Delhi’s Air Improves Rapidly After Hazardous Diwali Start. Here's Why

Delhi woke up to a toxic haze after Diwali, with the city’s Air Quality Index (AQI) rising to 347 at 7 am on October 21, up from 238 the day before.

An AQI between 0 and 50 is considered "good", 51 to 100 "satisfactory", 101 to 200 "moderate", 201 to 300 "poor", 301 to 400 "very poor", and 401 to 500 "severe".

However, the PM2.5 concentration fell sharply from 675 µg/m³ at midnight on October 21 to 82 µg/m³ by 3 pm. Experts told ThePrint that the unusual dip was due to favourable weather conditions and fewer farm fires compared to previous years.

Shambhavi Shukla, programme manager at the Centre for Science and Environment (CSE), said that this year’s Diwali fell in October before winter fully set in, and the higher mixing height of pollutants allowed them more space to disperse, leading to a reasonable reduction in PM2.5 levels.

The Supreme Court had permitted “green crackers” in the Delhi-NCR region, restricting their use to specific hours. However, Delhi Environment Minister Manjinder Singh Sirsa said on October 21, that the impact of green crackers on pollution was negligible.

Even after the drop, PM2.5 levels remain well above India’s safe limit of 60 µg/m³. PM2.5 particles, just 2.5 microns in diameter, can enter the lungs and bloodstream, posing long-term heart and lung risks.