The air quality improved further to reach "moderate" levels at Noida, Greater Noida, Ghaziabad and Faridabad, while it stayed in the "poor" category in Gurugram on Tuesday, according to a government agency.
According to the Central Pollution Control Board's (CPCB) Sameer mobile application, the average 24-hour air quality index (AQI) was 166 in Ghaziabad, 172 in Faridabad, 178 in Noida, 186 in Greater Noida and 204 in Gurugram at 4 pm.
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".
On Monday, the average AQI was 186 in Faridabad, 207 in Ghaziabad, 226 in Greater Noida, 243 in Noida and 246 in Gurugram, showing a drastic improvement over the previous day due to a spell of rain in the National Capital Region (NCR).
On Sunday, the average AQI was 448 in Ghaziabad, 441 in Noida, 417 in Greater Noida, 425 in Gurugram and 414 in Faridabad.
According to the CPCB, an AQI in the "poor" category may cause breathing discomfort to most people on a prolonged exposure, while a "moderate" AQI may cause such discomfort to people with asthma, lung and heart diseases.
The AQI for each city is based on the average value of all air quality-monitoring stations there. Noida, Faridabad and Ghaziabad have four such stations each, while Gurugram has three and Greater Noida two, according to the app.