Chennai: The city’s high pollution levels, which pushed air quality into the ‘very poor’ category and reduced visibility on Diwali, may gradually ease over the next two to three days as winds strengthen and change direction.IMD officials said winds were northwesterly at less than five knots (9kmph) on Diwali, limiting dispersion of pollutants. They shifted to northeasterly at around 14 knots (26kmph) on Monday. Stronger winds could disperse pollutants by carrying polluted air away from the city.V R Durai, director, Area Cyclone Warning Centre, RMC Chennai, said low temperatures on Diwali kept the atmospheric boundary layer, the lowest layer of the atmosphere, shallow and close to the surface. This restricted vertical mixing and allowed pollutants to accumulate near the ground. On Sunday, maximum temperatures dropped to 29°C in Nungambakkam and 28.3°C in Meenambakkam, around 1.3°C and 2°C below normal respectively.On Monday, maximum temperatures rose to 31.7°C and 32.2°C respectively, around 1.4°C and 1.9°C above normal.“Throughout the day on Diwali, the wind speed was less than 10kmph. It picked up on Monday. The winds are now coming from the sea, so it can easily wash away the pollutants and clear the air,” he said.Mahesh Palawat, chief meteorologist at Skymet Weather, said wind speeds were moderate and it could take time for pollutants to clear completely. “It may take two to three days for the pollutants to clear and the air quality to become better,” he said.Meanwhile, northeast monsoon rainfall may take a break over Chennai, with much of the heavy rain activity likely to remain over the delta and southern districts. Durai said long-range forecasts indicate a low-pressure area could form over the south Andaman Sea around Nov 13 and intensify, potentially bringing back monsoon activity over the city after Nov 15. “Till Nov 15, there may be light drizzles here and there,” he said.On Tuesday, Chennai and its suburbs may receive light rain in some areas. Partly cloudy skies may keep temperatures between 24°C-25°C and 32°C-33°C.Since Oct 1, Chennai has recorded 4% below-normal rainfall, while Kancheepuram and Chengalpet recorded deficits of 20% and 35%, respectively. Tiruvallur district, which has the city’s drinking water reservoirs, received 9% above-normal rainfall. Tamil Nadu as a whole has recorded 4% excess rainfall so far.
