The air quality improved slightly and was recorded in the "moderate" category in Noida and in the "poor" zone in Greater Noida, Ghaziabad, Gurgaon and Faridabad, according to data issued by a government agency on Friday.
Pollutants PM 2.5 and PM 10 remained high 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 on Friday was 263 in Ghaziabad, 240 in Greater Noida, 199 in Noida, 243 in Faridabad and 240 in Gurgaon, according to CPCB's Sameer app.
On Thursday it was 287 in Ghaziabad, 307 in Greater Noida, 260 in Noida, 277 in Faridabad and 268 in Gurgaon.
The CPCB states that an AQI in the "poor" category may lead to breathing discomfort to most people on prolonged exposure, while an air quality in the "moderate" zone may cause breathing discomfort to the people with lungs, asthma and heart diseases.
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.