An AQI of above 400 is considered severe and it can affect healthy people.
Pollution levels in Delhi continued to remain in the severe category as the 24-hour average air quality index stood at 447 on Saturday, the Central Pollution Control Board said.
However, it improved slightly from severe to very poor as 30 of the 37 monitoring stations recorded the AQI below 400 mark at 6 pm.
Areas that recorded severe AQI are Bawana (406), Jahangirpuri (404), Narela (408), R K Puram (403) and Sonia Vihar (407), according to the CPCB.
The AQI continued to remain in the very poor in Noida (354), Gurugram (353), Faridabad (328), Ghaziabad (315) and Greater Noida (308).
An AQI of above 400 is considered severe and it can affect healthy people and seriously impact those with existing illnesses.
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'.
According to the World Health Organization, a 24-hour average PM 2.5 concentration of up to 15 microgram per cubic metres is considered safe.
The maximum temperature settled at 30.6 degrees Celsius. Partly cloudy sky or shallow fog is expected in the next two-three days. The relative humidity at 5.30 pm was 73 per cent, the weather department said.
The hazardous pollution levels prompted Chief Minister Arvind Kejriwal to announce that primary schools would be closed from Saturday in a bid to protect children.
The final stage of Graded Response Action Plan, including a ban on non-BS VI diesel-run light motor vehicles, has also been enforced. Entry of trucks other than electric and CNG ones in Delhi is banned too. Those carrying essential commodities are exempted.
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