Air pollution can reduce the life expectancy of Indians by nine years, says a report by a US research group.

The study says 480 million people in northern India face the "most extreme levels of air pollution in the world" and, over time, these high levels have expanded to cover other parts too.

Strong clean air policies can add up to five years to people's lives, it adds.

Indian cities routinely dominate global pollution rankings and bad air kills more than a million people every year.

The report by The Energy Policy Institute at the University of Chicago (EPIC) says that north India breathes "pollution levels that are 10 times worse than those found anywhere else in the world".

This air pollution has spread over decades beyond the region to western and central Indian states such as Maharashtra and Madhya Pradesh where the average person is now losing between two and a half-to-three years of life expectancy as compared to early 2000, it adds.

New data from the Air Quality Life Index report by EPIC says that residents in the capital, Delhi, could see up to 10 years added to their lives if air pollution was reduced to meet the World Health Organisation (WHO) guideline of 10 µg/m³.

In 2019, India's average particulate matter concentration was 70.3 µg/m³ - the highest in the world.

The report says that Bangladesh, India, Nepal and Pakistan, which together account for nearly a quarter of the global population, consistently figure in the top five most polluted countries on earth.

EPIC acknowledges certain policy changes made by the Indian government to fight air pollution, such as the 2019 National Clean Air Programme (NCAP), which aims to reduce dangerous particulate pollution in the country.

"Achieving these goals would have a major impact on the life expectancy levels of Indians - it would increase the national life expectancy level by nearly two years, and three-and-a-half years for residents of Delhi," it says.

China, the report says, is one example of how effective policy can produce "sharp reductions in pollution in short order". Since 2013, the country has reduced its particulate production by 29%.