Authorities on Saturday said Delhi’s air quality level was in the “very poor” category and is likely to worsen to the “severe” level on Sunday because of the decreasing temperatures. The Central Pollution Control Board and the Centre-run System of Air Quality and Weather Forecasting and Research, known as Safar, pegged the overall air quality index at 389 and 369, PTI reported.

An Air Quality Index 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 pollution control board, 15 areas in the national Capital recorded “severe” air quality, while 21 areas recorded in the “very poor” category. “Air quality over Delhi is very poor which may improve slightly as winds are relatively high during day but predicted to deteriorate by tomorrow as winds speed is unlikely to remain the same and other meteorological conditions are already not favourable,” Safar said. “Cold wave conditions are likely to persist at least for next 2 days.”

Delhi recorded the coldest December day on Saturday as minimum temperature dropped to 2.6 degrees Celsius. The visibility on Saturday morning was 1,500 metres in most parts of the national Capital, an unidentified official of the India Meteorological Department said. Visibility in Palam dropped to 800 metres.

The air quality levels have been fluctuating between the “severe” and “very poor” levels over the last 10 days. On December 23, air quality level index was recorded at 450, the second-worst pollution level recorded so far this year.