Delhi and Mumbai have emerged as the worst offenders in breaching safe levels of ground-level ozone, according to the Central Pollution Control Board (CPCB). The pollution watchdog shared its findings with the National Green Tribunal (NGT) in response to a suo motu case on rising ozone pollution in Indian cities.
The CPCB analysed data from 178 monitoring stations across 10 cities in 2023. Of these, 65 stations breached the safety benchmark of a 2% exceedance in eight-hour average ozone concentration. Delhi reported violations at 25 of its 57 stations, while Mumbai saw breaches at 22 of 45 stations. Kolkata ranked sixth, with one of its 10 stations recording unsafe ozone levels.
This report marks a shift from the earlier 5% exceedance threshold to a 2% threshold, offering a more sensitive measure of pollution and its health impacts. Elevated ozone levels were attributed to emissions from transport, power plants, and industries, along with natural sources like volatile organic compounds, soil-based nitrogen oxides, wildfires, and methane emissions.
Ground-level ozone, or tropospheric ozone, is not emitted directly but formed through complex photochemical reactions involving volatile organic compounds and nitrogen oxides, the CPCB noted.

Dense smog over Delhi roads as vehicles emit pollutants

65 of 178 monitoring stations in 10 cities reported unsafe ozone concentrations

Delhi, Mumbai Worst in Ozone Pollution: CPCB

65 of 178 monitoring stations in 10 cities reported unsafe ozone concentrations

September 29, 2025 | 09:32 IST