Diesel, with its lower CO 2 emissions, was a policy priority but NOx failed to fall despite the ‘stringent’ regulations

From backroom deals between European leaders to the burying of the bad news of 23,000 premature UK deaths on the day Jeremy Corbyn was elected Labour leader, the scandal that has engulfed the diesel car is a startling tale.

It is a story of good intentions being relentlessly undermined and has a nasty twist in the tail: even the real rationale for Europe’s drive for diesel – to curb global warming – has run into the wall.

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The story begins in the early 1990s, when the diesel car was the noisier, clunkier and largely unloved cousin of the petrol car. But with climate change a growing concern, diesel’s lower carbon dioxide emissions caught the attention of politicians looking for easy ways to cut carbon. Sales of diesels in Europe crept up from 15% of new cars in 1990 to 25% by 1995, as politicians cut the taxes levied on diesels.

But the slow-burn rise of diesels accelerated into a boom after 1998, thanks to the arrival of a new quieter and more powerful engine – called the common rail – and a landmark agreement between Europe’s leaders and its car industry to drive down CO 2 . By 2008, half of all new cars taking to Europe’s roads were diesel powered.

It was known right from the start that diesel engines produced more lung-clogging soot and irritating nitrogen oxides. But it was believed that problem could be neutralised.

“The policy priority was climate change, [but] it was thought that air pollution regulations on vehicles would work,” said Martin Williams, who headed the UK government’s Air Quality Unit for 20 years and is now at King’s College London. “People said ‘sure, diesels emit more particulates and nitrogen oxides (NOx) but we have really stringent regulations”. Twenty years on, we have found out we were wrong.”

“Everyone expected the new standards to deliver improvements in air quality,” said Greg Archer, at campaign group Transport & Environment. “But the motor manufacturers found ways to circumvent the tests.”

The tiny particles of pollution pumped out of diesel exhausts have long been known to be very harmful to health, working their way deep into lungs and leading to heart attacks, strokes and cancers. Filters that became mandatory in exhausts in 2010 have heavily reduced that problem, although some unscrupulous garages still offer to remove them and give the car’s performance a tiny boost.

But, lurking in amongst the soot, were NOx. “People knew NOx were harmful. There were reports going back to the 1990s that NOx were associated with asthma, but it wasn’t as clear as the health hazards of particulates,” says Archer. “What is clear today is that NOx has at least as harmful an effect as particulates.”

A key step forward in the understanding of the health effects of NOx came with a WHO report in 2013, which indicated for the first time that the chemicals were dangerous by themselves and were not simply an irritating accompaniment. This mattered because, out in the real world, NOx emissions were stubbornly failing to obey the commands of the politicians’ regulations and fall.

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In 2010, Williams and his team showed why, by standing by the side of British roads and watching 84,239 vehicles putter by. As each passed, beams of infrared and ultraviolet light took a snapshot its exhaust fumes, while a camera recorded the registration plate, which could be used to look up the make and model.

When the numbers were crunched, the conclusion was stark: there was a chasm between the levels of NOx that the vehicles were actually emitting and what they should have been emitting according to the regulatory tests they had passed. This chasm was exposed most luridly this month, when VW was caught in the US using “cheat devices” to cut emissions drastically when the car’s computer detected it was being tested.

But the discrepancy between real-world driving and regulatory test results – if not outright illegal cheating – had been known for years, and it was getting worse. In 2000, diesel cars on the road pumped out double the NOx they did under test conditions, according to the ICCT, the group who rumbled VW’s cheating in the US. In 2005, the test limit was halved, but road performance of the diesel cars was three times worse.

The NOx limit shrank again in 2009 and in 2014, but now the cars were over seven times worse on the road than in test labs as motor manufacturers refined their techniques for gaming the tests. Few people believe VW are the only company doing so, legally or otherwise. “VW appear to have been caught red-handed, but it would seem highly likely that others have also played dubious games to pass emissions tests,” said Professor Alastair Lewis, an air pollution expert at the University of York.

This gaming explained why NOx air pollution would not fall: the regulations were in place but were as useful as a smoke alarm with a dead battery. In 1999, a European Union directive set strict air pollution limits for NO 2 (the toxic gas formed from NOx emissions) and gave member states just over a decade to get ready. The UK, like others, assumed the ever-stricter emissions regulations on diesel cars would strangle the NO 2 problem.

The choking truth was revealed in 2010, when London used up its annual allowance for NO 2 in the first three weeks of monitoring. “The breaches were colossal,” said Alan Andrews at environmental lawyers, Client Earth. They quickly started pursuing the government through the courts to force them to deal with the illegally high air pollution.

A long battle ensued but in April, Client Earth won: ministers would have to present a plan to tackle the problem. This plan was sneaked out by the Department of Environment, Food and Rural Affairs (Defra) on the morning of 12 September, the Saturday when the entire nation’s media was transfixed by Jeremy Corbyn’s election as leader of the Labour Party. “That tells you everything you need to know about the government’s attitude to this issue,” said Andrews. “They were embarrassed at how little they had to offer.”

The Defra document put out that Saturday stated the problem starkly: “The failure of the Euro standards to deliver the expected emission reductions under real world driving conditions means that road transport is by far the largest contributor to NO 2 pollution.”

But it also contained a bombshell. For the first time anywhere in the world, UK officials had used the WHO data to calculate the toll of premature deaths caused by NO 2 : the figure was 23,500 every year, on top of the 29,000 still dying from particulate pollution. “The combined impact of these two pollutants represents a significant public health challenge,” said the officials, with some understatement.

With the NOx tests long known to be useless in the real world and the toll of the pollution slowly being realised, the question was why did politicians ignore it for so long? Simple lobbying, says Andrews: “It’s driven by big business, industry, farming. They are worried about the costs to them, but they completely ignore the costs to society. The UK government itself estimates that air pollution costs the country £12-18bn a year.”

Glimpses of the high-stakes deals done over emissions regulations – whether NOx or CO 2 – are occasionally seen. In 2013, Germany was reported to have gone “rogue” in attempts to sideline greener car regulations that would impact its huge car industry, threatening Ireland over its Euro bail-out, Hungary with car plant closures and the Netherlands with cuts in plant investment.

A month earlier, Germany had offered to derail an EU cap on bankers’ bonuses, which the UK opposed, in return for UK support in sidelining the stricter car regulations. Those regulations were duly kicked into the long grass and the lobbying has not stopped. Germany, France and the UK have all lobbied recently against reforms to flawed emissions tests.

“If ‘dieselgate’ has taught us one thing, it is that you need regulations that are robust, transparent, enforceable and not designed by industry for industry,” says Andrews. A new emission test that actually reflects real-world driving has been proposed by the European Commission.

Williams says: “That needs to happen fast. The EC wants 2017, though some would say that is too late. But the industry is on record as saying nothing can possibly be done before 2020.”

The final bitter note in the smoggy tale of diesel’s rise is that it did not even achieve its overarching goal. The emissions of carbon dioxide from diesels are indeed lower than those of petrol cars, but other efficiency improvements to cars in the last decade, such as lighter bodies, have been 10 times more effective.

And the sooty particles diesels pumped out in great volumes turned out to be excellent at absorbing sunlight and warming up the atmosphere. The scientists Michel Cames and Eckard Helmers sum it up simply in their analysis: “The European diesel car boom did not cool down the atmosphere.”