MUMBAI: A thick layer of haze hung over Mumbai on Saturday as the city’s air quality deteriorated, with the overall Air Quality Index (AQI) rising to 120 from 101 (moderate) a day earlier, according to the Central Pollution Control Board’s (CPCB) Sameer app. The worsening conditions were particularly evident in some neighbourhoods, where readings on different monitoring platforms crossed 200, falling in the poor category.

The city’s coastal location usually helps disperse pollutants, but weakening winds and unfavourable atmospheric conditions have allowed them to accumulate, leaving a layer of haze over Mumbai. Experts expect the conditions to persist for another two days, with some improvement likely around October 27.

Of the 24 active monitoring stations across Mumbai, 17 recorded AQI levels in the moderate category on Saturday. Malad West recorded the highest reading at 171, while Ghatkopar reported the lowest at 54, according to the Sameer app.

However, readings varied considerably across monitoring platforms, highlighting differences in the air quality reported across the city. AQI.in recorded an AQI of 206 in Andheri and 197 in Bandra West, while IQAir reported 193 in Borivali and 189 in Bandra-Kurla Complex (BKC). Under the CPCB’s national AQI classification, readings between 201 and 300 fall in the poor category, while those between 101 and 200 are classified as moderate.

Gufran Beig, chair professor at the National Institute of Advanced Studies on the IISc campus, said Mumbai’s coastal location generally works in its favour by allowing pollutants to disperse. However, this advantage diminishes when wind speeds weaken and atmospheric conditions do not support the movement of pollutants.

The lack of sufficient vertical movement in the atmosphere, combined with weak winds, is preventing pollutants from dispersing and leaving them suspended over the city. An India Meteorological Department (IMD) scientist said the conditions were likely to remain similar over the next two days, with a change expected as wind movement strengthens and helps disperse the accumulated pollutants.

“Slow wind speed and lower temperatures [in the winter months] lead to stagnation of pollutants, resulting in higher concentrations, which is the reason for hazy skies in Mumbai,” said Sunil Dahiya, founder and lead analyst at Envirocatalysts, a think tank.

The CPCB’s Sameer app recorded Mumbai’s overall AQI at 120 on Saturday. In comparison, AQI.in reported a reading of 192, alongside PM2.5 concentrations of 114 micrograms per cubic metre and PM10 concentrations of 133 micrograms per cubic metre. The platform also showed readings across the city in the moderate and poor categories.