Overnight rain and high-speed winds helped Mumbai on Tuesday record its lowest pollution levels since air-quality monitoring began in 2015. The air quality index (AQI) equalled the all-time record of the past five years, which was on September 4, 2019.
The pollutant-measuring indicator for PM2.5 pollutant — breathable particulate matter which is 2.5 microns in size or smaller that can cause ailments — was 12, falling under the ‘good’ category, according to the System of Air Quality Weather Forecasting and Research.
It was 13 (good) during the day and improved further by the evening. The AQI has been predicted at 10 for Wednesday.
Mumbai’s air on Tuesday was cleaner than major international cities such as London (21), Tokyo (52), Sydney (25), Singapore (25), but New York’s AQI was better at 10. All 10 locations where AQI is monitored in the city recorded ‘good’ air quality, and AQI levels did not cross 30. Colaba had the cleanest air with an AQI of 2, followed by Mazagaon at 5, Bhandup and Chembur at 8, Borivli 10, BKC 15, Andheri 16, Malad 17, Worli 18, and the highest of 26 at Navi Mumbai.
Researchers from SAFAR said a combination of factors had led to the drop in air quality. “The lockdown period due to the Covid-19 pandemic had already brought down PM concentration to its background levels (concentration without being influenced by human-induced emissions). It takes time for PM levels to rise again even after emissions resurface. Intense rain over Mumbai between Monday night and early Tuesday morning, high moisture content in the city’s air, combined with wind speed up to a maximum of 30kmph, allow swift dispersion of pollutants close to the surface,” said Gufran Beig, director, SAFAR. “This is a characteristic of the monsoon, but it is getting further enhanced due to restrictions in place over the past few months. AQI and PM concentration is likely to remain in the ‘good’ category as rainfall has been predicted in the coming days.” The concentration of PM2.5 was as low as 7 micrograms per cubic metre (µg/m3), against the prescribed limit of 60µg/m3 for 24 hours as national safe standard, and 25 µg/m3 as the World Health Organization (WHO) safe standard. PM2.5 levels are likely to fall further to 6µg/m3 on Wednesday and 10 µg/m3 on Thursday, said SAFAR. PM10 was 14 µg/m3, against the safe limit of 60 µg/m3. It is expected to be 11µg/m3 on Wednesday and 16µg/m3 on Thursday.