Delhi's overall air quality deteriorated to the severe category from "very poor" on Wednesday morning.

The national capital's AQI was in "severe" category on November 15 the last time but after that it had improved and remained in either "poor" or "moderate" category until November 22.

According to the Central Pollution Control Board(CPCB) mobile app, SAMEER, the city's air quality index (AQI) was recorded at 401.

It was 388 on Tuesday. The AQI in the city was 302 on Monday, 274 on Sunday, 251 on Saturday, 296 on Friday and 283 on Thursday.

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".

The Ministry of Earth Sciences' monitoring system SAFAR had predicted improvement in the AQI for Wednesday.

Stubble burning share in PM2.5 in Delhi's air was 5 per cent on Tuesday.

Stubble burning accounted for 6 per cent of Delhi's PM2.5 pollution on Monday and 12 per cent on Sunday. It was 13 per cent on Saturday, 15 per cent on Friday, 20 per cent on Thursday and eight per cent on Wednesday.