Delhi recorded its worst air quality of the season on Monday, with pollution levels inching towards 'severe plus emergency' category due to a change in wind direction and rampant stubble burning in neighbouring states.
The PM2.5 (particles in the air with a diameter of less than 2.5 micrometres) and PM10 concentrations touched 365 and 503 respectively, touching the 'severe-plus emergency' category, according to Central Pollution Control Board data.
PM2.5 levels above 300 and PM10 levels above 430 are considered 'severe-plus emergency' category.
Delhi's overall air quality index on Monday was recorded at 434, which falls in the 'severe' category, a drastic decline from Sunday's 'moderate' level at 171.
An AQI between 0 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'.
In NCR, Faridabad, Ghaziabad, Noida and Greater Noida recorded 'severe' pollution levels while Gurgaon recorded 'very poor' air quality, CPCB data showed.
Officials attributed the sudden deterioration in the air quality to a change in wind direction, which is now blowing from the northwestern region towards Delhi and bringing dust and smoke from stubble burning in neighbouring states with it.
On Sunday, Delhiites breathed the cleanest air in three weeks, according to CPCB data.
The national capital woke up to a thick haze on Monday morning, two days ahead of Diwali, following which, experts have warned, the air quality is likely to worsen further due to local factors.
CPCB chairman S P Singh Parihar said the deterioration of the air quality will continue till Tuesday morning.
"But the good news is that speed of surface wind has improved, which may help in dispersing the pollutants," he said.
The CPCB has called a meeting of transport department to discuss the deteriorating air quality in the national capital.
An official of the Centre-run System of Air Quality Forecasting and Research (SAFAR) said intensified stubble burning is contributing nearly 24 per cent of the air pollution in Delhi.
Another official said if the air quality continues to remain in the 'severe' category for 48 hours, they would consider implementing more regulations.
The SAFAR said Delhi's air quality is expected to deteriorate to 'severe plus emergency' category after Diwali and the air quality 'will be bad on November 8 even if partially toxic crackers are burned compared to last year'.
The Indian Institute of Tropical Meteorology said biomass burning is also contributing to the spike in PM2.5 concentration.
The increase in pollution levels comes despite strict control measures imposed by the government in Delhi.
It had launched an aggressive 10-day 'Clean Air Campaign' on November 1 to monitor and report polluting activities and ordered halting of construction activities and regulating vehicular traffic.
Civil construction has been suspended in Delhi and surrounding areas of the National Capital Region.
All stone crushers and hot mix plants generating dust pollution have also been closed.
The Delhi Pollution Control Committee has directed the transport department and the traffic police to intensify their drive against polluting vehicles until November 10.
Union Environment Minister Harsh Vardhan on Monday said no leniency would be shown to those violating pollution control norms. He again warned that legal action was being initiated against people violating the regulations.
Delhi Chief Minister Arvind Kejriwal has said stubble burning in Punjab is the main reason behind the current cycle of air pollution in Delhi.
On Sunday, Punjab Chief Minister Amarinder Singh termed his claim as 'nonsense'.
But satellite images by NASA on Monday showed a large number of farm fires in Ludhiana, Jalandhar, Sirsa and other areas of Punjab and Haryana.
Enforcement data provided in response to an RTI query by activist Deepak Juneja has showed that despite the Delhi government deregistering 40 lakh old petrol and diesel vehicles to curb air pollution, only 3,196 vehicles have been impounded, which is less than 1 per cent of the total.