Delhi's air quality dipped to the ''very poor'' category again on Sunday due to an increase in incidents of stubble burning and a change in the wind direction.
The government's air quality monitoring and forecasting service SAFAR said the city's air quality is expected to turn ''severe'' by Tuesday.
The Central Pollution Control Board (CPCB) registered Delhi's air quality index (AQI) at 321 at 4 pm on Sunday, up from Saturday's 283. Most of the 37 air quality monitoring stations in Delhi recorded air quality in the ''very poor'' category.
Neighbouring Greater Noida with an AQI of 347, Ghaziabad (374) and Noida (353) also recorded an increase in pollution levels.
With the winter setting in, a dip in the minimum temperature makes the air cold and heavy leading to accumulation of pollutants close to the ground, the System for Air Quality and Weather Forecasting and Research (SAFAR) said.
It said the boundary-layer winds are northwesterly which are favourable for stubble plume intrusion.
"The only positive factor is the forecast of high local wind speed in Delhi during day hours for efficient ventilation of pollutants, but its accumulation is expected during stable and calm night hours," it said.
An AQI between 201 and 300 is ''poor'', 301-400 ''very poor'' and 401-500 ''severe''. An AQI above 500 falls in the severe plus category.
Meanwhile, Delhi Environment Minister Kailash Gahlot has again urged the neighbouring states to stop stubble burning immediately and expedite distribution of machinery to farmers for in-situ stubble management to ensure that this problem does not recur.
Mr Gahlot raised the issue of stubble burning at a meeting convened by Union Environment Minister Prakash Javadekar on Saturday to review steps taken to combat air pollution. Representatives of Rajasthan, Uttar Pradesh, Haryana and Punjab also attended the meeting.
The Supreme Court had on November 6 ordered the Centre to prepare a comprehensive scheme, in consultation with the states, within three months to wean small and marginal farmers away from stubble burning, which has been identified as a major source of air pollution choking the national capital.
Acting on a slew of directions from the top court, implementing agencies in Delhi have taken "major action" at 13 pollution hot spots in the city, including closing 23 polluting industrial units, over the last three days, officials said on Sunday.
Municipal corporations in the national capital have lifted 400 metric tonnes of construction and demolition waste and 1,200 metric tonnes of garbage during the period, they said.