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Monday, November 29, 2021

Day after Diwali: crackers, farm fires, N-W winds turn Delhi air ‘severe’

Levels of pollutants rose sharply from Thursday night onwards, data from the Delhi Pollution Control Committee (DPCC) indicates. At the Jawaharlal Nehru Stadium station for instance, PM2.5 levels increased from 389 µg/m3 at 8 pm Thursday to a high of 1,553 µg/m3 at 1 am on Friday.

By: Express News Service | New Delhi |
Updated: November 6, 2021 3:38:13 am
Delhi smog, Delhi firecrackers pollution, Delhi pollution after Diwali, Delhi Diwali pollution, Delhi AQI, Delhi News, Delhi latest news, Indian Express newsNew Delhi: Vehicles ply amid low visibility due to a thick layer of smog, a day after Diwali celebrations in New Delhi, Friday, Nov. 5, 2021. (PTI)

Delhi’s air quality plummeted to the ‘severe’ category for the first time this season on Friday, the day after Diwali when the city saw widespread violation of the ban on firecrackers. Experts also pointed to an increase in stubble burning — its share in Delhi’s pollution was 36% on Friday — and winds from the northwest that brought pollutants to the city’s air.

The air quality index (AQI) as a 24-hour average for Delhi was 462, with PM2.5 being the main pollutant, according to a bulletin issued by the Central Pollution Control Board (CPCB) at 4 pm. The NCR cities of Noida (475), Gurgaon (472), Ghaziabad (470), Faridabad (469), and Greater Noida (464) fared worse.

AQI between 401 and 500 is considered ‘severe’.

In New Delhi, a day after Diwali. (Credit: Praveen Khanna)

For Delhi, the day-after-Diwali AQI was the worst since 2016, when the index read 445. In 2017, 2018, 2019, and 2020, the 24-hour average AQI on the day after Diwali was 403, 390, 368, and 435 respectively.

Data from the Delhi Pollution Control Committee (DPCC) showed a dramatic increase in the level of pollutants on Thursday night and in the early hours of Friday. The wind speed picked up later on Friday, helping to disperse the pollutants.

The PM2.5 level at the Jawaharlal Nehru Stadium monitoring station peaked at 1,553 µg/m3 at 1 am on Friday, which was almost 26 times the standard value of 60 µg/m3. This figure fell to 249 µg/m3 by 4 pm.

PM10 levels peaked at 1,643 µg/m3 around the same time at the station, and had fallen to 342 µg/m3 by 4 pm on Friday. The standard value for PM10 is 100 µg/m3.

The PM2.5 level on the day after Diwali was higher this year than in both 2020 and 2019, according to data from SAFAR. Last year, the PM2.5 average on the day after Diwali was 298 µg/m3; in 2019 it was 377 µg/m3.

On Friday, the PM2.5 level was 457 µg/m3 at 10 am, and 435 µg/m3 at 6 pm. This was lower than the 624 µg/m3 figure recorded in 2018.

The peak of the stubble-burning contribution to pollutants in Delhi appears to have coincided with Diwali firecrackers this year, which explains the higher figures compared to the last two years, Gufran Beig, the founder project director of SAFAR, said. This is what had happened in 2018 as well, Beig pointed out.

While stubble-burning contributed around 36% to PM2.5 levels on Friday, firecracker emissions contributed around 30%-35%, Beig said.

Air quality in Delhi had been in the ‘very poor’ category since November 2, two days before Diwali. A SAFAR update on Friday said firecracker emissions had degraded the air quality from the ‘very poor’ to the ‘severe’ category. In an earlier forecast, SAFAR had said that even half the firecracker emissions of 2019 could lead to air quality falling to the ‘severe’ category post-Diwali.

When Delhi recorded its first ‘very poor’ air day on November 2, the share of farm fires in pollutants in Delhi was only 6%, and local sources contributed the major chunk of pollutants. However, the contribution of stubble burning to PM2.5 levels rose steeply from 8% on Wednesday to 25% on Thursday, and peaked at 36% on Friday, according to the SAFAR forecasting system.

The wind direction on Friday was mostly from the northwest of Delhi, making it conducive for the transport of pollutants from areas where crop residue is being burnt.

The Air Quality Early Warning System for Delhi attributed the deterioration in air quality to the contribution of firecrackers, biomass burning, and weather conditions. If strong winds disperse the pollutants, AQI could improve to the ‘very poor’ category over the weekend.

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