Explainer: Why Delhi's air quality is still 'moderate' in September

India Sep 30, 2025

September 2025 saw Delhi hit its longest run of "moderate" air quality days since 2016, with the average AQI at 104.7.
Usually, monsoon rains help clear out pollution by now, but in 2025 things didn't go as planned.

Health risks of breathing in such pollution

An early end to the monsoon and dry weather in September 2025 meant less rain to wash away pollutants.
With hotter days (peaking at 38.1°C) and more ozone building up, pollution stuck around—and it's expected to linger into October.
This means ongoing health risks for anyone breathing Delhi's air right now.

Factors behind the unusual phenomenon

The monsoon left earlier than it has since 2002, in September 2025, leaving behind dry skies and northwesterly winds that trapped pollutants instead of clearing them out.