A recent analysis by a Delhi-based think tank has revealed a troubling rise in ground-level ozone pollution across the National Capital Region (NCR) during the summer of 2025. The study found that ozone levels breached national safety standards nearly every day from March to May, with a wider spread and longer duration compared to previous years.
Between May 25 and June 11, ozone emerged as the dominant pollutant on 12 of 18 days in the city’s official Air Quality Index readings, surpassing fine particulate matter (PM2.5) for the first time over such an extended period. However, the city’s current pollution control framework under the Graded Response Action Plan (GRAP) does not include specific measures to curb ozone or its precursor gases, leaving a critical gap in efforts to manage this growing problem.
The report showed that Delhi exceeded the eight-hour ozone standard on all 92 summer days this year, while neighbouring NCR towns crossed the limit on 83 days. Some of the worst affected areas included Nehru Nagar in South Delhi, which recorded unsafe levels every day, as well as Sector 125 in Noida and Vasundhara in Ghaziabad, which also saw frequent breaches.
Ozone pollution behaves differently from PM2.5, as it is not directly emitted but formed through chemical reactions involving gases like nitrogen oxides, volatile organic compounds, and carbon monoxide in sunlight. Hot and sunny summer conditions accelerate this process, raising ozone concentrations to dangerous levels.
The analysis also highlighted that ozone levels remained elevated into the night more often this year. On average, Delhi monitoring stations recorded ozone exceedances for over 14 hours daily, while stations in surrounding NCR cities reported even longer durations of 15 hours. Gwal Pahari in Gurugram saw the highest number of night-time ozone events.
The highest ozone reading this summer came from the CRRI Mathura Road station in Delhi, with an alarming eight-hour average of 472 micrograms per cubic metre on May 19 — more than four times the national standard. Such extreme values had previously gone unnoticed due to data reporting caps that were not applied this year.
Interestingly, the study found that ozone pollution hotspots were often located in areas with low nitrogen dioxide and PM2.5 levels, since ozone breaks down faster in more polluted environments. However, places like Wazirpur and Loni in Ghaziabad displayed high levels of all three pollutants, pointing to complex pollution patterns in these locations.
The findings have raised concern over the health risks posed by rising ozone exposure. Ozone is a harmful gas that can irritate airways, reduce lung function, and worsen respiratory diseases such as asthma and bronchitis. Experts warned that without urgent action, this trend could lead to a serious public health crisis.
The report called for immediate updates to Delhi’s pollution control plans to include ozone and its precursor gases. It also recommended stronger long-term measures like promoting zero-emission vehicles, cleaner industrial fuel use, and eliminating waste burning. Effective control of ozone pollution, the study noted, requires coordinated action across both urban and rural areas to safeguard health and agricultural productivity.