Aerosol optical properties have been measured on the island of Lampedusa (35.5°N, 12.6°E) with seven-band multifilter rotating shadowband radiometers (MFRSRs) and a CE 318 Cimel sunphotometer (part of the AERONET network) since 1999. Four different MFRSRs have operated since 1999. The Cimel sunphotometer has been operational for a short period in 2000 and in 2003-2006 and 2010-present. Simultaneous determinations of the aerosol optical depth (AOD) from the two instruments were compared over a period of almost 4 years at several wavelengths between 415 and 870 nm. This is the first long-term comparison at a site strongly influenced by desert dust and marine aerosols and characterized by frequent cases of elevated AOD. The datasets show a good agreement, with MFRSR underestimating the Cimel AOD in cases with low Ångström exponent; the underestimate decreases for increasing wavelength and increases with AOD. This underestimate is attributed to the effect of aerosol forward scattering on the relatively wide field of view of the MFRSR. An empirical correction of the MFRSR data was implemented. After correction, the mean bias (MB) between MFRSR and Cimel simultaneous AOD determinations is always smaller than 0.004, and the root mean square difference is ≤0.031 at all wavelengths. The MB between MFRSR and Cimel monthly averages (for months with at least 20 days with AOD determinations) is 0.0052. Thus, by combining the MFRSR and Cimel observations, an integrated long-term series is obtained, covering the period 1999-present, with almost continuous measurements since early 2002. The long-term data show a small (nonstatistically significant) decreasing trend over the period 2002-2013, in agreement with independent observations in the Mediterranean. The integrated Lampedusa dataset will be used for aerosol climatological studies and for verification of satellite observations and model analyses.

Abstract. The Mediterranean Basin atmosphere is influenced by both strong natural and anthropogenic aerosol emissions and is also subject to important climatic forcings. Several programs have addressed the study of the Mediterranean basin; nevertheless important pieces of information are still missing. In this framework, PM10 samples were collected on a daily basis on the island of Lampedusa (35.5° N, 12.6° E; 45 m a.s.l.), which is far from continental pollution sources (the nearest coast, in Tunisia, is more than 100 km away). After mass gravimetric measurements, different portions of the samples were analyzed to determine the ionic content by ion chromatography (IC), the soluble metals by inductively coupled plasma atomic emission spectrometry (ICP-AES), and the total (soluble + insoluble) elemental composition by particle-induced x-ray emission (PIXE). Data from 2007 and 2008 are used in this study. The Positive Matrix Factorization (PMF) model was applied to the 2-year long data set of PM10 mass concentration and chemical composition to assess the aerosol sources affecting the central Mediterranean basin. Seven sources were resolved: sea salt, mineral dust, biogenic emissions, primary particulate ship emissions, secondary sulfate, secondary nitrate, and combustion emissions. Source contributions to the total PM10 mass were estimated to be about 40 % for sea salt, around 25 % for mineral dust, 10 % each for secondary nitrate and secondary sulfate, and 5 % each for primary particulate ship emissions, biogenic emissions, and combustion emissions. Large variations in absolute and relative contributions are found and appear to depend on the season and on transport episodes. In addition, the secondary sulfate due to ship emissions was estimated and found to contribute by about one-third to the total sulfate mass. Results for the sea-salt and mineral dust sources were compared with estimates of the same contributions obtained from independent approaches, leading to an estimate of the water content bound to the sea salt in the marine source.

Abstract. Particulate matter with aerodynamic diameters lower than 10 µm, (PM 10 ) aerosol samples were collected during summer 2013 within the framework of the Chemistry and Aerosol Mediterranean Experiment (ChArMEx) at two sites located north (Capo Granitola) and south (Lampedusa Island), respectively, of the main Mediterranean shipping route in the Straight of Sicily.The PM 10 samples were collected with 12 h time resolutions at both sites. Selected metals, main anions, cations and elemental and organic carbon were determined.The evolution of soluble V and Ni concentrations (typical markers of heavy fuel oil combustion) was related to meteorology and ship traffic intensity in the Straight of Sicily, using a high-resolution regional model for calculation of back trajectories. Elevated concentration of V and Ni at Capo Granitola and Lampedusa are found to correspond with air masses from the Straight of Sicily and coincidences between trajectories and positions of large ships; the vertical structure of the planetary boundary layer also appears to play a role, with high V values associated with strong inversions and a stable boundary layer. The V concentration was generally lower at Lampedusa than at Capo Granitola V, where it reached a peak value of 40 ng m −3 .Concentrations of rare earth elements (REEs), La and Ce in particular, were used to identify possible contributions from refineries, whose emissions are also characterized by elevated V and Ni amounts; refinery emissions are expected to display high La / Ce and La / V ratios due to the use of La in the fluid catalytic converter systems. In general, low La / Ce and La / V ratios were observed in the PM samples. The combination of the analyses based on chemical markers, air mass trajectories and ship routes allows us to unambiguously identify the large role of the ship source in the Straight of Sicily.Based on the sampled aerosols, ratios of the main aerosol species arising from ship emission with respect to V were estimated with the aim of deriving a lower limit for the total ship contribution to PM 10 . The estimated minimum ship emission contributions to PM 10 were 2.0 µg m −3 at Lampedusa and 3.0 µg m −3 at Capo Granitola, corresponding with 11 and 8.6 % of PM 10 , respectively.

Measurements of downwelling shortwave (SW) and longwave (LW) irradiance were carried out on an oceanographic buoy close to the island of Lampedusa (Italy), in the central Mediterranean Sea. Irradiance measurements on the buoy were acquired at high time resolution together with the radiometer pitch and roll angles. The measurements carried out during 2016 have been compared with ground-based observations made at the Lampedusa Atmospheric Observatory, about 15 km northeast of the buoy. The radiometers were compared before and after deployment on the buoy and are traceable to the World Radiometric Reference scale. The SW measurements were corrected for the thermal offset. A small bias (measurements over the sea are smaller than on land) of about −2 W m−2 is found in the daily mean SW, and a moderate bias of +6.2 W m−2 (irradiance over the sea is larger than on land) is found in the LW. Similar biases are found when instantaneous measurements obtained with horizontal radiometers, clean domes, and cloud-free conditions are selected, suggesting that impacts of the moving platform and poor dome cleaning are minor at this site. The effect of the mean tilt angle was also investigated. Deviations in the hourly mean SW irradiance are on the order of 20% for a mean offset of 4° with respect to the solar zenith angle; the effect of tilt angle on LW irradiance appears to be negligible. Radiative transfer calculations show that the observed biases may be ascribed to the differences in the instrument altitude (through radiation absorption, scattering, and emission by the atmospheric constituents in the lowest atmospheric layers) and in the SW surface albedo.

Abstract. Measurements of global and diffuse photosynthetically active radiation (PARproperties also contribute to produce small radiative effects on PAR in summer. 34The cloud radiative effect has been de-seasonalized to remove the influence of annual irradiance variations.