Delhi has the worst air pollution in the world: WHO study

Reacting to the report, Anumita Roychowdhury of the Centre for Science and Environment (CSE) said the new WHO data base only confirms the health concerns in India.

"According to global burden of disease estimates, air pollution is the fifth largest killer in India. Tiny particles (PM10 and PM2.5) go deep inside our lungs and trigger respiratory and cardiac problems as well as lung cancer," she told PTI.

The WHO said that in most cities where there is enough data to compare the situation today with previous years, air pollution is getting worse.

"Many factors contribute to this increase, including reliance on fossil fuels such as coal fired power plants, dependence on private transport motor vehicles, inefficient use of energy in buildings, and the use of biomass for cooking and heating," it said.

"Too many urban centres today are so enveloped in dirty air that their skylines are invisible," said Dr Flavia Bustreo, WHO Assistant Director-General for Family, Children and Women's Health.

"Not surprisingly, this air is dangerous to breathe. So a growing number of cities and communities worldwide are striving to better meet the needs of their residents - in particular children and the elderly," Bustreo said.

Last month, the WHO issued new information estimating that outdoor air pollution was responsible for the deaths of some 3.7 million people under the age of 60 in 2012.

The organisation also emphasised that indoor and outdoor air pollution combined are among the largest risks to health worldwide.