The AQI for each city is based on the average value of all monitoring stations there. (File)
The average air quality was recorded in the "very poor" category in Greater Noida, while it was "poor" in Noida, Ghaziabad, Faridabad and Gurgaon, according to data issued by a government agency on Friday.
Pollutants PM 2.5 and PM 10 also remained high in the air of the five immediate neighbours 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 Friday was 276 in Ghaziabad, 301 in Greater Noida, 250 in Noida, 268 in Faridabad and 273 in Gurgaon, according to CPCB''s Sameer app.
On Thursday, it was 332 in Ghaziabad, 298 in Greater Noida, 302 in Noida, 312 in Faridabad and 218 in Gurgaon.
The CPCB states that an AQI in the "very poor" category may cause respiratory illness on prolonged exposure while "poor" leads to breathing discomfort to most people on prolonged exposure.
The AQI for each city is based on the average value of all monitoring stations there. Ghaziabad, Gurgaon and Noida have four such stations while Greater Noida and Faridabad have two stations each, according to the app.