Over the past two decades, surface ozone has breached safe limits set by the World Health Organization (WHO) in every region of the country during the pre-monsoon hot season, the study revealed. the nature Journal NPJ Clean Air explains. During heat waves, the levels become particularly intense.
India has been witnessing an increase in the frequency of violence and heat waves in recent years. The latest, which started in April, reached above maximum temperatures 47 degrees Celsius in May
Jayanarayan Kuttipurath, a climate scientist and co-author of the study at the Center for Ocean, River, Atmosphere and Land Sciences at the Indian Institute of Technology in Kanpur, said. SciDev.Net: “In this study we present the first comprehensive long-term assessment of surface ozone changes during heat waves in India for 2004–2024 using surface, satellite, and reanalysis data measured at the peak of the heat wave during the pre-monsoon months of March, April, May, and June.
“The pre-monsoon increase in ozone concentration is attributed to intense solar radiation, which accelerates the chemical dynamics of ozone production, exacerbated during heat waves, which increase ozone production and reduce air quality.”
Between 2004 and 2024, 188 heat wave events were recorded in the seven regions covered by the study during which the surface ozone layer exceeded the WHO threshold of 70 micrograms per cubic meter. North India has seen the highest concentrations, 85-110 micrograms per cubic meter.
“As the frequency and intensity of heatwaves increase, so do surface ozone concentrations and associated health problems,” Kuttipurath said.
In 2024, the researchers estimated that 15,615 deaths were associated with chronic obstructive pulmonary disease and 10,898 with ischemic heart disease during the heat wave. This compares with 15,125 and 10,556 respectively before the heatwave, both a 3.2 percent increase.
growing threat
Ozone exposure contributes greatly to mortality from cardiovascular and chronic obstructive pulmonary disease, State of Global Air 2025 ReportWhich places India third among the countries exposed to ozone pollution
Particulate matter remains the leading cause of air pollution deaths, but surface ozone is catching up fast.
The report attributes India’s vulnerability to ozone pollution to high emissions of the precursor gas, and a combination of intense sunlight and rising temperatures.
These precursor gases, including nitrogen oxides, volatile organic compounds, carbon monoxide and methane, form ozone through reactions driven by solar radiation and atmospheric chemistry. They come from the burning of fossil fuels, industrial activities and vehicle emissions, as well as natural processes by trees and plants.
In the stratosphere, ozone protects the Earth from harmful ultraviolet rays. At ground level, the same gas is a toxic, highly reactive pollutant. This tropospheric ozone forms when sunlight breaks down nitrogen dioxide in the presence of volatile organic compounds, releasing an oxygen atom that combines with oxygen (O2) to form ozone (O3).
Policy response
Bomidi Lakshmi Madhavan, a scientist at India’s National Atmospheric Research Laboratory, said the research is significant because it shifts the focus from just particulate matter to ozone, which is gaining importance in a warming climate.
“By linking heatwave-enhanced ozone exposure to higher mortality risks from respiratory and cardiovascular disease, the authors emphasize the need for coordinated policy responses that combine climate adaptation, heat-action planning and ozone precursor emission control,” Madhavan said. SciDev.Net.
“As heat waves across India become more frequent and intense, ozone pollution may emerge as a major environmental health challenge.”
Ronita Vardhan, Professor of Sustainable Built Environment and Health at the University of Cambridge, said the research reveals an important pathway through which climate change affects human health.
“The significance of the study lies in showing that populations are often exposed to multiple environmental hazards rather than heat or air pollution in isolation,” Vardhan said. SciDev.Net.
He warned that: “From a risk and vulnerability perspective, the true burden may be more complex than current estimates.
“Heat-related risk is shaped by a range of interacting factors, including housing quality, occupational exposure, access to cooling, health care availability, burden of pre-existing diseases and characteristics of the built environment.”
Roxy Mathew Cole, a climate scientist at the Indian Institute of Tropical Meteorology, Pune, said that since 2000, temperatures in the Indian subcontinent have risen sharply, intensifying heat waves and disrupting monsoons.
“Sustained investment in people, policies and long-term planning – is essential to reduce heatwave-related deaths and health impacts, especially as heatwaves are now an annual phenomenon from February to June and are expected to intensify in the future,” he said.
This piece was produced by SciDev.Net’s Global Desk.
