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The end of the road for diesel?

Smoggy day in Bristol

The Volkswagen (VW) emissions scandal is now into its second week, and with each day the enormity of the deception seems to increase. What started off as a few hundred thousand cars in the US has now become an astonishing 11 million cars worldwide that VW says may have to be recalled. In addition to the VW brand, diesel models of Audi, Skoda and SEAT cars have all been affected, with 1.2 million in the UK alone.

At the heart of this deception is the use of software, designed to be able to detect when a car was under test conditions, in order to reduce the emissions of a group of nitrogen and oxygen compounds, commonly referred to as NOx.  However, these emissions controls would not be switched on during normal driving.

Given that the cars were clearly built with the potential to emit less NOx, it’s not immediately clear why the emissions controls were applied only under test conditions.  Although VW have admitted they “screwed up”, they don’t seem to have said why. However, it’s a fair assumption that the emissions controls would affect the performance of the car, both in terms of drive and fuel economy. Since fuel economy is probably the main selling point of a diesel car, anything detrimentally affecting it, could easily lead to a decline in sales.

In addition to the flouting of the rules by VW, the wider issue is the NOx emissions themselves, which are a seemingly inevitable product of diesel powered vehicles.

The use of diesel as a fuel in cars has been on the up (in Europe at least) over the last couple of decades, with a supposedly superior fuel economy and hence lower CO2 emissions, meaning they have been incentivised in Britain with lower tax. However, this policy failed to take into account other pollutant emissions such as NOx and particulate matter that have been linked with thousands of premature deaths. Indeed, this push to diesel was labelled in a Channel 4 documentary earlier this year “the great car con” and just this week former science minister Lord Drayson called this policy a mistake.

Due in part to this push for more diesel vehicles on the roads in the UK and Europe, Bristol is just one of many cities which fail to meet the 40 μg/m3 annual mean WHO guideline level for NO2 (one of the collection of NOx gases). NOx levels in the UK have seen only a very small decline over the last decade or so, despite vehicle manufacturers telling us they make the cleanest cars yet. This contrasts with petrol vehicles, which have seen a dramatic decrease in NOx emissions over this time.

Why is NOx bad?


The presence of NOx in the lowermost part of our atmosphere, along with other pollutants such as volatile organic compounds (VOCs) promotes the formation of ozone. Not to be confused with the protective ozone layer which is much higher up in the atmosphere, ozone near the surface has detrimental health effects, mostly involving the respiratory system, in addition to being a greenhouse gas. Furthermore, NO2 has itself been linked with certain respiratory health problems

Is there a simple solution?


Well, technologies exist to reduce NOx emissions from diesel vehicles, such as urea injection, only it seems that the VW group chose to cheat the system rather than use it, since it would add cost and weight to the car. If these technologies are implemented manufacturers claim to be able to filter out particulate emissions and greatly reduce NOx emissions. But, given the current furore, why on earth should we believe them?

In addition, a recent report from the International Council of Clean Transportation (ICCT) said that the real-world CO2 emissions of diesel (and petrol) cars are well above those in tests. There go the supposed CO2 savings of diesel then. Again you can’t help but question why diesel cars continue to enjoy a tax break in this country.

The death knell tolls for diesel…


…Ok, maybe not. Given the massive investment that the automobile industry has put into diesel over the last 20 years or so, they’re unlikely to suddenly jack it all in. What will probably follow is a splurge of marketing diarrhoea about how each new car is the ‘greenest yet’, all the while completely ignoring the fact that the simplest way to cut emissions would be to have fewer cars not more. Nevertheless, the current news story highlights how frivolously pollutant regulations, and the health implications, are taken when set against generating a profit. It also serves to impress the need for independent verification of emissions, such as those that uncovered VW’s fraudulent behaviour. The Atmospheric Chemistry Research Group here at Bristol, performs similar verification at the national level for greenhouse gases. It has been said that not taking the time to verify emissions statistics is like dieting without weighing oneself. Well, in this case I guess they did make it to the scales, but no one bothered to check they’d been calibrated properly. 

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This blog has been written by Cabot Institute member Mark Lunt, from the University of Bristol's Atmospheric Chemistry Research Group.
Mark Lunt


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