1,721,005 research outputs found
Application of a high-temporal resolution model for the identification of columnar aerosol components
No full textA high-temporal resolution model for the identification of columnar aerosol composition was applied to two sets of radiometric measurements obtained one in a semi-rural site of South Italy and the other in an urban/traffic site of the Po Valley, northern Italy. Inputs of the model are the spectral Aerosol Optical Depths (AODs) from direct solar radiation data to derive the contribution to the total extinction of nine aerosol species, i. e Water Soluble (WS), Black Carbon (BC), Sea Salt accumulation (SSacc), Sea Salt coarse (SScoa), Biogenic (Bio), Mineral Coarse (Mcoa), Mineral Accumulation (Macc), Small Organic Matter (SOM), and Large Organic Matter (LOM). In order to better parameterize the absorptive properties of dust and organic particles, a wavelength dependent imaginary part of the refractive index was used for dust and organics. Despite the differences between the two sites, a prevalence of fine aerosols (organics, WS and BC) was found in both cases suggesting the relevance of anthropogenic sources such as traffic. The retrieved AOD BC component was compared to Equivalent BC (EBC) concentrations measured in situ by an aethalometer at both sites. For mean daily values good correlations were found (R2 = 0.7), whereas high-temporal resolution (hourly basis) columnar composition was verified to be more reliable in cases of surface-column coupling. The possibility to apply this simple model to direct irradiance data from portable radiometers in areas where no routine measurements are available, and obtaining results with an increased temporal resolution, can help to gather information on aerosol columnar composition to be used in radiative, climate and transport models
A correlation study between aerosol size distribution and meteorological parameters for a desertic area in Namibia.
No full textA seasonal measurements campaign of ground-based aerosol optical depth for correlation with TOMS aerosol index.
No full text
On the structural response of flat-bottom silos under seismic excitation: Analytical developments and experimental investigations
Full text linkThe structural design of steel silos containing granular materials represents a challenging issue. Silos differ from many other civil engineering structures in that the weight of the silo structure is significantly lower than the one of the ensiled granular material and, in case of earthquake events, the particle-structure interaction plays an important role in the global dynamic response. The complex mechanism through which the ensiled material interacts with the silo wall has been studied since the XIX century. Nonetheless, several issues are still to be addressed and structural failures still occur during filling and, especially, discharging phases, as well as during strong ground motions. It is well known that both metal and concrete silos are characterized by a relatively high failure rate (both ground- and columns-supported silos), particularly during earthquakes. This thesis focus on different aspects related to the structural behavior of flat-bottom steel silos filled with granular material. Part I begins with a comprehensive review of the main analytical, numerical and experimental research devoted to the study of the static, dynamic and seismic behavior of filled silo systems, together with a review of the current design code provisions for the seismic design of silo systems. A comparison between the current code provisions on the seismic behavior of these particular structures and the actual body of knowledge is provided. Finally, a comprehensive review on the use of the seismic isolators in industrial facilities is reported as well. Part II presents a detailed description of experimental campaign conducted with the main aim of developing a non-standard test capable of measuring in a direct way the coefficient of friction of the stored material with the corrugated wall section of a silo structure. Part III is focused on developing a representative analytical framework of the induced horizontal forces by the granular material onto the internal silo wall during a seismic event. It starts by reviewing the historical development of the formula adopted by Eurocode EN1998-4:2006 and other current standards starting from the early research work in the 70s and 80s, passing by the main analytical model of [Silvestri et al., 2012] on which this work is based. Later on, a novel method for predicting the dynamic overpressure for other silo categories than those covered by the original development is presented. Therefore, it collects all the details of the new proposed refinements, introducing the main assumptions, the technical specifications, and the limits of validity. At the end, Part IV presents the interpretation of the results of a series of shaking-table tests on a full-scale flat-bottom manufactured steel silo filled with a granular material in fixed-base and isolated-base configurations. The isolators put between the table and the r.c. plate are Curved Surface Sliders friction pendulum devices. The results are relevant to the identification of the basic dynamic properties (frequencies and damping ratios) of the filled silo system, the experimental assessment of the static pressure (during filling phase) and seismic response (acceleration amplification values, dynamic overpressures and effective mass) of the system and the effectiveness of the isolation system at the base of the silo. Finally, the experimental results were exploited to provide a proof of concept for the proposed analytical model
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Analysis of equivalent black carbon multi-year data at an oil pre-treatment plant: Integration with satellite data to identify black carbon transboundary sources
No full textThis study analyzes a multi-year dataset of equivalent black carbon (EBC) concentration collected in 2012–2015 by a 7-wavelengths Aethalometer at Centro Olio Val d'Agri (COVA) in southern Italy, which is the largest European oil pre-treatment plant. These data, together with the local air circulation analysis, were used to identify the black carbon (BC) sources in Agri valley, specifically the COVA plant and vehicular traffic. During a limited period of 2012–2013, simultaneous measurements of PM10 concentration were available for comparison with the EBC data, which revealed correlation values of 0.31–0.43 between PM10 and EBC indicating a relevant contribution of BC to particulate matter at the site. On average, EBC/PM10 ratio is 7%, a value equal to that found at an urban-background site in Rome measured during non-rush hours. Moreover, an ad hoc procedure combining EBC data, Hybrid Single-Particle Lagrangian Integrated Trajectory back-trajectories (HYSPLIT), and satellite fire data enabled detection of days affected by the transport of carbonaceous particles. Both Visible Infrared Imaging Radiometer Suite (VIIRS) and Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data were used as input for the algorithm, and the corresponding results were compared and discussed. VIIRS showed a better performance in detecting smaller/cooler hotspots especially in cases of flaring, as observed during flaring events at the COVA plant itself. Application of the procedure suggests that both regional and non-regional biomass burning episodes, which occur mainly during summer, could contribute to the BC load at the site. The approach applied to the case study of the present work can be useful for estimating the relative contributions of local and remote sources of BC
Valutazione dell’impatto di un piccolo scarico civile su un torrente appenninico incontaminato: parametri biologici,’ecotossicologici e chimici.
No full textOzone correction to the aerosol optical depth in the Chappius band.
No full textAerosol optical depth in the visible range is affected by ozone absorption (Chappuis band). In order to derive reliable information from extinction measurements of solar irradiance, a suitable correction has to be considered. Ozone correction based on climatological data sets has been proved ineffective. Better results are typically obtained on the basis of indirect methods which, nevertheless, require some nd hoc assumptions such as the wavelength dependence on aerosol optical depth. A validation of these indirect methods is provided in this paper. Direct estimations of ozone profiles have been derived from ultra-violet and visible spectral scattered solar radiation. The Umkehr method was resorted for implementing a suitable inversion scheme for the ozone profile. Our results show that indirect ozone correction procedures are really capable of yielding absorption ozone-free aerosol optical depth. (C) 1998 Elsevier Science Ltd. All rights reserved
Black carbon and its impact on air quality in two semi-rural sites in Southern Italy near an oil pre-treatment plant
Full text linkOne-year-long data (October 2017–October 2018) of the equivalent black barbon (EBC), absorption Ångström exponent (AAE), and gaseous compound concentrations in two semi-rural sites in the Agri Valley, Southern Italy, were analyzed. This study aimed to assess the effects of combustion emissions on the air quality and people's health in these sites. The first measurement site, VZI, is located close to the plant, whereas the second is in Grumento, one of the towns at the edge of the valley, approximately 3 km away from the COVA. The emissions mainly originate from the biggest European on-shore pre-treatment plant of crude oil, the Centro Olio Val d'Agri (COVA), which hosts three incinerators and three torches continuously burning. EBC and gaseous pollutants from the COVA mainly affect the area close to the plant. A reduced effect is observed in Grumento where the AAE analysis highlighted the contribution of local domestic heating as an additional source during the cold season. A procedure combining EBC measurements, high-resolution fire satellite visible/infrared imaging radiometer (VIIRS) data, and hybrid single-particle Lagrangian integrated trajectory (HYSPLIT) back-trajectories allowed the identification of the measurement days influenced by both regional and transboundary transport of biomass burning emissions. The identified days were mostly in July, August, and October 2018. The comparison between EBC and PM2.5 data, only available for the Grumento site, showed a good correlation (R2 = 0.6 on a yearly basis), revealing the relevant contribution of the EBC to the fine particulate matter at the site. Finally, a risk communication methodology was applied to associate the number of daily passively smoked cigarettes (PSC) to the measured EBC concentrations. The daily PSC were 2.8 for VZI, and 1.4 for Grumento, which are closer to the results at the remote sites (0.7) than those at the urban sites (10.1≤ PSC≤ 159.0)
- …
