The findings are alarming as India, home to some of the world’s most polluted cities, is also facing record-breaking temperatures and more intense heatwaves due to climate change
As India braces for another searing summer, researchers have found that severe air pollution combined with high temperatures caused 1.5 higher mortality than periods with low pollution and moderate heat in 10 cities. The findings are concerning since India is home to some of the most-polluted cities in the world and experiences record-breaking temperatures with more intense heatwaves due to climate change.
The latest study conducted by a global team of scientists, including those from Centre for Chronic Disease Control, New Delhi, and Banaras Hindu University (BHU), Varanasi, analysed the data for 10 cities, including Delhi, Ahmedabad, Bengaluru, Chennai, Hyderabad, Kolkata, Mumbai, Pune, Shimla and Varanasi from 2008 to 2019.
Among 3.6 million deaths in these cities with daily mean PM2.5 levels between 20 to 100 μg/m3, researchers found that air pollution had a stronger impact on the death rate, especially during days with higher temperatures.
PM2.5 LEVELS WAY BEYOND SAFE LIMITS
At moderately high temperature, which could vary among the cities depending on their geographical location, a 10 µg/m³ increase in PM2.5 levels was linked to a 0.8 per cent increase in heat-related mortality. But association of PM2.5 on daily mortality increased, especially at extreme temperatures with the death rate surged up to 4.6 per cent.
The death risk increased steadily from 8.3 per cent at 20 µg/m³ of PM2.5 to 63.9 per cent at 100 µg/m³ of PM2.5 exposure level with consequent increase in extreme ambient temperature. “So, the risk of mortality is high on days when daily PM2.5 concentration and temperatures is extreme, and such trend was specifically noted in Ahmedabad, Chennai, Delhi and Kolkata,” said co-author Tirthankar Banerjee from BHU, Varanasi.
The researchers also pointed out that air pollution’s impact is generally underplayed in summers due to good visibility, but the pollution persists. “In cities like Delhi, the PM2.5 level even during summer is way beyond the safe limits prescribed by the World Health Organization (WHO). The annual daily PM2.5 level has remained typically high, and now there is increasing heat stress too.”
The study found a linear association of temperature with daily mortality as air pollution levels increased. The analysis is based on city-wide PM2.5 data available with Centre for Chronic Disease Control, New Delhi, fed into two models which estimated daily exposure levels and temperatures.
