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Faster wind speeds, lower stubble burning contribution: Why November has seen better air this year

The average AQI this November – 320 – has also been better than the past two years. In 2020, the average AQI in November was 327, while it was 376 in 2021.

The daily peak contribution of stubble burning to particulate matter in Delhi was 34% on November 3 this year. This is lower than the daily peak of 48% last year, 42% in 2020, and 44% in 2019. (file)

This November, Delhi has seen the lowest number of ‘severe’ air days since 2015.

The average AQI this November – 320 – has also been better than the past two years. In 2020, the average AQI in November was 327, while it was 376 in 2021. The average AQI this November is the second best from 2015 onwards, according to Central Pollution Control Board (CPCB) data. From 2015, a lower average AQI of 312 was recorded only in November 2019.

This year, November has recorded three ‘severe’ air days, when the AQI was between 401 and 500, according to CPCB data. Last year, there were 11 ‘severe’ air days in November, nine in 2020, seven each in 2019, 2017 and 2015, five in 2018, and 10 in 2016.

Data from the SAFAR forecasting system shows the contribution of stubble burning to PM2.5 levels in Delhi has also been lower this year. From October 1 to November 30, the average percentage contribution of biomass burning to PM2.5 levels in Delhi was 10.43% this year, half of around 20.31% recorded last year. This contribution was around 16.20% in 2020, according to figures provided by Gufran Beig, founder and project director, SAFAR.

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The daily peak contribution of stubble burning to particulate matter in Delhi was 34% on November 3 this year. This is lower than the daily peak of 48% last year, 42% in 2020, and 44% in 2019.

Beig pinned the better air quality this November down to a better wind speed. “The surface wind speed remained high and conditions did not turn calm for most of November. With the large-scale circulation associated with the monsoon, for a prolonged period, the local wind speed remained moderate in the Indo Gangetic Plain. This means that dispersion of pollutants happened adequately. Pollutants did not accumulate enough for the AQI to reach the ‘severe’ level on more days. Now, winds are turning calm after about a month or so,” he said.

Beig added that the impact of control measures on air quality is difficult to quantify.

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While figures from the Indian Agricultural Research Institute (IARI) indicate that the paddy stubble burning related fire count has been lower this year when compared to previous years in Punjab and Haryana, scientists said the fire count is yet to be co-related with the figure of the area that has been burnt this year.

From September 15 to November 30, there were 49,922 paddy residue burning events in Punjab, which is the lowest figure from 2018 onwards, according to IARI data. In 2021, the fire count in Punjab was 71,304 till November 30, while it was 79,093 in 2020, and 50,738 in 2019, and 59,695 in 2018. In Haryana as well, the fire count this year till November 30 (3661) is the lowest since 2018. Last year, Haryana recorded a fire count of 6,987.

The IARI bulletins are based on data from NASA satellites. Vinay Sehgal, principal scientist, IARI, said, “By this weekend we will know the final area burnt also. Then, we will be able to compare. The fire count is lower but we don’t know yet if that’s less burning on the ground or if the satellites were not able to capture it. Farmers sometimes burn in the evening, and from around 3 pm to 10 pm, satellites are not around. So, if they are burning at that time, satellites might not be able to pick that up. There is also the effect of cloud cover. There were three such cloudy spells this time when satellites couldn’t detect fires.”

First published on: 30-11-2022 at 21:01 IST
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