Persistent harmful ozone threatens city’s air quality
Ground-level ozone is emerging as a major air pollution challenge in Bengaluru, with a new analysis by the Centre for Science and Environment (CSE) showing that the city is witnessing prolonged exposure to the harmful pollutant during summer months. Of 25 major Indian cities analysed between March 1 and May 10, 2026, Bengaluru recorded 55 days when the eight-hour National Ambient Air Quality Standard (NAAQS) for ozone was found to have exceeded. The city also reported one of the longest durations of daily exposure, with ozone concentrations remaining above safe limits for an average of 15.9 hours in a day, thereby placing it among the worst-affected cities across the country. Experts say that, traditionally considered to be a daytime pollutant, ozone is now persisting after sunset due to atmospheric conditions that prevent its rapid breakdown. Bengaluru recorded 14 nights with ozone levels exceeding the prescribed standards, second only to Delhi-NCR ( which recorded 46 such nights). While Delhi-NCR remains the country’s largest ozone hotspot, CSE says Bengaluru is among the cities where ozone pollution is expanding both spatially and in duration. Ground-level ozone is not emitted directly. It forms when nitrogen oxides (NOx) and volatile organic compounds (VOCs), largely released from vehicles, industries and other combustion sources, react under intense sunlight and high temperatures. According to CSE, rising temperatures and increasing emissions are accelerating ozone formation, making it a growing year-round concern rather than a seasonal problem.