Surprising increase in aerosol amid widespread decline in pollution over 1 India during the COVID 19 Lockdown 2

Using ground-based and satellite observation along with aerosol reanalysis products, we 10 show a widespread reduction in aerosol loading over the Indian subcontinent during the 11 COVID19 lockdown. In terms of aerosol optical depth (AOD), loading has reduced up to 40 12 % over the most populated region of India. However, the central part of India shows an 13 unexpected increase (~+20 %) in aerosol optical depth. Using meteorological reanalysis data, 14 it is shown that a simultaneous increase (decrease) in mid-tropospheric relative humidity 15 (wind speed (WS) at 850 hPa) by +85±6.0 % (-12±3.9 %) occurred during the lockdown. It is 16 found that on a daily scale, the mean AOD is positively (negatively) correlated, with mid17 tropospheric RH (WS) with a statistically significant linear correlation coefficient 0.53 (18 0.43). An increase (decrease) in RH (WS) of 20 % (1 ms -1 ) was observed to increase AOD by 19 0.10 (0.04). Thus we hypothesize that during the lockdown, the increased AOD over central 20 India was due to increased atmospheric moisture coupled with stagnant circulation condition. 21 Also, aqueous-phase chemistry may have played a role by enhancing new particle formation. 22