Classification of atmospheric particles over the Urmia Lake: Two case studies

Abstract

In this study, we examined the aerosols in the Urmia Lake atmosphere, using a polarization lidar, looking for traces of salt particles. Urmia Lake is a hypersaline lake and most part of it now is dry. We have applied the two-step POLIPHON method to classify particles in three categories, i.e., dust, non-dust, and salt-dust/polluted dust. In the vicinity of the lake’s bed, salt-dust particles (mixture of dust and salt) exhibit lower particle depolarization ratios (PDRs) compared with pure dust; However, their PDRs are higher than urban pollution or other anthropogenic particles. Two case studies are presented here. These cases represent particles originating from both local and trans-regional sources. Particles transported from Africa and the Tigris-Euphrates basin mainly show higher PDR values (> 0.2), indicating the presence of dust as the dominant aerosol type. However, the PDR of particles that originated from the lake’s bed is close to that of the polluted dust. Since the measurements were conducted very close to the source, we called such particles that are rising from the lake bed as salt-dust. In both cases, the concentration of these particles is considerably enhanced at altitudes below 2 km AGL with respect to higher ranges.