Effect of COVID-19 Lockdown on Air Quality: Evidence from South Asian Megacities

Anthropogenic activities were greatly restricted in many South Asian cities during the COVID-19 (Coronavirus disease-2019) pandemic creating an opportunity to observe source reduction of air pollutants. This study analyzed the change in columnar nitrogen dioxide (NO2) and particulate matter (PM2.5, aerodynamic diameter ≤2.5 µm) in five megacities of South Asian countries (Delhi, Dhaka, Kathmandu, Kolkata, and Lahore) from April 1 - May 31 over the previous three years (2018-2020). The Dutch-Finnish Ozone Monitoring Instrument (OMI) provided satellite-based daily tropospheric columnar NO2 values for this study. Ground-based hourly PM2.5 data were collected from the World's Air Pollution: Real-time Air Quality Index Project. The study observed a decrease of tropospheric columnar NO2 in selected cities in 2020 compared to 2018 and 2019 from April 1 - May 31. The mean daily reading of PM2.5 was 36.56% and 45.44% less in Delhi; 12.67% and 23.46% less in Dhaka; in Kathmandu 28.32% and 37.42% less; in Kolkata 41.02% less in 2020 than 2018 and 34.08% less in 2019 during April 1 - May 31. The PM2.5 was 44.26% less in 2020 than in 2019 during April 9 - May 31 in Lahore. The daily mean difference in concentration during April 1 - May 31, 2018-2020 was significantly lower at α=0.01 level for both pollutants. Introducing appropriate mitigation measures would provide safer environments and reduce future air pollution in South Asian cities.