New Delhi, Nov 4 : Delhi's Air Quality Index (AQI) reached the "severe" category on Diwali night on Thursday with majority of the city's areas seeing the index well above the 400 level, according to the Central Pollution Control Board (CPCB). At 4 p.m., AQI at ITO, Rohini, DTU Delhi, Dwarka, Mandir Marg, and Najafgarh stood under the "very poor" category. However, at 9 p.m., it deteriorated to "severe". AQI of Anand Vihar in the evening was recorded at 412 and by the night increased to 439, in Alipur, it went from 426 to 444, Dwarka (410 to 427), Bawana (432 to 449), Chandini Chowk (401 to 435), Jahangirpuri (463-469), Patparganj (404-432), and Wazirpur (441-450). Delhi's air quality worsened despite a complete ban on firecrackers. National Capital Region (NCR) too fell in the same category. However, no such ban was imposed in the latter region. Even before bursting of crackers, the air quality of Delhi-NCR region had started worsening further as AQI of eight cities had crossed the 400-mark and settled at "severe" category in the afternoon. The meteorological agencies have predicted an AQI of 500 plus for Thursday and Friday after Delhiites burst crackers on Diwali day. According to health experts, an AQI of such an extent may cause respiratory impact even on healthy people, and serious health impacts on people with lung or heart disease. The health impact may be experienced even during light physical activity. With stubble burning share in Delhi's air pollution set to increase over the next three days, SAFAR has projected an AQI of 500 plus on November 5 even if Delhiites burst 50 per cent less crackers compared to last year. SAFAR, or the System of Air Quality and Weather Forecasting And Research under the Indian Institute of Tropical Meteorology (IITM) - an agency under the Ministry of Earth Sciences - said as per sensitivity simulation, stubble share on November 4 is predicted to increase to 20 per cent and will touch a peak of 35-40 per cent on November 5 and 6, if fire counts are considered same (3,500-4,000). This is largely due to transport level winds reaching Delhi from North-Westerly, where stubble burning large hot spots are expected, it said. /IANS