An assessment of the impact of a nation-wide lockdown on air pollution – a remote sensing perspective over India

Abstract. The nation-wide lockdown imposed over India from 25th March 2020 onwards, in response to the COVID-19 pandemic, placed severe restrictions upon the industrial and transport sectors, which together form a significant chunk of anthropogenic emissions of pollutants into the atmosphere. Atmospheric concentrations of Nitrogen dioxide (NO₂), carbon monoxide (CO) and aerosol optical depth (AOD) for lockdown and pre-lockdown periods were investigated with observations from Aura/OMI, Terra/MOPITT, Sentinel-5p/TROPOMI and Aqua-Terra/MODIS satellite sensors. Mean NO₂ levels over India during the lockdown period showed a dip of 17 % as compared to pre-lockdown period and a decrease of 18 % against the 5-year average. Over New Delhi in particular, there was a sharp decrease of 62 % in NO₂ levels as compared to 2019 and a decline by 54 % relative to the preceding 5-year period (2015–2019). Aerosol levels reduced over the country by ~ 24 % from the 5-year mean levels, with a marked reduction over the Indo-Gangetic plains region. An increase in CO levels was noticeable, probably due to its longer life-time as compared to NO₂ and aerosols. This study also reports the rate of change of NO₂, CO and AOD, indicating increase/decrease in pollutant emissions over the different states of India.