Air quality in Delhi plummeted to 'severe' category on Tuesday, with overall Air Quality Index (AQI) recorded at 421 at 7 am, according to data from Central Pollution Control Board. Several areas in Delhi reported AQI levels above 400, including Anand Vihar (412) and Bawana (462). Following this, authorities have imposed Graded Response Action Plan (GRAP) Stage 3 anti-pollution restrictions.