Aerosol optical properties at seven AERONET sites over Middle East and Eastern Mediterranean Sea

Abstract

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), Ångström 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.