A cold wave gripped Delhi on Tuesday as icy winds blowing from the snow-covered western Himalayas brought the minimum temperature down to 4.1 degrees Celsius, the lowest in the city this season so far, the India Meteorological Department (IMD) said.

For the plains, the IMD declares a cold wave when the minimum temperature is 10 degrees Celsius or below and is 4.5 notches less than the normal for two consecutive days.

"However, for small areas such as Delhi, a cold wave can be declared if the criteria is fulfilled even for a day," Kuldeep Srivastava, the head of the IMD's regional forecasting centre, said.

At 4.1 degrees Celsius, the minimum temperature at Safdarjung Observatory, which provides representative data for the city, was five notches below normal on Tuesday morning.

At Jafarpur, the mercury dipped to 3.6 degrees Celsius.

The Ayanagar and Lodhi Road weather stations recorded a minimum of 4 degrees Celsius and 4.2 degrees Celsius respectively, the IMD said.

On Monday, the maximum temperature in the national capital had dropped to 19.4 degrees Celsius, four notches below normal and the lowest so far this month, as cold winds swept the city.

The air quality has also improved to the "moderate" category due to the strong winds.

The city's air quality index (AQI) was 190 at 10 am. The 24-hour average AQI was 160 on Monday, 305 on Sunday and 356 on Saturday.

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".