杏吧原创

WHEN you hear 鈥渁ir pollution鈥�, you probably think of the brown pall of soot that hangs over so many Asian cities. But if you travel on, work or live near a busy road in Europe, you鈥檙e also breathing in a hidden killer, even when the sky is a brilliant blue.

We now know that the invisible gas nitrogen dioxide can seriously damage our health 鈥� and cities in Europe and the US have some of the .

The good news is that these levels are declining. The bad news is that in many cities they are not declining fast enough to meet legal standards any time soon.

Worse still, even if air does meet those legal limits, it still won鈥檛 be safe to breathe. Nearly half a million people in Europe die from air pollution every year 鈥� and most of those deaths are being caused by breathing air that is supposedly 鈥渟afe鈥�. It kills more people than obesity or alcohol 鈥� only smoking is more dangerous.

If we want to live longer, healthier lives, we need to go way beyond the current standards. That means changing our transport systems: ditching diesel cars for hydrogen or electric ones, and cycling or walking more.

Diesel vehicles are the biggest source of NO₂, and Europe鈥檚 roads are now full of diesel cars thanks to low-carbon policies that encouraged people to buy them.

It used to be debated whether NO₂ was harmful itself, or merely appeared to be because high levels of it usually coincide with high levels of particulate pollutants. Now there is strong evidence that NO₂ on its own has a wide range of harmful effects.

It lowers birthweight, stunts lung growth in children and increases the risk of respiratory infections and cardiovascular disease. Particulate pollutants like soot cause a wider range of problems, including lung cancer.

While air pollution doesn鈥檛 kill directly, statisticians express its life-shortening effects in terms of deaths per year. A concluded that particulate pollution causes the equivalent of 30,000 deaths in the UK every year, while NO₂ kills 10,000. These figures suggest air pollution is second only to smoking in terms of the harm it does.

鈥淎ir pollution kills more people than obesity or alcohol 鈥� only smoking is more dangerous鈥�

And this is just what we have good evidence for. Air pollution is also suspected to increase the risk of conditions including diabetes, dementia and . Earlier this year, a study found millions of tiny iron particles in brain tissues, probably from exhaust fumes.

The bottom line is clear. 鈥淩educing pollution levels in cities is likely to have massive health benefits,鈥� says at the Queensland University of Technology in Australia.

According to European Union regulations that came into force in 2010, NO₂ should average no more than 40 micrograms per cubic metre over a year (the US standard is less strict: 100 渭g/m³ over a year), and should not exceed an average 200 渭g/m³ over an hour more than 18 times in a year. These limits are still breached in half of EU countries.

Take London: the city centre exceeds the 40 渭g/m³ annual average limit, and in some parts the hourly maximum limit was breached in the very first week of January this year.

Off road solution

There is no doubt about the main cause of the problem: road traffic 鈥� mostly diesel vehicles 鈥� produces about half of the air pollution in our cities. In theory, cleaner exhaust systems should have reduced NO₂ pollution despite the rising numbers of diesel cars, but as the Volkswagen scandal made clear, newer vehicles are not as clean as they are supposed to be.

So in simple terms, lowering air pollution boils down to getting the most-polluting diesel vehicles off busy city roads. Some nations are taking this seriously: many German cities already have clean air zones, for instance. The UK government, however, has done so little that it is being taken to court for a second time by environmental campaign group ClientEarth over its failure to act 鈥� having already lost the first case.

The mayor of London, Sadiq Khan, this year announced plans to tackle air pollution in the city. But more needs to be done if London is to meet the legal limits within a decade, says Richard Howard from the think tank in London.

For instance, one plan is for owners of diesel cars made before 2005 to pay a 鈥渢oxicity charge鈥� from 2017 if they enter central London. But this will make little difference: while diesel cars made between 2005 and 2014 do better in lab tests, they produce just as much NO₂ in real-world driving as older models, Howard says.

Some clean air campaigners want to see diesel vehicles phased out entirely. 鈥淚n the longer term, we need to be looking beyond diesel,鈥� says Alan Andrews of ClientEarth. 鈥淭he days of diesel cars are numbered.鈥�

But getting them off our roads is a huge challenge. While opinion polls suggest strong support for cutting air pollution, there could be a big backlash when millions of drivers realise they will be hit by an 鈥渦ltra low emissions zone鈥� planned for London in 2019. Paris has already seen protests against its air pollution efforts. 鈥淚鈥檇 be amazed if Sadiq manages to push the policy through,鈥� says Howard.

For this reason, many campaigners are calling for a national scrappage scheme to help people cover the cost of replacing diesel cars with hybrid or electric ones. It will be money well spent, they argue, given the price of inaction on air pollution.

Indeed, a estimated that dirty air costs the UK some 拢5 billion a year in terms of lost working days, admissions to hospitals and so on. When a , based on what people say they are prepared to pay to reduce their risk of dying early, the figure soars to up to 拢50 billion a year.

Cash-strapped governments aren鈥檛 keen on scrappage schemes, yet without central government support, big cities like London will struggle to meet the legal limits for air pollution. And here鈥檚 the real shocker: even meeting these limits won鈥檛 solve the air pollution problem.

鈥淚f we are serious about improving health, meeting current legal limits should just be the start鈥�

Remember those 30,000 deaths per year from particulate pollution? Almost all are due to . 鈥淭he particulate matter limit is not currently protecting health,鈥� says of King鈥檚 College London.

The EU limit for particulates smaller than 10 micrometres in diameter (PM10s) is twice that recommended by the World Health Organization, says Kelly. All of central London exceeds this stricter limit, which some say still isn鈥檛 enough. 鈥淭here鈥檚 no safe level of air pollution,鈥� says Barnett.

So if we are serious about improving health, meeting the current legal limits should just be the start. The next stage is to get air pollution down to negligible levels, says at the Institute for Public Policy Research in London. 鈥淚t鈥檚 a much deeper and longer battle.鈥�

The implications are enormous. Not all air pollution from road traffic comes from exhaust fumes. In cities, about . Another quarter comes from traffic stirring up dirt on roads.

So even switching to electric vehicles won鈥檛 solve the problem. One 2016 study (Energies, ) estimated that electric cars still produce an eighth of the PM10s that new diesels do and half as much as petrol cars do.

This leads to a conclusion that many won鈥檛 like: if we want to cut air pollution in big cities to low levels, we need to cut traffic. Looking on the bright side, tackling air pollution the right way could be a win-win situation. Switching to electric vehicles will slash CO₂ emissions, and encouraging more people to walk and cycle has health benefits.

鈥淲e are not in a situation where there are no alternative options to dirty cars,鈥� says Laybourn-Langton. 鈥淭here are more alternative options than ever before.鈥�

This article appeared in print under the headline 鈥淚nvisible killer鈥�