**2. Materials and Methods**

MERRA-2 is a NASA reanalysis product from 1980 onward. With a 0.625◦ × 0.5◦ longitude-by-latitude grid, MERRA-2 offers data collections including AOD products, radiation diagnostics, and so on. The resolution of MERRA-2 is approximately 50 × 50 km. In this study, monthly MERRA-2 AOD, BCAOD, OCAOD, SO4AOD, DUAOD, and SSAOD were used to study the long-term variation of aerosol over the SCS. Three regions of interest over the SCS were chosen for a better analysis of the aerosol variation. In addition, linear regression method was used to calculate the MERRA-2 AOD variation trend over the SCS in two periods, including 1980–2007 and 2008–2020.

Figure 1 showed the map of the SCS and the locations of the northern part of the South China Sea (NSCS), the middle part of the South China Sea (MSCS), and the southern part of the South China Sea (SSCS).

**Figure 1.** Map of the South China Sea (SCS). The black boxes represent the three selected regions of interest: the northern part of the South China Sea (NSCS), the middle part of the South China Sea (MSCS), and the southern part of the South China Sea (SSCS).
