Last modified on Sat 10 Nov 2018 13.39 GMT
Why is air pollution a fast-growing concern?
Nothing is more vital to life than breathing: in a lifetime, about 250m litres of air passes through your lungs. Yet walk along a busy city street and you will inhale something like 20m particles in a single lungful.
Toxic air is now the biggest environmental risk of early death, responsible for one in nine of all fatalities. It kills 7 million people a year, far more than HIV, tuberculosis and malaria combined, for example. Dr Maria Neira, the World Health Organisation director with responsibility for air pollution, is blunt: “It is a global public health emergency.”
How much does it cost us?
The lost lives and ill health caused are also a colossal economic burden: $225bn in lost labour income in 2013, or $5.11tn per year (about $1m a minute), if welfare losses are added in, according to a 2016 World Bank report, which called the figure “a sobering wake-up call”.
Air pollution is getting worse in the developing world and, while it is getting better in some developed nations, our knowledge of how comprehensively it damages our bodies and minds is growing even faster.
Dirty air has been with us for centuries – previously, we simply lived with it – and no one has yet had air pollution as a cause of death on their death certificate. It is only in recent decades that the damage to health has become clear, and in recent years that the health crisis has received widespread attention, thanks to research revelations, government legal defeats and the Volkswagen diesel scandal.
But there is a silver lining to air pollution’s cloud of smog: action to cut it not only brings immediate benefits but also helps fight climate change in the longer term.
Who does it affect?
Almost everyone. Over 90% off the world’s population lives in places where air pollution is above WHO guidelines. It is worst in south and east Asia, where most of humanity lives, with traffic, dirty industry and the open burning of waste delivering a triple whammy.
India has almost half of the top 50 most polluted cities in the world, China has eight and Iran has three. Africa is highly polluted but little measured: in 2015 Paris had three times more monitoring stations than the entire continent.
But air pollution still affects rich nations too. “The trends are positive if we look at the last 50 years, but it depends how many deaths are you ready to accept,” says Neira. “We still have 500,000 deaths in Europe [per year] and this is totally unacceptable.”
Children’s developing bodies are uniquely vulnerable, but 300 million live in places with extreme air pollution, where toxic fumes are six times higher than international guidelines.
Are there different types of air pollution?
Yes. The most damaging but best understood are tiny particles. These not only damage the lungs, but enter the bloodstream. They are increasingly thought to enter vital organs, including the brain and have been shown the reach the liver, spleen, kidneys and testes in lab animals.
The particles can be made of black carbon, nitrates, sulphates, ammonia or mineral dust. Most are produced by burning fossil fuels or wood, for driving, heating, power plants and industry.
While improvements have been made in some countries, for example, to coal-fired power stations and cars, other sources have lagged behind. Farming is one such source of pollution, with ammonia from livestock manure and fertilisers blowing into cities and forming particles, particularly in spring time when crops are sown and muck is spread.
Nitrogen dioxide, produced by diesel vehicles, not only forms particles but is now known to cause harm when breathed as a gas. It is still illegally high in much of urban Britain, for example, where it results in about 23,500 early deaths.
Other pollutants include sulphur dioxide, which is usually stripped out of vehicle fuels but still very high in ship and aviation fuels. Ground-level ozone, which forms on sunny days, harms people but also crops: 7-12% of the global wheat crop is estimated to be lost. In India, crop yields are reduced by 28% by ozone.
There are some natural sources of outdoor air pollution, such as dust storms and smoke from forest fires, but human-caused pollution far exceeds these. Outdoor air pollution causes 4.2 million early deaths, according to the WHO.
What about indoors?
This is also a huge killer, causing 3.8 million early deaths. (Some people are exposed to both indoor and outdoor pollution). Half the world’s population cook on open fires with dirty fuels such as wood, dung and charcoal, and kerosene in wick lamps also produces dangerous smoke.
More people are getting access to better fuels and stoves. Among farmers in Xuanwei in China, for example, cases of lung cancer fell by 40% when they switched to stoves with chimneys in their homes. But with the global population rising, the number of people exposed to indoor pollution is not falling.
What harm does air pollution do?
Increasingly, it is easier to ask what harm does air pollution not do. Research is now linking toxic air not only to almost every part of the body, but also to the mind.
The dangers of toxic air are a surprisingly recent discovery. The landmark research linking air pollution to lung diseases, heart attacks and strokes – the Harvard six cities study – was first published in 1993. Since then dirty air has been linked to many other conditions, such as diabetes. Air pollution contributed to 3.2m new cases of this illness in 2016, according to one study. Kidney disease appears to be influenced by air pollution, as does Alzheimer’s disease. The skin is affected too, ageing more rapidly in dirty air.
The research on babies and children is particularly worrying. A large recent study found toxic air significantly increases the risk of low birth weight, leading to lifelong damage to health. The doctors involved called this finding alone “something approaching a public health catastrophe”.
Millions of premature births may be linked to air pollution; another study makes the connection to birth defects and another to cot deaths. The first direct evidence of pollution particles in mothers’ placentas has also been revealed. “It is a worrying problem – there is a massive association between air pollution a mother breathes in and the effect it has on the foetus,” said the lead researcher.
The estimated annual death toll of 7 million is certain to be an underestimation, as it only includes particle pollution and the five most firmly linked causes of death, such as heart attacks. Early estimates using improved models suggest a total figure of 9 million from particle pollution.
But even this is only “the tip of the iceberg” of harm, according to researchers. That is because the ubiquitous exposure to air pollution is likely to damage the health of almost everyone in some way, even if it doesn’t lead to a visit to the doctor.
The WHO is clear: “The burden of disease from [outdoor] air pollution is expected to greatly increase”.
Can I protect myself?
The rise of concern over air pollution has prompted a plethora of protection products. Masks are now commonly advertised, but experts say they are of limited use unless they have an airtight seal on the face, which is rare.
Giant towers, street-side benches and living, green walls have all been proposed to filter dirty air. A new bus aims to filter the air in Southampton, UK, as it travels. Trees can help too, unless they block the breezes that blow pollution away, in which case they make things worse.
Other suggestions are pollution-monitoring apps, so people can choose to avoid the worst times, and alternative city walking routes that keep pedestrians away from the filthiest roads.
People in cars are often exposed to more pollution than those outside, as fumes become trapped in the cabin. Closing the air circulation in your car before hitting the city centre is certainly a good idea.
Isn’t that treating the symptom, not the cause?
Yes. The only practical way to tackle the global health emergency is to cut levels of pollution at source. There is an ethical angle too, says Dr Gary Fuller, at Kings College London: “Morally it is not right to make the victims change their behaviour, instead of the culprits.”
Poorer people are also most exposed to air pollution. “There are huge injustices at the heart of the air pollution problem,”’ says Fuller. “By using our air to dispose of their waste, polluters are destroying a shared resource and avoiding the full cost of their actions.”
The solutions are simultaneously perfectly possible and incredibly hard, because they require little new technology but involve action across many areas, and are usually neither politically palatable – yet – or very profitable to implement.
“There are two big transitions we need to have,” says Neira. “One is a healthy energy transition and the other is the healthy urban planning transition. We need to stop the use of coal, to stop the massive use of private cars in cities and make our buildings more efficient.”
Coal burning is declining globally and China has shown how industrial pollution can be rapidly curbed. Particle pollution is down by a third, just four years after a “war on pollution” was declared, and eight after Beijing’s air was labelled “crazy bad” when pollution leapt off the charts. But cities around the world are expanding rapidly, with 4.2 billion urban dwellers set to swell to 6.7 billion by 2050.
How those expanded cities are constructed is vital, say experts like Fuller: “We will pay a heavy price if we get it wrong now.”. Mobility should focus on walking, cycling and public transport – even electric vehicles throw up particle pollution from road abrasion and brake dust. The remaining cars and lorries need to be set – and stick to – much stricter pollution controls.
Buildings ought to be heated and cooled using renewable energy and waste should not be burned without stringent controls.
Progress is being made in some places. Some Dutch and Danish towns have turned their back on cars and Seoul in South Korea has demolished 15 expressways in favour of bus lanes and a new river. But some motoring lobbies and car manufacturers remain obstacles to citizens breathing clean air.
Neira, a former health minister in Spain, says politicians should play the health card to win the argument: “If you reduce cases of asthma, everybody will love it.” Other reasons for action are the climate change benefits of cutting coal, oil and gas burning and the reduction in obesity that follows more active travel, such as cycling.
What must be done to end the air pollution emergency is not the issue, says Neira, it is the lack of serious political will: “There are plenty of ideas and solutions. It takes leadership.”
• This article was amended on 5 November 2018 to correctly state the title of Dr Gary Fuller.