After Diwali, Delhi’s Air Is The Cleanest Since 2015, Many Factors Are At Work

There was the cleanest air in the city on Diwali day since 2019.

Delhi’s air quality after Diwali has improved for the first time since 2015. Meanwhile, pollution levels spiked when firecrackers were set off in violation of the Delhi government’s ban following Diwali and the following day.

An AQI (air quality index) of 312 was recorded on Diwali day, while one of 303 was recorded on Tuesday, according to the Central Pollution Control Board (CPCB). Air quality between 301 and 400 is considered extremely poor. This Diwali, the air quality in the city was the cleanest it has been since 2019.

The worst air quality post-Diwali was seen last year, when an AQI of 462 was recorded the day after Diwali, in the ‘severe’ category. As of last year, AQIs on the day after Diwali were 382. Since 2015, the day after Diwali has been characterized as ‘severe’ air quality four times.

It was the weather this time around that influenced the improved air quality. According to Gufran Beig, founder project director at SAFAR, the air quality was improved because the wind speed prevented the accumulation of pollutants and because Diwali was early this year, the temperature remains mild.

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In the early hours of Tuesday morning, the wind speed picked up. Pollutants would normally have accumulated in the early hours when temperatures are cooler, the boundary layer comes down and winds are slower. But the wind speed picked up, accelerating dispersion. Beig said the highest levels of air quality occurred at midnight, but then it improved and settled at 323 in the morning.

As compared to last year, firecracker emissions appear to have been down. While air quality didn’t deteriorate as much as it could have, Beig said it will take a few days to determine how firecrackers contributed to the emissions load.

Since Monday, the burning of crop residue has been low in Punjab and Haryana as well. In Beig’s view, the wind direction in Delhi has not been conducive to transporting smoke from stubble burning from the northwest since the wind has been westerly-southwesterly since Monday. In Delhi, the SAFAR forecasting system indicates that 5.6% of stubble burned to PM2.5 levels on Tuesday. According to SAFAR data, stubble burning contributed 25% to Delhi’s air on Diwali day (November 4) last year, and 36% on the day after Diwali.

Despite their sound, firecrackers may have released fewer toxic fumes so some control measures may have worked, Beig said.

IIT Kanpur professor Sachchida Nand Tripathi also said that meteorology may have been involved. Compared to previous years, crop residue burning has also not intensified. Additionally, lower temperatures would make the boundary layer thinner, making particulate matter difficult to disperse quickly, but strong winds have compensated for this.

It was a combination of factors that caused Diwali to occur early, much earlier than the intense inversion conditions set in, according to Anita Roychowdhury, executive director of research and advocacy at the Centre for Science and Environment. Compared to the past, there have been better winds and crop fires. “It’s hard to say whether firecracker emissions have decreased,” she said.

Between September 15 and October 25, the Indian Agricultural Research Institute recorded 5,798 crop residue burning events in Punjab. Last year, there were 6,134 crops residue burning events by the same date.

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