The average air quality was recorded in the "poor" category across Ghaziabad, Noida, Greater Noida, Faridabad and Gurgaon, according to data issued by a government agency on Sunday.
Pollutants PM 2.5 and PM 10 were also present 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 4pmon Sunday was 260 in Ghaziabad, 300 in Greater Noida, 251 in Noida, 264 in Faridabad and 297 in Gurgaon, according to CPCB's Sameer app.
The CPCB states that an AQI in thevery poor category may cause respiratory illness to people on prolonged exposure, while "poor" may cause breathing discomfort to most people on prolonged exposure.
On Saturday it was 336 in Ghaziabad, 324 in Greater Noida, 269 in Noida, 248 in Faridabad and 258 in Gurgaon.
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.