Delhi: Grap 4 and anti-pollution curbs in play as AQI hits season’s peak

A thick, grey haze cloaked Delhi on Sunday, smudging out silhouettes as the air quality index (AQI) surged to the season’s highest and sent authorities scrambling to contain the devolving crisis, with the Commission for Air Quality Management (CAQM) ushering in Stage 4 of its pollution control measures that ban all constructions and allow schools to call off classes for most students.
The Capital clocked a 24-hour average AQI of 441 (severe) on Sunday, according to the Central Pollution Control Board’s (CPCB) 4pm bulletin. This was worse than the 417 reading at the same time on Saturday, even as the air quality continued to slide towards the far reaches of the “severe” zone through the evening. At 7pm, the AQI worsened to 457, the worst hourly reading yet this year.
At 12am on Monday, the AQI touched 474. CPCB classifies an AQI over 400 as “severe”.
Weather scientists pinned the deterioration to the increased influx of fumes from farm fires in Punjab, where farmers are ratcheting up blazes to clear out their fields ahead of the winter crop. These thick, black fumes, scientists said, were being swept into Delhi and the National Capital Region (NCR) by strong transport winds and being trapped close to the ground by sluggish surface winds.
AQIs of this level can trigger severe respiratory and cardiac illnesses even in healthy people, while exposing the elderly and immunocompromised to life-threatening hazards, warned experts.
Meanwhile, scientists also warned of the formation of “super fog” around Delhi-NCR, with the India Meteorological Department (IMD) issuing an orange alert for Monday, warning of severely impaired visibility.
CAQM, a central agency tasked with controlling pollution in the National Capital Region (NCR), convened an emergency meeting on Sunday evening as the crisis grew more acute.
Measures under Stage 4 of the Graded Response Action Plan (Grap) will come into effect from 8am on Monday, said the agency, with forecasts predicting no significant change in weather conditions.
Stage 4, the strictest measures under Grap, open the door for state governments to implement the “odd-even” rationing plan for private cars.
That apart, the curbs include a complete ban on all constructions and demolitions, including public projects such as roads, highways, flyovers, overbridges and pipelines; a ban on entry of trucks into Delhi (excluding CNG, BS-6 and electric trucks, and those carrying essential goods); a ban on the entry of light commercial vehicles registered outside Delhi into the capital (excluding CNG, BS-6 and electric trucks, and those carrying essential goods).
Further, the rules say medium and heavy goods vehicles that meet emission standards BS-4 or below are also not allowed into Delhi, unless they are involved in essential or emergency services.
NCR governments can take a call to move lessons for students in classes six to nine and Class 11 online.
The administration can also consider allowing 50% government employees to work from home.
To be sure, all curbs under Grap stages 1, 2 and 3 continue to remain in force.
At 4pm, when CPCB records its official daily AQI reading, 32 of Delhi’s 34 monitoring stations clocked indices in the ‘severe’ category. The highest AQI was 481 (Bawana), followed by 477 at Ashok Vihar. Only two – DTU (399) and Lodhi road (400) were marginally off that mark and in the “very poor” range.
The pollution, combined with dipping temperatures and a soupy smog, hampered visibility across the city all day.
Experts said a weather condition known as “inversion” was at play. This phenomenon is characterised by a layer of warm air sitting on top of cooler air, trapping it. The warm layer tends to lock in the smog. This condition is called inversion because, normally, cool air tends to exist above warm air.
IMD said the lowest visibility on Sunday was 500m at Palam between 8.30am and 9am. It dipped to 300m at 7am at Safdarjung. However, with the sun’s rays not being able to penetrate to the surface, the visibility remained poor throughout the day, touching a maximum of just 900m at Palam (5.30pm) and 800m at Safdarjung (2.30pm).
“The visibility did not rise above 1,000 metres during the day, which is usually when we see some relief through sunshine. In comparison, the highest visibility on Saturday during the day was 2,200 metres. After 6 pm, visibility had started dipping again and was at 600 metres at Palam and 400 metres at Safdarjung,” said an IMD official, adding that winds remained below 6km/hr through the day. “At night, the wind speed was zero.”
Delhi’s minimum temperature on Sunday was 15.9°C, two degrees above normal. However, the maximum was at a season’s low of 27.2°C, a degree below normal.
“Since the sun was not visible, temperature did not rise significantly during the day, leading to a low maximum,” the Met official added, stating mainly smog conditions were seen in the day.
Low temperatures slow down the dispersion of pollutants.
Another key factor impacting Delhi’s air negatively was the intrusion of stubble smoke. Data from the central government’s Decision Support System (DSS) showed the contribution of farm fires to Delhi’s PM 2.5 was 25.10% on Saturday, as transport level winds remained northwesterly.
Strong upper-level northwesterly winds blowing towards the Capital since November 13 have brought in stubble smoke from Punjab and Haryana. This has meant stubble burning has been the largest contributor to Delhi’s PM2.5 levels in this time, which has also coincided with a spell of severe air.
Delhi’s AQI turned “severe” for the first time this season on November 13, on a day when the contribution of farm fires to Delhi’s PM 2.5 concentration was 30.80%, data from the Centre’s Decision Support System (DSS) showed, which calculates the contribution on the basis of the actual farm fire count recorded a day earlier. The average AQI touched 418 (severe) at 4 pm and a high of 454 by 9 pm. The daily contribution has remained over 25% since, with transport-level winds remaining northwesterly.
“Prior to November 13, the wind direction was mainly variable, meaning it kept fluctuating. These last five days, it has consistently been northwesterly, which not only leads to a layer of fog spreading across the Indo-Gangetic plains, but invariably brings smoke from Punjab and Haryana towards Delhi too,” explained Mahesh Palawat, vice president at Skymet meteorology.
The AQI touched 424 (severe) at 4 pm on November 14, on a day the contribution was 33.33%.
The next day, it touched a season high 37.51%, but an increase in local surface winds helped disperse pollutants somewhat.
“These are transport level winds that blow over 5 km. On November 15, we had surface winds pick up, which helped in dispersion, but by the next day, these same surface winds had become calm again,” said Palawat.
The daily contribution was pegged 25.10% on Saturday, with Sunday’s daily contribution to be shared by the DSS on Monday, after analysing the day’s fire count. Palawat says northwesterly winds are expected to continue, meaning farm fires will still remain a factor.
IMD issued an orange alert in place for Monday, warning of dense to very dense fog in the early hours of the day, followed by smog throughout the day.