The air quality was recorded in the "very poor" category in Ghaziabad, while it was "poor" in Greater Noida, Noida, Faridabad and Gurgaon, according to data issued by a government agency on Sunday.
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 Sunday was 329 in Ghaziabad, 270 in Greater Noida, 278 both in Noida and Faridabad and 216 in Gurgaon, according to CPCB''s Sameer app.
On Saturday it was 213 in Ghaziabad, 204 in Greater Noida, 182 in Noida, 169 in Faridabad and 177 in Gurgaon.
The CPCB states that an AQI in the "poor" category may lead to breathing discomfort to most people on prolonged exposure, while air quality in the "very poor" zone may cause respiratory illness 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.