Petrol or Diesel emissions – what’s actually worse?


Are we witnessing the end times for diesel motors? On the 2nd December at the biennial C40 climate summit in Mexico, the mayoral representatives of Paris, Madrid, Mexico City and Athens all signed off on a commitment to fully ban diesel motors in their cities by 2025. Meanwhile, in the UK on the 10th December the campaign group Doctors Against Diesel issued a statement calling on the London mayor, Sadiq Khan, to commit to phasing out access to the capital by what are considered to be the ultimate in polluting vehicles. The group claims that 9,400 deaths in the city per annum are attributable to diesel fumes. The major, an asthma sufferer, is known to be sympathetic to the cause; he has said: “Toxic air in London is a health emergency that requires bold action, including introducing charges for older polluting vehicles and expanding the Ultra Low Emission zone.”

There are two areas of concern in regards to diesel engine exhaust pollution: nitrogen oxides and particulate matter. Diesel vehicles are the biggest producer of nitrogen oxides (NOx) which have been linked to respiration difficulties, and are said to cause or exacerbate asthma and bronchitis. There is even evidence to suggest that prolonged exposure may lead to an increased risk of heart problems and stroke.

Secondly, diesel exhausts eject particulate matter into the environment which has been indicated as carcinogenic. The exhaust filters which are fitted on diesel cars as standard, and which effectively reduce the harmful particulate emissions, can be easily and legally removed, and some diesel owners will do this to increase fuel efficiency. The government has done nothing to limit this.

Urban areas suffer most from a buildup of this pollution and overall, according to a 2015 DEFRA study, it is thought that over 23,000 deaths per annum can be attributed to diesel exhaust, with a further indefinite number of people suffering long term detrimental health risks, all of which constitutes a high cost burden on the NHS.

Diesel owners, however, can be forgiven for feeling somewhat aggrieved at their new found pariah status. Many of them would not indeed be diesel drivers had they not previously been persuaded to buy into the market by various government agencies, the erstwhile champions of these engines. Diesel, we were told had distinct benefits, they were environmentally sound because they produced less carbon dioxide. This benefit is largely due to the perceived efficiency of diesel engines as compared to petrol. They still produce CO2, but they produce less of it per mile by dint of burning less fuel. However the fact is that if equivalent amounts of diesel and petrol are burned the diesel will produce far more CO2. Given the fact that diesel cars tend to be more powerful and that the smaller petrol cars are becoming ever more fuel efficient it would seem that any advantage diesel could once claim are fast evaporating.

Moreover, recent tests have debunked any supposed advantage, indicating that diesel cars emit levels of pollutants far in excess of that previously discovered in controlled laboratory tests which fail to emulate realistic driving behavior out on the roads. The true levels are feared to routinely exceed the EU limit for NOx by staggering amounts.

Opinion seems to be justly against diesel. However, some have raised doubts over the supposed effectiveness of smaller direct fuel injection petrol engines, expressing fears that their efficiency is bought at the cost of extra particulate exhaust. Particulate are a problem that is by no means confined to diesel engines, and in these smaller petrol cars the issue is left unchecked because there is no necessity for them to come equipped with an emission filter.

There are further concerns over petrol/electric hybrid engines. These hybrids are promoted as the green standard, but the real picture is obscure. Hybrid cars are currently exempt from MOT emission checks. Doubts can be legitimately raised concerning the decreased efficiency of the catalytic converters in these cars, which only run at full capacity when at full temperature. When they are consistently running at the lower temperatures the hybrids subject them to their effectiveness is manifestly diminished. This is especially marked in the heavy traffic in built up urban areas, precisely the areas which are most blighted with the problems of pollution.

So, is it right for green campaigners to back petrol over diesel so strongly? Furthermore, should diesel owners, who were once encouraged so fulsomely to adopt the new diesel technology, now be looked upon as the environment’s enemy number one, and be made to live in fear of a fast ticking expiry date on the use of cars that are surely losing their value hand over fist as their pariah status increases? We all want cleaner air but surely it is more sensible to move forward with care rather than suddenly implementing draconian measures against blameless diesel drivers. Rather than procedures which would penalize and punish it would be more sensible to offer incentives for change. But without a clear viable alternative in switching back to petrol the outcome of a diesel ban is hard to evaluate.

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