Doctor Diesel

Soapbox – London Air Pollution

Diesel cars have been getting a bad reputation recently, but what you read in the national press is inevitably sensationalised and only a selective part of the big picture. EC limits for two key air pollutants are undeniably being exceeded regularly in certain locations of London, as in other British cities and many similar highly urban areas throughout Europe.

The pollutants in question are PM10 particulates, and oxides of nitrogen (nitrogen dioxide in particular) which have both been associated with raised mortality rates, mostly from respiratory diseases. The press and air pollution experts are pointing the finger at diesel cars, and some of the mud is sticking; for example, I’ve recently had a letter from a reader who says that many of his friends are scoffing at his enthusiasm for his Mazda CX-5 and talking about shunning “dirty diesels” as a result of what they read. So let’s get a few basics clearly established. Airborne PM10 particulates come from a good number of sources, 50 per cent from industrial sources, power generation, and other non-vehicle sources. Of the 50 per cent transport derived PM10, only half comes from vehicle exhaust, with the rest derived from brake dust, tyre dust, and other non-combustion sources. And of the 25 per cent of all PM10s originating from vehicle exhaust, only around fifty per cent of that is generated by diesel cars! The other fifty per cent comes from buses, HGVs, light goods vehicles, and taxis. If legislation were to ban all diesel cars from the streets of London tomorrow, the likely reduction in PM10 levels would be of the order of at best 12 to 15 per cent.

Regarding oxides of nitrogen, EC regulations, demanding massive investment by manufacturers, have reduced the allowable limit for NOx exhaust emissions of new cars by 84 per cent over the last 15 years – quite an achievement. The problem is that the EC test cycles understate emissions of oxides of nitrogen, just as they overstate fuel economy, and these emissions are not falling as fast as was predicted; but banning diesel cars would be a knee-jerk reaction, and is just not the answer. Too many other concerns cloud the issue; HGVs still enter cities in significant numbers, often on multi-drop stop-start journeys that mean their emissions control systems are often not hot enough to work efficiently. Search the web and you’ll find dozens of companies offering to remove HGV SCR (selective catalyst reduction) emissions control systems, mostly to avoid the cost of the AdBlue urea-based additive that neutralises the oxides of nitrogen. So how many dirty, and illegal trucks, are boosting the pollution figures?

Vast amounts of city emissions are produced by vehicles that are not even moving, and better stop-start technology and improved emissions systems could vastly reduce this – particularly on taxis and buses. If London’s air is so bad, how come that London mortality rates are falling steadily every year compared with the rest of Britain? How come mortality rates in Westminster and Camden, two of London’s “dirtiest” boroughs, are somewhat lower than those for Barnet and Bromley, two of the “cleanest” boroughs?

Web_soap02Now is not the time for a blanket ban on diesel cars in London, and any other cities. It just won’t achieve the desired result, and it isn’t fair to their owners. Neither are the raised parking charge bills that some diesel-owning London residents are now receiving from their local councils. Get your thinking caps on, you experts, and do something positive, rather than negative! How about “Park and Drive”, where you could park up any conventional car in the suburbs and rent a pollution-free EV for the trip into the city centre? How about focussing the current £5,000 electric vehicle buying subsidy exclusively on the big cities, which is where they really deliver their benefits? Tell us what you think!

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