Measurement report: An assessment of the impact of a nationwide lockdown on air pollution – a remote sensing perspective over India

Abstract

Abstract. The nationwide lockdown was imposed over India from 25th March to 31st May 2020 with varied relaxations from phase-I to phase-IV to contain the spread of COVID-19. Thus emissions from industrial and transport sectors were halted during lockdown (LD) which resulted in a significant reduction of anthropogenic pollutants. The first two lockdown phases were strictly followed (phase-I and phase-II) and hence are considered as total lockdown (TLD) in this study. Satellite-based tropospheric columnar nitrogen dioxide (TCN) from the years 2015 to 2020, tropospheric columnar carbon monoxide (TCC) during 2019–2020 and aerosol optical depth (AOD550) from the years 2014 to 2020 during phase-I and phase-II LD and pre-LD periods were investigated with observations from Aura/OMI, Sentinel-5P/TROPOMI, and Aqua-Terra/ MODIS satellite sensors. To quantify lockdown induced changes in TCN, TCC, and AOD550, detailed statistical analysis was performed on de-trended data using student’s paired statistical t-test. Results indicate that mean TCN levels over India showed a dip of 18 % compared to the previous year and also against the 5-year mean TCN levels during the phase-I lockdown, which was found statistically significant (p-value <0.05) against the respective period. Furthermore, drastic changes in TCN levels were observed over hotspots namely the eastern region and urban cities. For example, there was a sharp decrease of 62 % and 54 % in TCN levels as compared to 2019 and against 5-years mean TCN levels over New Delhi with a p-value of 0.0002 (which is statistically significant) during total LD. The TCC levels were high in the North East (NE) region during the phase-I LD period, which is mainly attributed to the active fire counts in this region. However, lower TCC levels are observed in the same region due to the diminished fire counts during phase-II. Further, AOD550 is reduced over the country by ~16 % (Aqua and Terra) from the 6-years (2014–2019) mean AOD550 levels, with a significant reduction (Aqua/MODIS 28 %) observed over the Indo-Gangetic plains (IGP) region with a p-value of

Impact of COVID-19 induced lockdown on land surface temperature, aerosol, and urban heat in Europe and North America

“…The Aerosol Optical Depth (AOD) is a proxy of atmospheric pollution level, which measures how light is attenuated by suspended particles through the atmosphere. During the COVID-19 lockdowns, satellite-derived AOD data revealed that the aerosol levels reduced substantially by 40–60% across urban areas in south and southeast Asia ( Kanniah et al, 2020 ; Pathakoti et al, 2021 ; Ranjan et al, 2020 ). Recent works also revealed a large reduction in BC levels, as well as significant modulations in aerosol scattering and absorption properties enabling to modify the radiation budget and temperature at the surface and in the lower atmosphere ( Anil & Alagha, 2020 ; Kaskaoutis et al, 2021 ; Wang et al, 2021 ).…”

Air Pollution: A Review of Its Impacts on Health and Ecosystems, and Analytical Techniques for Their Measurement and Modeling

“…Satellite-based remote sensing provides extensive coverage and allows for the monitoring of air pollution on a global scale. It measures various parameters, including aerosol optical depth, tropospheric ozone, and nitrogen dioxide concentrations (Demetillo et al, 2020;Chudnovsky, 2021;Muthukumar et al, 2021;Pathakoti et al, 2021;Roy, 2021;Xiong et al, 2021;Ji et al, 2022;Scheibenreif et al, 2022;Zhu et al, 2022;Zhang et al, 2022;Abu El-Magd et al, 2023;Wang et al, 2023). Ground-based remote sensing techniques, such as lidar and sun photometry, provide detailed information about the vertical profiles of pollutants and can be used to validate satellite measurements.…”