.

Despite Donald Trump tweeting that climate change was, “created by and for the Chinese in order to make US manufacturing non-competitive,” the British government has an empirical view on global warming and stands by its commitment to cutting its carbon footprint.

Would ministers give away the 16% CO2 advantage - according to Emissions Analytics' testing - diesel has over petrol for the same distance driven in real-world operation, until there is a viable alternative?

In the future electric and hybrid vehicles may deliver the CO2 advantage required, as well as greatly reducing, or eliminating, NOx and other harmful emissions, at which point diesel powered engines for passenger cars may come to the end of the road.

However, with a share of the market of less than 2%, there is still a way to go for these vehicles.

Until then, our data strongly suggests the policy focus should be on sorting the clean from the dirty diesels and incentivising manufacturers to bring forward clean technology.

> See the latest EQUA Aq Index results.

* 'High Court rules UK government plans to tackle air pollution are illegal'

Author: Nick Molden (pictured), chief executive, Emissions Analytics