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

Abstract

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.

An improved understanding of NOx emissions in South Asian megacities using TROPOMI NO2 retrievals

“…Comparison of two sites in Lahore showed that both experienced high concentrations, but the more central, commercial site had lower concentrations than the residential/industrial site to the south. Finally, a study of OMI columns during the COVID-19 lockdowns for the four cities in our study plus Kathmandu found significant reductions in all five, but the plots also show that the urban signatures are more diffuse in the OMI retrievals than in the TROPOMI retrievals [35].…”