Ground-level ozone has emerged as a fast-expanding, multi-season air pollution challenge across 25 major Indian cities, according to a recent analysis by the Centre for Science and Environment (CSE). Mumbai faces significant risks, recording some of the highest ozone peaks in the country, prolonged exposure durations, and persistent ozone levels at night.
Ground-level ozone is a highly hazardous and invisible "secondary" pollutant formed when emissions from vehicles and industries react with strong sunlight.
Delhi-NCR has emerged as the largest regional hotspot, with major impacts also seen in Chandigarh, Jaipur, Ahmedabad, Mumbai, Chennai, Bengaluru and Patna.
Among all the cities analysed, Chandigarh recorded the highest average summer ozone concentration, followed by Ahmedabad and Jaipur.
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The report added that ground-level ozone pollution is no longer confined to northern India and is increasingly affecting southern and coastal regions as well.
Mumbai registered one of the highest ozone peaks, along with prolonged exposure durations and persistent ozone levels at night. Bengaluru is witnessing sustained exposure and a wider spatial spread of ozone pollution, while Chennai recorded the highest episodic ozone concentration.
The report warned that rising temperatures and increasing gaseous emissions could further aggravate the ozone problem.
CSE has called for the implementation of a multi-pollutant framework under the National Clean Air Programme (NCAP) to curb emissions from vehicles, industries, household fuels, waste and biomass burning in order to prevent ozone formation. The report also warned of a silent, year-round health and climate crisis unfolding across major cities.
"Our analysis reveals that rising ground-level ozone and prolonged exposure windows are transforming India's localised, winter-time particulate problem into a year-round, transboundary crisis that peaks during the summer across all regions. Ozone is damaging public health, agricultural productivity and regional climate systems," said Anumita Roychowdhury, Executive Director, CSE, and the lead researcher and author of the analysis.
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"As a climate pollutant, ozone traps heat in the atmosphere, raising temperatures and triggering the formation of even more ozone, creating a dangerous feedback loop," she added.
"While the current National Clean Air Programme (NCAP) focuses on particulate matter reduction, NCAP 2.0 must adopt a multi-pollutant strategy. By targeting precursor gases such as NOx and VOCs that form ozone in the atmosphere, the new framework can accelerate the transition towards clean combustion, zero-emission pathways and integrated regional airshed management," Roychowdhury further said in the report.
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