What is the science regarding diesel emissions?

Sunday 12th March 2017




Robert Flello, a member of the Transport Select Committee and Labour MP for Stoke-on-Trent South

There is a new villain in town, and it goes by the name of diesel.

We are told that diesel is deadly, rotten to its chemical core.  Worse still, diesel used to be our friend but now it has betrayed us.  Remember when we were told that diesel was far cleaner for the environment than petrol?  Remember when we were told that diesel was better for us because we could go so much further on so much less of it?

Of course, anyone who uses diesel is stained with its wickedness.  Car drivers who bought diesel vehicles, in good faith, are now mass poisoners who should be ashamed of themselves.  Manufacturers who produce diesel vehicles are like the Ernst Stavro Blofeldts of the motoring world, stroking their pristine white cats and smiling whilst asthma sufferers choke, not to mention the faking of emissions tests by some car makers.  As for lorry and bus drivers, how can they look themselves in the eye in their smut-stained mirrors?

However, before we start burning effigies of Rudolf Diesel and haranguing in the street drivers of vehicles powered by the engine he is credited with inventing, we ought to remember how we arrived here.

In the 1990s, drivers were roundly encouraged to opt for diesel vehicles because of their lower carbon dioxide emissions.  In 2001, the government reorganised excise duty (car tax) to recognise that fact, charging less for cars which produced lower levels of CO2.  Today, a third of vehicles on Britain’s roads run on diesel, including, of course, almost all of the lorries and many of the vans which are so so vital to our logistics sector.

There seems to be an emerging consensus that diesel should be demonised en route to an all-out ban.  But how practical is that?  If everyone had to replace their diesel motors over a period of time, how much more pollution would be caused by the production of so many new vehicles?  Certainly it would be a boost for the car industry but it would also mean overall consumption of petrol would grow massively, with all the attendant cost and environmental implications.  Further to that, if drivers are forced to replace their diesel cars, who is going to compensate them for purchases made in good faith?

What is more, how dirty is diesel anyway?  A quick Google search of that, or similar questions, will produce a variety of interpretations, running from miraculously pure and safe, all the way to instantly lethal.  How catastrophic would the increase in CO2 emissions be if everyone reverted to petrol?

Perhaps the biggest problem lies with HGVs.  Running big trucks on petrol is ruinously expensive and environmentally disastrous.  On a long haul, the mileage achieved by a diesel-driven machine is markedly better than a petrol equivalent.  Diesel engines produce much higher torque at lower revolutions than their petrol equivalents, and the engines, themselves, last considerably longer as do the exhaust systems, saving greatly on cost but also in terms of the environmental damage caused by new manufacture.  Perhaps most crucially of all, where are the new fuels ready to take up the strain in place of “dirty diesel”?
In short, we cannot get too far ahead of ourselves in seeking to consign diesel to our local hazardous waste recycling centre.  Removing and replacing it is going to take time, and we must be sure that the science is right before we go leaping ahead with alternatives.

Not many people were saying, sixteen years ago, that government should not incentivise diesel drivers through taxation.  Let us not rush into another fuel faux pas, in case we damage or destroy yet more lives in the process, not to mention a big chunk of our vital transport industries.

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