Delhi’s air quality deteriorated on Monday morning and remained in the “very poor” category with a hazy sky. The odd-even road rationing plan, which intends to curb pollution by reducing the number of vehicles on roads, will be relaxed on Monday and Tuesday due to a festival.

At 10 am, the 24-hour-average air quality index in the city was 331, a tad higher compared to 321 on Sunday evening, according to the Central Pollution Control Board. Out of the 37 monitoring stations whose readings are used by the board, Rohini, at 380, recorded the worst level at 10 am, followed by Bawana at 375.

In several localities, the 24-hourly index is likely to slip significantly during the day as the pollutants PM10 and PM2.5 have deteriorated to the worst possible level of 500 in the last few hours.

An index reading between 0 to 50 is considered “good”, 50 to 100 “satisfactory”, 100 to 200 “moderate”, 200 to 300 “poor”, 300 to 400 “very poor” and 400 to 500 “severe”.

On Friday, Chief Minister Arvind Kejriwal announced that there will be no odd-even restrictions on vehicles on November 11 and 12 due to Guru Nanak Dev’s 550th birth anniversary falling on the second day. The road rationing system is being implemented from November 4 to November 15 but may be extended if pollution levels remain high. It prohibits plying of vehicles based on the last digit of their registration numbers – vehicles with odd digits are only allowed to ply on odd days, and cars with even numbers on even days.

The share of stubble burning in Delhi’s pollution is expected to increase, according to the Centre-run SAFAR, or System of Air Quality and Weather Forecasting And Research. The number of stubble fires increased from 415 on November 8 to 1,882 the next day.

Also read: Explainer: Why does the same part of Delhi show different Air Quality readings at the same time?