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Clearing the air

Air pollution is a high-profile issue. Half a century ago, coal was still the main source of domestic heat and electricity. City buildings were covered in a permanent layer of soot deposited from the air, the rest being breathed in by residents and workers. In London, the Great Smog of 1952 was but the worst of a pattern of such events, but it led to the passing of the Clean Air Act in 1956.

Since then, air quality in the UK capital and other major cities in the developed world has improved enormously, but pollutants such as nitrogen dioxide and ozone, as well as microscopic particles (PM2.5) are still present at levels that can harm the health of vulnerable people. Cities such as London are beginning to introduce road traffic restrictions to limit the problem; this week Paris has (not for the first time) introduced a system allowing only cars with odd- or even-numbered licence plates to enter the city on alternate days. Some cities are even considering banning diesel vehicles altogether (Four major cities move to ban diesel vehicles by 2025).

Paris, not surprisingly, is one of these, with the others being Mexico City, Madrid and Athens. However, what is perhaps surprising is that the target of the mayors appears to be all diesel cars, including the most recently developed, which are effectively as good as petrol engines in terms of emissions. But perhaps we can see why, when we see them quoted as saying they "commit to doing everything in their power to incentivise the use of electric, hydrogen and hybrid vehicles".

The battle against diesels seems to be just one campaign in the overall war against internal combustion engines in urban areas. Certainly, there is a case for hybrid drives if they eliminate most of the exhaust gases during journeys in cities. Although more expensive (and heavier) than conventional cars, hybrids do have the potential to replace both pure petrol- or diesel-fuelled vehicles for all journeys. Pure electric vehicles, in the meantime, have a long way to go before they would be a full replacement. Meanwhile, the severe difficulties of handling and storing hydrogen, together with the relative lack of progress on reducing the cost of fuel cells, make the ‘hydrogen economy’ a long shot at best.

The problem with air pollution is that, despite the enormous strides made in recent decades, the health response is not a linear one. Even the relatively clean air those outside central city areas enjoy still contains enough particles – many from sources other than car engines – to exacerbate problems for vulnerable people. Getting below the threshold where there is absolutely no hazard would mean bringing city air in line with that in some of the most pristine wildernesses in the world. There would have to be a ban on all traffic as it exists today, since tyres and brakes are also a significant contributor of fine particulates to the air.

So, having made great strides, and undoubtedly improved both the quality of life and the health of many people, we are now in a situation in rich countries where large efforts are needed for relatively small gains, and the realistic best case we can reach is simply not known. But in poor countries, meanwhile, many people live with daily pollution far worse than most people in Paris, London or Madrid have ever experienced. Traffic and industrial emissions are largely to blame in cities such as Beijing and Delhi, but for the vast numbers of the rural poor the big problem is the use of inefficient cooking stoves burning wood, dung or other ‘traditional biomass’.

The received wisdom has been that replacing these stoves with something better would save lives and improve health, particularly of women and children who are most exposed. It is estimated that about 6 million deaths are caused by air pollution globally every year. Of these, the most recent WHO figures suggest 4.3 million are due to indoor air pollution, almost exclusively a problem confined to the developing world. As I’ve pointed out previously, there is some disconnect with the reported figure of 40,000 deaths a year in the UK due to (outside) air pollution, which seems similar to the average global figure, implying that the UK’s relatively clean air makes precious little difference to health.

This is not the place to find an explanation for this, although any suggestions from readers would be welcome (it may simply be that there are other factors that cause death before air pollution takes its toll). Nevertheless, such incongruities make it difficult to be certain about the impact of cleaner air. This seems to be compounded by a recent study published in the Lancet and reported by the BBC under the headline Do smoke-free stoves really save lives?

There is a major push underway through the Global Alliance for Clean Cookstoves (GACC) to improve the quality of air breathed by 100 million households by 2020. It seems obvious that reducing the appalling smokiness of indoor air would improve health but, according to a two-year study in Malawi, this isn’t so. 5,000 children in families with clean stoves were monitored regularly and compared with those in households continuing to use their traditional ones.

Kevin Mortimer, author of the study, said “…our results basically show that there is no difference in cases of pneumonia between the intervention and the control group. The hard science - certainly from our study - is perhaps at odds with the claim that stoves along the lines of the ones we've used here save lives and reduce illness."

The answer seems to be that simply burning wood and other traditional fuels more efficiently and venting the smoke better (as the stoves in question do) is only a step in the right direction. The solution, borne out by the GACC itself, is that people need to use cleaner fuels such as LPG or electricity to make big health improvements. However, even if the stoves were handed out free, the fuels are often beyond the reach of the poor people they would benefit.

Only economic development is going to make a real improvement to the situation. Lucky people in the developed world can worry about how to make city air still cleaner, but the real problems are in shacks across Africa and Asia and the answer is both straightforward and relatively inexpensive.