More than 7% of deaths in ten big Indian cities are connected to air pollution from PM2.5 concentrations that surpass the World Health Organization’s (WHO) safe limits, according to a study published in The Lancet Planetary Health journal.

The study took into consideration the data from cities including Bengaluru, Ahmedabad, Chennai, Mumbai, Hyderabad, Delhi, Kolkata, Pune, Shimla, and Varanasi. It found that PM2.5 levels, tiny pollutants that can penetrate deeply into the lungs and bloodstream, exceeded the WHO’s safe limit of 15 micrograms per cubic meter on 99.8% of the days. The capital city of Delhi recorded the highest fraction of daily and yearly deaths that can be attributed to PM2.5 air pollution, which mainly comes from vehicular and industrial emissions. The national capital sees around 12,000 deaths annually linked to air pollution, making up about 11.5% of its total deaths.

Researchers discovered that daily exposure to PM2.5 pollution in Indian cities is linked to a higher risk of death, with locally generated pollution possibly causing these fatalities.

An alarming finding of the study showed that a 10 microgram per cubic meter increase in PM2.5 concentration over two days is associated with a 1.4% rise in daily mortality. This risk doubles to 2.7% when observations are restricted to levels below the Indian air quality standards, which are less stringent than WHO guidelines. City-specific data revealed a 0.31% rise in daily mortality per a 10 microgram per cubic meter increase in PM2.5 levels in Delhi, compared to a 3.06% rise in Bengaluru.

The study indicated that the link between daily exposure to PM2.5 and locally produced pollutants was stronger in the causality models used by the researchers, suggesting that local pollutants significantly contribute to these deaths.

The research also highlighted that the causal effects were particularly strong in cities with lower overall air pollution levels, such as Bengaluru, Chennai, and Shimla.

This study, the first multi-city time series analysis of short-term exposure to PM2.5 and daily mortality in India, analyzed approximately 3.6 million daily deaths across ten Indian cities from 2008 to 2019. Other cities involved in the study included Ahmedabad, Hyderabad, Kolkata, Pune, Shimla, and Varanasi.

The international research team included members from Varanasi’s Banaras Hindu University and the Centre for Chronic Disease Control in New Delhi. Joel Schwartz from Harvard University, a co-author of the study, emphasized that lowering and enforcing stricter air quality limits “will save tens of thousands of lives per year.”