Measurements of Aerosol Optical and Microphysical Properties in Tizi Ouzou

ABSTRACT

To characterize the optical behavior of atmospheric particles located above the region of Tizi Ouzou, a micro-LIDAR and a sun/sky-photometer have been used. The analysis of three years of observation has revealed a large variability in the optical properties of the particles present in the atmosphere of this region. The aerosol extinction optical depth (τ) at 500 nm varies from 0.03 to about 2. The Angstrom Exponent (α), in the range 440–870 nm, varies from 0 to 1.8 and is indicating a large variability in size. The combination of micro LIDAR and sun/sky photometer measurements allowed us to determine the vertical profiles of the aerosol extinction coefficient (σ_ext). The vertical profile helps to separate local from transported particles origins. The observation site is located in the city and surrounded by high mountains (2300 m asl). The aerosol optical depth at 500 nm and the Angstrom exponent respectively having the values τ > 0.5 and α < 0.25 indicate the high presence of desert dust particles from Saharan origin. This type of particles is frequently observed for α ranging between 0.25 and 0.35. The analysis of back-trajectories helped to identify the probable origin of air masses affecting the region. Our results show that a routinely operating LIDAR / photometer observing system coupled with back-trajectories analysis is a relevant tool for aerosols monitoring. They show, for the first time, the high temporal variability of aerosols present in the atmosphere of the Tizi Ouzou region.