*3.1. Accuracy of MERRA-2 AOD*

As AOD are retrieved and assimilated from AERONET, MISR, MODIS, and AVHRR, MERRA-2 AOD agreed well with the ground-based measurements [45]. The correlation coefficients between AERONET and MERRA-2 AOD were 0.84, 0.88, and 0.90 in Xianghe, Beijing, and the Yangtze River Basin [46]. MERRA-2 AOD was compared with groundbased AOD from 29 CARSNET stations throughout China during 2002–2014, and good agreement was also obtained [47]. The good agreement between MERRA-2 and groundbased AOD offered an important theoretical basis for the following study of temporal and spatial distributions of MERRA-2 AOD over the SCS from 1980 to 2020.
