Here's some cheerful news from the World Health Organisation (WHO): just 12 per cent of the world's city dwellers are breathing clean air. Around half, in fact, are exposed to air pollution at least two-and-a-half times safe levels, putting them at risk of what it reassuringly describes as "serious, long-term health problems".

Still thinking of going for that after work jog, are you?

All this may seem like a statement of the obvious to any Londoner who's been for a walk on a hazy day, and spent the next three hours trying to get the taste out of their mouth. Actually, though, the capital fares relatively well in the WHO’s most recent figures. The data published last week shows that Londoners face an average of 16µg/m3 of air pollution, a mere 1.6 times the recommended safe level. (All these figures are what is known as PM2.5, the number of micrograms of pollution particles smaller than 2.5 thousandths of a millimere across found in the average cubic metre of air. These particles are the worst for your health, for the faintly upsetting reason that they’re small enough to get right down into your lungs.)

The cities that suffer from really bad pollution, you'll be unsurprised to hear, are in Asia – though not, perhaps, in the places that you'd expect. The most polluted city in China is Lanzhou, which despite posting a terrifying sounding average of 71µg/m3, still only made 36th place in the league table of shame.

The smoggiest cities of all, in fact, are to be found in South Asia. Pakistan takes four of the top 20 slots; India takes 13, including the top four. Topping the chart is Delhi, whose roads reportedly gain another half a million cars every year, and whose PM2.5 consequently clocks in at an average of 153µg/m3. For those keeping score, that's nine times as polluted as London, and 15 times safe levels. The air in Beijing, at a mere 56µg/m3, looks positively sweet by comparison.

The WHO compiles statistics on more than 1,600 cities. Here's the full list of the top 10:



Rank City Annual mean PM2.5, µg/m3 1 Delhi, India 153 2 Patna, India 149 3 Gwalior, India 144 4 Raipur, India 134 5 Karachi, Pakistan 117 6 Peshwar, Pakistan 111 7 Rawalpindi, Pakistan 107 8 Khoramabad, Iran 102 9 Ahmedabad, India 100 10 Lucknow, India 96

To give you a sense of quite how far ahead of the pack Delhi is on this, here’s its pollution rate, compared to those of a few other major world cities.

This is clearly doing a tremendous amount of damage – but you'd be hard pressed to find any of the parties competing in India's recent election talking about it. For some days, in fact, Indian officialdom seemed in denial about the problem. A spokesman for the country's System of Air Quality Weather Forecasting & Research went as far as to dispute the WHO's figures for Delhi and Beijing, claiming that both should actually have been around the 110µg/m3 mark. "Delhi's air quality is better than Beijing in summer and much better in monsoon season," he added. "It is winter pollution in Delhi and sudden spikes – which is quite high as compared to Beijing – triggered by meteorology."

This seems just a tad complacent: the WHO also reckons that India has the worst death rates from chronic respiratory disease of any country in the world, not to mention the worst death rates from asthma. What’s more, the problem is getting steadily worse. According to a study in the Journal of Atmospheric Pollution Research, Delhi's poor quality air caused 11,394 deaths in 2000. A decade later, that figure stood at 18,229.

On Monday, Delhi's Lieutenant Governor Najeeb Jung belated established an official committee to find ways of tackling the issue. It’s a start. Improving the air quality of India's cities isn't going to be easy – but the first step to fixing anything is to admit that you have a problem.

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