La Niña Effect Deepens Mumbai’s Post-Monsoon Pollution Crisis

Mumbai’s air quality has taken a sharp downturn since the withdrawal of the monsoon on October 10, marking the beginning of a worrying trend.

Until early October, the city’s Air Quality Index (AQI) remained in double digits, signalling relatively clean air. However, soon after the rains receded, AQI readings surged into the triple digits, revealing a steady decline. On Wednesday, the Central Pollution Control Board (CPCB) recorded Mumbai’s overall AQI at 139 classified as ‘moderate’. Yet, some pockets such as Bandra Kurla Complex (BKC) and Deonar have already slipped into the ‘poor’ category, with readings of 221 and 235, respectively.

Experts point to the onset of La Niña as the primary cause behind this deterioration. La Niña, marked by the cooling of surface waters in the equatorial Pacific Ocean, disrupts atmospheric circulation and reduces wind speed.

This lack of sufficient air movement prevents pollutants from dispersing, trapping them near the ground for longer durations. Coastal cities like Mumbai, which depend on sea breezes to maintain air quality, become particularly vulnerable during such conditions.

According to Gufran Beig, chair professor at the National Institute of Atmospheric Sciences (NIAS), the early arrival of La Niña has slowed wind patterns across the western coast. Similar trends were observed during the 2021–2022 La Niña phase, when Mumbai experienced one of its worst post-monsoon air quality episodes. As winter approaches, experts warn that stagnant air and cooler temperatures may further aggravate pollution levels, pushing AQI readings to alarming highs once again.