Worst October air since 2020: What's behind Delhi's toxic AQI?

The transition from monsoon to winter is already showing up in Delhi's air, with pollution rising for five straight days, foreshadowing an early start to the pollution season.

In Short

• Delhi's AQI rose to 187 on Oct 4, highest in 83 days
• October 1-4 AQI at 174.5, worst in 6 years
• Farm fires not main cause yet, winter pollution expected to rise

Delhi's air quality has taken a turn for the worse just days after the capital recorded its cleanest September in years.

Pollution has risen for five consecutive days, with the city's average AQI reaching 187 on Sunday, October 4, its highest level in 83 days.

The first four days of October have also been among the most polluted starts to the month in recent years.

Delhi's average AQI for October 1–4 stood at 174.5 in 2026, compared with 119.75 in 2025, 167.25 in 2024, 155 in 2023, 161.25 in 2022, 107.25 in 2021.

The only time October has been worse was at 176.25 back in 2020, making the 2026 figure the worst since the last 6 years.

On October 4, 14 of Delhi's 43 active monitoring stations recorded "Poor" air, as per the 4 pm bulletin issued by the Central Pollution Control Board (CPCB).

Mundka recorded the highest AQI at 273, followed by 257 each at CRRI Mathura Road and Narela, and 237 at Jahangirpuri.

WHY IS DELHI'S AQI RISING?

This poor start to the month, bringing up the air quality that only arrives later in the month or early November, can be attributed to the change in weather.

Late-September rain and stronger winds had helped disperse pollutants, giving Delhi a brief spell of cleaner air. But as rainfall stopped, wind speeds fell and local emissions began accumulating again.

PM10, which includes larger particles commonly associated with road dust and construction activity, emerged as the dominant pollutant during the recent deterioration.

Delhi's temperature has also remained unusually high for early October.

On Sunday, the maximum was 36.4°C, 2.2 degrees above normal, while the minimum was 24.1°C, 1.8 degrees above normal.

LOCAL POLLUTION ADDS TO PROBLEM

There is evidence that local sources are also contributing to the worsening air.

The Commission for Air Quality Management (CAQM) flagged several violations involving visible road dust and construction-and-demolition waste during inspections of stretches covering about 35 km of Delhi's Inner and Outer Ring Road.

Farm fires have also begun appearing across northern India, but there is not enough evidence yet to attribute the current deterioration in Delhi primarily to stubble burning.

As October progresses, however, the usual winter pollution sources, including vehicles, industries, power plants, biomass burning and farm fires, can increasingly add to the problem.

For now, there is no single source behind the worsening AQI.

The clearest immediate blame lies with weaker winds in the absence of monsoon, lack of rain and local emissions, with seasonal pollution sources likely to become more important as winter approaches.

- Ends