More than seven percent of all deaths in 10 of India's largest cities are caused by air pollution, according to a new study. For the study, published Thursday in the journal The Lancet Planetary Health, researchers looked at particulate pollution in the cities of Ahmedabad, Bengaluru, Chennai, New Delhi, Hyderabad, Kolkata, Mumbai, Pune, Shimla and Varanasi.

Specifically, it was so-called PM2.5 fine dust, which is particularly harmful to health. When inhaled, these small particles of fine dust with a diameter of less than 2.5 micrometers can penetrate deep into the lungs and from there into the bloodstream. They cause cardiovascular and respiratory diseases such as asthma and lung cancer.

According to the study, more than 33,000 deaths per year in the Indian cities surveyed between 2008 and 2019 could be attributed to PM2.5 pollution above the World Health Organization's (WHO) recommended upper limit of 15 micrograms per cubic meter. This corresponds to 7.2 percent of all deaths recorded in the cities during this period.

India currently recommends an upper limit of 60 micrograms of PM2.5 per cubic metre, four times higher than the WHO guideline.

The study's authors are now calling for stricter air quality rules in India. Lower limits on particulate matter “would save tens of thousands of lives a year,” said study co-author Joel Schwartz of Harvard University in the United States. “There are methods of controlling air pollution that are being used elsewhere. It is urgent that they are also applied in India,” Schwartz said.

According to the study, 12,000 deaths per year in the Indian capital New Delhi, or 11.5 percent of all deaths, can be attributed to polluted air. And even cities with relatively low air pollution — such as Mumbai, Kolkata and Chennai — have high mortality rates from particulate matter, the researchers say. According to the WHO, almost everyone on Earth breathes more polluted air than the recommended amount.