The study, co-authored by climate scientist Jayanarayanan Kuttipurath of the Indian Institute of Technology’s Centre for Ocean, River, Atmosphere and Land Science in Kanpur, finds that surface ozone rose across India during the pre-monsoon hot season and often exceeded the World Health Organization safe limit. Published in npj Clean Air, the work is the first long-term assessment of ozone changes during heatwaves in India and shows levels become particularly intense during such events.
The team analysed surface, satellite and reanalysis data for 2004–2024 in the months of March, April, May and June. They link the pre-monsoon ozone rise to intense solar radiation, which speeds the chemical reactions that form ozone from nitrogen dioxide in the presence of volatile organic compounds. From 2004 to 2024 the seven study regions recorded 188 heatwave events with ozone above the WHO threshold of 70 micrograms per cubic metre; northern India peaked at about 85–110 micrograms per cubic metre. The latest heatwave, which began in April, saw maximum temperatures above 47 °C in May.
The State of Global Air 2025 report ranks India third for ozone exposure and notes that ozone contributes heavily to deaths from cardiovascular disease and chronic obstructive pulmonary disease, while particulate matter remains the leading cause. In 2024 researchers estimated higher deaths during heatwaves for COPD and ischemic heart disease, about a 3.2 per cent increase compared with before the heatwaves. Experts advise policies combining climate adaptation, heat-action plans and stronger controls on precursor gases to reduce health risks, and they warn the true burden is shaped by housing, work exposure, access to cooling, healthcare and the built environment.
- Key precursor gases: nitrogen oxides, volatile organic compounds, carbon monoxide, methane.
- Main sources: burning fossil fuels, industry, vehicle exhaust, natural plant processes.
Difficult words
- ozone — a toxic gas formed in the lower atmospheresurface ozone
- pre-monsoon — seasonal period before the start of the monsoonpre-monsoon hot season
- volatile organic compound — organic gases that react chemically in airvolatile organic compounds
- precursor — substances that help form other air pollutantsprecursor gases
- particulate matter — tiny solid or liquid particles in the air
- heatwave — period of unusually high temperatures over several daysheatwaves, heatwave events
- ischemic heart disease — disease where reduced blood flow harms the heart
Tip: hover, focus or tap highlighted words in the article to see quick definitions while you read or listen.
Discussion questions
- Which of the policies mentioned (climate adaptation, heat-action plans, stronger controls on precursor gases) do you think would be most effective locally, and why?
- How might housing, work exposure and access to cooling change the health risks from ozone and heat? Give examples from your area or city.
- What practical actions could cities take before the pre-monsoon season to protect vulnerable people during heatwaves?
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