Observed and simulated vertically resolved optical properties of continental aerosols over southeastern Italy: A closure study

Abstract

[1] A 2.5-year data set of Raman lidar measurements performed in Lecce within the European Aerosol Research Lidar Network and a numerical model are used to characterize continental aerosols over southeast Italy. Continental conditions are selected by means of back trajectories, limiting the data set to cases of advection from the European continent. The model is used to constrain the relevant aerosol microphysical parameters needed to reproduce the altitude-resolved optical properties measured by lidar, namely, aerosol extinction ( ), backscatter ( ), and lidar ratio (LR = / ) at 351 nm. The observed variability of , , and LR is simulated by randomly varying, within appropriate ranges, all the microphysical parameters describing the aerosol composition and size distribution (assumed as bimodal). An optimal model configuration capable of reproducing within ±10% the mean optical properties retrieved by lidar, including their vertical pattern, is presented and discussed with sensitivity studies. Results indicate rather clean continental aerosols to characterize the site, with water-soluble fine-mode aerosols (dry modal radius of 0.05-0.10 m) accounting for 98-99% of the total number of particles. The (dry) imaginary refractive index of fine-mode particles is extended up to 0.02 to better fit the lidar data. This suggests some mixing of water-soluble substances with more absorbing material. Coarse-mode particles (modal radius 0.4-0.5 m) are shown to play a crucial role in determining the observed vertical profile of and LR.

Advection patterns and aerosol optical and microphysical properties by AERONET over south-east Italy in the central Mediterranean

“…Figure 10a (grey solid line) reveals that total Lr values vary between 20 and 120 sr and are peaked at ∼ =80 sr. These data are in satisfactory accordance with those retrieved by Raman lidar measurements at 351 nm performed in Lecce during 2.5 year measurements, which provided lidar ratios spanning the 5-130 sr range (Barnaba et al, 2007) for air masses advected from north and east-European countries. Figure 10a In conclusion, the above reported analysis indicates that air masses carrying moderately-absorbing (0.8<SSA<1.0 and 20 sr <Lr<120 sr), fine-mode (0.8<η<1.0 and 0.6<g<0.8) particles are advected over south-east Italy and hence over the central Mediterranean basin, from the urban/industrial European countries.…”

“…According to d ' Almeida et al (1991) and Hess et al (1998), AOD, η, SSA, and g frequency distribution plots indicate that the Sector A aerosol can be considered representative of "continental average aerosol", mostly made of water soluble and a small amount of soot and insoluble components. A closure study between a 2.5-year data set of Raman lidar measurements (performed in Lecce within the European Aerosol Research Lidar Network) and a numerical model, also indicated that rather clean continental aerosols, with watersoluble fine-mode aerosol accounting for 98-99% of the total number of particles, characterized the aerosol load advected over south-east Italy from north and east European countries (Barnaba et al, 2007).…”

“…The Mediterranean Sea that is bounded to the north by the European continent and to the south by North Africa, is largely affected by different types of particles: desert dust, from the Sahara desert and surrounding arid regions; anthropogenic particles, produced mainly in urban and industrial areas of Europe; marine aerosol, from the Mediterranean itself or transported from the North Atlantic; and biomass burning particles, often produced in forest fires (e.g. Lelieveld et al, 2002;Barnaba et al, 2004;Pace et al, 2006;Barnaba et al, 2007). The strength of dust outbreaks over the Mediterranean tends to facilitate the Saharan dust detection by both ground and space based observations, allowing the quantification of its transport and optical and microphysical properties (e.g.…”

Physical and optical properties of atmospheric aerosols by in-situ and radiometric measurements

“…All measurements have been performed in a semi-rural site belonging to the Mediterranean area that is a proper site for monitoring variability of aerosol properties in a complete way due to the influence of different air masses, as confirmed also by systematic LIDAR measurements for vertical optical and physical aerosols properties study (Barnaba et al, 2007;Papayannis et al, 2005). In particular seaborne particles both from the Mediterranean itself and transported from the Atlantic Ocean are present, together with dust from Sahara desert and polluted and smoke aerosols mainly from Central and Eastern Europe.…”

On the differences of ultraviolet and visible irradiance calculations in the Mediterranean basin due to model- and satellite-derived climatologies of aerosol optical properties

“…It is generally characterized by clean continental aerosols and a mixing of water-soluble and more absorbing particles is evident (Barnaba et al, 2007). …”