Cold Wave, Toxic Air: Why Delhi's Pollution Peaks in November-December

Every winter, Delhi's air turns toxic, and this year is no exception. After the monsoon, pollution levels rise, but the real crisis begins when temperatures plunge. The city is now blanketed in haze, with Air Quality Index (AQI) readings often crossing 400, a level considered 'severe' and harmful even for healthy individuals.

The persistent smog has sparked protests across the capital, from India Gate to Jantar Mantar. Residents, students, and activists carried placards reading "We Can't Breathe" and wore gas masks to highlight the severity of the crisis. Some demonstrations turned tense, with reports of police detaining protesters and using pepper spray.

How Temperature Drives Pollution

As December begins, Delhi is witnessing one of its sharpest winter pollution surges. Temperatures have dropped to around 5 degrees Celsius, while AQI remains above 300, in the 'very poor' to 'severe' range. This happens every winter because cold air traps pollutants near the ground. With temperatures expected to fall further, the smog will persist.

Data from the Central Pollution Control Board (CPCB) and India Meteorological Department (IMD) shows a clear inverse relationship between temperature and AQI from October 1 to December 5, 2025.
The data shows that as temperatures drop from around 20 degrees Celsius to single digits, air quality gets progressively worse. October starts with moderately polluted mornings, November sees hazardous levels, and by December, cold and still air traps pollutants, making the situation severe.
 
What Numbers Say

In October, Delhi moves from mild autumn and relatively low pollution to the first signs of smog. Early in the month, temperatures stay between 22 degrees Celsius and 25 degrees Celsius, and AQI levels range from 80 to 150, indicating mild pollution. 
 
By mid-to-late October this year, as temperatures fell to 18-20 degrees Celsius, the AQI rose sharply and stood between 230 and 310. On October 30, the figure touched 373, marking the season's first severe smog spike. This shows a clear pattern - once temperatures drop below 20 degrees Celsius, air quality begins to deteriorate fast. Another factor that impacts pollution is stubble burning, which becomes more widespread during October and tapers off by mid-November.

November marks a worsening in Delhi's pollution. Early in the month, temperatures hover around 16-19 degrees Celsius, and AQI climbs to 290-360. By the middle of the month, temperatures fall to 10-12 degrees Celsius, and the city records some of its highest AQI readings: 428 on November 11 this year, 418 on November 12, and 404 on November 13. Late November sees temperatures between 8-10 degrees Celsius, while AQI remains high at 350-390. 

As colder days have arrived in the first week of December, with temperatures dropping to 5-6 degrees Celsius, AQI has hovered between 300 and 370. This confirms that once winter sets in, pollution becomes locked in place, with little chance of dispersion, and the situation is only likely to get worse as the month progresses.