Heatwaves are triggering sharp increases in ground-level ozone pollution across India, creating a growing threat to public health as climate change drives more frequent and intense periods of extreme heat, according to new research.
The study, published in npj Clean Air, is the first comprehensive assessment of how heatwaves influence surface ozone levels across India over a 20-year period. Researchers analysed data from satellite observations, atmospheric reanalysis and meteorological records covering 2004 to 2024.
The findings show that ozone concentrations rise significantly during heatwaves, particularly across northern India, where levels reached between 85 and 110 μg/m³. In every region studied, concentrations exceeded the World Health Organization’s recommended guideline of 70 μg/m³ during heatwave events.
Researchers identified 188 heatwaves during the study period and found that ozone levels typically remained elevated for several days after extreme temperatures had subsided, suggesting the effects of heatwaves on air quality continue beyond the hottest days themselves.
The study also found long-term increases in ozone pollution in several regions, with the strongest upward trends recorded in North Central and North West India. Higher temperatures, stronger sunlight and stagnant weather conditions during heatwaves all contribute to faster chemical reactions that produce ground-level ozone.
Using health data, the researchers estimated that elevated ozone levels during heatwaves were associated with increases in deaths linked to chronic obstructive pulmonary disease (COPD) and ischaemic heart disease (IHD).
During the 2024 pre-monsoon season, heatwave-related ozone pollution was estimated to contribute to around 490 additional COPD deaths and 342 additional deaths from ischaemic heart disease compared with the period before heatwaves. The highest health impacts were concentrated in densely populated regions, where large populations were exposed to elevated pollution levels.
The researchers point out that heatwaves not only increase ozone formation but can also amplify its health impacts, creating a compound risk for vulnerable communities.
The authors argue that stronger action to reduce emissions of ozone-forming pollutants, alongside improved heatwave preparedness and public health planning, will become increasingly important as rising temperatures make these compound pollution events more common across South Asia.
The full research can be read here.
Photo: Mohit Hambiria
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