Ground Level Ozone Heatwave Health Risks India

d to increased ozone concentrations caused by extreme heat, the study has said.

The study, ‘Heatwaves trigger severe surface ozone pollution in India: Regional Hotspots, Trends and Health Effects’, has been published in Clean Air, a part of Nature stable of journals, and is the first of its kind attempt to assess the health impacts of increased levels of surface-level ozone concentrations due to heatwaves in India.

Ozone is naturally produced, and found, in the middle atmosphere, at an altitude between 15 and 50 km from the Earth’s surface. This ozone actually protects the Earth from the harmful ultraviolet rays in the sunlight. It absorbs these rays, acting as a natural sunscreen for the Earth. But ozone close to the ground is an air pollutant. Surface-level ozone is not naturally produced, but is by-product of chemical reactions between other common air pollutants like nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the presence of sunlight. Heat has the effect of accelerating these reactions.

“Ozone concentrations of about 30 parts per billion (ppb) at the ground level is usually considered safe. In most parts of India, this background ozone concentration is around 50-55 ppb. This is particularly true of northwestern India and the Gangetic plains, which carries a very high pollution load. During heatwaves, the ozone concentration is driven up even higher,” said Jayanarayanan Kuttippurath, an associate professor at the Centre for Ocean, River, Atmosphere and Land Sciences at IIT Kharagpur, who authored the study, along with Parambat Sangeetha of Kerala University of Fisheries and Ocean Studies, Kochi.

Exposure to ozone affects lungs and heart, and can lead to Chronic Obstructive Pulmonary Disease (COPD) and Ischemic Heart Disease (IHD), apart from cancer and diabetes. A large number of deaths, in tens of thousands every year, is already associated with ozone exposure. The State of Global Air report for 2025 had said there were about 234,000 COPD deaths in India in 2023 in which ozone exposure was the aggravating factor.

Heatwaves are now exacerbating the problem. The summer months in India are generally a relief from air pollution, but the rise in ozone concentrations could be adding a new threat.

“Under climate change scenarios, because of general increase in temperatures all across, more and more regions are likely to have high concentrations of ozone. The frequency and severity of heatwaves is expected to rise, and so would the threat from ozone exposure,” Prof Jayanarayanan said.

He said agencies like the India Meteorological Department (IMD), or the Central Pollution Control Bureau (CPCB), needed to extensively monitor the concentrations of ground-level ozone, as actively as they do for a number of other parameters, and include this information in their bulletins and alerts.

The increased levels of ozone caused by heatwaves persists for about three to four days on an average after the end of the heatwave, the study said based on their analysis of data over the last 21 years.