India could save an estimated 11 million life-years annually by replacing coal-fired power plants with clean, renewable energy, according to a Harvard study.

The 2.7 billion people who live in India and China -- more than a third of the world's population -- regularly breath some of the dirtiest air on the planet, said researchers from the Harvard University in the US.

Air pollution is one of the largest contributors to death in both countries, ranked 4th in China and 5th in India, and harmful emissions from coal-fired power plants are a major contributing factor, they said.

In the study, published in the journal Environment International, researchers wanted to know how replacing coal-fired power plants in China and India with clean, renewable energy could benefit human health and save lives in the future.

They found that eliminating harmful emissions from power plants could save an estimated annual 15 million years of life in China and 11 million years of life in India.

Previous research has explored mortality from exposure to fine particulate matter (known as PM2.5) in India and China but few studies have quantified the impact of specific sources and regions of pollution and identified efficient mitigation strategies, researchers said.

Using state-of-the-art atmospheric chemistry modelling, they calculated province-specific annual changes in mortality and life expectancy due to power generation.

The researchers were able to narrow down the areas of highest priority, recommending upgrades to the existing power generating technologies in Shandong, Henan, and Sichuan provinces in China, and Uttar Pradesh in India due to their dominant contributions to the current health risks.

"This study shows how modelling advances and expanding monitoring networks are strengthening the scientific basis for setting environmental priorities to protect the health of ordinary Chinese and Indian citizens," said Chris Nielsen, executive director of the Harvard-China Project and a co-author of the research paper.

"It also drives home just how much middle-income countries could benefit by transitioning to non-fossil electricity sources as they grow," Nielsen said.