Across 10 cities — Ahmedabad, Bengaluru, Chennai, Delhi, Hyderabad, Kolkata, Mumbai, Pune, Shimla and Varanasi — more than 33,000 deaths could be attributed to air pollution every year on an average, the study said.

About 11.5 per cent of deaths in Delhi every year, roughly 12,000 deaths, can be attributed to air pollution, the highest for any city in the country, a first-of-its-kind multi-city study in India, published in the Lancet, has revealed.

The study, carried out by researchers from India and abroad, found that PM2.5 concentrations in these 10 cities, exceeded the safe limits defined by the World Health Organisation (15 micrograms per cubic metre) on 99.8 per cent of the days.

The study found 1.42 per cent rise in mortality for every increase of 10 micrograms/cu metre in the PM2.5 levels when all the ten cities were taken together. There was large variation among the cities, with Delhi showing a rise of 0.31 per cent in mortality while Bengaluru having an increase of 3.06 per cent. This suggested that people living in less polluted cities carried a higher risk of mortality due to increase in pollution than those living in polluted cities.