The air quality in the national capital turned severe on Friday due to low temperatures and wind speed and high humidity, officials said.
The overall air quality index of the city stood at 432, which falls in the severe category, at 4 pm.
Fog prevented the sunlight from heating the ground and the cold air trapped pollutants and low wind speed aided their accumulation, the officials said.
The city recorded a low of 6.4 degrees Celsius and a high of 17.5 degrees Celsius, which was five notches below the normal.
On Saturday, wind speed is expected to improve and a drizzle may also occur, they said.