Global impact on aerosol characteristics during COVID-19 using ground- and satellite-based observations

Abstract

Corona Virus Disease 2019 (COVID-19) caused global reductions in transportation and industrial activities, which provided an unprecedented opportunity to examine the effects of reductions in anthropogenic activities on aerosol characteristics on a global scale. The observational study of the impact on columnar aerosol characteristics and radiative effects during the COVID-19 pandemic outbreak period, when anthropogenic emissions are significantly suppressed globally, can be helpful in quantifying the anthropogenic influence on aerosol properties for the accurate assessment of radiative and climatic impacts of aerosols. This study utilizes the high-quality aerosol datasets from Aerosol Robotic Network (AERONET) over 224 sites covering the entire globe, and satellite-based Moderate Resolution Imaging Spectroradiometer (MODIS) retrieved aerosol optical depth (AOD) to analyze the difference in columnar aerosol properties between the year 2020 (COVID) and 2017-2019 (normal) on a seasonal scale over 10 different regions of the world. The most significant reduction in AOD by AERONET and MODIS observations is observed over most of the regions during the summer season, followed by the spring season of 2020 compared to the respective seasons of 2017-2019, when many countries imposed lockdowns. During summer, the highest reduction in AOD is observed over South Asia by MODIS (−0.09, 20% reduction) and AERONET (−0.07, 15% reduction), where aerosol loading is relatively higher during normal scenario. Over East North America and Europe, AERONET AOD reduced by −0.02 and −0.04, respectively. A significant reduction in Angstrom exponent (AE) and fine mode fraction (FMF) in most regions confirms the reduction in fine mode anthropogenic aerosols. However, a significant increase in AE and FMF (~20%) in South Asia is observed due to significant reduction in dust AOD (natural), which decreased the amount of coarse mode aerosols during the COVID period. Furthermore, the difference in aerosol radiative forcing at the surface (ARFSFC) by Clouds and Earth’s Radiant Energy Budget Scanner (CERES) data shows a significant reduction in ARFSFC in most regions during COVID period, whereas the highest reduction in ARFSFC of ~20% is observed over South Asia consistent with the reduction in aerosol emissions. This observational study over a global scale during the unprecedented COVID-19 period can be helpful for undertaking future mitigation strategies related to anthropogenic aerosol emissions and their precursors to reduce their impact on the climate.