Lidar Ratios and Depolarization Ratios of Arabian, Saharan, Turkish Dust, and of Complex Mixtures of Dust, Smoke, and Urban Haze Over the AERONET/EARLINET Site at Limassol, Cyprus
Mamouri, Rodanthi-Elisavet1; Nisantzi, Argyro1; Hadjimitsis, Diofantos1; Ansmann, Albert2
1Cyprus University of Technology (CUT), Department of Civil Engineering and Geomatics, CYPRUS; 2Cyprus Leibniz Institute for Tropospheric Research University of Technology (CUT), Department of Civil Engineering and Geomatics, GERMANY
Due to the vicinity to western Asia (Arabian desert), northern Africa (Saharan desert), and southern and eastern Europe (anthropogenic haze, biomass burning smoke), the Mediterranean island of Cyprus (continuously influenced by marine aerosol in the boundary layer) is an almost ideal place for monitoring and studying of very different aerosol mixtures, vertical layering, and contrasting aerosol transport in the marine boundary layer and free troposphere. Continuous aerosol observations with sun-sky photometer (AERONET, since April 2010) and 532 nm polarization lidar (since May 2010) are performed at CUT, Limassol, Cyprus. Based on backward trajectory cluster analysis air masses from the north, east, south and west are investigated in terms of free-tropospheric extinction-to-backscatter ratio (lidar ratio) and particle depolarization ratio at 532 nm. The main findings can be summarized as follows: Lidar ratios of Arabian dust are rather low with values of around 30 sr. For eastern Saharan dust we found lidar ratios of 30-40 sr. For western Saharan dust, it is known that lidar ratios are 50-60sr. The west-to-east decrease of the lidar ratio is related to the decreasing illite concentration in the dust particles, decreasing from 80% for western Saharan dust particles to less than 5% in Arabian dust. Correspondingly the real part of the refractive index of the dust particles decrease from >1.55 for western Saharan dust to <1.45 for Arabian dust. Depolarization ratio profiling yields 532 nm particle depolarization ratios of 30-35% for pure desert dust disregarding the dust source (east and south clusters, Arabian and Saharan desert, mainly coarse-mode particles according to the AERONET observations). But a significant lower depolarization ratio of 2-10% (north cluster, in cases without fire smoke detection along the air mass flow and thus minor contribution of fire-induced convectively injected soil dust), and 10-20% when the air masses crossed areas with biomass burning and strong convective activities triggering considerable injection of soil dust. Fine-mode soil dust causes 532 nm depolarization ratios of 15-20%. The depolarization ratio in combination with the retrieved backscatter and extinction coefficient profiles can be used to determine the relative contribution of soil dust to the observed optical properties. Acknowledgments This research form part of the projects PENEK/0311/05 and WEBAIR 2 which are funded by the Cyprus Research Promotion Foundation.