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An 8-year dataset from 7 AERONET (Aerosol Robotic Network) sites is used to analyzed the variation characteristics of aerosol optical and microphysical properties over the Middle East (ME) and Eastern Mediterranean Sea (EMS) regions. The aerosol optical properties, including aerosol optical depth (AOD), Angstrom exponent (AE), volume size distribution (VSD), aerosol absorption optical depth (AAOD), single scattering albedo (SSA), dominant types, aerosol radiative forcing (ARF) and its efficiency (ARFE), are presented and analyzed over the two regions. The regional mean AODs (AEs) are 0.31 (0.69) and 0.19 (1.10) over ME and EMS, respectively. Although the linear trend of annual averages is not significant at these sites, the variations of seasonal and annual AODs and AEs are remarkable. The mean AODs are generally higher over ME than over EMS, while the AEs show the opposite pattern. AOD appears the maximum in summer and the minimum in winter both at ME and EMS sites. AE shows the maximum in autumn and winter over ME, while in summer over EMS. The lowest AE appears in spring over both regions due to the frequent dust events. The AAOD ranges from 0.03 to 0.04 and the SSA from 0.89 to 0.93 at these sites. The seasonal AAOD presents very different features over the two regions. The AAOD appears its minimum in winter at most ME sites, while the maximum appears in the same season at EMS sites. The differences of seasonal SSAs at ME sites are relatively small, while at EMS sites the SSAs are much higher in summer and autumn than those in spring and winter. The aerosol types are discussed based on four selected classification methods. It shows that the desert dust (DD) and the mixtures (Mix) are the two dominant aerosol types at most sites except ERD which is dominated by urban industry aerosol (UI). To the radiative forcing, the ARF at bottom of atmosphere (BOA) is generally larger at ME sites than at EMS sites, while the ARFs at top of atmosphere (TOA) are numerically similar at most sites. The ARFE shows higher value at sites in Arabian Peninsula both at BOA and TOA.

The distribution and transportation characteristics of dust aerosol over the Tibetan Plateau (TP) and Taklimakan Desert (TD) were analyzed during 1980–2017 using MERRA-2 (second Modern-Era Retrospective analysis for Research and Applications) and CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) products. The aerosol optical depth (AOD) of MERRA-2 were compared with those of AERONET (Aerosol Robotic Network) at six sites and the corresponding MISR (Multi-angle Imaging SpectroRadiometer) data. The correlation coefficients were 0.73–0.88 and 0.94, respectively. The yearly AOD over the IGP (Indo-Gangetic Plain) and the TD showed a significant increasing trend. The variations of seasonal AOD and dust AOD (DAOD) over the research region were similar, showing the values decreasing from north to south and the higher values appearing in spring and summer. The DAOD/AOD ratio exceeded 0.5 during March–August and throughout whole year in the north part of the TP and the TD, respectively. The duration, strength and area of the high DAOD region over the TD have enhanced during the past 38 years. From the CALIPSO observation, it showed the dust moving from the TD to the TP was mainly through the Qaidam Basin in the layer of 4–8 km aloft and could transport as south as 30°N, with the maximum lifting height in spring. In winter, the dust over TP was mainly from the Qaidam Basin due to the suppression effect of the inversion layer over the TD. The largest profile of dust extinction coefficient appeared in spring over the TD, while in summer over the TP. The distribution and annual regional averages of base, top and thickness of dust layer were calculated and presented. It shows a long-standing dust layer of about 1 km appearing over the TP with the maximum in spring.

The spatial-temporal distributions, historical trends and affecting factors of black carbon (BC) concentration both for the surface and atmospheric column in East China (110°E ~ 123°E, 23°N ~ 42°N) during 2000–2016 were investigated through MERRA-2 (Modern-era Retrospective Analysis for Research and Applications, Vision2) reanalysis data. Although a little overestimate at most inland stations and underestimate at most coastal ones, BC concentrations of MERRA-2 generally presented a good correlation (R = 0.83) compared with 598 monthly samples from ground-based observations at 14 stations. From the long-term records, the variation characteristics of BC surface concentration and column density over East China can be summarized as follow: The overall annual mean of BC surface concentration, column density and the concentration ratio of surface BC and PM2.5 (BC/PM2.5) over East China were 3.41 μg m−3, 3.78 mg m−2 and 8.71%, respectively. The highest annual mean (~6.00 μg m−3) and the fastest growth rate (~0.06 μg m−3•a−1) of surface concentration were both shown in the region of Beijing-Tianjin-Hebei (BTH) and Henan area. The seasonal mean BC surface concentrations of this region were between 5.00 and 9.00 μg m−3, with the highest in winter and the lowest in summer. As to column density, the highest annual mean (~6.00 mg m−2) and the fastest growth rate (~0.02 mg m−2•a−1) appeared in BTH and the border area of Hebei, Henan and Shandong. Unlike the surface concentration, the high-density center moved toward south and extended its coverage from summer to winter, but shrunk to north from winter to summer. The region of relatively high (14.00%–16.00%) BC/PM2.5 ratio was over BTH area and central Shanxi area, while the lowest (2.00%–6.00%) regions were in part of Inner Mongolia and south coastal area. The yearly BC concentration increased rapidly since 2000 and reached the peak in 2007. It decreased obviously in the south part of East China during 2008-2016. The BC/PM2.5 ratios experienced a “increase-decrease-increase” variation, with the maximum and minimum in 2005 and 2010, respectively.