Pune was the only city among four metros which had lower pollution levels this Diwali than last year due to rainfall, according to SAFAR
Diwali 2021 in Delhi. Photo: Vikas Choudhary / CSE Air pollution during the Diwali period in 2021 was higher compared to 2020 in the three metropolitan cities of Delhi, Ahmedabad and Mumbai. The findings were from a multi-year (last four years) analysis done by SAFAR (System of Air Quality and Weather Forecast and Research), under the Union Ministry of Earth Sciences in four cities.
Pune was the only city among the four which had lower pollution levels.
Delhi was the worst among the four as concentration of PM10 and PM2.5 during the Diwali period (five days before and after Diwali) was higher than the last two years and the Air Quality Index (AQI) remained in the ‘severe’ category.
The particulate matter (PM) concentration started to increase from 7 pm onwards on Diwali day (November 4) and reached a peak at 2 am November 5. PM2.5 concentration increased by 3.5 times from 7 pm November 4 to 2 am November 5.
Air pollution was slightly lower in 2018, compared to the 2021 levels.
“The higher concentration of PM during the Diwali period is due to high local emissions, combined with the biomass burning effect. Calm surface winds and moderate mixing layer height lead to poor ventilation resulting in accumulation of pollutants,” according to the analysis.
In Ahmedabad, the air quality was in the ‘poor’ category November 5, with PM2.5 levels reaching 97 µg / m3 (microgramme per cubic metre) which was slightly higher than that observed in 2020 (93 µg / m3 ).
Hourly variation of PM2.5 indicated that the early morning hours of November 5 (from 1 am to 5 am) were the hot spot hours, with AQI levels ranging from ‘very poor’ to ‘severe’.
The 2021 levels in Ahmedabad were also higher than 2018, when the air quality was in the ‘very poor’ category. However, 2019 was the cleanest Diwali in the last four years, with a PM2.5 concentration of 41 µg / m3.
Air pollution levels increased during the 2021 Diwali period in Mumbai, compared to 2019 and 2020. However, the air quality was recorded in the ‘moderate’ category.
“Due to the low-pressure system in the central Arabian sea, light rain was observed over the Mumbai region. These weather conditions worked positively to keep air quality in the satisfactory range,” the analysis said.
The PM10 and PM2.5 concentration in Pune during the Diwali period of 2021 was lower, as compared to 2018 and 2020 due to the rainfall activity over the city. However, the concentration levels in 2021 were higher compared to 2019, even though rainfall was observed during that year too.
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