Impact of Nationwide COVID-19 Lock-down on Indian Air-Quality in terms of Aerosols as Observed from the Space

Abstract:

Air pollution in India, especially in metro cities and the entire Indo-Gangetic (IG) plain, has exceeded all standards in the recent past. The development of an effective pollution control strategy requires knowledge of the pollutant sources, their spatio-temporal variability, and the efficacy of control strategies such as limiting the anthropogenic activities. The Indian government has imposed a nationwide lockdown (LD) during March and April 2020 to contain the spread of infectious disease COVID-19. LD can also be considered as an uncommon opportunity to evaluate the efficacy of restricting anthropogenic activities in controlling air pollution. In the present paper, using data from space-borne sensors, a detailed analysis of the impact of LD on the state of aerosols in the Indian atmosphere is presented. The aerosol optical depth (AOD), fine mode fraction (FMF), absorbing aerosol index (AAI), active fire/thermal anomaly and the HYSPLIT model is used to study and analyze the instantaneous state and spatio-temporal transportation of aerosols. On average, an overall decrease in AOD is observed after LD was imposed. About 60% of the Indian landmass shows an average decrease of 0.16 in AOD. A significant decrease in FMF indorses decreased AOD solely due to restricted anthropogenic activities, especially in IG plain, which confirms the positive impact of LD on air quality. However, central, northeast and partially western India show contrasting results, in fact in some parts a clear increase in AOD is observed. The investigation shows poor air quality during LD in these regions is associated with smoke emitted from active-fires. An increase of 30% in fire spots is observed during LD in these regions. The city-level analysis shows a strong positive impact of LD on air quality in most of the cities located in the IG plain. The cities located in the west, north-west and east India have shown a small decrease in AOD during LD, while in central, north-east, and few in the southern region, the increased AOD is observed inspite of LD due to increase in biomass burning.