City air quality worsens as weak winds lead to surge in PM2.5 levels
Times of India | 10 December 2025
Kolkata: Kolkata woke up on Tuesday to dense smog and heavy, stagnant air, as pollution levels climbed steadily through the day and plunged the city into one of its worst air-quality spells this season. By late afternoon, nearly every monitoring station across the city displayed dark brown (‘poor') and red (‘very poor') on the Air Quality Index (AQI) scale — a visual warning of the health emergency unfolding in real time.
What made the episode particularly alarming was the dominance of PM2.5, the tiniest and most dangerous class of particulate pollutants. These fine particles are small enough to penetrate deep into the lungs and enter the bloodstream, eventually reaching the brain, heart, and blood vessels. Experts warn that toxic chemical compounds often attach themselves to PM2.5, increasing the risk of respiratory, cardiac, and neurological disorders.
A sharp dip in temperature and a seasonal thermal inversion trapped pollutants close to the surface, preventing them from dispersing. A senior scientist from the West Bengal Pollution Control Board (WBPCB) said: "Thermal inversion means a lowering of vertical wind movement. It occurs in winter when the soil cools rapidly, reducing heat transfer from the ground. Wind speeds drop — often below 2 metres per second — creating calm conditions in the lower atmosphere where pollutants get trapped."
With weak winds and dense haze, pollution built up hour after hour. Among the monitoring stations, Victoria Memorial emerged as the worst hit, with the AQI shooting past 341, firmly in the ‘very poor' range (301–400). Only one category worse — 'severe' (401–500) — remains above it. Jadavpur followed closely at 320, while traditionally high-traffic corridors such as Ballygunge (285) and Salt Lake (240) also recorded troubling spikes.
Even the northern and eastern zones, which usually fare better, reported poor air: