A thick layer of smog covered Delhi on Thursday as the national capital recorded 'very poor air' quality with AQI of 400, according to the Central Pollution Control Board. Out of Delhi’s 39 monitoring stations, 21 showed 'severe' air quality. Wazirpur, the most polluted locality, recorded AQI of 477. Anand Vihar logged 427, while Anand Vihar recorded AQI of 427.