From Fog To Filth: Delhi Records 3rd-Worst December AQI In A Decade

Delhi is battling a dangerous mix of dense fog and severe pollution, pushing the Air Quality Index (AQI) close to 400, a level classified as 'severe.' While the Delhi-NCR woke up under a thick fog blanket, the real threat lies in the toxic air residents are breathing.

According to the India Meteorological Department, visibility at IGI Airport at 10:00 UTC was just 1.1 km, with runway visual range around 2 km. The poor visibility disrupted flight operations, with 78 arrivals and 70 departures cancelled, and two flights diverted. Yesterday, 118 flights were cancelled, and delays persist despite CAT-III protocols.

Experts warn that fog traps pollutants near the surface, worsening air quality. As fog lingers, AQI is expected to climb further, intensifying health risks. Is this the first time AQI has reached such severe levels?

December AQI

Over the past decade, Delhi's average AQI in December has consistently remained in the 'very poor' to 'severe' category, reflecting persistent pollution challenges.

The worst December was in 2016 (AQI 365), followed closely by 2018 (360). After a slight improvement in 2024, when AQI dropped to 294, the city saw a sharp rebound in 2025, reaching 350, making it the third-highest December AQI in 10 years.

Which Pollutant Dominates?

According to the Central Pollution Control Board, Delhi air quality data from 2016 to 2025 shows persistently high pollution levels, with PM2.5 and PM10 concentrations far exceeding.

In December 2025, Delhi's average PM2.5 level was 212 microgrammes per cubic metre, while PM10 was higher at 341 microgrammes per cubic metre, continuing its trend as the dominant pollutant.

Historically, PM10 has overshadowed PM2.5 by a wide margin, but the gap is gradually narrowing - PM2.5 surged by over 50% between 2023 and 2025, reducing the difference between the two pollutants. This shift signals that while coarse particles remain a major concern, the rise in fine particulate matter poses an increasingly severe health risk.

Worst AQI Days in 2025

Delhi recorded its most polluted day of the year on 14 December 2025, when the Air Quality Index (AQI) hit a staggering 461, placing it in the "Severe" category. Most of the top 10 worst days fell in November and December, including 13 December (431), 15 December (427), and 11 November (428), reflecting the seasonal spike in pollution during winter.

This surge is largely driven by cold temperatures, low wind speeds, and atmospheric inversion, which trap pollutants close to the ground.