Why did Parts of Mumbai have Very Poor Air Quality Last Week?

By: Rishabh Negi
24 Nov 2021 9:16:15 PM Shoolini University, Solan, Himachal Pradesh

Over the past week, Colaba and Mazagaon in South Mumbai have emerged as the city’s most polluted localities, with the air quality index (AQI) exceeding 330 — indicating “very poor” air quality — as per data from the System of Air Quality and Weather Forecasting And Research (SAFAR) on November 17 and 18. 


Though, today both places show far healthier AQIs at under 90.


SAFAR has a network of 10 monitoring locations across Mumbai.


Colaba’s AQI was 370 on November 17 and 320 on November 18, while Mazagaon recorded AQIs of 331 and 316, falling in the “very poor” category. In comparison, areas further inland in both the eastern and western suburbs of the city recorded “moderate” air quality — Borivali 133, Andheri 140 and Chembur 183.


Dr Gufran Beig, Founder-Project director of SAFAR, told the Indian Express that during the onset of winter, in areas close to the sea such as Colaba, the temperature is always one to two degrees lower than in other areas of the city. But the low pressure in the Arabian Sea is causing the temperature to increase slightly, to the point where the air is becoming just humid enough to hold more particulate matter in place.


The sea salt in water vapour reacts with other pollutants like PM 2.5 and sulphur oxides from vehicles present in the air to create secondary pollutants. 


The sea breeze over Mumbai usually keeps the air clean. But wind speed has been low or stagnant for three days. Thus, emissions from road and metro construction activities and vehicular movement are getting trapped in the air, raising the AQI. A source estimation analysis by SAFAR has found that vehicular emissions are the most significant contributor to the city’s poor air quality.


Other than high on-road vehicular emissions, the seacoast right up to Mazagaon has an increased movement of diesel fume-emitting cargo ships, boats and fishing trawlers — all of which also contribute to the pollutants.


In their bid to get the AQI back on track, the Mumbai municipality had to enforce a ban on vehicle movement and industrial work in the areas. The dispersal of the low pressurising cloud cover has also helped in bringing down the AQI.


Today, the AQI at Colaba and Mazagaon was recorded at 91 and 92, respectively. As a result, all restrictions have been relaxed. However, Citizen Matters reports that the municipal authorities will be enforcing stricter testing and pollution control for vehicles. They will also conduct random checks on factories to determine whether they abide by the electrostatic precipitator recommendations.

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