London in the haze

WHO air pollution statistics challenged by experts

Image credit: Press Association

London is less polluted than Sandy, Bedfordshire, according to the latest World Health Organisation (WHO) statistics, although the figures only took into account ultra-fine particles, not NOx or CO.

Port Talbot has been named the UK’s most-polluted town by the World Health Organisation (WHO).

The Welsh steel town is one of 32 places in the country found by the WHO to be exceeding airborne limits of PM2.5 deemed ‘safe’ by global experts.

Levels of PM2.5 particles in the air in Port Talbot were recorded as 18 micrograms per cubic metre, nearly double the WHO recommended limit of 10.

Surprisingly, London was listed as having almost safe levels of polluted air, with its atmospheric toxicity judged as having declined dramatically.

The ‘Big Smoke’, as London has colloquially been known for decades, has apparently been surpassed in the toxic air stakes by such comparatively rural locations as Sandy in Bedfordshire, Royal Leamington Spa in Warwickshire and the diminutive, remote Scottish fishing town of Prestonpans.

Transport writer Joe Dunckley cast doubt on the usefulness of the statistics, warning on Twitter that it “depends where in Sandy and where in London they measured! Quick Google Earth, it looks like Sandy has the A1 and East Coast Mainline (which still has some dirty Intercity 125s) through it, aggregates quarry nearby and arable agriculture can be dusty.”

He added: “I suspect they’ve just picked the least representative category of pollution to report on and [have] done a bad job of explaining the complexity of the issue.”

The WHO stats do not measure levels of NOx or CO, or low-level ozone.

Liza Selley, a PhD student at Imperial College London who is studying pulmonary responses to traffic pollutants, told E&T in response to the figures: “There’ll be lots of factors coming together here, like what sort of industries there are in an area as well, of course, as transport.”

Hitherto underappreciated factors like waste incineration, types of fuels used by agricultural vehicles and even rural topography - the ‘lie of the land’, in other words - could have an impact on the level at which tiny particles with an aerodynamic diameter of 2.5μm or less are present in the air, she said.

Valleys or ‘dips’ in the landscape might be retaining pollutants at a higher rate than flat areas, she surmised.

Professor Kevin McConway, emeritus professor of applied statistics at the Open University, also questioned the usefulness of the WHO statistics, saying factors like prevailing winds and temperature inversions - as well as the location of the measuring station - could affect data collected.

“Biggin Hill is in London and that’s virtually in the countryside and Oxford Street is in London and that’s horrendously polluted,” he said. “How you get an average out of that, I don’t know. With smaller towns it will probably be more accurate as there’ll be a measuring station in the centre of the town and the outskirts aren’t that far away.”

He added: “Diesel-fuelled motor vehicles always get both barrels in this debate, but what people don’t seem to realise is a lot of the particulates don’t come from the fuel vehicles use.”

Some particles could even be blown in from as far away as the USA or the Sahara, he said. 

Many of the UK’s main cities - including London - exceed the WHO limit of 10 micrograms per cubic metre, according to the WHO. However, London’s level of 11 micrograms per cubic metre represents a significant drop from the figure of 17 recorded around six years ago.

Salford and Scunthorpe recorded levels of 15, Manchester recorded 13, while Liverpool, York and Nottingham measured 12.

Birmingham, Brighton and Newcastle were among those whose PM2.5 levels were at the limit of what the WHO defines as being safe.

A Defra spokesman said: While air quality in the UK has improved significantly since 2010, this report from the WHO clearly shows the impact air pollution is having on the health of men women and children in the UK and across the world.

Tackling this important issue is a priority for this government, which is why we have a £3.5 billion plan to improve air quality and reduce harmful emissions and will set out further actions through a comprehensive Clean Air Strategy later this year.

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