The 24-hour average Air Quality Index (AQI) stood at 357 at 4 pm, improving from 365 at 4 pm on Thursday. The AQI in Anand Vihar (463) and Ashok Vihar (396) was recorded in the 'severe' category at 6:30 pm, the CPCB data showed.

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 maximum temperature settled at 31.3 degrees Celsius while the minimum temperature was at 14.6 degrees Celsius, one notches below the normal, the weather office said. Relative humidity oscillated between 98 per cent and 48 per cent throughout the day, the weather office said. ?

"It will mainly clear the sky on Saturday. The maximum and minimum temperatures on Friday are likely to hover around 31 and 15 degrees Celsius respectively," an IMD official said. Pollution levels crept up on the night of October 23 amid a drop in temperature and wind speed and due to people bursting firecrackers and a rise in the number of farm fires.

On October 19, the sub-committee of the Commission for Air Quality Management (CAQM) had implemented Stage II of the Graded Response Action Plan (GRAP) — a set of anti-air pollution measures followed in Delhi and its vicinity according to the severity of the situation in the capital.

GRAP's Stage II includes banning the use of coal and firewood in hotels, restaurants and open eateries. The use of diesel generators, except for essential services, is also banned.

GRAP is classified under four stages depending on the air quality in Delhi. Stage I in a case of 'poor' air quality (AQI 201-300), Stage II for 'very poor' air quality, Stage III for 'severe' air quality (AQI 401-450), and Stage IV for 'severe plus' air quality (AQI>450).

If the situation turns 'severe' (Stage III), authorities will enforce a ban on construction and demolition activities in the NCR, except for essential projects (such as railways, metros, airports, ISBTs and national security/defence-related projects of national importance).?

(With PTI Inputs)