Delhi's air quality remained stagnant in the "very poor" category on Tuesday, with experts warning that it may deteriorate to "severe" levels in the next 24 hours due to a change in wind patterns.

None of the 39 monitoring stations in the capital recorded the air quality in the "severe" category on Tuesday.

According to data from the Central Pollution Control Board (CPCB), the city's 24-hour average Air Quality Index (AQI) recorded at 4 pm was 343 against 349 the previous day.

The AQI peaked at 419 on November 20 while it was recorded at 371 the next day. On Friday, the air quality level stood at 393, even as it rose to 412 on Saturday and on Sunday, it was 318.

An AQI between 0 and 50 is considered "good", 51-100 "satisfactory", 101-200 "moderate", 201-300 "poor", 301-400 "very poor", 401-450 "severe" and above 450 "severe plus".

Mahesh Palawat, vice-president of Skymet Weather Services, said the air quality might deteriorate in the next 24 hours and fall into the "severe" category again as easterly winds are expected to arrive.

He explained that while there were westerly winds so far, they will now change and the calm easterly winds will contribute to increased pollution.

At 3 pm on Tuesday, the CPCB data indicated that PM2.5 was the primary pollutant, with levels of 143 µg/m³ and PM10 at 325 µg/m³.

These fine particles, particularly PM2.5, pose significant health risks as these can penetrate deep into the lungs and enter the bloodstream.

The Centre's Decision Support System (DSS) for Air Quality Management estimated that 22.2 per cent of Delhi's pollution on Tuesday was due to vehicular emissions. Stubble burning, another major contributor, accounted for 6.9 per cent of the pollution on Monday.

The DSS provides daily estimates for vehicular emissions, while the data on stubble burning is typically available the following day.

Meanwhile, authorities intensified their action against violations of anti-pollution norms, a day after the Supreme Court slammed the Delhi government and police for a "serious lapse" in implementing the restrictions under the fourth stage of the Graded Response Action Plan (GRAP).

A senior police officer said the number of teams deployed to ensure the implementation of the restrictions has been increased, particularly in the border areas.

The city police, in coordination with teams from the Municipal Corporation of Delhi (MCD), transport department and civil defence volunteers, is conducting thorough vehicle checks at the border points.

Another officer mentioned that the local police is working alongside the traffic police to enforce traffic regulations, with challans being issued to violators.

Under the stage 4 of the GRAP, the entry of trucks, except for those run on CNG, electric and BS-VI diesel, is banned in Delhi.

According to the traffic police, more than 1.64 lakh challans amounting to Rs 164 crore were issued in the capital against vehicles lacking valid Pollution Under Control (PUC) certificates from October 1 to November 22.

Police have also impounded 6,531 10-year-old petrol and 15-year-old diesel vehicles this winter season.

Since October 15, a total of 13,762 non-destined trucks approaching Delhi were diverted through the Eastern and Western Peripheral expressways, while the number stood at 2,944 since the implementation of GRAP-4 on November 18.

The maximum temperature was recorded at 26.7 degrees Celsius on Tuesday, while the minimum temperature settled 0.6 notches above normal at 11.9 degrees Celsius. Humidity fluctuated between 81 and 63 per cent during the day.

The weather department has forecast moderate conditions for Wednesday, with the maximum and minimum temperatures likely to hover around 27 degrees Celsius and 11 degrees Celsius respectively.

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