The average air quality was recorded in the "very poor" category in Ghaziabad while it was "poor" in Noida, Greater Noida, Faridabad and Gurgaon, according to data issued by a government agency on Monday.
Levels of PM2.5 and PM10 also remained high in the air of the five cities neighbouring 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 AQI at 4 pm was 318 in Ghaziabad, 294 in Greater Noida, 290 in Noida, 265 in Faridabad and 296 in Gurgaon, according to CPCB's Sameer app.
On Sunday, it was 260 in Ghaziabad, 300 in Greater Noida, 251 in Noida, 264 in Faridabad and 297 in Gurgaon.
According to the CPCB, an AQI in the ''poor'' category can lead to breathing discomfort for most people on prolonged exposure while a ''very poor'' AQI may cause respiratory illness on prolonged exposure.
The AQI for each city is based on the average value of all air quality monitoring stations there. Ghaziabad and Gurgaon have three such stations and Noida, Greater Noida and Faridabad have two each, according to the app.
