The average air quality deteriorated and was recorded "very poor" in Noida, Greater Noida and Ghaziabad, while it was "poor" in Gurgaon and Faridabad, according to a 24-hour data issued by a government agency on Sunday.
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).
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 346 in both Ghaziabad and Greater Noida, 333 in Noida, 294 in Faridabad and 262 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 Saturday was 301 in Noida, 295 in Ghaziabad, 292 in Greater Noida, 260 in Faridabad and 260 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.