Research nails climate change as cause of poor AQI during 2022 winter

In a first, a scientific research has linked climate change as one of the key triggers for poor air quality recorded in Mumbai during the winter of 2022.

The recently-published study stated that Mumbai’s air faced the worst deterioration in the country—with PM2.5 levels increasing by 30 per cent — last winter, owing to climate change and La Nina phenomenon.

Of the 92 days between November 2022 and January 2023, Mumbai had recorded 66 days of poor air. Even as Mumbai is currently experiencing moderate air quality—overall AQI of Mumbai on Sunday stood at 144 —the study has set off warning bells that last year’s poor AQI could become a regular phenomenon during winters in Mumbai, owing to climatic changes, if “a number of drastic steps are not taken to target the root cause of deteriorating air quality and climate change, that is emissions at the source”.

The paper titled, “Triple dip La-Nina, unorthodox circulation and unusual spin in air quality of India” by scientists from Bangalore’s National Institute of Advanced Studies, Indian Institute of Tropical Meteorology–Pune and Ministry of Environment found that Mumbai, despite its proximity to the sea, saw the worst decline in AQI during 2022 winters, owing to delayed wind reversals from the sea and less frequent calm winds, triggered by La Nina and Climate Change.

Researchers said that while normal wind conditions in Mumbai would have swept away biomass emissions, dust from construction and excavation due to Metro and coastal line work between Oct 22–Jan 23, it was the delayed wind reversals that trapped the pollutants, preventing them from dispersing, thereby leading to spike in AQI levels.

In its ‘Death By Breath’ series, The Indian Express had shed light on how unmonitored construction work and violation of civic mitigation norms had deteriorated the condition of Mumbai’s air quality.

Dr Gufran Beig, senior scientist and an author of the paper, told The Indian Express, “Even though Mumbai has high emissions owing to large scale construction works, the city usually has good air quality due to its geographical advantage. However, last year’s winter proved that this natural advantage can’t be taken for granted. In the previous cycle, La Nina lasted three years, which itself is unprecedented, and because of climate change, Mumbai experienced weather it has not experienced even in the previous La Nina years. We are highly vulnerable to climate change. Climate change was the root cause of polluted air last year. AQI is better this winter but we must be cautious. Since next year too is a La Nina year, Mumbai could experience similar poor air again.”

Published in “Science of the Total Environment”, the paper also revealed that while Mumbai’s air quality underwent the worst deterioration, where PM 2.5 levels increased by 30 per cent, the same factors led to improvement of air in northern states, with Ghaziabad recording the best improvement at 33 per cent, followed by Rohtak at 30 per cent, and despite stubble burning, Delhi’s AQI improved by 10 per cent during 2022-23 winter.

On why Delhi fared better than Mumbai, Beig said, “Our research revealed that the change in La Nina affected wind direction and led to significant intrusion from stubble-induced particulate pollution from Punjab-Haryana to western India via the upper air channel, including Mumbai, which in the usual case, goes to Delhi and surrounding region.”