Stable boundary layer conditions are long known for causing increasing concentration of pollutant. The region of the Po Valley has a particularly unfortunate topographical conformation which favours low wind and strong inversion situations, a meteorological characteristic that leads to so-called episodic conditions, especially during the cold season. ARPAV-CMT has recently installed a network of boundary layer profilers consisting of four passive microwave radiometers and four SODAR, funded in the framework of the DOCUP 2000-2006 project (DOCumento Unico di Programmazione) and of the Project 'Air pollution in the city of Padua'. This network is briefly presented and an illustration is given as to its potential to analyse the PM10 (particulate matter with diameter lower than 10 ?m) concentration evolution. An entire year of data, as well as for a highconcentration episode is analyzed. In particular, emphasis is given to the documentation of the diurnal cycle of PM10 in relation to the atmospheric stability. It was found that PM10 is strongly modulated by synoptic-scale forcing and exhibits a strong diurnal cycle, especially in synoptically undisturbed conditions, when PM10 can exhibit large variations in just a few hours. A conceptualization is proposed which accounts for the daily emission cycle for the interpretation of the diurnal cycle of PM10 concentrations in anticyclonic conditions. It pinpoints the fundamentally different accumulation and removal mechanisms of the particulate matter from the atmosphere in stable and unstable conditions, highlighting the importance of the atmospheric stability at the time of the evening emission peak during the cold season. Zusammenfassung Es ist bekannt, dass stabile Grenzschichtbedingungen zu erhöhten Schadstoffbelastungen führen können. Die Poebene hat eine besonders unglückliche topographische Beschaffenheit, die Schwachwindlagen mit starken Temperaturinversionen begünstigt; meteorologische Eigenschaften, die besonders in der kalten Jahreszeit zu sogenannten episodischen Bedingungen führen. ARPAV-CMT hat kürzlich ein Netzwerk von Grenzschichtprofilern installiert, das aus vier passiven Mikrowellenradiometern und aus vier SODAR-Geräten besteht. Die Finanzierung kam dabei vor allem aus dem DOCUP Projekt 2000-2006 (DOCumento Unico di Programmazione). Dieses Netzwerk wird vorgestellt und beispielhaft angewendet, um die PM10-Entwicklung für ein ganzes Jahr und für eine Episode mit hohen PM10-Konzentrationen zu analysieren. Insbesondere wird dabei die Beschreibung des PM10-Tagesgangs in Beziehung zu den Eigenschaften der atmosphärischen Stabilität gesetzt. Es wurde herausgefunden, dass PM10 stark von synoptisch-skaligem Antrieb moduliert wird und einen ausgeprägten Tagesgang besitzt, vor allem in synoptisch ungestörten Verhältnissen, wenn PM10 große Variationen in wenigen Stunden aufweisen kann. Ein Schema für die Interpretation des PM10-Tagesgangs während stabiler Hochdrucklagen wird vorgestellt, das den Tagesgang der Emissionen berücksichtigt. Es hält die fundamental versch...
Hexagonally ordered mesoporous silica materials MCM-41 and SBA-15 have been synthesized and loaded with Ag nanoparticles, utilizing both chemical synthesis and ultrashort pulsed laser ablation in liquid.In laser ablation, a silver target, immersed in aqueous suspension of ordered mesoporous silica SBA-15, was irradiated by ultra-short laser pulses to generate silver nanoparticles. For comparison samples of similar silver contents were prepared either by incorporating silver into the SBA-15 during a hydrothermal synthesis or by introducing silver in MCM-41 by template ion-exchange. Samples were characterized by XRD, N 2 physisorption, TEM and UV-vis spectroscopy. All preparations contained significant amount of 5-50 nm size silver 2 agglomerates on the outer surface of the silica particles. The laser ablation process did not cause significant destruction of the SBA-15 structure and metallic silver (Ag 0 ) nanoparticles were mainly generated. It is demonstrated that by laser ablation in aqueous silica suspension smaller and more uniform metallic silver particles can be produced and loaded on the surface of the silica support than by synthesis procedures. Catalytic properties of the samples have been tested in the total oxidation of toluene. Because of its favorable Ag dispersity the Ag/SBA-15 catalyst, generated by the laser ablation method, had better catalytic stability and, relative to its Ag load, higher activity than the conventional Ag/SBA-15 preparations.
In the present study, the pulsed laser ablation in liquid technique was used to produce palladium nanoparticles in acetone and in water. The composition, morphology and oxidation state of the obtained nanoparticles have been characterized by HR-TEM, XPS and XRD techniques. The results evidence that the nature of the solvent influences the physical–chemical properties of the products. In acetone non-aggregate metallic nanoparticles have been obtained, while in water the oxidation of the particles surface is present, as showed by the XPS analysis.\ud
Moreover, the particles obtained in water are aggregated and the coalescence effect is evident. The different size distributions of nanoparticles obtained in the two liquids have been interpreted considering the different cavitation bubble dynamics
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