Delhi's air quality remained 'very poor' today, with four areas recording severe air quality, due to unfavourable weather conditions like low wind speed, according to authorities.
The Central Pollution Control Board (CPCB) recorded an overall air quality index (AQI) of 343.
An AQI between 201 and 300 is considered 'poor', 301 and 400 'very poor' and 401 and 500 is 'severe'.
The air quality in four areas -- Mundka, Nehru Nagar, Rohini and Wazirpur -- was recorded in 'severe' category. It was 'very poor' in 24 areas and 'poor' in four areas, according to the CPCB.
The overall PM2.5 (fine particulate matter in the air with a diameter of less than 2.5 micrometre) level was recorded at 210 and the PM10 level at 396, it said.
In NCR, Ghaziabad, Faridabad and Noida recorded 'very poor' air quality, the CPCB data showed.
The Centre-run System of Air Quality and Weather Forecasting (SAFAR) said the overall air quality of Delhi continues to remain in the 'very poor' range.
"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," it said.
According to the Indian Institute of Tropical Meteorology, the maximum ventilation index was likely around 7,500 sqm/second on Thursday.
A ventilation index lower than 6,000 sqm/second with average wind speed of less than 10 kmph is unfavourable for dispersion of pollutants, it said.
A CPCB task force has identified 21 high pollution hotspots in Delhi-NCR and directed the respective municipal corporations to take "focussed actions".
The task force has also asked authorities to carry out inspection in Ghaziabad's Loni Bhopura, from where repeated complaints of violation of pollution control norms have been received, according to minutes of a meeting of the task force held in Delhi Tuesday.
The task force has identified 15 hotspots in Delhi -- Anand Vihar, Bawana, CRRI Mathura Road, DTU, Dr Karni Singh Shooting Range, Dwarka-Sector 8, Jahangirpuri, Mundka, NSIT Dwarka, Narela, Okhla Phase-2, R K Puram, Rohini, Shadipur and Wazirpur.
Many of the hotspots are already experiencing severe pollution levels.
Six hotspots have also been identified in NCR areas -- 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.