The Commission for Air Quality Management (CAQM), the government’s air quality panel for the national capital region (NCR) of Delhi, on Monday invoked restrictions under stage three of the Graded Response Action Plan (GRAP) after air quality deteriorated rapidly and could turn to a ‘severe’ category due to unfavourable meteorological conditions.

Delhi’s 24-hour average air quality index (AQI), recorded at 4 p.m. daily, was 379 on Monday and 398 by 9 p.m. The Supreme Court on December 5 allowed relaxations of restrictions GRAP IV, which was implemented from November 18 only after air quality improved.

According to the Central Pollution Control Board data at 9 p.m., as many as 23 out of 37 spots from where data was available had more than 400 AQI, while Anand Vihar had the worst 460, followed by 446 in Rohini, 444 at Wazirpur, 442 at Jahangirpuri and Vivek Vihar, and 441 at Punjabi Bagh.

The GRAP for Delhi-NCR is divided into four stages of air quality: Stage 1 for “poor” Air Quality Index (AQI) between 201 and 300, Stage 2 for “very poor” AQI of 301-400, Stage 3 for “severe” AQI of 401-450, and Stage 4 for “severe plus” AQI more than 450.

At a review meeting, the CAQM noted that Delhi’s AQI breached the 350 mark on Monday afternoon, worsening between 1 p.m. and 4 p.m. It also noted that the AQI may worsen owing to extremely calm wind and the “buildup of an inversion layer adversely affecting the vertical mixing height”, the height above the surface throughout which a pollutant can be dispersed.

Forecasts from the India Meteorological Department and the Indian Institute of Tropical Meteorology also indicate that owing to continued adverse meteorological conditions, the air quality may fluctuate between the higher end of the ‘Very Poor’ to ‘Severe’ category in the coming days.

“Keeping in view the prevailing trend of air quality, and in an effort to prevent further deterioration of air quality in the region, the Sub-Committee today has taken the call to invoke all actions as envisaged under Stage-III of revised GRAP – ‘Severe’ Air Quality (DELHI AQI ranging between 401-450), with immediate effect, in the entire NCR. This is in addition to the actions under in Stages I & II of GRAP already in-force in NCR,” the government said.

According to the revised plan, schools and colleges in Delhi, Gurugram, Faridabad, Ghaziabad and Gautam Budh Nagar must shift classes up to Class V to hybrid mode under GRAP Stage III. Students and parents will have the option to choose online education wherever it is available.

Stage III also bans non-essential diesel-operated medium goods vehicles with BS-IV or older standards within Delhi and non-essential diesel light commercial vehicles of BS-IV or older standards registered outside Delhi.

The Delhi and NCR state governments have also been directed to stagger the opening hours of public offices and municipal bodies under stage III. The Centre may decide on similar staggered opening hours for its offices in Delhi-NCR.