A thick layer of toxic smog enveloped the national capital on Saturday as air quality deteriorated sharply, prompting the Commission for Air Quality Management (CAQM) to invoke the strictest curbs under Stage IV of the Graded Response Action Plan (GRAP) across Delhi-NCR.
The 24-hour average Air Quality Index (AQI) stood at 431, slipping into the 'severe' category and marking the worst air quality recorded so far this year, according to the Central Pollution Control Board (CPCB).
This surpassed the previous high of 428 recorded on November 11. The Air Quality Early Warning System also predicted 'severe' air quality to persist on Sunday.
Earlier in the day, the CAQM's Sub-Committee on GRAP had decided to enforce Stage III measures across the NCR.
However, noting a further sharp rise in pollution levels, it convened an urgent meeting at 6.30 pm to review the situation and weather forecasts by the India Meteorological Department (IMD) and the Indian Institute of Tropical Meteorology (IITM), and subsequently invoked Stage IV with immediate effect.
Delhi's AQI, which stood at 401 at 10 am, continued to rise steadily due to very low wind speeds, a stable atmosphere and unfavourable meteorological conditions that prevented dispersion of pollutants. It climbed to 431 at 4 pm, 436 at 5 pm, 441 at 6 pm and 448 at 7 pm, the panel said, adding that calm winds and mist or haze during the night were likely to further trap pollutants over the region.
Among Delhi-NCR cities, Delhi recorded the third worst AQI after Noida (455) and Greater Noida (442).
In the morning hours, 21 monitoring stations in Delhi reported 'severe' air quality, with Wazirpur (445), Vivek Vihar (444) and Jahangirpuri (442) recording the highest levels.
Stage IV of GRAP brings the toughest restrictions, including a complete ban on all construction and demolition activities, even linear public projects such as highways, roads, flyovers, power transmission lines and telecom works.
The entry of trucks into Delhi is barred, except those carrying essential commodities or providing essential services, though CNG, LNG, electric and BS-VI diesel trucks are allowed.
The plying of Delhi-registered diesel heavy goods vehicles of BS-IV and below norms has also been prohibited, barring those involved in essential services.
Schools have been directed to run classes in a hybrid mode for students from primary classes to Classes VI-IX and XI in Delhi and the most affected NCR districts, with the option of online attendance where feasible.
State governments have been asked to consider additional emergency measures, including the closure of colleges and educational institutions, shutting non-essential commercial activities and implementing odd-even vehicle rules if the situation worsens further.
According to the Decision Support System for Air Quality Management, Delhi's pollution load was led by the transport sector, contributing 14.2 per cent, followed by industries in Delhi and its periphery at 6.8 per cent.
Ghaziabad emerged as a major contributor among neighbouring NCR cities with 13.7 per cent, followed by Baghpat (9.8 per cent) and Gautam Buddh Nagar (7.6 per cent).
The Air Quality Early Warning System said conditions remained unfavourable for pollutant dispersion, with the ventilation index below 6,000 square metres per second and average wind speeds of less than 10 kmph.
On the weather front, Delhi recorded a maximum temperature of 25.5 degrees Celsius on Saturday, 2.5 notches above normal, while the minimum settled at 8 degrees Celsius, 0.6 notch below normal.
The IMD has forecast moderate fog on Sunday, with temperatures expected to range between 10 and 24 degrees Celsius, a combination likely to further aggravate pollution levels.