There have been some accusations, recently, in the media, about diesel cars being responsible for the recent smog and an unhealthy air quality, apparently leading to respiratory problems for many people. Could the Doctor summarise the situation for me and other readers, as to whether it all makes sense, or is pure scaremongering? Does this mean, as some might suggest, that the future of diesel engined cars, which are surely so much cleaner now, is actually under threat?
Bill Pugh

Thanks Bill, for offering me the opportunity to air some facts and opinions on the subject, which I will do at some length, because this is an important matter. There is no doubt that, in urban areas, like some of our cities, the air quality is regularly below specified EU standards and can result in official EU notifications that these safe limits have been exceeded. They refer specifically to PM2.5 particulate levels and NOx (oxides of nitrogen) that are considered to represent the main urban health threats, so I’ll focus my response on these two areas, and without getting too bogged down with actual numbers and statistical data.

It is undeniable that in certain regularly monitored locations, the limits are being regularly exceeded; it’s no use suggesting that limits are ridiculously low, as we know that people in good health have suffered breathing difficulties recently, and that the normal weather and the joy of life were significantly affected for several days. We are not alone though in Britain, and Paris and some other European cities are having similar problems. (Cue interesting quote from a French lung specialist, Professor Jean-Philippe Derenne, “In 50 years, I have never come across anyone who died from air pollution. Between those people who smoke two packets of cigarettes a day and those people who walk in the streets of Paris, there is not the beginnings of a comparison.”)

As far as our readers will be concerned, the main issue is whether diesel cars are really to blame, how much to blame, or whether the true picture is less clear. We might also well wonder, though, just how all this has come about, with the progressively tighter regulation of diesel exhaust emissions through Euro 4, 5, and 6, and since 2005 limits for new car emissions of PMs (particulate matter) have been reduced by 80 per cent, and NOx by 68 per cent. What’s gone wrong, if diesel cars are to blame? Well of course the newer, cleaner cars can only progressively replace older, dirtier cars, as those (including, we must mention, diesel taxis) are taken off the roads, so the numbers regarding emissions for the average UK car are far less impressive, particularly with low new car sales for several years after the banking crisis. But, to quote some Department for Transport official statistics: “total particulate matter from all cars in use has fallen by 35.8 per cent, nitrogen oxides by 61.9 per cent and carbon monoxide emissions by 81.6 per cent, between 2000 and 2011.” With those kinds of big reductions from cleaning up car emissions, it is surely quite reasonable to suggest that climate change, or other unusual climatic effects, could have played a significant part in the recent problems?

Further to this, DEFRA, which has been recently pointing the finger at diesel cars, particularly in London, said in December 2013 that “road transport still (only) accounts for around one third of total NOx atmospheric emissions. Catalytic converters and stricter emission regulations have resulted in a strong downward trend.” Furthermore, DEFRA said “the recent increase in NOx emissions between 2011 and 2012 was due to higher consumption of coal, (in power stations) at the expense of natural gas”. These statements are not quite consistent with another recent DEFRA statement that “nitrogen oxide emissions from diesel cars peaked around the year 2000, but has overall shown little change during the last 20 years.” They also say “emissions from road transport accounted for around one fifth of the total emissions for both PM2.5 and PM10 in 2012.” So it’s definitely not a clear-cut issue, and road transport, and specifically diesel cars, cannot be totally to blame. But a number of areas relating to diesel power and emissions certainly do need some urgent research and development:

1. The reductions of diesel NOx emissions in real life city motoring have definitely not been as great as should have resulted from lowering of Euro 4,5,6 NOx limits. This suggests that, just as the EU test cycles are poor indicators of real life fuel economy, so similarly their measurements are a poor indication of real life NOx emissions. Action is needed on urban test cycles, to make them more representative of actual emissions.
2. The bulking together of all the oxides of nitrogen as NOx emissions is not a good indication of pollution and related health risks, as more recent diesel engines of higher power output produce a higher proportion of the more dangerous NO2 than came from older engines.
3. Emissions control systems like EGR and catalytic processes to reduce NOx emissions work poorly in city motoring conditions, when engines and catalyst boxes don’t reach optimum operating temperatures. Better systems are needed that work in all conditions.
4. Diesel cars produce higher outputs of NOx at high engine speeds. Low-revving large HGV engines are relatively low producers of NOx and particulates, when emissions control equipment is operating correctly. Is small engine development going in the right direction?
5. The persistent problem is in city areas, precisely the areas where hybrids and EVs (electric vehicles), along with clean public transport, are most practical and most efficient, and diesel and petrol cars least efficient. Do the government and the cities need to consider urgent regulatory and financial action to force people into such city-friendly clean transport?

I hope that covers a few of the relevant points Bill. The Government has too many eggs in the diesel basket for any sudden threat to diesel cars to emerge, and the same applies all over Europe. But it’s disappointing to see that chasing for low carbon dioxide figures seems to have distracted people from the wider picture of emissions and air quality. If there’s anything to really protest about, it’s the maintenance of a set of EC Test cycles that don’t replicate real motoring conditions, and, sadly, the prospects for rapid improvement in this area don’t look promising!
Doc