Delhi's air quality worsened again and slipped into the 'severe' category on Tuesday morning.

At 9:36 am, the air quality index (AQI) was 414. The AQI at Bawana, Wazirpur, Anand Vihar and Rohini was 445, 442, 442 and 440, respectively.

According to the government air quality monitoring service, Safar, the city's air quality was in the 'very poor' category on Monday which turned into 'severe' by the evening. The average AQI stood at 360 on Sunday.

In the National Capital Region (NCR), the AQI in Noida was 436, while Ghaziabad recorded an AQI of 445. Greater Noida, Gurgaon and Faridabad recorded AQI of 436, 365 and 404, respectively.

On Monday, most of the 37 air quality monitoring stations in Delhi recorded the air quality as 'severe'.

An AQI between 0-50 is considered 'good', 51-100 'satisfactory', 101-200 'moderate', 201-300 'poor', 301-400 'very poor' and 401-500 'severe'. Above 500 falls in the 'severe plus' category.

With the winter setting in, a dip in the minimum temperature makes the air cold and heavy leading to accumulation of pollutants close to the ground.