diamond geezer

 Thursday, October 05, 2017

Yesterday the Mayor of London published a particularly scary press release.
Revealed: Every Londoner is exposed to dangerous toxic air particles
The Mayor reveals shocking research revealing all Londoners live in areas exceeding WHO levels for the most toxic air.
Can living in London really be that dangerous? Sadiq seems to think so.
The Mayor of London, Sadiq Khan, has today released shocking new research which reveals that every Londoner in the capital lives in an area exceeding World Health Organization (WHO) guidelines for the most dangerous toxic particles known as PM2.5.
PM2.5 is one of a basket of pollutants we breathe in every day. Sadiq's "shocking new research" explains more.
PM2.5, also known as fine particulate matter, is the blanket term used to refer to solid particles and liquid droplets with a diameter less than 2.5 micrometres across (that’s one 400th of a millimetre). Some PM2.5 is naturally occurring, such as dust and sea salt, and some is manmade, such as particulates formed in combustion processes.
How frightening that every single Londoner is at risk. Sadiq's research appears to have uncovered something big. [the report] [the data]
The research, based on the latest updated London Atmospheric Emissions Inventory, also shows that 7.9 million Londoners – nearly 95 per cent of the capital’s population – live in areas of London that exceed the guidelines by 50 per cent or more.
That sounds bad. There's even a map.



The World Health Organisation limit for PM2.5 is 10µg/m³. The map confirms that everywhere in London exceeds 10µg/m³, and almost everywhere exceeds 15µg/m³. Only rural extremities in boroughs like Enfield, Havering and Bromley duck under the 15µg/m³ threshold. The average reading is 16µg/m³. As for central London, and certain main roads, they top 18µg/m³, which sounds appalling.
New data, based on updated 2013 exposure estimates, shows that in central London the average annual levels of PM2.5 are almost double the WHO guideline limits of 10 µg/m³.
Ghastly. Except hang on, these figures aren't exactly new. They're estimates for 2013, first released in 2016, and updated six months ago "due to revised road transport emission factors". To prove how not new the figures are, here's the same data in a Mayoral consultation document from October last year, but coloured differently.



What's intriguing is that one year ago officials weren't anywhere near as worried by the same data.
London is now broadly compliant with legal limits for PM2.5. Annual mean concentrations of PM2.5 are well within the legal limit of 25 µg/m³.
It seems there's been a switch in which PM2.5 threshold is politically expedient. Last October the key measure was the legal limit of 25 µg/m³, and every part of London was comfortably under that. This October the key measure is the WHO target of 10 µg/m³, and every part of London is suddenly toxic.

There was recognition last year that PM2.5 concentrations need to come down.
Further reductions are needed (especially to PM2.5) to protect human health. Although compliance has officially been achieved, by reducing PM2.5 concentrations even more, the health benefits will be even greater.
But blimey, now the goalposts have been changed, how different the message twelve months later.
The Mayor of London, Sadiq Khan, said: "This research is another damning indictment of the toxic air that all Londoners are forced to breathe every day. It’s sickening to know that not a single area of London meets World Health Organisation health standards, but even worse than that, nearly 95 per cent of the capital is exceeding these guidelines by at least 50 per cent."
As an example of how you can prove anything you like using statistics, this is cracking.

In addition, Sadiq appears to be making a big fuss about something he has very little control over.
"I urge the government to devolve powers to me so I can get on with tackling the dangerous toxic air particles – known as PM2.5 – that we know come from construction sites and wood burning stoves. It's measures like these that we need to get on with now to protect our children and our children’s children."
The Mayor of London has relatively few powers, and curtailing the use of wood-burning stoves isn't one of them. Wood-burning isn't even the real problem anyway, not compared to vehicles.
Of the local London PM2.5 sources the biggest contributor by far is road transport, accounting for over half of local contributions.
What's more these aren't the usual issues with exhaust fumes. Instead it's wear and tear from braking and tyres that's most significant, and such particles will emerge whether your car is petrol, diesel or electric. Don't expect the new T-Charge or Low Emission Zone to save us here, they tackle other particulates, not the toxic PM2.5.

The fact that PM2.5 exceeds 10µg/m³ isn't even new, it's been the case for years. Boris could have put out a press release saying "all Londoners live in areas exceeding WHO levels for the most toxic air" several years ago, had he been so minded. This research paper Sadiq is crowing about hasn't discovered anything new, it's simply picked a different threshold.

Meanwhile there's one sentence in the press release which turns out to be more important than all the others, and understates the issue.
Around half of PM2.5 in London is from external sources outside the city.
That's right - the majority of PM2.5 particles in the capital haven't come from London at all, they've drifted in from elsewhere. The press release says "around half", but the associated research paper says something different, and the true proportion is much higher.
A big component of PM2.5 in London comes from regional, and often transboundary (non-UK) sources. In 2013 the background concentration for PM2.5 was 12µg/m³, meaning in 2013 the external contribution to London’s PM2.5 levels alone were above the WHO standard of 10µg/m³.
Let me restate that. What the research paper confirms is that London breaks the WHO 10µg/m³ limit solely thanks to PM2.5 generated elsewhere (12µg/m³), with mainland Europe a major contributor. The extra amount generated by vehicles, construction and wood-burners within the capital averages only around 4µg/m³. Even if Sadiq could cut this to zero, which he can't, PM2.5 levels would still exceed the WHO threshold.
Much of the background emissions come from areas outside of the Mayor’s jurisdiction. This highlights one of the key messages of this report, that London needs national and international support to tackle this issue.
In the research paper's conclusion, the need for broader action well beyond London is apparent.
The Mayor expects PM2.5 emissions to reduce by approximately 41% by 2030 compared to 2013. A key finding of our research is national and international co-operation will be essential in meeting this target.
Without external assistance London's basically at the mercy of whatever PM2.5 drifts in from outside. Those of us living beside main roads may be getting it worse than the rest of the capital, but not hugely worse, because background levels are more significant.

Sadiq can do no more than tinker with the PM2.5 problem without concerted efforts from the UK government and the EU. But it's only become a pressing problem because he's adopted the 10µg/m³ WHO aspiration rather than the 25µg/m³ legal limit.



Sadiq is absolutely right to want PM2.5 levels in London to be as low as they can be. But getting righteously angry about this, in the face of a pollutant he can do little about, is somewhat disingenuous.

Average PM2.5 by borough
18µg/m³: City of London
17µg/m³: Westminster, Kensington & Chelsea, Camden
16µg/m³: Islington, Tower Hamlets, Southwark, Hammersmith & Fulham, Hackney, Lambeth, Wandsworth, Newham, Lewisham, Brent, Haringey
15µg/m³: Ealing, Greenwich, Waltham Forest, Merton, Hounslow, Barnet, Richmond, Redbridge, Barking & Dagenham, Croydon, Kingston, Sutton, Enfield, Bexley, Bromley, Harrow, Hillingdon
14µg/m³: Havering

Average (urban) PM2.5 by country
Finland 6µg/m³, Sweden 7µg/m³, Spain 10µg/m³, Ireland 11µg/m³, UK 13µg/m³, Germany 15µg/m³, France 16µg/m³, Greece 17µg/m³, Romania 18µg/m³, Italy 21µg/m³, Slovakia 22µg/m³, Poland 27µg/m³, Bulgaria 30µg/m³.


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