Delhi’s air quality on Christmas Day was “very poor” as nine out of 17 stations of the Central Pollution Control Board recorded “severe” air quality after sunset, The Times of India reported on Tuesday. Train and flight operations took a hit on Monday and Tuesday in the national Capital as a result of heavy fog.

An Air Quality Index higher than 400 is classified as “severe”.

The average Air Quality Index on Monday was 372 while the reading was 305 on Sunday, the Hindustan Times reported. The concentration of the particulate matter of diameter less than 2.5 microns – PM2.5 – rose from 226.9 micrograms per cubic metre at 6 am to 268.9 micrograms per cubic metre at 6 pm. Meanwhile, the PM10 concentration surged to 403.6 micrograms per cubic metre at 6 pm from 365.8 micrograms per cubic metre at 6 am.

Weather experts have predicted a clear day on Tuesday, The Times of India reported, adding that minimum and maximum temperatures are expected to be around 7 and 23 degrees Celsius, respectively. However, the air quality is not expected to improve on Tuesday.