Maria Rita Perrone

Laser damage dependence on structural and optical properties of ion-assisted HfO2 thin films

Abstract Laser damage studies at 248 nm (KrF excimer laser) have been performed on HfO 2 films of 300 nm thickness deposited on silica substrates by the Xe ion-assisted electron beam evaporation technique. The assistance parameters (ion mass, energy and current density) have been adjusted to investigate the effect of the Xe-ion momentum transfer parameter P on the film optical and structural properties. Then, the dependence of laser damage fluence on film properties has been studied. Higher laser damage fluences have been found for the HfO 2 films deposited at lower P values and characterized by a fully crystalline structure with the grain of smaller size and randomly oriented.

Particulate matter characterization at a coastal site in south-eastern Italy

Several samples of airborne particulate matter (PM), collected from 6th November to 6th December 2003 at a coastal site in the south-east of Italy, have been analyzed by different techniques to characterize elemental composition and morphological properties of the inorganic PM fraction and obtain preliminary results on anthropogenic contributions. Al, Cr, Cu, Fe, Mn, V, Pb, Ti, Ca and Zn mass concentrations, evaluated by an inductively coupled plasma atomic emission spectrometer, account for up to l% of the bulk PM mass in the investigated samples. According to geochemical calculations, Ca, Al, Fe and Mn are predominantly of crustal origin, while Cr, Cu, Pb, V, Ti and Zn heavy metals are of anthropogenic origin. Ion chromatography analyses have identified sulfate (SO(4)(2-)) nitrate (NO(3)(-)), sodium (Na(+)), and ammonium (NH(4)(+)) as the main ionic components accounting for up to 38% of the total PM mass and up to 90% of the total ionic mass. Besides ion chromatography, X-ray energy dispersive (EDX) microanalyses have revealed the high variability of Cl: its weight concentration varies from about 24% to below the detection limit (>or=0.5%) in the investigated samples. The marked anti-correlation between the excess of S and the Cl/Na ratio has allowed inferring that reactions between sea salt particles and acidic sulfates, which liberate HCl gas to the atmosphere leaving particles enriched in non-sea-salt sulfates, have significantly contributed to chloride depletion. Morphological analyses by scanning electron microscopy have shown that about 90% of the total sampled particles have a diameter <or=5 microm.

Application of MODIS Products for Air Quality Studies Over Southeastern Italy

Aerosol optical thicknesses (AOTs) by the MODerate Resolution Imaging Spetroradiometer (MODIS) on-board Aqua and Terra satellites, and ground-based measurements of PM10 mass concentrations, collected over three years (2006–2008) at two suburban sites which are 20 km apart, are correlated to assess the use of satellite data for regional air quality studies over Southeastern Italy, in the central Mediterranean. Due to the geographical location, this area is affected by local and long-range transported marine, desert (from Sahara), and anthropogenic (from continental Europe) aerosols. 24-hour averaged PM10 mass concentrations span the 1.6–152 µg/m 3 range. Yearly means of PM10 mass concentrations decrease from 2006 to 2008 and vary within the 26–36 µg/m 3 range. Daily mean values of MODIS AOTs vary up to 0.8 at 550 nm, while yearly means span the 0.15–0.17 range. A first assessment of the regression relationship between daily averaged PM10 mass concentrations and MODIS-AOTs shows that linear correlation coefficients ( R ) vary within the 0.20–0.35 range and are affected by the sampling year and the site location. The PM10-AOT correlation becomes stronger (0.34 ≤ R ≤ 0.57) when the analysis is restricted to clear-sky MODIS measurements. The cloud screening procedure adopted within the AERONET network is used in this study to select clear-sky MODIS measurements, since it allows obtaining larger R values than the ones obtained using the cloud fraction MODIS product to select clear-sky MODIS measurements. Using three years of clear-sky measurements to estimate PM10 mass concentrations from MODIS-AOTs, the empirical relation we have found is: PM10 ( m g/m 3 ) = 25 ( m g/m 3 ) + 65 ( m g/m 3 ) × AOT. Over 80% of the differences between the measured and satellite estimated PM10 mass concentrations over the three years are within ±1 standard deviation of the yearly means. The differences between yearly means of calculated and measured mass concentrations that are close to zero in 2006, increase up to 4 m g/m 3 at one siteand 8 m g/m 3 at the other site in 2008. The PM10 mass concentration decrease from 2006 to 2008 contributes to this last result. Our results demonstrate the potential of MODIS data for deriving indirect estimates of PM10 over Southeastern Italy. It is also shown that a stronger relationship between PM10 and MODIS-AOTs is obtained when the AOT is divided by the product of the mixing layer height with the ground wind speed and the analysis restricted to clear sky MODIS measurements. However, we have found that the stronger correlation (0.52 ≤ R ≤ 0.66) does not allow a significant improvement of MODIS-based-estimates of PM10 mass concentrations.

Imaginary refractive-index effects on desert-aerosol extinction versus backscatter relationships at 351 nm: numerical computations and comparison with Raman lidar measurements

A numerical model is used to investigate the dependence at 351 nm of desert-aerosol extinction and backscatter coefficients on particle imaginary refractive index (mi). Three ranges (-0.005 < or = mi < or = -0.001, -0.01 < or = mi < or = -0.001, and -0.02 < or = mi < or = -0.001) are considered, showing that backscatter coefficients are reduced as /mi/ increases, whereas extinction coefficients are weakly dependent on mi. Numerical results are compared with extinction and backscatter coefficients retrieved by elastic Raman lidar measurements performed during Saharan dust storms over the Mediterranean Sea. The comparison indicates that a range of -0.01 to -0.001 can be representative of Saharan dust aerosols and that the nonsphericity of mineral particles must be considered.

EARLINET correlative measurements for CALIPSO

The European Aerosol Research Lidar Network (EARLINET) was established in 2000 to derive a comprehensive, quantitative, and statistically significant data base for the aerosol distribution on the European scale. At present, EARLINET consists of 25 stations: 16 Raman lidar stations, including 8 multi-wavelength Raman lidar stations which are used to retrieve aerosol microphysical properties. EARLINET performs a rigorous quality assurance program for instruments and evaluation algorithms. All stations measure simultaneously on a predefined schedule at three dates per week to obtain unbiased data for climatological studies. Since June 2006 the first backscatter lidar is operational aboard the CALIPSO satellite. EARLINET represents an excellent tool to validate CALIPSO lidar data on a continental scale. Aerosol extinction and lidar ratio measurements provided by the network will be particularly important for that validation. The measurement strategy of EARLINET is as follows: Measurements are performed at all stations within 80 km from the overpasses and additionally at the lidar station which is closest to the actually overpassed site. If a multi-wavelength Raman lidar station is overpassed then also the next closest 3+2 station performs a measurement. Altogether we performed more than 1000 correlative observations for CALIPSO between June 2006 and June 2007. Direct intercomparisons between CALIPSO profiles and attenuated backscatter profiles obtained by EARLINET lidars look very promising. Two measurement examples are used to discuss the potential of multi-wavelength Raman lidar observations for the validation and optimization of the CALIOP Scene Classification Algorithm. Correlative observations with multi-wavelength Raman lidars provide also the data base for a harmonization of the CALIPSO aerosol data and the data collected in future ESA lidar-in-space missions.

Chemical composition of PM1 and PM2.5 at a suburban site in southern Italy

Organic (OC) and elemental carbon (EC), inorganic ions (Cl−, NO3−, SO42−, Na+, NH4+, K+, Ca2+), methanesulfonate (MSA−) and metals (Al, Fe, Pb, Mn, Ba, V) were monitored in PM1 and PM2.5 samples collected at a suburban site in south-eastern Italy, to contribute to the characterisation of fine particles in the Central Mediterranean. Mean mass concentrations are 13 µg/m3 and 22 µg/m3 in PM1 and PM2.5, respectively. OC, EC, SO42−, NH4+, NO3−, K+ and Ca2+ are predominant components and account for 54% and 56% of the PM1 and PM2.5 mass, respectively. OC, EC, SO42−, NH4+, K+ and Ca2+ concentrations lie in the range of the corresponding ones measured in PM1 and PM2.5 samples collected at suburban/urban Mediterranean sites. NO3− and trace element concentrations lie in the range of the corresponding ones measured in PM1 and PM2.5 samples collected at remote/background Mediterranean sites. The biogenic nss-SO42− accounts for ~5% and 4% of nss-SO42− in PM1 and PM2.5, respectively. The seasonal trend of the components partitioning and the interspecies correlation analysis in PM1 and PM2.5-1 indicated that the PM1 and PM2.5-1 components depend on season and are likely not controlled by similar sources, and/or similar generation processes, and/or similar transport patterns. The sulfur and nitrogen oxidation ratios were calculated to contribute to the understanding of the seasonal dependence of nitrate and sulfate concentrations in PM1 and PM2.5-1. The mass closure analysis showed that organic matter (OM), EC, and nitrate mass percentages are larger in autumn–winter. NH4+, nss-SO42−, and crustal matter mass percentages are larger in spring–summer. Finally, the ratio of the crustal matter in PM1 to that in PM2.5-1, which is 0.2 and 0.3 in spring–summer and autumn–winter, respectively, and the higher (OM+EC) contribution in PM1 than in PM2.5-1 led to the conclusion that PM1 would be a better indicator for fine-anthropogenic particles than PM2.5.

Laser damage studies on MgF2 thin films

The results of laser damage studies performed at 248 nm (KrF excimer laser) on MgF2 thin films deposited by different techniques (electron-beam evaporation, thermal boat evaporation, and ion-beam sputtering) on fused silica and CaF2 substrates are presented. We find that the films deposited on CaF2 substrates by the electron-beam evaporation technique present the highest damage threshold fluence (9 J/cm2). The photoacoustic (PA) beam deflection technique was employed, in addition to microscopical inspection, to determine laser damage fluences. We confirm, by scanning electron microscopy analysis of the damaged spots, the capability of the PA technique to provide information on the mechanisms leading to damage. The dependence of both laser damage fluence and damage morphology on the film deposition technique, as well as on the film substrate, is discussed.

Optimization of lidar data processing: a goal of the EARLINET-ASOS project

EARLINET-ASOS (European Aerosol Research Lidar Network - Advanced Sustainable Observation System) is a 5-year EC Project started in 2006. Based on the EARLINET infrastructure, it will provide appropriate tools to improve the quality and availability of the continuous observations. The EARLINET multi-year continental scale data set is an excellent instrument to assess the impact of aerosols on the European and global environment and to support future satellite missions. The project is addressed in optimizing instruments and algorithms existing within EARLINET-ASOS, exchanging expertise, with the main goal to build a database with high quality aerosol data. In particular, the optimization of the algorithms for the retrieval of the aerosol optical and microphysical properties is a crucial activity. The main objective is to provide all partners with the possibility to use a common processing chain for the evaluation of their data, from raw signals to final products. Raw signals may come from different types of systems, and final products are profiles of optical properties, like backscatter and extinction, and, if the instrument properties permit, of microphysical properties. This will have a strong impact on the scientific community because data with homogeneous well characterized quality will be made available in nearly real time.

Correlation between the structural and optical properties of ion-assisted hafnia thin films

The ion beam assistance during the film growth is one of the most useful method to obtain dense film along with improved optical and structural properties. Afnia material is widely used in optical coating operating in the UV region of the spectrum and its optical properties depend on the production method and the physical parameters of the species involved in the deposition process. In this work afnia thin films were evaporated by an e-gun and assisted during the growth process. The deposition parameters, ion beam energy, density of ions impinging on the growing film and the number of arrival atoms from the crucible, have been related to the optical and structural properties of the film itself. The absorption coefficient and the refractive index were measured by spectrophotometric technique while the microstructure has been studied by means of x-ray diffraction. A strictly correlation between the grain size, the optical properties and the laser damage threshold measurements at 248 nm was found for the samples deposited at different deposition parameters.

The European Aerosol Research Lidar Network (EARLINET): An Overview

The European Aerosol Research LIdar NETwork (EARLINET) is the first aerosol lidar network on a continental scale with the main goal to provide a comprehensive, quantitative, and statistically significant database for the aerosol distribution over Europe. Next, we present EARLINET along with the main network activities.