The average air quality was recorded "severe" in Ghaziabad, Noida, Greater Noida, while it was "very poor" in Fridabad and "poor" in Gurgaon, according to data issued by a government agency on Sunday.
Pollutants PM 2.5 and PM 10 also remained 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 onSunday was 416 in Ghaziabad, 416 in Noida, 402 in Greater Noida, 366 in Faridabad and 288 in Gurgaon, according to CPCB's Sameer app.
On Saturday it was 401 in Ghaziabad, 386 in Noida, 363 in Greater Noida, 362 in Faridabad and 310 in Gurgaon.
The CPCB states that an AQI in the"severe" category affects healthy people and seriously impacts those with existing diseases, while "very poor" may cause respiratory illness to people on prolonged exposure. An AQI in the "poor" range causes breathing discomfort to most people on prolonged exposure, it states.
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.