An AQI between 100 to 200 comes under the ‘moderate’ category, 201 and 300 is considered ‘poor’, 301 and 400 ‘very poor’, while that between 401 and 500 is ‘severe’.
The Centre-run System of Air Quality and Weather Forecasting (SAFAR) said the overall air quality index touched the upper level of ‘very poor’, but overall air quality remained in ‘very poor’ range.
“Slightly increased wind speed from - 2.5 kmph to 3.6 kmph - may disperse pollutants very slowly. Other than the wind speed, rest all meteorological factors are likely to be unfavourable. The AQI is expected to recover by weekend but will continue to remain in the very poor range,” the SAFAR said.
Moderate fog will prevail and cause both gaseous and particulate pollutants to become stagnant, the SAFAR said.
The overall PM2.5 level - fine particulate matter in the air with a diameter of less than 2.5 micrometre - was recorded at 244 and the PM10 level at 402, the CPCB said.
In Delhi, Ashok Vihar, DTU, Jahangirpuri, Jawahar Lal Nehru Stadium, Mundka, Nehru Nagar, North Campus, Pusa, R K Puram, Rohini, Sonia Vihar, Sri Aurobindo Marg and Wazirpur recorded ‘severe’ air quality, the CPCB said.
In NCR, Ghaziabad recorded the worst air quality which fell in the ‘severe’ category at an AQI of 411, CPCB data showed.
Faridabad and Noida recorded ‘very poor’ air quality while Gurgaon recorded ‘poor’ air quality, it said.
According to the Indian Institute of Tropical Meteorology, the maximum ventilation index Wednesday was 4,000 sqm/second.
A ventilation index lower than 6,000 sqm/second with an average wind speed of less than 10 kmph is unfavourable for dispersion of pollutants.