Using ground-based and satellite observation along with aerosol reanalysis products, we show
a widespread reduction in aerosol loading over the Indian subcontinent during the COVID-19
(COronaVIrus Disease 2019) lockdown. The pre-lockdown and lockdown period considered in the
present study is 20th February–20th March 2020 and 24th March–22nd April 2020. In terms of
aerosol optical depth (AOD), loading has reduced up to 40% over the most populated region of
India. However, the central part of India shows an unexpected increase (~+20%) in AOD. A
simultaneous increase (decrease) in mid-tropospheric relative humidity (wind speed (WS) at
850 hPa) by +85 ± 6.0% (–12 ± 3.9%) occurred during the lockdown. It is found that on a daily
scale, the mean AOD is positively (negatively) correlated with mid-tropospheric RH (WS) with a
statistically significant linear correlation coefficient of 0.53 (−0.43). An increase (decrease) in
RH (WS) of 20% (1 m s
–1
) was observed to increase AOD by 0.10 (0.04). Thus, we hypothesize that
during the lockdown, the increased AOD over central India was due to increased atmospheric
moisture coupled with stagnant circulation condition.