Why Mumbai’s air worsens as Delhi’s improves

Air pollution levels in Mumbai deteriorated even as Delhi’s air became marginally cleaner

Air pollution levels in Mumbai deteriorated even as Delhi’s air became marginally cleaner on Wednesday. The pollutant-measuring indicator – Air Quality Index (AQI) – recorded the city’s air at 242, falling under the ‘poor’ category, compared to 239 on Tuesday evening. Pollution levels fell from 500+ (severe) on Monday in Delhi to 460 (severe) on Tuesday and 397 (very poor) on Wednesday.

An AQI of 243 (poor) was predicted by the System of Air Quality Weather Forecasting and Research (SAFAR) for Thursday. (HT File Photo)

Officials from the weather bureau said a ridge line – a high pressure area – has developed 300 km north of Mumbai, a common phenomenon during winters, which pushed pollutants over the city.

“Mumbai is in the range of subsidence, wherein the pollution emanating from this ridge line is not ventilated properly. Owing to low temperatures, these pollutants are trapped closer to the surface,” said Biswajit Mukhopadhyay, additional director general, India Meteorological Department. “However, Mumbai being a coastal city, pollution levels will remain at this level as westerly winds from the sea will help dilute the trapped pollutants,” he added.

AQI levels between 201-300 falls under the ‘poor’ category and 301-400 is ‘very poor’, indicating a health risk for people sensitive to air pollution and 400+ is ‘severe’ – a health alert for everyone.

An AQI of 243 (poor) was predicted by the System of Air Quality Weather Forecasting and Research (SAFAR) for Thursday.

Meanwhile, night temperatures at the Santacruz weather station, representative of Mumbai, increased from 16.7 degrees Celsius, 5.2 degree Celsius below normal on Tuesday morning to 17 degrees Celsius, 4.9 degree Celsius below normal on Wednesday. Tuesday’s temperature was the lowest November minimum temperature since 2013. However, day temperatures over Mumbai and the night temperature at south Mumbai were closer to normal levels.

On Wednesday, Bandra Kurla Complex (BKC) was the most polluted location with an AQI of 303 (very poor). Worli was the cleanest, with an AQI of 194 (moderate). Eight of 10 locations in Mumbai fell under the ‘poor’ category.