Delhi's air quality remained in the "severe" category on Sunday owing to unfavourable weather conditions and a significant increase in contribution from stubble burning, authorities said.
The overall air quality index (AQI) was recorded at 423, according to data from the Central Pollution Control Board.
The city's air quality was recorded in the "very poor" category on Saturday morning, but it again slipped to the severe level in the evening.
On Sunday, the PM2.5 (particles in the air with a diameter of less than 2.5 micrometres) level was recorded at 299, while the PM10 (particles in the air with a diameter of less than 10 micrometres) level was recorded at 477, according to data from the CPCB.
Twenty-eight areas in Delhi recorded air quality in the "severe" category, while seven areas recorded "very poor" air quality, according to the CPCB.
An AQI between 0 and 50 is considered "good", 51 and 100 "satisfactory", 101 and 200 "moderate", 201 and 300 "poor", 301 and 400 "very poor", and 401 and 500 "severe".
According to the Indian Institute of Tropical Meteorology, the increase in PM2.5 concentration is due to stable meteorological conditions trapping of the pollutants in Delhi (very less dispersion) and significant increase in contribution from stubble burning.
Stubble burning in neighbouring states of Delhi on Thursday was the "largest-ever recorded" this year, the IITM had said Friday, adding that it could lead to a further deterioration in the already "severe" air quality of the national capital.
It said about 2,100 fire counts were observed on Thursday over north western region of India.
Delhi's air quality has remained in the "severe" category for the past two days with the highest pollution level of the year recorded a day after Diwali on Thursday at an AQI of 642.
The Environment Pollution Control Authority has asked the departments concerned to extend the ban on construction activities, industries using coal and biomass and entry of trucks till November 12 in view of the situation.
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