Impacts of irregular and strategic lockdown on air quality over Indo-Pak Subcontinent: Pre-to-post COVID-19 analysis

The COVID-19 pandemic has received enormous attention worldwide due to its environmental, and societal impacts. After the discovery of this novel virus in December 2019, the governmental bodies have suspended the social and economic activities and declare an unprecedented lockdown emergency. The present work sought to investigate the impact of COVID-19 containment measures on air quality in the region of Indo-Pak subcontinent (IPS). The satellite retrievals of aerosol optical depth (AOD), sulfur dioxide (SO2), nitrogen dioxide (NO2), and Ozone (O3) was used to estimate the spatial-temporal extent of major air pollutants in the region during lock down period (March-May 2020) in comparison to the pre-lockdown period (March-May 2015-2019) and post-lockdown (March-May 2021) across the IPS. From the results, a considerable reduction in air pollutants con-centration has been observed during the lockdown phase that in turns significantly improved the regional air quality. Moreover, we have also done comparative analysis among meteorological parameters and ambient air pollutants and observed that meteorological factors were not the main reason for the dramatic reductions of pollutants in the atmosphere. In addition, backward trajectory analysis has been done through the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model to find the path and direction of air particles parcels as large-scale atmospheric circulation is a critical factor in driving pollutant. Following the implementation of strict lockdown, reduction in anthropogenic activities led to a substantial decline in AOD, SO2 and NO2 whereas, a considerable increase in tropospheric O3 has been observed and well supported by other regional studies. Overall, the findings of this study are believed to be a useful addition to the regulatory authorities and will help the policymakers to formulate the air pollution mitigation strategies in a long-term perspective.