The national capital recorded its air quality in the very poor category on Friday morning, and it is likely to enter the "severe" zone on Diwali night.
The city recorded an air quality index (AQI) of 330 at 9 am. The 24-hour average AQI was 314 on Thursday.
The neighbouring cities of Faridabad (327), Ghaziabad (360), Noida (331), Greater Noida (329), and Gurgaon (328), which fall in the National Capital Region (NCR), also recorded their AQI is the "very poor" category.
An official of the India Meteorological Department (IMD) said the air quality is likely to deteriorate marginally during the day.
The IMD said a fresh western disturbance is likely to increase the wind speed and improve the air quality in Delhi-NCR post Diwali.
Light rain is likely on Sunday under the influence of a western disturbance. It is still to be seen if it is enough to wash away pollutants, Kuldeep Srivastava, the head of the IMD's regional forecasting centre said.
However, Delhi-NCR's air quality is likely to improve post Diwali due to an increase in the wind speed. On Sunday, the maximum wind speed is expected to be around 12 to 15 kilometers per hour, he said.
V K Soni, the head of the IMD's environment research centre, said calm winds and firecracker emissions may push the air quality to the severe zone on Diwali night.
The wind speed is expected to pick up thereafter and the wind direction will be east-southeasterly, he said.
There will be a significant improvement in air quality by November 16, Soni said.
The Ministry of Earth Sciences' air quality monitor, SAFAR, said the PM2.5 concentration in Delhi on Diwali is likely to be the lowest in the last four years if no firecrackers are burnt.
It said pollution levels in Delhi during the Diwali period are likely to remain in the higher end of the very poor category in the absence of emissions due to fireworks.
SAFAR said stubble burning-induced impact on AQI is expected to increase from negligible to moderate in the next two days.
A spike in PM2.5 in the wee hours of November 15 is likely in case of fire-related emissions, it said.
The Central Pollution Control Board (CPCB) had on Wednesday ordered closure of hot mix plants and stone crushers in Delhi-NCR till November 17 in view of a likely increase in pollution levels during the festive season.
It also asked the governments of Punjab and Haryana to take immediate stringent actions to curb stubble burning and authorities in Delhi-NCR to strictly check biomass burning.
