About a million and a half deaths every year from 2009 to 2019 is potentially linked with a long-term exposure to PM2.5 pollution, according to a study published in The Lancet Planetary Health journal.

Researchers, including those at Ashoka University, Haryana, and Centre for Chronic Disease Control, New Delhi, said that the entire 1.4 billion population of India live in areas having PM2.5 levels higher than World Health Organization-recommended five micrograms per cubic metre yearly average.

The team also found that nearly 82 percent of India's population, or 1.1 billion, lived in areas with yearly average PM2.5 levels exceeding those recommended by the Indian National Ambient Air Quality Standards (40 microns per cubic metre).

Fine particulate matter, or PM2.5, pollution is caused by particles sized under 2.5 microns in diameter.

A yearly increase in PM2.5 pollution of 10 microns per cubic metre was associated with 8.6 per cent higher annual mortality, the researchers found.

For the study, the authors looked at yearly deaths from 2009 to 2019 at a district level across India and obtained annual PM2.5 concentrations, using data from satellite and over a 1,000 ground-monitoring stations. Deaths data was taken from the Civil Registration System.

The team said that evidence on long-term exposure to air pollution and deaths in India is scarce and inconsistent with studies from other countries.

Exposure to PM2.5 pollution was found to be wide-ranging across the years, with the lowest yearly level noted in Lower Subansiri district, Arunachal Pradesh (11.2 microns per cubic metre) in 2019, and largest yearly level seen in Ghaziabad, Uttar Pradesh, and Delhi (119 microns per cubic metre) in 2016.