Low and ultra-low emission zones (ULEZs) are much in the news and in political argument across the UK. On the face of it, to reduce air pollution must be a good thing, and the arguments in support are so strong no reasonable person could argue against them. Or are they? Here is a brief summary of statements that I have read in the press recently:
Air pollution is causing a public health crisis.
Air pollution is the largest environmental cause of illness in Britain.
Air pollution causes 40,000 premature deaths every year.
Air pollution causes asthma and other chronic lung diseases.
Air pollution causes 20,000 admissions to the NHS each year.
There is no safe level of air pollution.
Yet when you look at the data you will see that levels of air pollution are at an historical low across the whole of the UK. The annual averages of indices most talked about, small particles (PM10) have fallen in UK cities from around 50µg/m3 in the 1970s to less than 20µg/m3 currently, and nitrogen dioxide (NO2) has shown similar falls. The smallest particles, PM2.5 have fallen from about 15 to 5µg/m3 on average over the past decade.
These significant reductions speak for continuing success in reducing emissions, mostly from motor vehicles – note that currently half the urban particles and NO2 come from combustion in our homes. This reduction in vehicle-caused pollution is one of the most important public health achievements of my lifetime, a life that encompasses exposure to pollution measured in milligrams rather than micrograms! But hospital admissions are not falling and we are on average living longer. So let's look at the claims in the media.
Is there a public health crisis in Britain? A crisis implies a dramatic and sustained increase in ill health, and the answer is yes, but selectively affecting the poorest. The important risk factors are poverty, poor housing and diet, obesity, alcohol, drugs and a sessile lifestyle, with accompanying diabetes and heart disease. The contribution of cigarettes is now on the wane, but we need to look out for one related to vaping if this is not to be regulated better. Some of the reduction in heart attacks is probably attributable to reduced urban air pollution but most is related to falling levels of cigarette smoking.
Does air pollution cause 40,000 premature deaths every year? Actually, only one death so far has been attributed (by a coroner) to air pollution and that in a child with severe asthma in whom the fatal attack was probably provoked by pollution. The truth is that the cumulative effects of many environmental factors such as those mentioned above add to genetic risks in causing most deaths, so if you as a statistician estimate deaths contributed to by pollution you will get a large number but most of them also would have multiple other risk factors such as obesity, poor diet, smoking and so on.
In other words, life-long exposure to pollution increases risks of several diseases that can be fatal and overall has been calculated to lop a few months off the average life expectancy of the whole population. Crucially, these effects reflect historic exposure to pollution and the much higher past levels. It is not known what effects reduction from the present low levels would have, but for most people today what matters is what we have already been exposed to.
The same logic applies to hospital admissions. In the 1950/60s winter cold weather, infections and pollution combined to make a noticeable surge in admissions though how much was due to pollution was not known. It remains difficult to know the influence of pollution on admissions as pollution is always related to adverse weather factors but I would not expect numbers to fall noticeably on average if the current low levels of pollution are reduced further, although it is possible some individuals would benefit.
In other words, there are many more important factors influencing hospital admission (viral infections, temperature changes, uneven healthcare, for example) and changes in current levels of pollution will have little or no impact across a population, though some individuals may benefit.
Does air pollution cause lung disease? It can, certainly in industries such as coal mining and it may well have in the past in the UK but recent worldwide evidence is that it does not cause asthma or chronic bronchitis in today's conditions, even in poor countries. There is no difference in the distribution of asthma across urban and rural Britain, but there is no doubt that if you have asthma you may be more susceptible to changes in pollution. However, even during recent pollution episodes in London there have not been any increases in asthma admissions to hospital. Increases in air allergens such as fungal spores and bits of pollen are probably more important causes overall.
Is there a safe level of air pollution? Of course there is, on an individual basis, for most of us can withstand levels of pollution 10 or 100 times current concentrations without noticing anything. However, there are in every large population people on the brink, ready to be pushed over by the slightest nudge.
In 1999, I was one such on a winter trip to London when an atheromatous plaque in a coronary artery went pop and I had a heart attack. Lots of people in London that day must have had the same experience as have many on every other day. A statistician might have concluded that more heart attacks had occurred that day than on other less polluted days, an excess of deaths, but which were due to pollution and which would have occurred anyway nobody can say. For me on that day the level of pollution may not have been safe – who knows? The only absolutely safe level is no pollution. But we also know that absolute safety in life is not achievable and nor is no pollution so long as we burn carbon.
The conclusion of this is that no lives are lost to air pollution but that pollution has had a definite effect in bringing forward deaths and thus reducing the average life expectancy of the population. The lower it is, the smaller this effect until it becomes difficult to detect in a population even the size of the UK's. It is clear that this effect is uneven and like many other risk factors pollution is highest in areas of relative poverty; those who suffer most from other risk factors are more likely to be affected by pollution as well.
So why this keenness to introduce ULEZs? There is a logic to it. We have now reached a very low level of pollution overall in our cities but there remain hot spots where traffic continues to make an undue contribution, especially in city centres where levels sometimes exceed aspirational concentrations advised by the World Health Organisation, levels that WHO admits are not firmly based on evidence of ill health. It is expected that ULEZs will reduce pollution in these by its aim of excluding or taxing older and less efficient cars. However, significant improvements in public health are, in my view, very unlikely from such a small reduction in an already low concentration of pollutants. We are fiddling.
Nevertheless, I remain an enthusiastic supporter of efforts to reduce air pollution in the UK, for one very good reason. They have the potential to reduce the amount of carbon dioxide emitted into the air and are therefore part of the effort to slow down the frightening progression of climate change. When our regulators see this, it will put a completely different perspective on ULEZ – is this the best way to reduce emissions of the silent pollutant, CO2, and is it the fairest?
All combustion vehicles produce CO2 and catalytic converters change other gases into CO2. Vehicles also produce nitrogen oxides which if not converted (as on cold morning drives) also contribute to climate change. If people with old cars switch to newer ones, they will produce less pollution but little less CO2. The bigger the car and the more powerful the engine, the greater the amount of energy in fuel is required to power it and the greater its production of CO2. It is thus obvious that ULEZs will make little or no difference to the fight against climate change. Is there a better way to tackle both aims?
It should now be obvious that there is – to target the larger cars with the biggest engines. ULEZ hits the poorest car owners and businesses and leaves the biggest offenders against our climate untouched. It is thus a highly regressive tax. An alternative would have been to exclude or charge cars with an engine over say 1500cc, whose owners would be in a much better financial position to switch to electric. This would have a significant effect on both air pollution and CO2 production. It would not be popular but it would be just.
For a decade in the 1990s, I chaired the UK Government's committee that advised on air quality standards. All were accepted and influenced the subsequent European standards. It has been pleasing to see that they have done their job pretty well, but there was one gas we did not consider as it is a natural constituent of the air: CO2.
If I were advising our next government, I would be urging everything possible be done to electrify all transport and to green all electricity production. We no longer need to obsess about fears of a health crisis from air pollution – there is a very real and international crisis causing heat waves, fires, floods, storms and mass migration, and not only leading to many more deaths than air pollution but also causing more air pollution by burning forests.
Every one of us with a carbon footprint is responsible and we all need to do whatever is possible to slow this down. We are fiddling while not only Italian cities but also the whole world, from Alaska to Siberia, from the Amazon to Australia, burns.
Anthony Seaton is Emeritus Professor of Environmental and Occupational Medicine at Aberdeen University and Senior Consultant to the Edinburgh Institute of Occupational Medicine. The views expressed are his own