The air pollution in Delhi deteriorated on Friday afternoon to “very poor” from “poor” levels the previous day.

The Air Quality Index was recorded at 357 at 1 pm on Friday, according to the Central Pollution Control Board. An index value between 201 and 300 is categorised “poor”, a value between 301 and 400 is “very poor”, and higher values are categorised as “severe”.

Asthmatics and those prone to dust allergies have been advised to keep medication handy and stay indoors. The advisory was issued on the website of the Centre-run System of Air Quality and Weather Forecasting.

Lower wind speed compared to last week was the cause of the rise in pollution, said the Central Pollution Control Board, adding that rainfall forecast in the next couple of days might reduce pollution.

Delhi’s PM 2.5 level, which measures the amount of fine particulate matter of a diameter of 2.5 micrometres in the air, was recorded at 247, while the PM 10 level stood at 396, PTI reported, citing data released by the pollution control board. Both these levels are in the “very poor” category

The air quality index was “severe” in areas such as Mundka, ITO and Nehru Nagar, while 30 places in the city recorded “very poor” air quality, the board said.

Noida, Ghaziabad and Faridabad in the National Capital Region did not fare any better than Delhi. But Gurgaon was better off, with air quality in the “poor” category.