One year of regular aerosol observations with a multi-wavelength Raman lidar in Portugal

Abstract

Data of one year (January to December 2010) has been analyzed regarding aerosol layers in the free troposphere. In total, 120 layers were observed above the boundary layer during 56 out of 78 performed measurements. The investigated aerosol types were anthropogenic (15% of all layers), forest fire plumes (10%), volcanic from Eyjafjallajokull (6%), desert dust (17%) and aerosol transported over the sea below an altitude of 2 km (18%). The remaining 35% of the layers could not be assigned to one aerosol type unambiguously. The seasonal variability was investigated as well. In winter, only 8% of the aerosol layers were detected. Most layers were observed during spring (40%) and summer (34%). The aerosol layer mean height, layer depth, lidar ratios, Angstrom exponents and aerosol optical depths as well as relative humidity were investigated with the aim of a characterization of the individual aerosol types. The variations of most of the analyzed properties within one cluster were high. This is partly due to differences in, aerosol mixing close to the source, aging processes or different transport paths of the aerosol layers in one cluster. Lidar ratios at 355 nm and extinction-related Angstrom exponents from 355 to 532 nm were (51 ± 17) sr and 1.7 ± 0.7, respectively, for anthropogenic aerosol, (43 ± 13) sr and 1.4 ± 0.5 for forest fire aerosol, (50 ± 11) sr and 1.9 ± 1.0 for volcanic aerosol, (58 ± 20) sr and 0.5 ± 0.3 for desert dust, (52 ± 20) sr and 1.8 ± 0.8 for aerosol transported over the sea below 2 km and (54 ± 21) sr and 1.8 ± 1.0 for all layers, which could not be assigned to any of the types.