India’s air pollution and extreme heat increase mortality

The Karolinska Institute, a new study at the Institute of Environmental Medicine, reveals that days due to both high air pollution and extreme heat significantly increase the risk of death in Indian cities, as well as more than either factor. The findings can be found in the Journal Environment International.

Previous studies on the interaction of air pollution and heat are limited, especially in regions like India, and both factors frequently reach extreme levels. The study included daily deaths from 10 major cities in India between 2008 and 2019.

The researchers applied two advanced space-time models to estimate daily exposure levels of ambient air pollution and temperature. By analyzing the deaths of around 3.6 million people, they found that the association between PM2.5 and mortality was particularly strong at high temperatures.

An increase of 10 μg/m³ in particulate matter (PM2.5) was associated with a 4.6% increase in daily deaths on very hot days. Similarly, when temperature shifted from warm to very high at a contamination level of 20 μg/m³, the risk of death increased by 8.3%, but when PM2.5 reached 100 μg/m³ it spiked to 64%. These results highlight concerns about the synergistic effects of heat and air pollution, indicating that the effects of their combination on health are harmful to both factors alone.

This study employed a time series analysis to assess exposure outcome association using a generalized additive Poisson regression model. Interaction effects between air pollution and temperature were incorporated and the effect of their combination on mortality was understood. This allowed us to estimate the effects of air pollution at various temperature levels.

“Our findings highlight the interaction between air pollution and extreme heat, especially in densely populated areas where these factors frequently match,” says Jeroen de Bont, assistant professor at the Institute of Environmental Medicine. “Mitigating health impacts requires immediate efforts to reduce emissions from common sources of air pollution and climate change.”

The study highlights the need for an integrated strategy to address both air pollution and climate change in India, where global warming is expected to exacerbate the situation.

“Given some common pollutants for air pollution and climate change, lower air pollution levels will have an almost immediate effect on both lower mortality from both air pollution and heat, as well as the reduction in symbiosis for health,” says Petter Ljungman, IMM’s lead researcher. “A key adaptation strategy is the development of an integrated monitoring and warning system that takes into account both climate hazards and air pollution levels.”