The air quality level in Delhi was in the higher end of the “poor” category on Saturday after two days of Diwali festivities.

According to data from the Central Pollution Control Board, the national capital recorded an average air quality index of 297 at 1 pm. Anand Vihar recorded the worst air quality with the index at 394, which falls under the “severe” category.

An index value between 0 and 50 indicates “good” air quality, between 51 and 100 indicates “satisfactory” air quality and between 101 and 200 indicates “moderate” air quality.

A value between 201 and 300 indicates “poor” air quality while between 301 and 400 indicates “very poor” air. Between 401 and 450 indicates “severe” air pollution while anything above the 450 threshold is termed “severe plus”.

Despite being prohibited, firecrackers were lit across the city as part of the Diwali festivities. On Friday morning, Delhi’s air pollution level was nearly 14 times more than the “safe” limit prescribed by the World Health Organization.

The average concentration of PM2.5 in the national capital was 209.3 μg/m3 (micrograms per cubic metre of air) at 8 am on Friday, data from the Central Pollution Control Board showed.

PM2.5 refers to respirable airborne particles smaller than 0.0025 mm in width.

India’s National Ambient Air Quality Standards prescribe a “safe” PM2.5 concentration of 60 μg/m3, averaged over 24 hours. The World Health Organization prescribes 15 μg/m3 as the acceptable limit for human exposure.

The average Air Quality Index value in Delhi was recorded to be in the “very poor” category, with a reading of 362 at 9 am on Friday.

The national capital also recorded its most polluted Diwali in three years on Thursday. The average Air Quality Index in the national capital was 330 during the day. On Diwali day in 2023, the index stood at 218, while in 2022 it was 312.

On October 14, the Delhi government ordered a ban on the use of firecrackers in the city till January 1. Similar bans have been imposed and violated by citizens in previous years.

Air quality deteriorates sharply in the winter months in Delhi, which is often ranked the world’s most polluted capital. Stubble burning in Punjab and Haryana, along with falling temperatures, decreased wind speeds and emissions from industries and coal-fired plants contribute to the problem.