The average air quality across Noida, Greater Noida, Ghaziabad, Gurgaon and Faridabad improved slightly on Wednesday and was recorded in the "moderate" category, according to data issued by a government agency.
The concentration of pollutants PM 2.5 and PM 10 remained high in the air of the five immediate neighbours of Delhi during the day, 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 Wednesday was 198 in Ghaziabad, 189 Greater Noida, 168 in Noida, 197 in Faridabad and 164 in Gurgaon, according to CPCB's Sameer app.
On Tuesday, it was 218 in Ghaziabad as well as in Greater Noida, 153 in Noida, 198 in Faridabad and 172 in Gurgaon.
The CPCB states that an AQI in the "moderate" category may cause breathing discomfort to people with asthma, lungs 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.