The average air quality was recorded "very poor" in Noida and "poor" in Ghaziabad, Greater Noida, Gurgaon and Faridabad in the national capital region, according to a 24-hour data issued by a government agency on Saturday.
Presence of pollutant PM 2.5 and PM 10 also remained high in the five immediate neighbours of Delhi, according to the air quality index (AQI) maintained by the Central Pollution Control Board (CPCB).
As per 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 301 in Noida, 295 in Ghaziabad, 292 in Greater Noida, 260 in Faridabad and 260 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 "poor" may lead to breathing discomfort to people.
The average AQI on Friday was 304 in Ghaziabad, 297 in Greater Noida, 288 in Noida, 214 in Faridabad and 224 in Gurgaon. On Thursday, it was 277 in Ghaziabad, 283 in Greater Noida, 267 in Noida, 213 in Faridabad and 241 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.