Kolkata, Dec 7 : Sporadic drizzles triggered by Cyclone Michaung continued on Thursday substantially improving the city's Air Quality Index (AQI). The AQI started deteriorating fast for the last couple of weeks signalling the advent of winter with the levels of PM 2.5 at almost all the AQI monitoring stations in the city showing "very poor" standards. However, since Thursday morning, the same PM 2.5 levels at these monitoring showed "satisfactory" standards, as the natural water sprinklers acted as sanitizers in settling down the toxic pollutants thus making the air cleaner. As per the records of the seven AQI monitoring stations, the PM 2.5 levels in the air hovered between 70 and 91, with the lowest being at Rabindra Sarobar in South Kolkata at 70 and the lowest being at Fort William in central Kolkata at 91. Just two weeks back, the same PM 2.5 levels in the air was recorded above 300 in all the monitoring stations in the city. According to acclaimed green technologist and the environmental activist Somendra Mohan Ghosh, the rate of photosynthesis has improved because the stomata on the surface of leaves are free from dust pollutants and thus resulting in better nutrients generation. "With better oxygen supply, the AQI in Kolkata has become satisfactory," he added. /IANS