Ground level ozone pollution is no longer limited to a few cities or the summer months. A new analysis by the Centre for Science and Environment (CSE) has found that ozone pollution has become a widespread, year round air quality problem across India with Delhi NCR emerging as the country’s largest regional hotspot.
The six year analysis, covering data from 2021 to 2026, shows that rising temperatures, stronger sunlight, and increasing emissions of ozone forming gases are driving a sharp increase in ground level ozone across many Indian cities. Unlike the protective ozone layer high in the atmosphere, ground level ozone is a harmful air pollutant that poses serious risks to human health, agriculture, and the climate.
According to the report, 15 of the 25 major Indian cities analysed between March 1 and May 10, 2026, recorded average summer ozone levels above the National Ambient Air Quality Standard (NAAQS) limit of 100 micrograms per cubic metre for an eight hour exposure period.
Among all the cities studied, Chandigarh recorded the highest average summer ozone concentration, followed by Jaipur and Ahmedabad. Delhi NCR stood out as the region with the most persistent ozone pollution, exceeding the national standard on every single day during the 71 day study period. Bhopal, Bengaluru, Patna, and Muzaffarpur also experienced frequent ozone exceedances, indicating that the pollution problem is expanding beyond traditional hotspots.
Within Delhi NCR, ozone pollution was found to blanket large parts of the region. Monitoring stations at Pusa IMD in Delhi, Greater Noida Knowledge Park-V, Sector 125 in Noida, and Vasundhara in Ghaziabad recorded some of the highest pollution levels. On average, nearly nine monitoring stations in Delhi and more than three stations across the NCR crossed safe ozone limits every day during the study period.
The report also highlights that ozone pollution is lasting much longer each day than before. Bhopal recorded the longest average exposure, with ozone concentrations remaining above safe limits for around 17 hours daily. Lucknow followed with an average of 16.3 hours, while Mumbai and Bengaluru recorded nearly 16 hours of daily exposure. Researchers warn that prolonged exposure increases health risks even if pollution levels exceed safety limits for only part of the day.
Another worrying trend identified by the study is the rise in night time ozone pollution. Traditionally, ozone concentrations declined after sunset, but researchers found that harmful levels are now persisting well into the night, particularly during heatwaves. Delhi NCR recorded the highest number of night time ozone exceedances, with 46 nights above safe levels during the study period. Bengaluru, Bhopal, Patna and Muzaffarpur also experienced significant night time ozone pollution.
According to CSE Executive Director Anumita Roychowdhury, rising ozone pollution is transforming India air pollution challenge from a seasonal particulate matter problem into a year round regional crisis. She said ozone not only threatens public health and reduces agricultural productivity but also acts as a climate pollutant by trapping heat, creating a feedback loop in which higher temperatures generate even more ozone.
The report notes that ozone forms when pollutants such as nitrogen oxides (NOx), volatile organic compounds (VOCs), and carbon monoxide react under intense sunlight and high temperatures. As climate change increases the frequency of heatwaves, conditions for ozone formation are becoming more favourable across many parts of the country.
CSE has urged the government to broaden its air pollution strategy by including ozone control in the next phase of the National Clean Air Programme (NCAP). The organisation recommends that NCAP 2.0 move beyond its current focus on particulate matter and adopt a multi pollutant approach that targets ozone forming gases alongside fine particulate pollution.
The think tank also called for coordinated regional action instead of city specific measures. It recommends controlling emissions from transport, industries, power generation and households through cleaner combustion technologies, rapid adoption of zero emission solutions, and integrated airshed management across states.
The findings suggest that ozone pollution is becoming one of India’s fastest growing environmental challenges. Experts warn that without stronger action to reduce emissions of ozone forming pollutants, rising temperatures and more frequent heatwaves could make the problem even more severe, increasing risks to public health, food security, and the country climate resilience.