Air pollution has been a serious problem in northern India and Nepal. The main cause of air pollution in this area is exhaust gas from automobiles and factories, and the polluted air tends to stagnate due to the topographical characteristics of the basin.
On March 25, 2020, the Government of India implemented a strict lockdown across India to control the transmission of COVID-19. Traffic volumes and activity at factories had decreased significantly. As a result, air pollution had reduced, and the Himalayas could be seen from northern India for the first time in several decades in March.
Fig. 1 shows northern India and Nepal observed by TANSO-CAI-2.
The top figures show false color Red, Green, Blue (RGB) composite images of TANSO-CAI-2 band2 (441nm) in red, band4 (865nm) in green and band1 (339nm) in blue.
The middle figures show color-coded images emphasized atmospheric aerosols in northern India and Nepal on March 31, 2019, and on March 31, 2020 which is after lockdown. The center figures show the difference between reflectance at the top of atmosphere on the respective day and the surface reflectance derived from two months data at band 2 (441nm).
The large value means that the amount of aerosol is large.
The bottom figures show the ratio of band 2 (441nm) to band 1 (339nm). The large value means that the amount of absorbent aerosol (such as black carbon) is large.
These figures show that aerosols decreased and air pollution in this area improved in March 2020.
Fig 1. GOSAT-2 CAI-2 RGB image (top), difference between band2 reflectance at the top of atmosphere and surface reflectance (middle), emphasizes UV absorption by aerosol particles (bottom).
The simple screening of cloud and snow have been processed.