The air quality in Delhi turned severe with pollution levels crossing the 400 mark in several parts of the city on Saturday. Monitoring stations reported an AQI of 404 at Alipur, 402 at ITO, 406 at Nehru Nagar, 411 at Vivek Vihar, 420 at Wazirpur and 418 at Burari, according to CPCB's app data from 38 stations across the capital.