At 4 pm on Friday, the Air Quality Index (AQI) was 468, according to the AQI dashboard. Mundka recorded the worst air quality at 498, followed by Bawana at 496.

AQI at Lodhi Road area was at 438, Jahangirpuri at 491, RK Puram area at 486 and around IGI Airport (T3) 473.

As per the Central Pollution Control Board, an AQI of zero to 50 is considered ‘good’, 51-100 ‘satisfactory’, 101-200 ‘moderate’, 201-300 ‘poor’, 301-400 ‘very poor’, and 401-500 ‘severe’.

For the first time this season, Delhi’s air quality breached the 400­ mark to enter the ‘severe’ category and reached 575 at 7.23 pm on Thursday. The previous high in the season was 412 on 30 October. At least 18 out of 37 monitoring stations in Delhi recorded Air AQI in the ‘severe’ category.

The development prompted chief minister Arvind Kejriwal Thursday to declare the closure of all primary schools until Saturday.

The Commission for Air Quality Management has banned all non-essential construction activity and imposed restrictions on certain categories of vehicles as a thick and pungent yellow haze enveloped the skies above the nation’s capital.

The transport department said a fine of ₹20,000 would be imposed on BS-III petrol and BS-IV diesel vehicles. The restrictions on these vehicles will be applicable in the surrounding areas of Gurgaon, Faridabad, Ghaziabad and Gautam Buddh Nagar too.

“Cold temperatures create stable atmospheric conditions, known as temperature inversions, where a layer of warm air traps cooler air near the ground, allowing the accumulation of pollutants,” as per the India Meteorological Department.

One of the major factors behind the accumulation of pollutants in recent days is the lack of rain during this post­-monsoon season. Delhi’s air quality this October was the worst since 2020 as adequate rainfall was not recorded last month. About 5.4mm of precipitation was recorded in October 2023 as against 129 mm in October 2022 and 123 mm in October 2021.

Stubble-burning incidents in north Indian states, especially in Punjab are also adding to the pollution. Smoke from stubble burning accounted for 25 % of the

PM2.5 pollution in Delhi on Thursday, which may go up to 35% on Friday, a model-based study by the Indian Institute of Tropical Meteorology in Pune revealed.

The PM2.5 concentration in Delhi reached 282 microgrammes per cubic metre, higher than the limit fixed by the World Health Organisation’s (WHO’s) air quality guidelines. PM2.5 is fine particulate matter that can penetrate deep into the respiratory system and trigger respiratory problems and its safe limit is 60 microgramme per cubic metre.

Air pollution in Delhi generally peaks between 1-15 November when the stubble burning by the farmers of Punjab and Haryana increases after paddy harvest.

The Commission for Air Quality Management reported that this year the incidents of stubble burning in both Punjab and Haryana have been lower on year since 15 September, though there was a significant jump in the last few days.

While scientists warned of a spike in pollution levels in Delhi-NCR over the next two weeks owing to unfavourable meteorological and climatic conditions, doctors expressed concerns over a potential rise in respiratory problems.

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Updated: 03 Nov 2023, 10:49 PM IST