New Delhi has world's worst air pollution: WHO

A World Health Organisation (WHO) study ranks New Delhi as the world's worst city for air pollution, with an annual average of 153 micrograms of small particulates, known as PM 2.5, per cubic metre.

The WHO study of 1,600 cities released on Wednesday found air pollution had worsened since a smaller survey in 2011, putting city-dwellers at a higher risk of cancer, stroke and heart disease.

"The number of vehicles has increased exponentially and the number of diesel vehicles has increased. Diesel is particularly, extremely toxic, it is also the key reason why there are such high levels of particulate pollution in the city of Delhi," said Director-General of the Centre for Science and Environment Sunita Narain.

Growing traffic on city streets is a major cause of air pollution.

Thirteen of the dirtiest 20 cities were in India, the WHO said, with New Delhi, Patna, Gwalior and Raipur taking the top four spots.

Beijing, notorious for the smog that has prompted some Anglophone residents to dub it "Greyjing", was in 77th place with a PM2.5 reading of 56, little over one third of Delhi's pollution level.

"We may not be as bad as Beijing. We are not here in a match where we have to score over each other. But the fact is Beijing is bad and Delhi is bad. The fact also is that Bejing is taking tough steps to reduce its emissions and Delhi is not," said Narain.

Air pollution killed about 7 million people in 2012, making it the world's single biggest environmental health risk, the WHO, a United Nations agency, said last month.