Surprising Changes in Aerosol Loading over India amid COVID-19 Lockdown

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 20^(th) February-20^(th) March 2020 and 24^(th) March-22^(nd) 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.