City breathes cleanest air of the year, AQI drops to 28
The city recorded its cleanest air day during the lockdown period and this year so far on Wednesday with the air quality index (AQI) for PM2.5 - a breathable particulate matter of 2.5 micron or lesser - dropping to 28, falling under the ‘good’ category.
According to the System of Air Quality Weather Forecasting and Research (SAFAR), the AQI on Tuesday was 56 (satisfactory) and had shot up to 90 (satisfactory) on Sunday. Wednesday’s AQI however, increased to 32 (good) by the evening. Eight of 10 locations recorded ‘good’ air quality with only Worli and Mazagaon recording ‘satisfactory’ levels. Even the AQI published by the Central Pollution Control Board on Wednesday was 48, falling under the ‘good’ category.
The improvement in air quality was attributed to a marginal increase in wind speed and changing weather conditions influenced by the severe tropical cyclone Amphan over the east coast, said SAFAR researchers.
“The effect of the cyclone has an impact over the west coast and allows the increase in wind speed or sea breeze (westerly winds) temporarily,” said Gufran Beig, director, SAFAR adding that the AQI was likely to rise to 43 (good). “Combined with this high moisture incursions due to warm weather enhances the pollutant carrying capacity, and marginally high wind speed disperses this layer faster.”
The wind speed started increasing from Tuesday morning 4 knots (7.4 km/h) to 5 knots (9.2 km/h) by the evening and continued to be 4 knots through Wednesday at the Santacruz weather station while it ranged between 2 and 3 knots at Colaba, according to the India Meteorological Department (IMD).
“Cyclones do impact wind pattern and weather conditions in the influential radius of a 1,000 km or more and leads to northwesterly winds for peninsular India at a marginally higher speed. However, one has to check the data for Mumbai to see if this is the case,” said B Mukhopadhyay, former additional director-general of the meteorology of IMD, Pune.
Independent meteorologists said cyclone Amphan was too far from Mumbai for causing any prominent enhancement of surface wind speed for Mumbai. “However, surface winds have been persistently from the west due to the cyclone, which along with the lowdown effect has drastically improved the city’s air quality. The air quality worsens when the surface wind is from other direction such as the east,” said Akshay Deoaras, independent meteorologist and PhD researcher at the University of Reading, UK.