To stop the spread of COVID-19 infections, idea of complete and partial lockdowns was implemented in several countries. In the present work, variation of aerosol index (AI), aerosol optical depth (AOD) and SO2 concentration over Indo-Gangetic Basin regions (over highly polluted cities: Varanasi, Kanpur and Delhi) were analyzed to see the impact of lockdown periods during 2020. AI data were taken from satellite based ozone monitoring instrument while AOD and SO2 data were taken from moderate resolution spectroradiometer (MODIS). Lockdown periods of March, April, May and June months of 2020 were compared with the same months of 2017, 2018 and 2019. Significantly large difference in AI was observed associated with decreased value of AI during lockdown periods followed by AOD values and SO2 concentrations. All these cities of Northern India (Varanasi, Kanpur and Delhi) show significant decline in aerosol index which indicate less emissions of black carbon and other absorbing aerosol particles into the atmosphere. Trend of AI and SO2 concentration were found to be negative due to the sudden decrease in their values. Decline in the aerosol parameters (AI and AOD) and air pollutant (SO2) suggest improved air quality of the highly polluted cities of India.
