The air quality deteriorated to severe level in Ghaziabad and Greater Noida, while it remained "very poor" in Noida and Faridabad, and poor in Gurgaon, according to data from a government agency on Saturday.
Presence of pollutants 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 4pm on Saturday was 415 in Ghaziabad, 404 in Greater Noida, 393 in Noida, 348 in Faridabad and 296 in Gurgaon, according to CPCB's Sameer app.
On Friday, it was 347 in Ghaziabad, 330 in Greater Noida, 324 in Noida, 290 in Faridabad and 256 in Gurgaon. On Thursday, it was 330 in Ghaziabad, 322 in Greater Noida, 310 in Noida, 300 in Faridabad and 217 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 on prolonged exposure and poor may cause breathing discomfort.
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.