The national capital on Sunday recorded a maximum temperature of 15.8 degrees Celsius, five notches below the season's average, according to the India Meteorological Department.
The minimum temperature was 4.8 degrees Celsius while the humidity level at 5.30 pm was 71 per cent.
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According to the railways, 11 Delhi-bound trains were delayed by up to four hours on Sunday due to foggy conditions.
The weather office predicted mainly clear sky, dense to very dense fog and cold day conditions for January 22.
The Air Quality Index (AQI) at 6 pm was recorded at 344, which is in the 'very poor' category, according to the Central Pollution Control Board (CPCB).
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".