Kolkata: The city’s winter air has been slipping into the danger zone in Jan since 2024, with a new analysis showing that the month has seen near-continuous breaches of national air-quality standards for both fine (PM2.5) and coarse particulate matter (PM10).The study conducted by Respirer Living Sciences took into account station-level data from Respirer’s AtlasAQ platform to track trends in PM2.5 and PM10, identify recurring hotspots, and map hourly pollution patterns. Its central finding is stark: winter pollution in Kolkata is no longer episodic or driven by a handful of bad days, but structural and predictable.“In Jan 2026, both PM2.5 and PM10 crossed national safety limits on all 31 days in Kolkata,” said Ronak Sutaria, founder and CEO of Respirer Living Sciences. “That tells us winter pollution here is persistent and deeply embedded. While 2025 showed a short-lived improvement, Jan 2026 reversed those gains, with city-average PM2.5 rising again to over 92 micrograms per cubic metre.”According to the analysis, PM2.5 levels fell by nearly 22% in Jan 2025 compared to 2024, but rebounded by more than 18% in 2026. PM10 showed a similar pattern: a modest decline in 2025 followed by an increase the next year. Across all three years, PM10 remained elevated for almost the entire month, rarely dropping into cleaner categories.The study also highlights a strikingly consistent daily rhythm. Both PM2.5 and PM10 peak at 11 pm every Jan, with the highest concentrations clustering between 10 pm and midnight. This late-night spike suggests pollution accumulation driven by winter meteorology, rather than just fresh emissions.“The fact that pollution peaks so reliably at night points to trapped air and poor dispersion,” Sutaria said. “For residents, especially children, the elderly, and those with respiratory illnesses, there were virtually no safe breathing days.”Another key insight was the persistence of geographic hotspots. Neighbourhoods such as Ballygunge, Jadavpur, and the area around Rabindra Bharati University repeatedly recorded the highest pollution levels across years. While PM2.5 hotspots shifted slightly, PM10 hotspots showed remarkable consistency, underlining the role of dust, construction activity, and road resuspension.“These are not random spikes,” Sutaria added. “They’re location-specific exposures that demand targeted, seasonal interventions. Winter air quality needs to be treated as a continuous public-health risk, not an occasional emergency.”
