The air quality in Noida and Greater Noida deteriorated to the 'severe' category on Sunday, according to the CPCB. Greater Noida, with an AQI reading of 418, was the most polluted city in the country on Sunday. The average 24-hour AQI at 4 pm in Ghaziabad was 407, 405 in Noida, 404 in Faridabad and 359 in Gurugram.