The air quality was in the "very poor" category in Noida, Ghaziabad and Greater Noida, while it was recorded in the "poor" zone in Faridabad and Gurgaon, a 24-hour data issued by a government agency said on Saturday.
The presence of pollutant PM 2.5 and PM 10 remained high in 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 Saturday was 367 in Ghaziabad, 355 in Greater Noida, 344 in Noida, 300 in Faridabad and 269 in Gurgaon, according to CPCB''s Sameer app.
The CPCB states that an AQI in the "very poor" category may cause respiratory illness on prolonged exposure while air quality in the "severe" zone affects even healthy people and seriously impacts those with existing diseases.
The average AQI on Friday was 391 in Ghaziabad, 376 in Greater Noida, 386 in Noida, 328 in Faridabad and 302 in Gurgaon. On Thursday, it was 440 in Ghaziabad, 448 in Greater Noida, 441 in Noida, 408 in Faridabad and 361 in Gurgaon.
The AQI for each city is based on the average value of all stations there. Noida, Faridabad, Ghaziabad have four stations each, while Gurgaon has three and Greater Noida two, according to the app.