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1.
Long-term brown carbon spectral characteristics in a Mediterranean city (Athens)
Eleni Liakakou, Dimitris G. Kaskaoutis, Georgios Grivas, Iasonas Stavroulas, M. Tsagkaraki, D. Paraskevopoulou, Aikaterini Bougiatioti, Umesh Chandra Dumka, Evangelos Gerasopoulos, Nikolaos Mihalopoulos, 2020, izvirni znanstveni članek

Opis: This study analyses 4-years of continuous 7-λ Aethalometer (AE-33) measurements in an urban-background environment of Athens, to resolve the spectral absorption coefficients (babs) for black carbon (BC) and brown carbon (BrC). An important BrC contribution (23.7 ± 11.6%) to the total babs at 370 nm is estimated for the period May 2015–April 2019, characterized by a remarkable seasonality with winter maximum (33.5 ± 13.6%) and summer minimum (18.5 ± 8.1%), while at longer wavelengths the BrC contribution is significantly reduced (6.8 ± 3.6% at 660 nm). The wavelength dependence of the total babs gives an annual-mean AAE370-880 of 1.31, with higher values in winter night-time. The BrC absorption and its contribution to babs presents a large increase reaching up to 39.1 ± 13.6% during winter nights (370 nm), suggesting residential wood burning (RWB) emissions as a dominant source for BrC. This is supported by strong correlations of the BrC absorption with OC, EC, the fragment ion m/z 60 derived from ACSM and PMF-analyzed organic fractions related to biomass burning (e.g. BBOA). In contrast, BrC absorption decreases significantly during daytime as well as in the warm period, reaching to a minimum during the early-afternoon hours in all seasons due to photo-chemical degradation. Estimated secondary BrC absorption is practically evident only during winter night-time, implying the fast oxidation of BrC species from RWB emissions. Changes in mixing-layer height do not significantly affect the BrC absorption in winter, while they play a major role in summer.
Ključne besede: spectral aerosol absorption, brown carbon, wood burning, organic aerosols, chemical composition, Athens
Objavljeno v RUNG: 10.05.2024; Ogledov: 294; Prenosov: 1
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2.
In situ identification of aerosol types in Athens, Greece, based on long-term optical and on online chemical characterization
Dimitris G. Kaskaoutis, Georgios Grivas, Iasonas Stavroulas, Eleni Liakakou, Umesh Chandra Dumka, Konstantinos Dimitriou, Evangelos Gerasopoulos, Nikolaos Mihalopoulos, 2021, izvirni znanstveni članek

Opis: Absorption Ångström Exponent (AAE) and Scattering Ångström Exponent (SAE) values, derived from aethalometer and nephelometer measurements during a period of 3 years at an urban background site in Athens, are combined for the first aerosol type classification using in situ measurements in the eastern Mediterranean. In addition, single scattering albedo (SSA) and its wavelength dependence (dSSA), as well as the chemical composition of fine aerosols and precursor gases from collocated measurements, are utilized to provide further insights on the optical-chemical characterization and related sources of seven identified aerosol types. Urban aerosols are mostly characterized as Black Carbon (BC)-dominated (76.3%), representing a background atmosphere where fossil-fuel combustion is dominant throughout the year, while 14.3% of the cases correspond to the mixed Brown Carbon (BrC)-BC type, with a higher frequency in winter. The BrC type is associated with the highest scattering and absorption coefficients during winter nights, representing the impact from residential wood-burning emissions. Dust mixed with urban pollution (1.2%) and large particles mixed with BC (5.3%) have a higher frequency in spring. Furthermore, aging processes and BC coating with organic and inorganic species with weak spectral absorption (AAE<1) account for 2.2%, with a differentiation between small and large particles. dSSA is recognized as a useful parameter for aerosol characterization, since fine aerosols are associated with negative dSSA values. The identified aerosol types are examined on a seasonal, monthly, hourly basis and by potential source areas, as well as in comparison with fine-aerosol chemical composition and apportioned organic aerosol source contributions, in an attempt to explore the linkage between optical, physical and chemical aerosol properties. Chemical analysis indicates high organic fraction (60–68%) for the BrC and BrC/BC, 20–30% larger compared to other types. The results are essential for parametrization in chemical transport models and for reducing the uncertainty in the assessment of aerosol radiative effects.
Ključne besede: aerosol types, classification, AAE, SAE, dSSA, chemical composition, sources, Athens
Objavljeno v RUNG: 10.05.2024; Ogledov: 260; Prenosov: 2
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3.
A European aerosol phenomenology - 7 : high-time resolution chemical characteristics of submicron particulate matter across Europe
M. Bressi, F. Cavalli, Jean-Philippe Putaud, R. Fröhlich, J. -E. Petit, W. Aas, M. Äijälä, A. Alastuey, J. D. Allan, M. Aurela, Iasonas Stavroulas, Marta Via, 2021, izvirni znanstveni članek

Opis: Similarities and differences in the submicron atmospheric aerosol chemical composition are analyzed from a unique set of measurements performed at 21 sites across Europe for at least one year. These sites are located between 35 and 62°N and 10° W – 26°E, and represent various types of settings (remote, coastal, rural, industrial, urban). Measurements were all carried out on-line with a 30-min time resolution using mass spectroscopy based instruments known as Aerosol Chemical Speciation Monitors (ACSM) and Aerosol Mass Spectrometers (AMS) and following common measurement guidelines. Data regarding organics, sulfate, nitrate and ammonium concentrations, as well as the sum of them called non-refractory submicron aerosol mass concentration ([NR-PM1]) are discussed. NR-PM1 concentrations generally increase from remote to urban sites. They are mostly larger in the mid-latitude band than in southern and northern Europe. On average, organics account for the major part (36–64%) of NR-PM1 followed by sulfate (12–44%) and nitrate (6–35%). The annual mean chemical composition of NR-PM1 at rural (or regional background) sites and urban background sites are very similar. Considering rural and regional background sites only, nitrate contribution is higher and sulfate contribution is lower in mid-latitude Europe compared to northern and southern Europe. Large seasonal variations in concentrations (μg/m³) of one or more components of NR-PM1 can be observed at all sites, as well as in the chemical composition of NR-PM1 (%) at most sites. Significant diel cycles in the contribution to [NR-PM1] of organics, sulfate, and nitrate can be observed at a majority of sites both in winter and summer. Early morning minima in organics in concomitance with maxima in nitrate are common features at regional and urban background sites. Daily variations are much smaller at a number of coastal and rural sites. Looking at NR-PM1 chemical composition as a function of NR-PM1 mass concentration reveals that although organics account for the major fraction of NR-PM1 at all concentration levels at most sites, nitrate contribution generally increases with NR-PM1 mass concentration and predominates when NR-PM1 mass concentrations exceed 40 μg/m³ at half of the sites.
Ključne besede: aerosol, chemical composition, mass spectrometry, phenomenology
Objavljeno v RUNG: 10.05.2024; Ogledov: 263; Prenosov: 2
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Astrophysical interpretation of energy spectrum and mass composition of cosmic rays as measured at the Pierre Auger Observatory
Eleonora Guido, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, objavljeni znanstveni prispevek na konferenci

Opis: The combined interpretation of the spectrum and composition measurements plays a key role in the quest for the origin of ultra-high-energy cosmic rays (UHECRs). The Pierre Auger Observatory, thanks to its huge exposure, provides the most precise measurement of the energy spectrum of UHECRs and the most reliable information on their composition, exploiting the distributions of the depth of maximum of the showers in the atmosphere. A combined fit of a simple astrophysical model of UHECR sources to the spectrum and mass composition measurements is used to evaluate the constraining power of the data measured by the Pierre Auger Observatory on the source properties. We find that our data across the “ankle” feature are well reproduced if two extragalactic populations of sources are considered, one emitting a very soft spectrum which dominates the region below the ankle, and the other taking over at energies above the ankle, with an intermediate mixed composition, a hard spectrum and a low rigidity cutoff. Interestingly, similar results can also be obtained if the medium-mass contribution at lower energy is provided by an additional galactic component.
Ključne besede: Pierre Auger Observatory, ultra-high energy cosmic rays, UHECR energy spectrum, UHECR mass composition
Objavljeno v RUNG: 24.01.2024; Ogledov: 826; Prenosov: 7
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6.
Investigation of multi-messenger properties of FR0 radio galaxy emitted ultra-high energy cosmic rays
Jon Paul Lundquist, Lukas Merten, Serguei Vorobiov, Margot Boughelilba, Albert Reimer, Paolo Da Vela, F. Tavecchio, G. Bonnoli, C. Righi, 2023, objavljeni znanstveni prispevek na konferenci

Opis: Low luminosity Fanaroff-Riley type 0 (FR0) radio galaxies are amongst potential contributors to the observed flux of ultra-high energy cosmic rays (UHECRs). Due to FR0s’ much higher abundance in the local universe than more powerful radio galaxies (e.g., about five times more ubiquitous at redshifts z≤0.05 than FR1s), they could provide a substantial fraction of the total UHECR energy density. In the presented work, we determine the mass composition and energy spectrum of UHECRs emitted by FR0 sources by fitting simulation results from the CRPropa3 framework to the recently published Pierre Auger Observatory data. The resulting emission spectral characteristics (spectral indices, rigidity cutoffs) and elemental group fractions are compared to the Auger results. The FR0 simulations include the approximately isotropic distribution of FR0s extrapolated from the measured FR0 galaxy properties and various extragalactic magnetic field configurations, including random and large-scale structured fields. We predict the fluxes of secondary photons and neutrinos produced during UHECR propagation through cosmic photon backgrounds. The presented results allow for probing the properties of the FR0 radio galaxies as cosmic-ray sources using observational high-energy multi-messenger data.
Ključne besede: ultra-high energy cosmic rays, UHECRs, Pierre Auger Observatory, UHECR propagation, UHECR interactions, UHECR energy spectrum, UHECR mass composition, UHECR sources, Fanaroff-Riley (FR) radio galaxies, FR0 galaxies
Objavljeno v RUNG: 24.01.2024; Ogledov: 680; Prenosov: 39
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7.
Combined fit to the spectrum and composition data measured by the Pierre Auger Observatory including magnetic horizon effects
Juan Manuel González, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, objavljeni znanstveni prispevek na konferenci

Opis: The measurements by the Pierre Auger Observatory of the energy spectrum and mass composition of cosmic rays can be interpreted assuming the presence of two extragalactic source populations, one dominating the flux at energies above a few EeV and the other below. To fit the data ignoring magnetic field effects, the high-energy population needs to accelerate a mixture of nuclei with very hard spectra, at odds with the approximate �−2 shape expected from diffusive shock acceleration. The presence of turbulent extragalactic magnetic fields in the region between the closest sources and the Earth can significantly modify the observed CR spectrum with respect to that emitted by the sources, reducing the flux of low-rigidity particles that reach the Earth. We here take into account this magnetic horizon effect in the combined fit of the spectrum and shower depth distributions, exploring the possibility that a spectrum for the high-energy population sources with a shape closer to �^(−2) be able to explain the observations. We find that a large inter-source separation �s and a large magnetic field RMS amplitude within the Local Supercluster region, such that �rms ≃ 100 nG (40 Mpc/�s) √︁25 kpc/�coh, are needed to interpret the data within this scenario, where �coh is the magnetic field coherence length.
Ključne besede: ultra-high energy cosmic rays, Pierre Auger Observatory, mass composition, extragalactic magnetic fiels
Objavljeno v RUNG: 22.01.2024; Ogledov: 560; Prenosov: 6
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Studies of the UHECR Mass Composition and Hadronic Interactions with the FD and SD of the Pierre Auger Observatory
J.M. Carceller, Andrej Filipčič, Gašper Kukec Mezek, Ahmed Saleh, Samo Stanič, Marta Trini, Serguei Vorobiov, Lili Yang, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2019, objavljeni znanstveni prispevek na konferenci

Opis: With data on the depth of maximum Xmax collected during more than a decade of operation of the Pierre Auger Observatory, we report on the inferences on the mass composition of UHECRs in the energy range E = 10[sup]17.2 − 10[sup]19.6 eV and on the measurements of the proton-air cross section for energies up to 10[sup]18.5 eV. We also present the results on Xmax obtained using the information on the particle arrival times recorded by the SD stations allowing us to extend the Xmax measurements up to 10[sup]20 eV. The inferences on mass composition, in particular using the data of the SD, are subject to systematic uncertainties due to uncertainties in the description of hadronic interactions at ultra-high energies. We discuss this problem with respect to the properties of the muonic component of extensive air-showers as derived from the SD data.
Ključne besede: ultra-high-energy cosmic rays (UHECRs), extensive air showers (EAS), EAS muonic component, EAS electromagnetic component, Pierre Auger Observatory, UHECR mass composition, UHECR hadronic interactions
Objavljeno v RUNG: 11.10.2023; Ogledov: 910; Prenosov: 8
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10.
Results from the Pierre Auger Observatory
Esteban Roulet, Andrej Filipčič, Gašper Kukec Mezek, Ahmed Saleh, Samo Stanič, Marta Trini, Serguei Vorobiov, Lili Yang, Danilo Zavrtanik, Marko Zavrtanik, Lukas Zehrer, 2019, objavljeni znanstveni prispevek na konferenci

Opis: Some of the results on ultrahigh-energy cosmic rays that have been obtained with the Pierre Auger Observatory are presented. These include measurements of the spectrum, composition and anisotropies. Possible astrophysical scenarios that account for these results are discussed.
Ključne besede: ultra-high-energy cosmic rays (UHECRs), Pierre Auger Observatory, UHECR energy spectrum, UHECR anisotropies, UHECR mass composition
Objavljeno v RUNG: 11.10.2023; Ogledov: 1009; Prenosov: 5
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