Impact of SARS-CoV-2 Pandemic Lockdown on Air Quality Using Satellite Imagery with Ground Station Monitoring Data in Most Polluted City Kolkata, India

Immediate lockdown (March 24–May 31, 2020) of industrial activity and traffic flows has been announced by the government of India across the country after the declaration of World Health Organization that the Novel Coronavirus (SARS-CoV-2) outbreak is pandemic. In this study, we tried to estimate the air quality improvement during the pre-lockdown period (January 1–March 23, 2020) by comparing the lockdown period (March 24–May 31, 2020). From the results, we found the highest reduction in the concentration of NO(2) (81.98%) during the lockdown period. The average concentration of NO(2) was 51.57 µg/m(3) during pre-lockdown has changed to 9.29 µg/m(3). The average PM(2.5) concentration was 80.09 µg/m(3) during the pre-lockdown period has reduced to 20.24 µg/m(3) with 74.72% of reduction during the lockdown period. From the overall analysis of various parameters, we observed significant improvement with the range of 73.27–78.26% in PM(2.5), 69.01–82.55% in PM(10), 72.12–87.62% in NO(2), 18.61–63.19% in SO(2) and 47.16–72.11% in CO with the highest improvements in Ballygunge, Rabindra Bharati University, Ballygunge, Bidhannagar, Rabindra Sarobar and Rabindra Bharati University, respectively, with an overall average reduction in air pollutants of 53.61%. Reduction in the concentration of PM(2.5), PM(10), CO, NO(2) and SO(2) is mainly due to the closure of on-road vehicle emission, industrial activities, shut down of malls, shops etc. This reduced level of air pollutants may help in the modification of all the environmental policies for better air quality in future.