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.