Stubble burning worsened Mumbai’s air quality last winter: study | Mumbai news - Hindustan Times
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Stubble burning worsened Mumbai’s air quality last winter: study

BySabah Virani
Feb 19, 2024 05:56 AM IST

Study shows stubble burning in north India worsened Mumbai's air quality. La Nina wind patterns brought pollutants, leading to high PM2.5 levels in the city.

Mumbai: Stubble burning in north India contributed majorly to the poor air quality in Mumbai during the previous winter season, said a new study published in Elsevier’s Science of the Total Environment journal. The study led by Gufran Beig, chair professor, National Institute of Advanced Studies indicates that three continuous years of the La Nina phenomenon distorted wind patterns in 2022-23, blowing northerly winds rich with pollutants from stubble burning towards the city. Frequent spells of calm winds in Mumbai made the pollutants stay in the region for longer, adding to local sources of pollution, the study notes.

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During the period under consideration (October 2022 to January 2023), cities in north India experienced an improvement in air quality, with PM2.5 levels reducing by 33% in Ghaziabad, 30% in Rohtak, 28% in Noida, and 10% in Delhi. But peninsular cities and those on the west coast encountered increased pollution, with PM2.5 levels spiking by 30% in Mumbai, 28% in Coimbatore, 20% in Bengaluru and 12% in Chennai. This was doubly unusual, said the study, as northern cities are generally subjected to pollution from stubble burning, while those on the coast have the natural advantage of the ocean and winds.

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Between November 2022 and January 30, 2023, Mumbai had witnessed 36 days with ‘poor’ AQI, suggesting a sharp uptick in the concentration of airborne pollutants. Such a high number of ‘poor’ air days was not witnessed by the city in at least four years, as per CPCB data. Mumbai had also not seen a single ‘satisfactory’ air day between October 22, 2022 and January 30, 2023. Poor air quality spurred the civic body and state to put in place air pollution mitigation measures in 24 civic wards for the first time.

“The culprit for the unusual trend in air pollution is climate change,” said Beig. “It is the reason why the La Nina phenomenon, which usually lasts between 9 to 12 months, lasted three years and was so intense. It is the reason why the change in the wind direction from stubble burning bypassed northern cities like Delhi, instead blowing to the west-south part of India.”

The polluted winds were trapped in the regions, including coastal Mumbai, and stayed longer along with local pollutants due to the relatively calmer winds, further hiking PM2.5 levels, the study noted.

“Climate change, and the larger climatic phenomenon it causes, can only exacerbate local air pollution sources. Mumbai produces emissions near to that of Delhi, but the persistent La Nina conditions cancelled out the natural advantage the city has due to being on the coast. The pollutants from the north only added to the burden,” said Beig.

He noted that although the air quality was bad in Mumbai this winter, the extent of pollution was lower, which proves their findings. Local sources of pollution within Mumbai had increased due to construction and other emissions at source, he noted.

“The only solution to reducing pollution is tackling it at the source, which include fossil fuel burning, construction activity, digging and so on,” he said.

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