Brought in winds from stubble burning regions in the north, says study
The PM2.5 levels in Mumbai air have increased significantly. File Photo/Shadab Khan
A recent study conducted by a team of scientists from the National Institute of Advanced Studies (NIAS) and the Indian Institute of Tropical Meteorology (IITM) revealed a contrasting trend in air quality among Indian cities in 2022-23. While North Indian cities like Ghaziabad, Noida, and Delhi witnessed a relative improvement in air quality, Mumbai experienced a significant deterioration, marked by a 30 per cent increase in PM2.5 levels. This shift has been attributed to climate change, according to the study.
The study—titled 'Triple dip La-Nina, unorthodox circulation and unusual spin in the air quality of India'—was published in Elsevier's international journal, ‘Science of the Total Environment’. It suggests the dominance of higher northerly winds at the transport level, forcing an influx, and relatively slower winds near the surface, trapping pollutants in peninsular India, thereby notably increasing PM2.5 concentration.
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Simplifying this, Dr Gufran Beig, the lead author of the study and former director of System of Air Quality and Weather Forecasting And Research (SAFAR), said, “The impact of stubble burning in the north is due to transport-level winds, which are normally towards Delhi and worsen air quality there. Now, those winds with PM2.5, which are 1 km above the surface, surpassed Delhi and impacted more of the peninsular India, which is unique for those years. So, stubble burning's impact in Delhi was minimal, but it significantly impacted Mumbai and other places.”
Usually, when these winds reach Delhi, due to its close proximity to the stubble-burning regions, the air quality worsens to hazardous levels. While the impact of these winds towards Mumbai and other peninsula regions was not as bad as what it is in Delhi, it was significant enough to cause a dent in the air quality. Moreover, the natural benefits in air quality control that coastal cities like Mumbai enjoy due to their close oceans were also minimised by these winds from the northern parts of the country, the study explained.
For Delhi and other cities in the north, it didn't matter that westerly disturbances—which bring about rainfall in the winter months, helping as a natural pollution control measure—were too feeble as the air quality improved regardless. However, the same lack of westerly disturbances contributed to poor air in the peninsular region. Mumbai saw the worst deterioration in air quality, followed by an increase in PM2.5 levels by Coimbatore (28 per cent), Bengaluru (20 per cent), and Chennai (12 per cent).
Among the North Indian cities, Ghaziabad registered the most significant improvement with a reduction of 33 per cent PM2.0 levels, followed by Rohtak (30 per cent) and Noida (28 per cent). Delhi, the most critical and landlocked city, registered an improvement of around 10 per cent.
La Niña effect
These changes in the weather patterns were attributed to a triple dip in the La Niña event from 2020 to 2023. Other triple-dip La Niña events recorded since 1950 were in 1998-2001, 1973-1976, and 1954-1956.
“Even as such dips have happened not too long ago, their severity matters. So what we are saying is that the severity brought about by the recent dip was because of climate change,” Dr Beig said.
La Niña is when cooler-than-average sea surface temperatures are recorded in the central and eastern Pacific Ocean, often leading to weather patterns such as increased rainfall in some regions and droughts in others. “This is a normal phenomenon that lasts about nine to twelve months. The wind changes but the impact does not affect air quality,” Dr Beig said.
The root cause of air pollution and climate change, which impacts human health and food security adversely, is the increasing emissions of chemical constituents which include fossil fuels and bio-fuels, from industries and thermal power plants, among other emission sources. This is also true for Mumbai.
“Such episodes, in all probability, are set to increase by leaps and bounds if a number of drastic steps are not taken to target the root cause of deteriorating air quality and climate change,” the study concludes.
10%
Level of improvement in Delhi air
A recent study
'Such episodes, in all probability, are set to increase by leaps and bounds if a number of drastic steps are not taken to target the root cause of deteriorating air quality and climate change’
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