Skip to main content

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. 

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


Popular posts from this blog

Converting probabilities between time-intervals

This is the first in an irregular sequence of snippets about some of the slightly more technical aspects of uncertainty and risk assessment.  If you have a slightly more technical question, then please email me and I will try to answer it with a snippet. Suppose that an event has a probability of 0.015 (or 1.5%) of happening at least once in the next five years. Then the probability of the event happening at least once in the next year is 0.015 / 5 = 0.003 (or 0.3%), and the probability of it happening at least once in the next 20 years is 0.015 * 4 = 0.06 (or 6%). Here is the rule for scaling probabilities to different time intervals: if both probabilities (the original one and the new one) are no larger than 0.1 (or 10%), then simply multiply the original probability by the ratio of the new time-interval to the original time-interval, to find the new probability. This rule is an approximation which breaks down if either of the probabilities is greater than 0.1. For example

1-in-200 year events

You often read or hear references to the ‘1-in-200 year event’, or ‘200-year event’, or ‘event with a return period of 200 years’. Other popular horizons are 1-in-30 years and 1-in-10,000 years. This term applies to hazards which can occur over a range of magnitudes, like volcanic eruptions, earthquakes, tsunamis, space weather, and various hydro-meteorological hazards like floods, storms, hot or cold spells, and droughts. ‘1-in-200 years’ refers to a particular magnitude. In floods this might be represented as a contour on a map, showing an area that is inundated. If this contour is labelled as ‘1-in-200 years’ this means that the current rate of floods at least as large as this is 1/200 /yr, or 0.005 /yr. So if your house is inside the contour, there is currently a 0.005 (0.5%) chance of being flooded in the next year, and a 0.025 (2.5%) chance of being flooded in the next five years. The general definition is this: ‘1-in-200 year magnitude is x’ = ‘the current rate for eve

Coconuts and climate change

Before pursuing an MSc in Climate Change Science and Policy at the University of Bristol, I completed my undergraduate studies in Environmental Science at the University of Colombo, Sri Lanka. During my final year I carried out a research project that explored the impact of extreme weather events on coconut productivity across the three climatic zones of Sri Lanka. A few months ago, I managed to get a paper published and I thought it would be a good idea to share my findings on this platform. Climate change and crop productivity  There has been a growing concern about the impact of extreme weather events on crop production across the globe, Sri Lanka being no exception. Coconut is becoming a rare commodity in the country, due to several reasons including the changing climate. The price hike in coconuts over the last few years is a good indication of how climate change is affecting coconut productivity across the country. Most coconut trees are no longer bearing fruits and thos