The AQI was recorded at 440 with PM10 and 264 with PM2.5 at 8 am, SAFAR said.
The air quality declined further and plunged to the "severe" category with the air quality index (AQI) crossing 450-mark on Monday, prompting the government to advise people to avoid outdoor activities.
An AQI between 0-50 is considered good, 51-100 is satisfactory, 101-200 moderate, 201-300 poor, 301-400 very poor and 401-500 is marked as severe/hazardous.
The AQI was recorded at 440 with PM10 and 264 with PM2.5 at 8 am, said System of Air Quality and Weather Forecasting And Research (SAFAR).
While Dilshad Garden recorded pollution levels at 419 with PM 2.5, it was at 494 in Okhla Phase-2 and 480 at Jawaharlal Nehru Stadium, according to the Central Pollution Control Bureau (CPCB). In Delhi airport area, the AQI was recorded at 431.
On Sunday, the air quality entered the "severe" category but pollution levels hovered around 400-mark. It was recorded "very poor" category on Saturday.
In an advisory, SAFAR asked everyone to avoid physical outdoor activities and morning walks. "Stop any physical activity if you feel unusual caughing, chest discomfort, breathing difficulty or fatigue," it said.
It has also advised people to close the window pan of their houses.