Very little commercial activityduring the ongoing lockdown and rain on Wednesday morning have improved the air quality in the city with the average index remaining in the 'good' category, an official said.The average air quality index (AQI) during the day was 16 (PM 2.5) at a monitoring station in Jadavpur, 18 in Rabindra Sarobar, 21 at Victoria Memorial, a West Bengal Pollution Control Board (WBPCB) official said.The air quality indices at Fort William and Ballygunj air monitoring stations were at 24 and 23 respectively, the official said.The average AQI was between 15 and 25 mark across different air monitoring stations on April 30, he said.The ongoing lockdown, which has been enforced by police strictly, led to much less accumulation of particulate matters in the air, coupled with heavy rain that cleansed the air further, the official said.An AQI between 0 and 50 is considered 'good', 51-100 'satisfactory', 101-200 'moderately polluted', 201-300 'poor', 301-400 'very poor' and 401-500 'severe', while the AQI above 500 falls in the 'severe plus' category.On an average, the AQI hovers between 160 and 200 across different air monitoring stations before the lockdown, the WBPCB official said."At Rabindra Sarobar, on April 6, PM 2.5 was 78 micrograms per cubic metre of air and today it was 18. It reduced significantly in a month," environmentalist Somendranath Ghosh said.More tortoises have been spotted in the buffer zone of Rabindra Sarobar in the past couple of days as compared to days when it was open for morning walkers, Kolkata Metropolitan Development Authority CEO Antara Acharya said.Morning walkers have not been allowed to enter into the lake during the lockdown.Senior KMDA official Sudhin Nandy said the number of tortoise sightings has gone up to 10-12 now from just 2 or 3 before the lockdown."As the air quality in the lake area has improved substantially from satisfactory to good levels during the over one-month-long lockdown, with almost no human interference, our surveillance staff have reported rise in sightings of tortoise and other aquatic creatures like fish in the lake water," he said.A large number of birds, including those sighted rarely in past, are now coming as there is no crowd on the premises of the lake, he said.
