Air quality in Delhi improved slightly on Friday but stayed in 'very poor' category with AQI at 370 at 8 am, according to Central Pollution Control Board (CPCB). The city had recorded AQI at 391 at 4pm on Thursday. However, Anand Vihar, Ashok Vihar, Rohini and RK Puram saw 'severe' air with AQI at 418, 411, 424 and 401 respectively.