Lockdown Due to COVID-19 Pandemic Improves Overall Air Quality: An Evidence Based Study from Siliguri Metropolitan, West Bengal, India

About more than two months of lockdown due to the COVID-19 pandemic, from the end of March to the end of May in the Siliguri city of West Bengal, India, results in a momentous change in the overall air quality. The study aimed to identify the propensity of the concentration of pollutants during the period pre, during and post lockdown through trend analysis and to evaluate the alteration of air quality at different phases of lockdown (including Phase I, II, III and IV). Also, to compares the changes in the concentration of various pollutants, including Air quality index (AQI) for pre-during and pre-post lockdown periods. Data were obtained for the time-span of before, during and after lockdown and the entire lockdown period (from 25th March to 31st May) was divided into four phases to better comprehend the extent of air quality variation. Each phase of lockdown reveals different air quality scenarios, with a tendency to reduce during the first phase, increase by the third phase, and again lessens to a minimum at the fourth phase. The result shows a significant reduction in the concentration of Particulate matter (PM2.5 and PM10) (upto -66% respectively), Nitrogen dioxide (NO2) (upto -46%), Sulphur dioxide (SO2) (upto -20%), Ammonia (NH3) (upto -19%) and AQI (upto -68%) during the lockdown period compared to before lockdown. On the other hand, overall Air quality was further improved after the lockdown as the concentration of the pollutants, including AQI, was further reduced to minimal. The changes for PM2.5 (upto -78%), PM10 (upto -76%), NO2 (upto -48%), SO2 (upto -40%), NH3 (upto -41%) and AQI (upto -80%) after the lockdown compared to the period of pre-lockdown. In contrast, the concentration of Ozone (O3) was increased by 21% and 25% for the same period. Similarly, the mean AQI of the city shows a poor AQI before lockdown, came to a satisfactory during the lockdown, which further changes to good air after the lockdown ended. Therefore, it is clear from the study that the lockdown has an impact on improving the overall air quality and further lockdown with appropriate planning in the future should be seen as an alternative solution to reducing excessive pollution.