The air quality improved on Saturday but remained in the "poor" category in Noida, Greater Noida, Ghaziabad, Gurgaon and Faridabad in the National Capital Region (NCR), according to a government agency. Presence of pollutant PM 2.5 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 4 pm on Saturday was 256 in Gurgaon, 246 in Faridabad, 238 in Ghaziabad, 231 in Noida and 228 in Greater Noida, according to CPCB's Sameer app.
On Friday, it was 325 in Ghaziabad, 306 in Noida, 314 in Greater Noida, 297 in Faridabad and 275 in Gurgaon.
The CPCB states that an AQI in the "poor" category may cause breathing discomfort to most people on prolonged exposure, while in the "very poor" category, it may may cause respiratory illness on prolonged exposure.
The average AQI on Thursday was 305 in Ghaziabad, 207 in Noida, 315 in Greater Noida, 255 in Faridabad and 284 in Gurgaon.
On Wednesday, it was 236 in Ghaziabad, 207 in Noida, 228 in Greater Noida, 172 in Faridabad and 141 in Gurgaon.
The average AQI on Tuesday was 166 in Ghaziabad, 172 in Faridabad, 178 in Noida, 186 in Greater Noida and 204 in Gurgaon.
On Monday it was 186 in Faridabad, 207 in Ghaziabad, 226 in Greater Noida, 243 in Noida and 246 in Gurgaon, showing drastic improvement over the previous day due to a spell of rain in the NCR.
On Sunday, the average AQI was 448 in Ghaziabad, 441 in Noida, 417 in Greater Noida, 425 in Gurgaon and 414 in Faridabad.
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.