Delhi recorded the highest number of air pollution-related deaths in the study period (Representational)
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.
India's clean air norms are presently well above the World Health Organisation guideline of 15 micrograms in every cubic meter of air. The report makes the point that India must drastically reduce its clean air norms to at least match WHO guidelines to protect citizens from the dangers of polluted air.
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."
Between 2008 and 2019, 7.2% of all deaths (approximately 33,000 each year) across all 10 of these cities could be linked to short-term PM2.5 exposure that was higher than the WHO guideline value of 15 micrograms in every cubic meter of air, the study found.
"Every 10 micrograms in every cubic meter of air increase in short-term PM2.5 exposure was associated with a 1.42% increase in daily deaths. This estimate nearly doubled to 3.57% when we used a causal modelling approach that isolates the impact of local sources of air pollution," the release said.
Delhi recorded the highest number of air pollution-related deaths in the study period - a staggering 11.5% i.e. 12,000 deaths each year. "The deaths were attributable to short-term PM.5 exposure higher than the WHO guideline value," the study showed.
"Every 10 micrograms per cubic meter of air increase in short-term PM.s exposure was associated with a 0.31% increase in daily deaths."
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.
It is the first multi-city study that assessed the relationship between short-term air pollution exposure and deaths in India, with the cities included spanning a wide range of air pollution concentrations and situated in different agro-climatological zones, a press release said.
The study was conducted by researchers from Sustainable Futures Collaborative, Ashoka University, Centre for Chronic Disease Control, Sweden's Karolinska Institutet, Harvard and Boston Universities, and other places.
There was a steep increase in the risk of deaths at lower concentrations of PM2.5 and tapering off at higher concentrations, with significant effects observed below the current National Ambient Air Quality Standard of 60 micrograms per cubic meter of air for a 24-hour exposure, it said.