India’s filthy air is cutting 660 million lives short by about three years, while nearly all of the country’s 1.2 billion citizens are breathing in harmful pollution levels, according to research.

The new study by environmental economists at US universities highlights how extensive India's air problems have become after years of pursuing an all-growth agenda with little regard for the environment.

While New Delhi last year earned the title of being the world’s most polluted city, the problem extends nationwide, with 13 Indian cities now on the World Health Organisation’s (WHO) list of the 20 most polluted.

That pollution burden is estimated to be costing more than half the population at least 3.2 years of their lives, according to the study led by Michael Greenstone of the University of Chicago and involving economists from Harvard and Yale universities.

The most polluted regions, falling generally in northern India, are also among India’s most populous.

“The extent of the problem is actually much larger than what we normally understand,” said study co-authors Anant Sudarshan, the India director of the Energy Policy Institute of Chicago.

“We think of it as an urban problem, but the rural dimension has been ignored.”