Saharan dust mixed with marine aerosols: lidar measurements and characterization

Abstract

Mineral aerosols from Sahara desert are frequently transported to Europe by regional or trans-continental air circulations. During such a long-range transport, Saharan dust is naturally mixed with other aerosols. The pathway of desert aerosols frequently passes over the Mediterranean Sea or the Atlantic Ocean. Under certain conditions, dust particles can blend with marine aerosols to form a mixture with specific volume/mass concentration and particle size distribution. These parameters are determinative for the climatologic, ecologic and medical impacts of the aerosols. Therefore, studies of desert-marine aerosols’ interacting and mixing are of considerable scientific and practical importance. In this work, we report results of lidar measurements and analysis of Saharan dust layers observed over Sofia, Bulgaria, possibly containing considerable amounts of marine aerosols captured and mixed with the dust particulate matter during the passage of air masses close to the surface of the Mediterranean Sea and/or Atlantic Ocean. The aerosol layer’s origin is proven by using air mass transport modeling and forecasting data. Measurements are carried out at two wavelengths (1064 nm and 532 nm) by means of the two aerosol channels of a lidar based on a frequency-doubled Nd:YAG laser. Topological, dynamical, optical, and microphysical properties of the dust/aerosol layers are studied and analyzed. Timeaveraged vertical profiles of the atmospheric backscattering coefficient at 1064 nm and 532 nm are presented. By using backscatter-related Ångström exponents, microphysical properties of aerosol particles are characterized qualitatively. Color map diagrams illustrate the temporal evolution of the aerosol density height distribution. Conclusions concerning the effects of dust mixing with marine aerosols are drawn.