A study published on 12 June 2026 in npj Clean Air found that heatwaves in India raise surface ozone concentrations, contributing to increased cardiac and respiratory deaths.
Key findings
- Study scope: First long-term, country-wide assessment; analysed 188 heatwave events from 2004–2024.
- Mortality estimates: About 26,500 deaths from ischaemic heart disease and COPD occurred on 2024 heatwave days attributable to ozone exposure; ~830 additional deaths were directly linked to heatwave-driven ozone increases.
- Publication: npj Clean Air, 12 June 2026; research led by scientists from Kerala University of Fisheries and Ocean Studies and IIT Kharagpur.
Ozone formation and standards
- Formation: Surface ozone is a secondary pollutant formed by sunlight-driven reactions among NOx and volatile organic compounds (e.g., HCHO); reaction rates rise with temperature.
- Persistence: Elevated ozone from heatwaves typically persists three to four days after the heatwave subsides.
- Standards: WHO guideline cited at 70 μg/m³; India’s NAAQS for ozone is 100 μg/m³ (2009), about 43% less stringent than the WHO guideline.
Health and concentration data
- Observed levels: During heatwaves northern India recorded 85–110 μg/m³, exceeding the WHO guideline nationwide.
- Health impact: Surface ozone exposure increases risk of ischaemic heart disease and chronic respiratory conditions such as COPD.
Geography and climate linkages
- Regional trend: Western Himalayas showed the steepest long-term ozone increase, exceeding WHO guideline by 115% in 2024.
- Climate driver: Severe heatwave years (2010, 2016, 2019, 2024) were associated with strong El Niño episodes.
IASPOINT Booster Facts
- NAAQS detail: India’s ambient air quality standard for ozone (2009) is benchmarked as 8-hour mean at 100 μg/m³.
- Technical term: NOx denotes nitrogen oxides; HCHO denotes formaldehyde, a reactive VOC and ozone precursor.