Updated: November 12, 2021 10:36:09 pm
With the air quality index in Delhi hitting this season’s highest figure of 471 on Friday, authorities have advised that government and private offices and other establishments reduce vehicle usage by at least 30% and outdoor activities be limited.
The AQI has reached the upper end of the ‘severe’ category, going by the Central Pollution Control Board’s 4 pm bulletin. This is worse than what was seen on November 5, the day after Diwali, when an AQI of 462 was recorded.
As per an order issued by Prashant Gargava, chairperson of the sub-committee on the Graded Response Action Plan (GRAP), people are advised to limit outdoor activities and minimise their exposure while government and private offices and other establishments have been advised to “reduce vehicle usage by at least 30%”.
The sub-committee, which met Friday, also said in its order, “Concerned states and implementing agencies must be in complete readiness for implementation of measures under ‘emergency’ category as per GRAP.”
Measures under the emergency category are implemented when the PM 2.5 level is 300 µg/m3 or more, and PM 10 concentration is 500 µg/m3 or more, for 48 hours or above. According to the minutes of the sub-committee meeting, PM 10 and PM 2.5 levels crossed this threshold at 3 am and 1 am respectively on Friday.
Emergency measures include stopping construction activities, introducing the odd-even scheme for private vehicles, and stopping the entry of trucks into Delhi, except for essentials.
Going by the minutes of the meeting, IMD scientist V K Soni told the sub-committee that meteorological conditions would be highly unfavourable for dispersion of pollutants till November 18 due to low wind speed and calm conditions at night. Increased instances of stubble burning and northwesterly winds mean that the contribution of stubble burning to pollution is likely to remain high.
Average PM 2.5 concentration at 6 pm Friday was 354 µg/m3, while the PM 10 level at the same time was 559 µg/m3, according to figures provided by Gufran Beig, founder project director, SAFAR. These figures are well above the threshold for the ‘emergency’ category under GRAP.
According to the SAFAR forecasting system, the contribution of crop residue burning to PM 2.5 levels was 35% on Friday, lower than the peak of 48% recorded on November 7. But the magnitude of this contribution remains high since the PM 2.5 levels are high, Beig said.
While PM 2.5 is usually seen as the main pollutant from crop residue burning, PM 10 is also becoming the lead pollutant now, Beig noted.
“This could be because the PM 2.5 particles are growing in size. Since there is a continuous flow of particles, humidity levels are high at night, and water sprinkling also increases the holding capacity of the air, PM 2.5 particles are growing towards PM 10. High fire counts over the past seven days and favourable conditions for transport of pollutants translate to a continuous flow of particulate matter. If there was no continuous flow, PM 2.5 particles would have died down in two or three days before it can convert to bigger particles,” Beig said.
He attributed the pollution levels to calm conditions combined with high fire counts: “Usually, by this time of the year, when temperature goes down further, the fire count starts going down. As the temperature cools, calm conditions start prevailing. If there is stubble burning at this point, it is more dangerous than it can be in warmer temperatures.”
Minimum temperature on Friday hit this season’s lowest so far at 12.6 degree Celsius, and is likely to fall further to around 10 degree Celsius by November 17, according to the IMD.
Drop in minimum temperature, increase in fire counts, and favourable wind speed and direction could keep the AQI in the ‘severe’ or upper end of the ‘very poor’ category for the next two days, according to the SAFAR system on Friday.
Data from the Delhi Pollution Control Committee indicates that PM 10 levels at Anand Vihar spiked at 10 am Friday to hit 1,153 µg/m3, against a standard of 100 µg/m3. Similarly, at Okhla Phase 2, PM 10 levels hit 1,081 µg/m3 at 10 am.
According to the WHO, PM 10 can penetrate and lodge deep inside the lungs, while PM 2.5 can penetrate the lung barrier and enter the blood system. “Chronic exposure to particles contributes to the risk of developing cardiovascular and respiratory diseases,” as per the WHO.
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