Toxic air that chokes Indian cities and kills hundreds of thousands of people also carries a grim economic burden for the country's companies of around $95 billion a year, according to researchers who urged firms to lead the drive against pollution.

Air pollution shortens lives worldwide by nearly three years on average, and causes millions of premature deaths annually.

India is one of the worst affected countries, with many regions often cloaked in a smog of hazardous particles.

The Lancet's Global Burden of Disease study estimated pollution caused some 1.7 million premature deaths in India in 2019 -- nearly 18 percent of all deaths in the country.

Building on this, a new analysis by consultancy firm Dalberg Advisors found that pollution-related absenteeism, productivity loss, reduced consumer and tourist spending all add up to cost Indian businesses $95 billion a year, roughly three percent of the country's gross domestic product.

"Clean air is a precondition for businesses to thrive," said Dalberg Asia Director Gaurav Gupta.

"Industry leaders should take more ownership and become advocates in the movement for cleaner air."

Lost working years from the hundreds of thousands of premature deaths were estimated to cost the Indian economy $44 billion in 2019, according to the report, which was commissioned by the Clean Air Fund, a philanthropic organisation.

Beyond that, Dalberg said the effects of pollution on Indian workers' health means they take 1.4 billion sick days a year, which they said amounts to around $6 billion in lost revenue.

New Delhi, pictured here in October 2019, is one of the world's most polluted cities New Delhi, pictured here in October 2019, is one of the world's most polluted cities Photo: AFP / Sajjad HUSSAIN

Those who continue to work may have reduced cognitive and physical performance that affects their productivity, decreasing business revenues by up to $24 billion.

The report also found that toxic air disincentivises people to venture out of their homes more generally, hitting consumer spending and ultimately costing businesses $22 billion in lost earnings.

Many of the estimates were based on Dalberg's analysis of India's IT sector, which it said was disproportionately affected, losing US$ 1.3 billion -- around one percent of sector value -- due to pollution-induced productivity loss per year.

If air pollution continues to increase at currently projected rates, the report said this figure could nearly double by 2030.

In February, a study in the journal Environmental Research estimated that fossil fuel pollution caused more than eight million premature deaths in 2018 -- nearly a fifth of adult mortality worldwide.

Half of those who died were in China and India.

The toxic cocktail of tiny particles cast off by burning oil, gas and especially coal was responsible for a quarter or more of the mortality in half a dozen nations, all in Asia.

The World Health Organization says that air pollution -- including indoors -- kills seven million people per year, with 4.2 million of those deaths due to ambient, or outdoor, pollution. But recent research suggests it has underestimated the impact on cardiovascular disease.