Aerosol Loading and Radiation Budget Perturbations in Densely Populated and Highly Polluted Indo-Gangetic Plain by COVID-19: Influences on Cloud Properties and Air Temperature

Aerosols emitted in densely populated and industrialized Indo-Gangetic Plain, one of the most polluted regions in the world, modulate regional climate, monsoon, and Himalayan glacier retreat. Thus, this region is important for understanding aerosol perturbations and their resulting impacts on atmospheric changes during COVID-19 lockdown period, a natural experimental condition created by the pandemic. By analyzing 5 years (2016-2020) data of aerosols and performing a radiative transfer calculation, we found that columnar and near-surface aerosol loadings decreased, leading to reductions in radiative cooling at the surface and top of the atmosphere and atmospheric warming during lockdown period. Further, satellite data analyses showed increases in cloud optical thickness and cloud-particle effective radius and decrease in lower tropospheric air temperature during lockdown period. These results indicate critical influences of COVID-19 lockdown on regional climate and water cycle over Indo-Gangetic Plain, emphasizing need for further studies from modeling perspectives. Plain Language Summary The COVID-19 control measures constrained human activities, reducing anthropogenic emissions around the world, including Indo-Gangetic Plain (IGP), one of the global aerosol hotspots. Aerosols emitted in the IGP can affect regional climate, water cycle, Himalayan glacier retreat, etc. Thus, understanding the impacts of COVID-19 lockdown in aerosol field and other associated components of the atmosphere over IGP is important for better understanding the roles of aerosols on climate and water cycle of South Asia and its vicinity. This study suggests reductions of both near-surface and columnar aerosol loadings by lockdown measures further reduced radiative cooling at the surface and top of the atmosphere and atmospheric warming. The effects were also noted in the cloud field by increasing cloud optical thickness and cloud-particle effective radius and in the meteorological field by reducing air temperature in the lower troposphere. These manifold impacts over this important source region indicate broad influences of COVID-19 on the regional climate and water cycle, underscoring further investigations. Key Points Aerosols reduced by COVID-19 lockdown perturbed atmospheric heat budget over the Indo-Gangetic Plain Cloud optical thickness and cloud-particle effective radius increased during COVID-19 lockdown period Air temperature in the lower troposphere decreased during COVID-19 lockdown period