India struggles with some of the worst air pollution in the world. Now scientists have worked out which of the country’s power plants are the worst in pollution terms, narrowing it down to 30 units which are responsible for about a quarter of the mortality burden.

Electricity generation accounts for nearly three-quarters of India’s use. But despite , of India’s power plants have modern systems to including sulphur and mercury.

from looked at the performance of the country’s power plants. The lead author, Kirat Singh, said: “We wanted to see if some power plants were disproportionately driving the mortality burden. Identifying these could move the needle on improving air quality.”

The first task was to assess the impacts of all of the power plants. The researchers then repeated this exercise 510 times, simulating the switching off of one power plant at a time. This was a massive computational task. To speed this up, Singh utilised spare capacity in the university computing systems. Each evening, he logged on to set more programmes running overnight. It still took three months before they were able to assimilate the findings.

Their hunch that some power plants were more harmful than others proved correct. The impact ranged from one or two extra deaths a year to 670. Importantly, about a quarter of the health burden came from plants that generated just 3% of India’s electricity.

The most harmful tended to burn low-quality lignite and emitted high qualities of sulphur pollution but, surprisingly, there was no clear relationship between the age of the power plant and the health damage.

Singh had a clear message for policymakers: “Prioritising action to reduce emissions at the most damaging units, such as deploying pollution control technologies or retiring and replacing their output with zero-emissions electricity, could achieve disproportionately large reductions in mortality.”

In 2021 the Indian government revised its regulations to focus on cleaning up power plants , but Singh and team showed that this criteria missed many of the most harmful installations.

The power plants with the largest impact were mainly in the south of the country. Fitting pollution controls takes time and rapid closures could lead to power shortages, but Singh and the team found big benefits from shifting generation from the most to the least harmful power plants. This could reduce early deaths by about 5,866 a year in the worst affected state of Tamil Nadu, and by about 8,000 across the four states that experience the most impacts.

India is increasing electricity generated from coal by 50% between 2018 and 2030. that 844,000 premature deaths could be avoided if these plants were not built.

Dr Arunabha Ghosh, CEO of the New Delhi-based , said: “In the past decade, India’s power capacity grew 82% while renewable energy grew 388%. Greater clean energy investment, at lower capital cost, could help India meet its ambitious clean electricity targets. These will have benefits for efficient power generation, greater grid resilience, increased energy security, and improved public health – in addition to stimulating a green economic transformation.”

Prof Drew Shindell, of and the chair of the scientific advisory panel to the , said: “This reinforces that decarbonisation isn’t just a difficult transition away from existing systems but is an incredible opportunity to improve wellbeing both immediately, via improved air quality, and over the longer term via reduced climate change.”