According to today’s Guardian, “The number of premature deaths attributed to particulate pollution has risen, government figures show.
According to Public Health England, the percentage of premature deaths attributable to minute particles known as PM2.5s rose to 5.3% in 2013 in England from 5.1% in 2012. The death rate in London rose to 6.7% from 6.6%. The figures follow significant improvements in air quality across England in 2010 and 2011.” (But only when monitored by technologies which are unable to even detect, let alone monitor the key pollutant – ultrafine particles – IPB)
“The figures were announced as scientists at King’s College London warned of “high” or “very high” particulate pollution across much of London and south-east England for a second day. People with heart conditions or breathing problems were advised to reduce exercise and to stay at home.”
It is estimated that there are currently 40,000 early deaths every year in the UK and over 500,000 a year across Europe. Our air does look cleaner than it used to do, but sadly it may be more toxic and hazardous than ever before – we just can’t see it with the tools we have been using.
Fine particles are produced when we burn fossil fuels; wood, coal, gas, oil – they will all produce fine particles when they are burned and we don’t seem to have a very effective respiratory defence system to cope with them. Years ago everyone was sick and fed up of all that black smoke billowing out of the back of fairly basic diesel engines. The fact that it was black meant that we could see it and the fact that we could see it meant that the particles were, relatively speaking – huge! Our respiratory tract knows how to get rid of such particles; their deposition onto the surfaces of the conducting airways was optimised by the design of these airways over millions of years. Once deposited, the particles are cleared within, let’s say 24-36 hours- tops! Off they go to the gut and, as they have a relatively small surface area, not much gets absorbed before they leave the body in the approved manner! So, engine manufacturers cleaned up their act; lean burn engines, cleaner fuels, better fuel economy all helped bring down the mass of black soot that belched forth into our breathing zones. After engine treatments further reduced the mass pollution and suddenly, diesel engines looked no dirtier than petrol engines, which, once TEL had been taken out was perfectly harmless right? Well no, not really.
True, the mass concentration had been much reduced, but all these incremental improvements had caused the fuel to be burned much more effectively and so the particles that were produced were much smaller. A single, easily visible 10µm particle has the same mass as 1,000,000 0.1 µm particles. Some, many 10µm particles were trapped before they could reach our urban air, and so the mass concentration of particulate started to drop. But some of those larger particles got broken down; they became smaller and smaller, broken down into fine particles and so the number of very fine particles began to increase – significantly.
Those charged with the assessment of our air quality hit a problem. Regulatory authorities do not like change – especially in key parameters used to define what is going on. National, International and global agencies rallied to prop up PM10 and PM2.5, despite the growing scientific evidence that observed health effects associated with poor air quality were no longer tracking mass based fractions of large particles anymore. In other words, we could have a pea souper of very large particles without a corresponding rush to A+E, but sometimes there were huge increases in admissions and referrals associated with respiratory and circulatory disease when accepted air monitoring requirements didn’t show any cause.
That’s because the particles are too small to even be seen by our conventional monitoring methods; they are too small to contribute to an upsurge in mass, but they do exist, and are highly toxic. As they have got smaller, particles’ surface area increases exponentially, by the square of the reduction in diameter, so two things happen in the respiratory tract: The particles are not effectively deposited onto the conducting airways so they pass straight through to the still air in the alveolar air sacs where gas exchange takes place. In the relatively still air they become deposited onto the surface of millions more cells than was previously the case and then they either stay around causing local effects, or because they are so small they can squeeze between cells and into the circulatory system where they can wreak havoc just about everywhere, but mainly in the heart, the circulatory system, the liver, kidneys and brain. Even if these fine particles are made up of the same material as those huge black smoke plumes used to be, their fate and their effects in our bodies are hugely different. Why? Because of their size – they are simply much, much smaller.
For years, we have had to resort to monitoring NOx gases (don’t ask!) which have tracked well with fine particles concentrations within urban air. But the technology to routinely, robustly, cost effectively and directly monitor fine particle number concentrations (or surface area) wasn’t available. Now it is. Pegasor, a company up in Finland has come up with a technology that can do all this and report moment by moment concentrations across cities and beyond. Here’s what the number concentration did a few days ago in Tampere:
You can see that those local hotspots and short term incidents mentioned in Dispatches last night on Channel 4 are not static, they can move around, passing through one location quite quickly depending on wind speed and direction etc, so maybe something with a little more resolution is needed for fine particles than the 15 minute time weighted average used for larger particles.
There is a growing mountain of evidence that suggests that fine particles simply are not the same as their larger counterparts; their biological fate and availability are substantially different. There is no credible evidence that suggest that they are the same. We don’t monitor “Gases”, we monitor specific gases with known hazards, so why would we monitor “particles” without taking note of their size, their morphology and their associated hazards, risks and toxicity.
You can expect a lot more in this vein during my talk at Air Quality – Science and Technology in Milan next month. Come along and find out how we finally got a handle on fine particles.