NEW DELHI: Delhi's air quality deteriorated sharply on Monday to fall in the severe category for the second time within a week due to a change in wind direction and rampant stubble burning in neighbouring states, authorities said.
The overall air quality index on Monday was registered in the severe category at 418, a drastic decline from a day before when the AQI was moderate at 171.
A thick haze has engulfed the national capital two days ahead of Diwali, following which, experts have warned, the air quality is likely to worsen further due to local factors.
On Sunday, Delhiites had breathed the cleanest air in three weeks, according to Central Pollution Control Board data.
The air quality turned severe for the first time this season on October 30.
Also, the PM2.5 (particles in the air with a diameter of less than 2.5 micrometres) and PM10 concentrations spiked to 'severe-plus emergency' category at 361 and 500 respectively, according to CPCB data.
Officials attributed the sudden deterioration to a change in wind direction, now blowing from the northwestern region towards Delhi, bring with it dust and smoke from stubble burning in neighbouring states.
An official with the Centre-run System of Air Quality Forecasting and Research said intensified stubble burning is presently contributing nearly 24 per cent of the air pollution in the national capital.
The Indian Institute of Tropical Meteorology, too, said the increase in PM2.5 concentration is due to a change in the wind direction and because of contribution from biomass burning.
The increase in pollution levels comes despite strict control measures imposed by the government in Delhi.
It has launched an aggressive 10-day 'Clean Air Campaign' from 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 said Monday that no leniency would be shown to those who are violating pollution-control norms.
He again warned that legal actions were being initiated against people violating regulations.
Delhi Chief Minister Arvind Kejriwal has blamed stubble burning in Punjab as the main reason behind the current cycle of air pollution in Delhi.
On Sunday, Punjab Chief Minister Amarinder Singh termed his claim "nonsense".
But NASA registered a large number of fire counts in Ludhiana, Jalandhar, Sirsa and other areas of Punjab and Haryana.
Also, enforcement data provide in response to an RTI query by activist Deepak Juneja has showed that despite the Delhi government deregistering 40 lakh old vehicles to curb air pollution, only 3,196 vehicles have been impounded, which is less than 1 per cent of the total.
Two agencies are responsible for enforcing the ban on 15-year old petrol vehicles and 10-year old diesel vehicles imposed by the National Green Tribunal in 2014, Delhi traffic police and transport department of the Delhi government.