Delhi AQI: Monsoon Rains Bring Temporary Relief to Air Quality; Pollution Persists

New Delhi, September 2025 – This year’s monsoon showers have once again highlighted their role as nature’s air purifier for the National Capital Region. With steady rainfall since July, Delhi has recorded some of its cleanest air in years — yet stubborn pollution sources ensure that the relief remains only temporary.

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Cleanest July in a Decade

According to CPCB data, July 2025 averaged an AQI of 79, the cleanest July in ten years. Rainfall consistently washed away fine particulate matter (PM2.5), helping air quality improve from “moderate” to “satisfactory” on several days.

On one particularly rainy day, AQI improved dramatically — dropping from 120 to 98 — alongside a temperature fall from 35.4°C to 30.2°C.

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Rainfall Boosted by Monsoon Revival

Delhi’s seasonal rainfall has already crossed 1,000 mm this year, significantly higher than the long-term average of ~774 mm. This surplus rainfall has been a major factor in dispersing pollutants and cleaning the atmosphere.

Yet, despite the rains, Delhi has not registered a single “Good” air quality day (AQI 0–50) in 2025. The best reading was 51 (Satisfactory) on July 15.

PM2.5 vs PM10: The Stubborn Divide

Scientific studies confirm that:

• PM2.5 (fine particles harmful for lungs) dropped into the ‘Good’ range almost throughout the monsoon season.
• PM10 (larger dust particles) remained above safe levels for over 50% of monsoon days, largely due to construction dust, road resuspension, and local emissions.

This stubborn trend shows that while rain effectively cleans finer particles, it is less successful in tackling coarse dust.

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Why Relief Is Only Temporary

Experts attribute Delhi’s air woes to persistent emission sources — vehicular exhaust, industrial smoke, and construction dust. Without systemic interventions, rainfall can only offer short-lived respite.

Outlook Ahead

With the monsoon gradually retreating by late September, AQI levels are likely to climb again. As winter approaches, stubble burning in Punjab & Haryana and falling wind speeds may push Delhi back into the “poor” and “very poor” categories.

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