An AQI between 201 and 300 is considered poor, 301 and 400 very poor and 401 and 500 is severe.
"It may improve a few notches tomorrow (Thursday) but will remain in very poor category. Moderate surface wind speed is the only weather factor not allowing pollution to accumulate significantly and working positively to an extent. Rest of the weather conditions are unfavourable for the air quality," the SAFAR said.
According to the Indian Institute of Tropical Meteorology, the maximum ventilation index was likely around 5000 sqm/second on Tuesday.
A ventilation index lower than 6,000 sqm/second with average wind speed less than 10 kmph is unfavourable for dispersion of pollutants, IITM said.
A Central Pollution Control Board taskforce has identified 21 hotspots of high pollution levels in Delhi-NCR and directed the respective area municipal corporations to take "focussed actions".
The taskforce has also asked authorities to carry out inspection in Loni Bhopura, in Ghaziabad, from where repeated complaints of violations of norms associated with pollution-causing activities have been received, according to minutes of a meeting of the taskforce held in Delhi Tuesday.
The taskforce has identified 15 hotspots in Delhi. They are: Anand Vihar, Bawana, CRRI Mathura Road, DTU, Dr. Karni Singh Shooting Range, Dwarka-Sector 8, Jahangirpuri, Mundaka, NSIT Dwarka, Narela, Okhla Phase-2, R K Puram, Rohini, Shadipur, Wazirpur.
Many of the hotspots are already experiencing severe pollution levels.
In NCR areas outside Delhi, six hotspots have been identified. They are: Sector-16A in Faridabad, Vikas Sadan in Gurgaon, Vasundhara in Ghaziabad, Knowledge Park-III in Greater Noida, Sector-125 in Noida and RIICO Industrial Area-III in Bhiwadi.
(With inputs from agencies.)