New Delhi, June 17 -- Ozone, not particulate matter, has emerged as the dominant pollutant in Delhi's air this summer - a major shift that highlights a growing and poorly addressed public health threat in the National Capital Region (NCR). A new analysis by Delhi-based think tank Centre for Science and Environment (CSE) revealed that ground-level ozone breached national safety limits on nearly every day between March and May 2025, with wider geographical spread and longer durations than seen in previous years.

Out of 18 days between May 25 and June 11, ozone was the lead pollutant on 12 days in the city's official Air Quality Index (AQI), displacing fine particulate matter (PM2.5) for the first time over such a sustained period. Despite ...