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Kolkata's Ozone Paradox: Clean Air, Dirty Sky?
17 Sep
Summary
- Ground-level ozone irritates respiratory systems, worsening lung conditions.
- Kolkata saw zero summer ozone exceedances in 2026.
- Leafy Kolkata neighborhoods paradoxically become ozone hotspots.
Kolkata faces a puzzling atmospheric situation concerning ground-level ozone, a pollutant that irritates the respiratory system and exacerbates lung diseases. This is distinct from the stratospheric ozone layer, which is globally on a path to recovery and is expected to reach 1980 levels by approximately 2040. While Kolkata recorded zero summer ozone exceedances in 2026, a significant improvement from previous years, the problem is not entirely resolved.
Episodes of elevated ozone levels were still noted between November 2025 and January 2026. Intriguingly, some of Kolkata's greener neighborhoods, like Rabindra Sarobar, have become ozone hotspots. This phenomenon occurs because ground-level ozone forms from chemical reactions of pollutants like NOx and VOCs in sunlight, and in some polluted areas, fresh nitric oxide can actually reduce local ozone levels through a process called titration.
Across the Hooghly river, Howrah reported even higher ozone exceedances during the summer of 2025, with 58 days exceeding the standard compared to Kolkata's 22. Scientists are investigating whether Kolkata's zero summer exceedance in 2026 is due to emission changes or meteorological factors. The city's ozone story is now less about the distant atmospheric layer and more about understanding this locally generated pollutant.
