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City breathes cleaner air; AQI drop is rare in Dec, say experts

By HT Correspondent, Mumbai
PUBLISHED ON DEC 04, 2019 12:28 AM IST

The city recorded a considerable drop in pollution levels on Tuesday, a rarity in December, according to experts.

The air quality index (AQI) for PM2.5 – 2.5-micron particulate matter which can easily enter lungs and cause ailments – fell from 144 (moderate) on Monday to 95 (satisfactory) on Tuesday morning and further dropped to 91 (satisfactory) by evening, according to the System of Air Quality Weather Forecasting and Research (SAFAR). PM10 – larger coarser 10-micron particles – were still in the moderate category (104). SAFAR researchers said the last time the AQI dropped below 100 (43) in December was when Cyclone Ockhi had brushed past Mumbai’s coast in 2017. “Rise in temperature combined with sudden rise in average wind speed, identified as gusts, allowed pollutants to disperse and reduced pollution levels in Mumbai on Tuesday,” said Dr Utkarsh Mukkannawar, scientist, SAFAR, adding while the average wind speed was 16 km/hour, sudden bursts ranged between 23-24 km/hour.

Even the AQI recorded by the Central Pollution Control Board (CPCB) fell from 151 (moderate) on Monday to 104 (moderate) on Tuesday. SAFAR and CPCB categorise AQI for pollutants in the 0-50 range as good; 51-100 as satisfactory; 101-200 as moderate; 201-300 as poor; 301-400 as very poor and above 400 as severe.

The weather bureau said the Arabian Sea was currently active with a number of weather systems affecting the wind and overall weather pattern over the west coast. “A low-pressure weather system over southeast Arabian Sea, off the Karnataka coast, is allowing an increase in cloud cover over the entire west coast and also leading to a change in wind pattern. This has helped improve the air quality too,” said SG Kamble, scientist, India Meteorological Department, Mumbai.

Independent meteorologists said there were three active weather systems in the Indian Ocean – a tropical depression formed off the coast of Somalia, which is expected to intensify into a tropical storm and move away from the Indian coastline, another system to the north of Madagascar, and the third one near the Karnataka coast. “The system offshore Karnataka will disintegrate by Wednesday. However, under its influence, cloud cover and drizzle are possible over western Maharashtra, including Mumbai, Pune, Nashik and other areas of the Konkan coast, and adjoining parts of central Maharashtra. However, dry weather is expected from Thursday onwards,” said Akshay Deoras, meteorologist and PhD researcher, University of Reading, UK.

Private weather forecasting agency Skymet predicted light rain for Tuesday and Wednesday. “The low-pressure system is expected to intensify into a depression by Tuesday night and lead to light showers,” said Mahesh Palawat, vice-president, meteorology and climate change, Skymet.

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