New Delhi: The average air quality improved from the "severe" to the "very poor" category in Ghaziabad, Noida, Greater Noida and Faridabad, and from the "very poor" to the "poor" in Gurgaon, according to 24-hour data issued by a government agency on Sunday.
The presence of pollutant PM 2.5 and PM 10 remained high in the five immediate neighbouring cities of Delhi, according to the air quality index (AQI) maintained by the Central Pollution Control Board (CPCB).
According to the index, an AQI between zero and 50 is considered 'good', 51 and 100 'satisfactory', 101 and 200 'moderate', 201 and 300 'poor', 301 and 400 'very poor', and 401 and 500 'severe'.
The average 24-hour AQI at 4 pm on Sunday was 384 in Ghaziabad, 348 in Greater Noida, 364 in Noida, 358 in Faridabad and 260 in Gurgaon, according to CPCB's Sameer app.
On Saturday, it was 462 i Ghaziabad, 450 in Greater Noida, 448 in Noida, 415 in Faridabad and 336 in Gurgaon.
The CPCB states that an AQI in the "very poor" category may lead to respiratory illness on prolonged exposure, while "poor" air quality causes breathing discomfort to most people on prolonged exposure.
The AQI for each city is based on the average value of all stations there. Ghaziabad and Gurgaon have three such stations while Noida, Greater Noida and Faridabad have two stations each, according to the app.