Vertically resolved aerosol properties by multi-wavelength lidar measurements

• Published in: Atmospheric Chemistry and Physics
• Main Authors: M. R. Perrone, F. De Tomasi, G. P. Gobbi
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2014
• Subjects: Physics; QC1-999; Chemistry; QD1-999; Aerosol Robotic Network
• Online Access: https://doi.org/10.5194/acp-14-1185-2014; https://doaj.org/article/38c9cf29e2eb40a4b3f5c6170f231513

An approach based on the graphical method of Gobbi and co-authors (2007) is introduced to estimate the dependence on altitude of the aerosol fine mode radius ( R f ) and of the fine mode contribution (η) to the aerosol optical thickness (AOT) from three-wavelength lidar measurements. The graphical method of Gobbi and co-authors (2007) was applied to AERONET (AErosol RObotic NETwork) spectral extinction observations and relies on the combined analysis of the Ångstrom exponent ( å ) and its spectral curvature Δ å . Lidar measurements at 355, 532 and 1064 nm were used in this study to retrieve the vertical profiles of å and Δ å and to estimate the dependence on altitude of R f and η(532 nm) from the å –Δ å combined analysis. Lidar measurements were performed at the Department of Mathematics and Physics of the Universita' del Salento, in south-eastern Italy. Aerosol from continental Europe, the Atlantic, northern Africa, and the Mediterranean Sea are often advected over south-eastern Italy and as a consequence, mixed advection patterns leading to aerosol properties varying with altitude are dominant. The proposed approach was applied to ten measurement days to demonstrate its feasibility in different aerosol load conditions. The selected days were characterized by AOTs spanning the 0.26–0.67, 0.15–0.39, and 0.04–0.27 range at 355, 532, and 1064 nm, respectively. Mean lidar ratios varied within the 31–83, 32–84, and 11–47 sr range at 355, 532, and 1064 nm, respectively, for the high variability of the aerosol optical and microphysical properties. å values calculated from lidar extinction profiles at 355 and 1064 nm ranged between 0.1 and 2.5 with a mean value ± 1 standard deviation equal to 1.3 ± 0.7. Δ å varied within the −0.1–1 range with mean value equal to 0.25 ± 0.43. R f and η(532 nm) values spanning the 0.05–0.3 μm and the 0.3–0.99 range, respectively, were associated with the å –Δ å data points. R f and η values showed no dependence on the altitude. 60% of the data points were in the Δ å – å space delimited ...