An Overview of the ASKOS Campaign in Cabo VerdeEleni Marinou
, Jesús Yus-Díez
, Griša Močnik
, 2023, objavljeni znanstveni prispevek na konferenci
Opis: In the framework of the ESA-NASA Joint Aeolus Tropical Atlantic Campaign (JATAC), the ASKOS experiment was implemented during the summer and autumn of 2021 and 2022. ASKOS comprised roughly 9 weeks of measurements in the Saharan dust outflow towards the North Atlantic, with operations conducted from the Cabo Verde Islands. Through its unprecedented dataset of synergistic measurements in the region, ASKOS will allow for the calibration and validation of the aerosol/cloud product from Aeolus and the preparation of the terrain for EarthCARE cal/val activities. Moreover, ASKOS marks a turning point in our ability to study Saharan dust properties and the processes affecting its atmospheric transport, as well as the link to other components of the Earth’s system, such as the effect of dust particles on cloud formation over the Eastern Atlantic and the effect of large and giant particles on radiation. This is possible through the synergy of diverse observations acquired during the experiment, which include intense 24/7 ground-based aerosol, cloud, wind, and radiation remote sensing measurements, and UAV-based aerosol in situ measurements within the Saharan air layer, up to 5.3 km altitude, offering particle size-distributions up to 40 μm as well as sample collection for mineralogical analysis. We provide an outline of the novel measurements along with the main scientific objectives of ASKOS. The campaign data will be publicly available by September of 2023 through the EVDC portal (ESA Validation Data Center).
Ključne besede: experimental campaign, remote sensing, lidar, radar, radiosondes, radiation, desert dust, in-situ, aerosol, optical properties, scattering, absorption, ASKOS
Objavljeno v RUNG: 25.09.2023; Ogledov: 312; Prenosov: 4
Celotno besedilo (4,87 MB)
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Secondary organic aerosol formation from semi- and intermediate-volatility organic compounds and glyoxal : relevance of O/C as a tracer for aqueous multiphase chemistryEleanor M. Waxman
, Katja Džepina
, Barbara Ervens
, Julia Lee-Taylor
, Bernard Aumont
, Jose L. Jimenez
, Sasha Madronich
, Rainer Volkamer
, 2013, izvirni znanstveni članek
Opis: The role of aqueous multiphase chemistry in the formation of secondary organic aerosol (SOA) remains difficult to quantify. We investigate it here by testing the rapid formation of moderate oxygen-to-carbon (O/C) SOA during a case study in Mexico City. A novel laboratory-based glyoxal-SOA mechanism is applied to the field data, and explains why less gas-phase glyoxal mass is observed than predicted. Furthermore, we compare an explicit gas-phase chemical mechanism for SOA formation from semi- and intermediate-volatility organic compounds (S/IVOCs) with empirical parameterizations of S/IVOC aging. The mechanism representing our current understanding of chemical kinetics of S/IVOC oxidation combined with traditional SOA sources and mixing of background SOA underestimates the observed O/C by a factor of two at noon. Inclusion of glyoxal-SOA with O/C of 1.5 brings O/C predictions within measurement uncertainty, suggesting that field observations can be reconciled on reasonable time scales using laboratory-based empirical relationships for aqueous chemistry.
Ključne besede: secondary organic aerosol, glyoxal, aqueous multiphase chemistry, oxygen-to-carbon ratio, single scattering albedo
Objavljeno v RUNG: 11.04.2021; Ogledov: 1740; Prenosov: 0
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Morphology and mixing state of aged soot particles at a remote marine free troposphere site : implications for optical propertiesSwarup China
, Barbara Scarnato
, Robert C. Owen
, Bo Zhang
, MarianT. Ampadu
, Sumit Kumar
, Katja Džepina
, Michael P. Dziobak
, Paulo Fialho
, Judith A. Perlinger
, 2015, izvirni znanstveni članek
Opis: The radiative properties of soot particles depend on their morphology and mixing state, but their evolution during transport is still elusive. Here we report observations from an electron microscopy analysis of individual particles transported in the free troposphere over long distances to the remote Pico Mountain Observatory in the Azores in the North Atlantic. Approximately 70% of the soot particles were highly compact and of those 26% were thinly coated. Discrete dipole approximation simulations indicate that this compaction results in an increase in soot single scattering albedo by a factor of <= 2.17. The top of the atmosphere direct radiative forcing is typically smaller for highly compact than mass-equivalent lacy soot. The forcing estimated using Mie theory is within 12% of the forcing estimated using the discrete dipole approximation for a high surface albedo, implying that Mie calculations may provide a reasonable approximation for compact soot above remote marine clouds.
Ključne besede: atmospheric aerosol, soot, long-range transport, free troposphere, single scattering albedo
Objavljeno v RUNG: 11.04.2021; Ogledov: 1742; Prenosov: 0
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Aircraft vertical profiles during summertime regional and Saharan dust scenarios over the north-western Mediterranean basin: aerosol optical and physical propertiesJesús Yus-Díez
, Marina Ealo
, Marco Pandolfi
, Noemi Perez
, Gloria Titos
, Griša Močnik
, Xavier Querol
, A. Alastuey
, 2021, izvirni znanstveni članek
Opis: Accurate measurements of the horizontal and vertical distribution of atmospheric aerosol particle optical properties are key for a better understanding of their impact on the climate. Here we present the results of a measurement campaign based on instrumented flights over north-eastern Spain. We measured vertical profiles of size-segregated atmospheric particulate matter (PM) mass concentrations and multi-wavelength scattering and absorption coefficients in the western Mediterranean basin (WMB). The campaign took place during typical summer conditions, characterized by the development of a vertical multi-layer structure, under both summer regional pollution episodes (REGs) and Saharan dust events (SDEs). REG patterns in the region form under high insolation and scarce precipitation in summer, favouring layering of highly aged fine-PM strata in the lower few kma.s.l.
The REG scenario prevailed during the entire measurement campaign. Additionally, African dust outbreaks and plumes from northern African wildfires influenced the study area. The vertical profiles of climate-relevant intensive optical parameters such as single-scattering albedo (SSA); the asymmetry parameter (g); scattering, absorption and SSA Ångström exponents (SAE, AAE and SSAAE); and PM mass scattering and absorption cross sections (MSC and MAC) were derived from the measurements. Moreover, we compared the aircraft measurements with those performed at two GAW–ACTRIS (Global Atmosphere Watch–Aerosol, Clouds and Trace Gases) surface measurement stations located in north-eastern Spain, namely Montseny (MSY; regional background) and Montsec d'Ares (MSA; remote site).
Airborne in situ measurements and ceilometer ground-based remote measurements identified aerosol air masses at altitudes up to more than 3.5 kma.s.l.
The vertical profiles of the optical properties markedly changed according to the prevailing atmospheric scenarios. During SDE the SAE was low along the profiles, reaching values < 1.0 in the dust layers. Correspondingly, SSAAE was negative, and AAE reached values up to 2.0–2.5, as a consequence of the UV absorption increased by the presence of the coarse dust particles. During REG, the SAE increased to > 2.0, and the asymmetry parameter g was rather low (0.5–0.6) due to the prevalence of fine PM, which was characterized by an AAE close to 1.0, suggesting a fossil fuel combustion origin. During REG, some of the layers featured larger AAE (> 1.5), relatively low SSA at 525 nm (< 0.85) and high MSC (> 9 m2 g−1) and were associated with the influence of PM from wildfires. Overall, the SSA and MSC near the ground ranged around 0.85 and 3 m2 g−1, respectively, and increased at higher altitudes, reaching values above 0.95 and up to 9 m2 g−1. The PM, MSC and MAC were on average larger during REG compared to SDE due to the larger scattering and absorption efficiency of fine PM compared with dust. The SSA and MSC had quite similar vertical profiles and often both increased with height indicating the progressive shift toward PM with a larger scattering efficiency with altitude.
This study contributes to our understanding of regional-aerosol vertical distribution and optical properties in the WMB, and the results will be useful for improving future climate projections and remote sensing or satellite retrieval algorithms.
Ključne besede: aerosol, climate change, Saharan dust, black carbon, aerosol absorption, aerosol scattering
Objavljeno v RUNG: 14.01.2021; Ogledov: 2073; Prenosov: 0
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Amorphous nanocomposite of polycarbosilanes and aluminum oxideAndraž Mavrič
, 2018, doktorska disertacija
Opis: This work presents a paradigm for high temperature stabilization of bulk amorphous aluminium oxide. The thermodynamic stabilization is achieved by preparing a nanocomposite, where polymethylsilane dendritic molecules are dispersed in an aluminium hydroxide gel. Upon heat-treatment the gel transforms to the amorphous aluminium oxide that is stable up to 900°C. The dispersion of the macromolecules and their covalent bonding to the alumina matrix induce homogeneously distributed strain fields that keep the alumina amorphous.
The first part of the thesis focuses on the synthesis, characterization and solubility properties of the dendritic polymethylsilane. The polymethylsilane is synthetized by electrochemical polymerization from trichloromethylsilane monomer. The polymerization mechanism, involving a single polymerization pathway, is identified. The polymer growth proceeds through reduction of the monomers to the silyl anions and their addition to the growing polymer.
The solubility of three chemically related but topologically different polysilanes (linear, dendritic and network) were studied by dynamic light scattering. At room temperature the agglomerates in a range from 500 to 1300 nm are present. They undergo de-agglomeration at slightly elevated temperatures of around 40°C. The de-agglomeration results in formation of stable solutions, where a hydrodynamic diameter of the individual polymer molecules was measured to be in a range from 20 to 40 nm.
The obtained diameters of two dendritic polymethylsilane macromolecules, synthesized under different electrolysis conditions, are much larger than the theoretical size estimated for an ideal dendrimer. We determined by 29Si NMR that the reason for this is in a large number of branching irregularities (defects) contained in the molecular structure. Combining the experimental values obtained by DLS and density measurements with a structural model that considers the branching irregularities, it is shown that the inclusion of the defects allows the dendritic polymer to exceed the sterical limitations and form the hyperbranched dendritic structure. The final size depends on a relative amount of the branching defects.
In the second part, the synthetized polymethylsilane molecules were successfully used for the nanocomposite formation. The aluminium hydroxide gel with the dispersed polymethylsilane molecules was prepared as a precursor. Upon heat-treatment it gives the amorphous aluminium oxide stable up to 900°C. The dispersed macromolecules induce homogeneously distributed strain fields that keep the aluminium oxide amorphous during the thermal treatment the dispersed macromolecules covalently bind to the matrix, inducing the interface strain. The amorphous state was confirmed by the presence of penta-coordinated aluminium detected by 27Al NMR and a low bandgap measured by UV-vis absorption spectroscopy.
Ključne besede: amorphous aluminium oxide, polymethylsilane, nanocomposite, electropolymerization, solubility, agglomeration, de-agglomeration, dendrimer, hyperbranched dendritic structure, dynamic light scattering, thermal analysis, transmission electron microscopy, scanning electron microscopy, X-ray diffraction, infrared spectroscopy, UV-Vis spectroscopy
Objavljeno v RUNG: 19.07.2018; Ogledov: 5589; Prenosov: 208
Celotno besedilo (5,07 MB)
Polymer Nanoparticle Sizes from Dynamic Light Scattering and Size Exclusion Chromatography: The Case Study of Polysilanes.Artem Badasyan
, Andraž Mavrič
, Irena Kralj Cigić
, Tim Bencik
, Matjaž Valant
, 2018, izvirni znanstveni članek
Opis: Dynamic Light Scattering (DLS) and Size Exclusion Chromatography (SEC) are among the most popular methods for determining polymer sizes in solution. Taking dendritic and network polysilanes as a group of least soluble polymer substances, we critically compare and discuss the difference between nanoparticle sizes, obtained by DLS and SEC. Polymer nanoparticles are typically in poor solution conditions below the theta point and are in globular conformation therefore. Determination of particle sizes in presence of attractive interactions is not a trivial task. The only possibility to measure aggregation-free, a true molecular size of polymer nanoparticles in such regime of solution, is to operate with the dilute solution of globules (below theta point and above the miscibility line). Basing on results of our polysilane measurements, we come to a conclusion that DLS provides more reliable results than SEC for the dilute solution of globules. General implications for the size measurements of polymer nanoparticles in solutions are discussed.
Ključne besede: Polymer Nanoparticle, Dynamic Light Scattering, Size Exclusion Chromatography, Polysilanes
Objavljeno v RUNG: 16.05.2018; Ogledov: 3962; Prenosov: 13
Celotno besedilo (3,17 MB)