[Spatial-temporal Distribution of Aerosol Optical Depth and Its Main Influence Types in China During 1990-2017]

In order to accurately understand the optical characteristics of aerosols in China, based on Mann-Kendall(MK) and Sen's slope trend analysis methods, the spatiotemporal variations of aerosol optical depth(AOD) derived from MERRA-2 reanalysis datasets were estimated in China for the period of 1990-2017. The results showed that ① for the interannual scale, there was a significant increasing trend in the annual mean AOD in China during 1990-2017. Besides, high aerosol loadings were observed in spring and summer, and the seasonal difference between the eastern and western regions was large. This was mainly due to the topographic and meteorological factors. ② At the spatial scale, the annual mean AOD values increased from the northwest to the southeast, with characteristically high AOD values occurring in Sichuan Pendi and the Tarim and Turpan basins and low values in the Qinghai-Xizang plateau region. Similarly, the AOD MK value and Sen's slope value showed significant decreasing trends from the southeast to the northwest, which was closely related to climate change and the human activity intensity. ③ In regard to black carbon aerosol, dust aerosol, organic carbon aerosol, sea salt aerosol, and SO₄ aerosol, dust and SO₄ aerosols were affected by the air humidity and human activity intensity, which have obvious regional differences in China.