Pollution levels in Delhi peaked to a three-year high on Sunday. According to the Central Pollution Control Board, the national capital's 24-hour average air quality index stood at 494 at 4 pm on Sunday. The highest before this was recorded on November 6, 2016 when it was 497. Twenty-one of the 37 air quality monitoring stations recorded the AQI between 490 and 500. In the wider National Capital Region, Faridabad with AQI 493, Noida (494), Ghaziabad (499) and Greater Noida (488), Gurugram (479), also breathed extremely polluted air. The spurt in pollution levels also prompted the administrations in Delhi, Ghaziabad, Noida, Greater Noida, Gurgaon and Faridabad to shut all government and private schools till November 5.