The air quality in the national capital was recorded in the "very poor" category on Friday due to poor dispersion of pollutants owing to weak winds, according to the India Meteorological Department (IMD).
The capital witnessed a clear morning on Friday with the minimum temperature settling a notch below normal at 14.6 degrees Celsius.
The relative humidity at 8:30 am was 90 per cent, the weather office said.
However, the air quality deteriorated from 333 on Thursday to 346 at 9:30 am on Friday, the Central Pollution Control Board (CPCB) data showed.
Delhi's Anand Vihar monitoring station recorded the AQI in the "severe" category with an index value of 443 at 9:20 am on Friday.
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Among the monitoring stations that recorded "very poor" air quality were Wazirpur (380), Patparganj (363), Vivek Vihar (397), Punjabi Bagh (370) and Jahangirpuri (397).
An AQI between zero 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 IMD, the sky will remain clear through the day and the maximum temperature is likely to settle around 32 degrees Celsius.
The maximum temperature on Thursday had settled at 32.3 degrees Celsius, a notch above normal.