Heatwaves and ozone together increase India’s cardiac deaths: study
During the 2024 heat wave, approximately 26,500 deaths from ischemic heart disease and chronic obstructive pulmonary disease (COPD) are linked to ozone exposure. File | Photo Credit: The Hindu
Surface ozone, a pollutant harmful to the heart and lungs, has already exceeded safe limits in much of India during the warm pre-monsoon months. new study finds heat waves pushing it to even higher levelsThus, several hundred more deaths were added to a much larger tally that the study linked to ozone during the season.
Peer-reviewed study published in the journal Nature Portfolio npj Clean Air On June 12, it reported that surface ozone in northern India reached 85-110 micrograms per cubic meter (μg/m³) during heatwaves, exceeding the World Health Organization guideline of 70 μg/m³ in every region of the country. Levels decline within three to four days after the heatwave ends.
Because ozone levels remain high throughout most of the season, the study notes that a large number of deaths are linked to it, even outside of heat waves. During the 2024 heat wave, approximately 26,500 deaths from ischemic heart disease and chronic obstructive pulmonary disease (COPD) are linked to ozone exposure. However, such health conditions exist both before and after heat. The heatwave’s contribution to the death toll comes from the increase seen in the previous days: around 490 additional heart disease deaths and 342 from COPD, for a total of around 830 deaths.
The overall figures are very large, mainly because of the way they are calculated. They do not count directly. The study applies a small increase in an individual’s risk of dying from these two common diseases to India’s population of more than one billion; Even a slight risk per capita spreads to many people and two of the nation’s leading causes of death, reaching tens of thousands.
The authors state that death figures need to be modelled.Because continuous ground-level ozone measurements were not available on certain heatwave days in most affected cities. Therefore, estimates are based on the assumed relationship between ozone exposure and disease rather than direct observation.
Surface ozone is not released directly, but is formed when sunlight reacts with other pollutants, a process that accelerates heat. “Ozone is very harmful, while NO₂ (nitrogen dioxide) and HCHO (formaldehyde) directly damage the respiratory system,” the authors write, referring to two gases that play a role in the formation of ozone.
The authors, Parambat Sangeetha (Kerala University of Fisheries and Ocean Studies) and Jayanarayanan Kuttippurath of IIT Kharagpur, combined two decades of temperature records from the India Meteorological Department with satellite data and global weather datasets to monitor ozone levels.and the gases that produce it. Heat waves between 2004 and 2024 were defined using standard temperature thresholds.
The authors describe the study as the first comprehensive, long-term, nationwide assessment of surface ozone during heatwaves in India, noting that previous studies have been largely limited to individual cities or regions. Following strong El Niño events, they counted 188 heat wave events over two decades, with the most severe years being 2010, 2016, 2019 and 2024. The Western Himalayas recorded the steepest long-term increase in ozone level, exceeding the WHO guideline by 115% by 2024.
The authors note that “heat-ozone extremes are intensifying and urgently require integrated climate-air quality policy action.”
The study follows the 16th Finance Commission’s recommendation to add heatwaves and lightning to India’s list of nationally notified disasters by November 2025; This will allow States to tap the State Disaster Response Fund for assistance.
It was published – 15 June 2026 23:39 IST
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