Nearly 33,000 deaths in 10 cities in India every year can be attributed to air pollution levels that are below India's national clean air threshold. The report has been published in Lancet Planetary Health. The authors used data on PM2.5 exposure in the 10 cities and the daily counts of mortality between 2008 and 2019.

Even levels of air pollution below current Indian air quality standards lead to increased daily mortality rates in the country, the study found.

"Across 10 cities in the country - Ahmedabad, Bengaluru, Chennai, Delhi, Hyderabad, Kolkata, Mumbai, Pune, Shimla, and Varanasi, around 33,000 deaths per year can be attributed to air pollution levels that are above the WHO guidelines.

"A significant number of deaths were observed even in cities not considered to have high air pollution, such as Mumbai, Bengaluru, Kolkata, and Chennai," it said, adding, "India's national air quality standards should be made more stringent, and efforts to control air pollution redoubled."

Varanasi logged the second highest number of deaths during the period - 10.2% or around 830 deaths a year, attributable to short-term PM2.5 exposure higher than the WHO guideline value. Every 10 micrograms per cubic meter of air increase in short-term PM.s exposure was associated with a 1.17% increase in daily deaths, the study showed.

Around 2,100 died in Bengaluru, 2,900 in Chennai, 4,700 in Kolkata, and around 5,100 each year in Mumbai each year due to the rising air pollution during the study period. The deaths were all attributable to short-term PM2.5 exposure higher than the WHO guideline value.

The lowest air pollution levels were recorded in Shimla. However, air pollution was still a risk in the hill city with 3.7% of all deaths - 59 per year - attributable to short-term PM2.5 exposure higher than the WHO guideline value. "The results from Shimla add credence to global evidence that there is no safe level of air pollution exposure," the study highlighted.