The research focused on fine particulate matter, or PM2.5, which refers to particles smaller than 2.5 micrometres in diameter. These particles can penetrate deep into the lungs and bloodstream, posing a severe health risk. The study assessed the link between PM2.5 exposure and mortality across 655 districts in India over a decade, from 2009 to 2019.
"We found that every 10 microgram per cubic metre increase in PM2.5 concentration led to an 8.6 percent increase in mortality," said Petter Ljungman, a researcher at the Institute of Environmental Medicine at Karolinska Institutet and the study's last author.
The analysis revealed that approximately 3.8 million deaths during the study period could be linked to air pollution levels exceeding India's air quality guideline of 40 micrograms per cubic metre. When compared to the World Health Organization's (WHO) stricter guideline of 5 micrograms per cubic metre, the number of deaths attributed to air pollution rose sharply to 16.6 million - accounting for nearly 25 percent of all deaths during the study period.
The findings also show that the entire Indian population, an estimated 1.4 billion people, is consistently exposed to PM2.5 levels above the WHO-recommended threshold. In some areas, concentrations reached as high as 119 micrograms per cubic metre, far exceeding what is considered safe by both the WHO and Indian standards.
"The results show that current guidelines in India are not sufficient to protect health. Stricter regulations and measures to reduce emissions are of utmost importance," Ljungman added.
India has implemented a national air pollution control program since 2017 to tackle the issue. However, the study notes that PM2.5 levels have continued to rise in many regions. The researchers highlight the necessity of reducing local emissions while also addressing the long-range transport of PM2.5 particles, which can travel hundreds of kilometers.
"Our study provides evidence that can be used to create better air quality policies, both in India and globally," said Ljungman.
The research was funded by Formas and involved a collaborative effort among experts from institutions in India, Sweden, the USA, Israel, and Italy.
Research Report:Estimating the effect of annual PM2-5 exposure on mortality in India: a difference-in-differences approach
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