The air quality remained "severe" in Noida, Greater Noida, Ghaziabad and Faridabad, while it improved to reach the "very poor" category in Gurugram in the National Capital Region (NCR) on Friday, according to a government agency.
Concentration of major air pollutants PM 2.5 and PM 10 also remained high in the five neighbouring cities 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 Friday was 433 in Ghaziabad, 421 in Greater Noida, 415 in Faridabad, 406 in Noida and 392 in Gurugram, according to the CPCB's Sameer app.
It was 464 in Ghaziabad, 457 in Greater Noida, 450 in Noida, 443 in Gurugram and 416 in Faridabad on Thursday.
PM 2.5 and PM 10 were the prominent pollutants in these satellite cities of Delhi, where the average AQI remained at 406 on Friday, according to the app.
The CPCB states that an AQI in the "severe" category affects healthy people and seriously impacts those with existing diseases.
The AQI for each city is based on the average value of all stations there. Noida, Faridabad, Ghaziabad have four stations each, while Gurugram has three and Greater Noida two, according to the app.