COVID-19 Lockdown and its Effects on Aerosol Optical and Radiative Properties over Indo-Gangetic Plain

Aerosol optical and radiative properties, measured with theground based sun-sky radiometer (under AERONET) were explored at Kanpur (26.5°N, 80.2°E) in the central and Gandhi College (Ballia) (25.8°N, 84.1°E) in the eastern Indo Gangetic Plain (IGP) innorthern India. The measurements were carried out during the period from January to July 2019 (non-lockdown) and 2020 (lockdown). Significant changes were observed in aerosol properties during the lockdown period due to COVID-19 pandemic.This year marked an overall reduction of 15.79% and 3.39% in aerosol optical depth (AOD) than year 2019 at Kanpur and Gandhi College, respectively. Lockdown phase1 (23^rd March to 14^th April, 2020) showed reduction of 52.52 % and 42.22% in AOD compared to pre-lockdown condition at Kanpur and Gandhi College, respectively. In addition to lockdown Phase 1 observations, an increasing trend in AOD values was found at both locations for subsequent lockdown phases. Higher values of angstrom exponent measured at Eastern region (1.13 ± 0.17) than central region (0.97 ± 0.26) indicating the dominance of fine particles at Gandhi College. During lockdown Phase-1, the values of atmospheric forcing and heating rate were decreased about 23.48% and 15.07% at Kanpur and Gandhi College,respectively compared to year 2019 values.There was overall 1.31% reduction in SSA at Kanpur while 4.34% reduction was observed at Gandhi college in year 2020 than 2019. Current year marked reduction in SSA by 1.56% at Gandhi College than Kanpur representing the absorbing particles due to biomass burning event during the lockdown period. The effects of lockdown were prominently seen for Kanpur region in terms of variations in aerosol properties. The resultant atmospheric forcing and heating rate shows 11.86% reduction at Kanpur while 35.27% increased at Gandhi College during the lockdown period in 2020 compared to 2019.As the lockdown progressed, increasing trend was observed in atmospheric forcing and heating rate.